On the road to sustainable energy supply in road transport ...

On the road to sustainable energy supply in road transport – potentials of CNG and LPG as transporta-tion fuels

Short study in the context of the

scientific supervision, support and guidance of the BMVBS in the sectors Transport and Mobility with a specific focus on fuels and propulsion technologies, as well as energy and climate

Federal Ministry for Transport, Building and Urban Development (BMVBS)

AZ Z14/SeV/288.3/1179/UI40

Main contractor: Deutsches Zentrum für Luft- und Raumfahrt e.V. (DLR) Institut für Verkehrsforschung Rutherfordstraße 2, 12489 Berlin Tel.: 030 67055-221, Fax: -283

Subcontractors: Institut für Energie- und Umweltforschung Heidelberg GmbH (IFEU) Wilckensstraße 3, 69120 Heidelberg Tel.: 06221 4767-35

Ludwig-Bölkow-Systemtechnik GmbH (LBST) Daimlerstraße 15, 85521 München/Ottobrunn Tel.: 089 608110-36

Deutsches Biomasseforschungszentrum gGmbH (DBFZ) Torgauer Straße 116, 04347 Leipzig Tel.: 0341 2434-423

Authors

C. Heidt, U. Lambrecht (IFEU), M. Hardinghaus, G. Knitschky (DLR), P. Schmidt, W. Weindorf (LBST), K. Naumann, S. Majer, Dr. F. Müller-Langer, Dr. M. Seiffert (DBFZ)

Heidelberg, Berlin, Munich, Leipzig, 26 September 2013

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Summary

Liquefied petroleum gas (LPG, ‘Autogas’) and compressed natural gas (CNG) are the most

common alternative fuels for motor vehicles worldwide. A number of countries subsidise the

utilisation of gaseous fuels in the transport sector for reasons including environmental bene-

fits, diversification of the fuel market and the reduction of supply dependency. In Germany,

CNG and LPG are subsidised with a reduced mineral oil tax rate under the German Energy

Tax Act (EnergieStG) until the 31.12.2018. In association with the Mobility and Fuels Strate-

gy of the German Federal Government, the present short study investigated the utilisation of

CNG and LPG in motor vehicles to inform the current debate on the possible extension of the

present subsidies. The focus is on recent and future developments of both the market and

associated environmental impacts in Germany. The following conclusions arise:

1. Despite competitive costs, CNG and LPG vehicles account for a low proportion of

the current overall stock. Financial benefits have resulted primarily in conversion

of petrol to LPG cars.

The total costs of ownership (TCO) of both CNG and LPG vehicles are competitive in com-

parison to conventional engines (diesel / petrol) in the present tax framework. However, ac-

cording to the German Federal Motor Transport Authority (KBA), CNG and LPG vehicles

account for approx. 1% of the total German vehicle stock (status in 2012). The majority are

petrol cars that were converted to LPG. CNG on the other hand is utilised more frequently in

production-line vehicles in the car and commercial vehicle sectors.

Without energy tax benefits, the TCO would be higher compared to diesel vehicles in most

cases. Thus, new registrations and conversion rates are expected to further decline without

subsidies after 2018. Yet, the present situation also indicates that TCO competitiveness is

only in part responsible for the overall acceptance and sales figures of CNG and LPG vehi-

cles. To further promote implementation, a number of additional measures are required.

These include improved consumer information, extension of the range of vehicles on offer

and concerted efforts to improve the fuelling station infrastructure.

2. The utilisation of CNG and renewable methane instead of petrol or diesel may re-

duce road transport emissions of greenhouse gases (GHGs) and pollutants. In

contrast, LPG offers fewer environmental benefits than CNG, and lacks overall po-

tential for integration of renewable energies.

CNG engines are currently associated with the lowest environmental impacts among current

powertrains. A natural gas vehicle operated with fossil fuels is generating the lowest GHG

emissions (-15 % in comparison with petrol cars). However, substantial GHG savings may be

achieved with the utilisation of biomethane (up to -66 % compared to petrol). The GHG emis-

sions of LPG vehicles show a modest -9% reduction.

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A look at the emission of pollutants reveals that both CNG and LPG vehicles compare fa-

vourable to diesel vehicles, in particular with respect to NOX emissions (TTW). In contrast,

LPG produced from crude oil is at a disadvantage compared to conventional fuels with re-

spect to NMHC und SO2 emissions, which ensue primarily during fuel supply (WTT).

Future potentials for the reduction of environmental burdens are greatest for CNG. Increas-

ing use of hybrid technology in vehicles is expected to result in reduced fuel consumption

rates. These advances in fuel efficiency could be more pronounced for CNG than for petrol

or diesel engines. Furthermore, CNG engines may utilise renewable methane from additional

supply pathways, e.g. synthetic methane derived from biomass or renewable electricity. If the

development of the renewable energy sector is accelerated, additional and surplus capacities

of renewable electricity could be utilised to produce synthetic, so-called ‘RE methane’. For

LPG, no novel renewable pathways ready for the market are expected at present. Nonethe-

less, mid-term advantages of LPG would include an additional diversification of the energy

supply in road transport. LPG in Germany is primarily produced from crude oil at present;

however, it may also be obtained from natural gas.

Promising applications for CNG may also be found in the commercial vehicle sector, which is

still dominated by diesel engines at present. Low exhaust emissions in CNG vehicles are

particularly beneficial in cities, and CNG city buses are already common. Moreover, the CNG

infrastructure may be able to contribute to the future fuel supply for long-distance freight

transport with liquefied natural gas (LNG).

3. Individual subsidisation of CNG and LPG may contribute to the sustainable energy

supply of the transport sector. In this context, the framework should target long-

term integration of renewable energies.

In the case of future subsidisation, renewable energy potentials of CNG should be consid-

ered above all. Thus, individual energy tax rates or statutory blending quotas may promote

renewable fuels in particular. Although CNG from fossil natural gas is associated with fewer

environmental benefits, tax benefits in the coming years would support both the development

of the CNG vehicle market and the CNG infrastructure. These measures could facilitate the

integration of renewable energies, e.g. biomethane and methane derived from renewable

electricity, into road transport.

There is less overall support for continued subsidisation of LPG. However, LPG greenhouse

gas emissions are lower than those of petrol, and the contribution to the diversification of the

fuel sector could be taken into consideration in the subsidy extension debate. Energy taxa-

tion could follow the principles of the EU alternative fuels strategy, i.e. seek to differentiate

between CO2 and GHG emissions.

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Table of contents

Summary ................................................................................................................................ 3

1 Background and aims of the study ................................................................................ 10

2 Market situation of natural gas vehicles ........................................................................ 11

2.1 Overview ................................................................................................................ 11

2.1.1 Fuel properties and engine technology ............................................................ 11

2.1.2 Range of models ............................................................................................. 12

2.2 Vehicle stock .......................................................................................................... 12

2.2.1 Development to date ....................................................................................... 12

2.2.2 Current trends for registration of CNG and LPG vehicles ................................ 13

2.3 Comparison of costs and perspectives for passenger cars ..................................... 14

2.3.1 Methodology for full cost accounting ............................................................... 14

2.3.2 Comparison of the full cost for new vehicles and conversions ......................... 15

2.3.3 Future perspectives for the vehicle stock ......................................................... 17

3 Environmental comparison and potentials for renewable energies................................ 19

3.1 Structure of the environmental comparison ............................................................ 19

3.2 Fuel supply – Well-to-tank (WTT) ........................................................................... 21

3.2.1 Overview of the emission factors under investigation ...................................... 21

3.2.2 Comments on fossil fuel production and supply............................................... 23

3.2.3 Comments on renewable fuel production and supply ...................................... 23

3.3 Vehicle operation – tank-to-wheel (TTW) ............................................................... 30

3.3.1 Vehicles under investigation ............................................................................ 30

3.3.2 Fuel consumption ............................................................................................ 31

3.3.3 Greenhouse gas and pollutant emissions ........................................................ 36

3.4 Well-to-wheel (WTW) comparison 2012 ................................................................. 39

3.4.1 Greenhouse gas emissions ............................................................................. 39

3.4.2 Primary energy consumption and pollutant emissions ..................................... 44

3.5 Well-to-wheel (WTW) comparison 2030 ................................................................. 47

3.5.1 Greenhouse gas emissions ............................................................................. 47

3.5.2 Primary energy consumption and pollutant emission ....................................... 49

4 Perspectives for the promotion of CNG and LPG in road transport ............................... 52

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4.1 Benefits from an environmental perspective ........................................................... 52

4.2 Potential subsidy framework ................................................................................... 53

Appendix I: Amortisation potential of LPG conversion for the German petrol vehicle fleet .... 55

Appendix II: Well-to-tank calculations ................................................................................... 56

Methodology ..................................................................................................................... 56

Physical energy content method ................................................................................... 56

Allocation of byproducts ................................................................................................ 56

Embodied energy ......................................................................................................... 57

Other impact categories ................................................................................................ 57

Fossil fuels ....................................................................................................................... 57

Petrol and diesel from crude oil .................................................................................... 57

Petrol and diesel from tar sands ................................................................................... 60

CNG from natural gas ................................................................................................... 61

LPG from crude oil/natural gas ..................................................................................... 63

Renewable fuels ............................................................................................................... 69

Biomethane .................................................................................................................. 69

Synthetic methane from renewable electricity (RE methane) ........................................ 72

Appendix III: Energy taxation for fuels .................................................................................. 74

Literature .............................................................................................................................. 75

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Table of figures

Figure 1: Development of the natural gas vehicle stock in Germany ...........................13

Figure 2: Comparison of the average full cost depending on type of drive of new

vehicles in the B-segment small cars ...........................................................15

Figure 3: Range of amortisation of LPG conversion (1800-3500 €) depending on

mileage and consumption ............................................................................17

Figure 4: Schematic of the environmental comparison ................................................19

Figure 5: Biofuels subject to energy tax benefits credited to the quota in 2011 and

2012 (DBFZ based on BLE 2013 and BAFA) ...............................................26

Figure 6: Methanation of H2 from electricity utilising CO2 from biogas upgrading ........28

Figure 7: Exemplary comparison of CO2 emissions and relevant vehicle design of

selected passenger cars ..............................................................................33

Figure 8: WTW Greenhouse gas emissions for passenger cars in 2012 .....................39

Figure 9: Comparison of the CO2 benefits of CNG and LPG from fossil supply

pathways for motors cars in 2010/2012 in recent studies .............................41

Figure 10: WTW greenhouse gas emissions of city buses in 2012 ...............................43

Figure 11: WTW pollutant emissions of passenger cars in 2012 ...................................44

Figure 12: WTW pollutant emissions for city buses in 2012 ..........................................46

Figure 13: WTW greenhouse gas emissions for passenger cars in 2030 ......................47

Figure 14: WTW greenhouse gas emissions for city buses 2030 ..................................48

Figure 15: WTW pollutant emissions for passenger cars 2030 .....................................49

Figure 16: WTW pollutant emissions for city buses in 2030 ..........................................51

Figure 17: Energy tax losses and GHG savings in relation to a petrol vehicle in 2012

(Calculation in Appendix III) .........................................................................52

Figure 18: Potential of conversion to LPG for the German vehicle fleet ........................55

Figure 19: Crude oil refinery .........................................................................................68

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List of tables

Table 1: CO2 emissions from fuel combustion ...........................................................20

Table 2: Overview of energy consumption and emissions WTT .................................22

Table 3: Overview of the marketability of the renewable supply pathways under

investigation .................................................................................................24

Table 4: ‘Dumped energy’ according to German Network Development Plan [NEP

2013, p. 64, Table 9] ....................................................................................27

Table 5: Fuel consumption of a small family car (Golf class) in the NEDC after JEC

2011 ............................................................................................................32

Table 6: Fuel consumption of average passenger cars in 2012 and 2030 .................35

Table 7: Fuel consumption of average city buses in 2012 and 2030 ..........................36

Table 8: Emission factors for greenhouse gases TTW ...............................................37

Table 9: Emission factors for air pollutants TTW ........................................................38

Table 10: System boundaries and fundamental assumptions of recent studies on

environmental comparisons of CNG/LPG with other fuels ............................40

Table 11: Supporting framework for the subsidisation of CNG and LPG ......................54

Table 12: Energy flows and emissions from crude oil production .................................58

Table 13: Energy flows and emissions from crude oil transport ...................................58

Table 14: Energy flows and emissions from the production of petrol and diesel in oil

refineries ......................................................................................................59

Table 15: Fuel consumption and GHG emissions of an inland waterway vessel ..........59

Table 16: Energy flows and emissions from the production of synthetic crude oil

(SCO) from tar sand deposits in Canada .....................................................60

Table 17: Fuel consumption and GHG emissions of an oil tanker ................................61

Table 18: Energy flows and emissions from the production and processing of

natural gas ...................................................................................................62

Table 19: Energy flows and emissions from transport of natural gas over great

distances .....................................................................................................62

Table 20: Natural gas consumption and emissions from gar turbines of natural gas

compressors ................................................................................................63

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Table 21: Energy flows and emissions for the production and processing of LPG .......64

Table 22: Fuel qualities of LPG....................................................................................65

Table 23: LPG transport vessel “Djanet“ [Kawasaki 2000] ...........................................65

Table 24: Fuel consumption and emissions of a 40 t lorry ...........................................67

Table 25: Energy demand and emissions from LPG production in a crude oil

refinery ........................................................................................................68

Table 26: Overview of data for ecological parameters of biomethane supply ...............70

Table 27: Parameters of the examined concepts for biomethane production from

renewable resources/liquid manure and biodegradable waste [Biogasrat

2011] ...........................................................................................................71

Table 28: Input/output data for the production of methane from CO2 and hydrogen

(incl. CO2 supply) .........................................................................................73

Table 29: GHG savings costs for energy tax benefits in comparison to petrol ..............74

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1 Background and aims of the study

Natural gas (CNG) and liquefied petroleum gas (LPG, ‘Autogas’) are subsidised with a re-

duced mineral oil tax rate under the German Energy Tax Act (EnergieStG) until the

31.12.2018. Public debate on the extension of these subsidies beyond 2018 is already under

way. The present study aims to compile facts, arguments and requirements in favour of and

against the extension of subsidies of the two energy carriers. The scope includes the follow-

ing sections:

Technologies and associated costs of CNG and LPG in comparison with diesel and

petrol vehicles based on the status quo, yet including future perspectives.

Development of the CNG/LPG fleet in road transport to date, including an assess-

ment of the potential influence of changes to current parameters on the development

of future vehicle stock.

Illustration of promising supply pathways for renewable methane including benchmark

values for typical GHG and pollutant emissions, complemented by a discussion of the

present and future market perspectives of biomethane and RE methane on the fuel

market.

Comparison of the environmental impacts of CNG and LPG vehicles with respect to

established and alternative fuel supply pathways today (2012) and in the future

(2030).

Discussion of the perspectives of CNG and LPG vehicles to advance integration of

renewable energies into the road transport sector.

Points argued in favour of and against further energy tax benefits of CNG/LPG be-

yond 2018, or rather necessary pre-requisites for such measures (e.g. based on re-

newable energies and sustainability criteria).

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2 Market situation of natural gas vehicles

2.1 Overview

2.1.1 Fuel properties and engine technology

LPG (Liquefied Petroleum Gas), also known as autogas, consists primarily of the hydrocar-

bons propane and butane. These arise as byproducts of natural gas and crude oil produc-

tion. The physical properties of LPG do not significantly differ from those of petrol (with the

exception of density), and LPG may be utilised as fuel in modified petrol engines. The lique-

faction of LPG is relatively simple (at 8 to 10 bar), thus facilitating storage and trade.

CNG (Compressed Natural Gas) or natural gas has a chemical composition of over 80 %

methane. In Germany, it is offered as H-Gas or L-Gas which differ in methane content and

heating value. At 200 bar, the compressions of natural gas for storage purposes on board the

vehicle requires higher pressure levels than LPG. For this reason, CNG is carried in a pres-

sure tank. Complex technology is required for the alternative liquid storage as Liquefied Nat-

ural Gas (LNG), as it requires cooling at -161.5°C. Compressed natural gas has a heating

value per kg similar to petrol, and is utilised in modified petrol engines.

The higher anti-knock capacity of CNG (octane number 120) allows combustion in CNG-

optimised engines with higher compression levels, thus resulting in higher energy efficiency

in comparison with LPG and petrol (octane number ≤100) [Stan 2005]. However, CNG fuel

storage under high pressure requires measures obsolete for LPG, i.e. solid large-volume

containers and high-pressure control of engine supply. In contrast, LPG may achieve better

mileage at relatively low pressure levels with small tank volumes.

LPG vehicles commonly pursue a bi-fuel concept, i.e. the vehicles are equipped with both

LPG and petrol tanks. In contrast, CNG vehicles are offered as bi-fuel or dedicated drives,

the latter being equipped with a small emergency petrol tank only.

Conversion from petrol to gas operation requires an additional pressurised tank, a separate

injection system with hoses fitted with a pressure gauge and an appropriate engine man-

agement. Due to differences in storage pressure, bi-fuel drive with CNG and LPG is not pos-

sible. Conversion costs for vehicles are much lower for LPG than for CNG. Technological

advances allow injection with internal or external mixture formation. In this context, modifica-

tion with direct injection is more elaborate. The conversion of diesel engines is also possible.

However, the fact that spontaneous combustion requires the installation of an ignition system

renders conversion distinctly more expensive and rarely viable from an economic angle.

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2.1.2 Range of models

The range of models on the market for gas vehicles to date is very limited. In Germany, 44

LPG models from 25 model ranges are available for order, whereas 21models from 12 model

ranges are available for purchase with CNG drive (status 07/2012). A selection of additional

vehicle features and options is virtually non-existent. The majority of vehicles on offer belong

to the MPV segment, or the small and large family car segments. The current vehicle market

is characterised by a multitude of options for vehicle body and equipment. Thus, the limited

selection for gas vehicles may prevent overall popularity and growing expansion.

2.2 Vehicle stock

2.2.1 Development to date

In 2011, the global number of natural gas vehicles registered was about 15 million [NVGA

2012]. Gas vehicles represent a high proportion of the total vehicle stock in Pakistan, Bang-

ladesh, Armenia, Iran, Bolivia and Argentina. The global market development for gas vehi-

cles is generally much more than dynamic compared to the situation in Germany. This trend

is driven by considerable expansion in Iran, China and Pakistan as well as by emerging mar-

kets in a number of newly industrialised countries.

The global number of vehicles operated with LPG in 2010 was about 17.5 million [WLPGA

2011]. Demand for LPG is also dynamic (+59 % between 2000 and 2010) with a small num-

ber of countries acting as major drivers of the demand. The most important markets are in

Poland, Turkey and Korea. With the exception of Korea, where a great number of LPG cars

are production-line vehicles, the great majority of LPG cars are converted petrol vehicles. In

the segment of heavy-duty commercial vehicles, LPG drives are rare due to the elaborate

conversion procedure involved. The global trend for countries with a well-developed fuelling

station infrastructure and established refineries is an increased integration of LPG due to the

low costs for modification and production. Countries with natural gas deposits (and poorly

developed infrastructure) tend to favour natural gas.

In Europe, natural gas vehicles have a high market share in Italy and Bulgaria (see [NGVA

Europe 2012]). Furthermore, a considerable number of CNG vehicles is operated in Germa-

ny and Sweden. According to WLPGA, the most important markets for LPG vehicles are in

Europe are in Poland and Italy (see [WLPGA 2011]).

According to the German Federal Motor Transport Authority, as of 01.01.2012 about 75,000

CNG vehicles and 455,000 LPG vehicles were registered, respectively. This is representative

of a proportion of 1.2 % of the total stock. A further 18,000 commercial vehicles are operated

with CNG, whereas the number of LPG commercial vehicles comes to 8700. Most CNG

commercial vehicles are registered in the category of light commercial vehicles below a two

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ton payload. Among heavy-duty commercial vehicles, operation with gas is virtually non-

existent except for CNG city buses.

Figure 1: Development of the natural gas vehicle stock in Germany

2.2.2 Current trends for registration of CNG and LPG vehicles

In recent years, the trend for increases in LPG vehicles has distinctly shifted from new regis-

trations to conversions. In this context, the new registration of LPG cars fell below 5000 vehi-

cles, or 0.15 % of all new registrations, in 2011. Simultaneously, conversion numbers

reached 95,000, thus representing over 95 % of the increase in LPG cars. Hence, the overall

increase remains constant. However, the increasing age of the LPG fleet was responsible for

an increase in end-of-life vehicles. For this reason, the overall stock increase was slowed.

The year 2012 saw a significant increase in LPG new registrations against the trend of recent

years. Despite this increase, the increase of vehicle stock was slower. Data on vehicle con-

version and end-of-life for 2012 are not yet available. Therefore, conclusive evaluations of

the newest trends in vehicle stock development are as yet unfeasible. Slightly lower levels of

conversions among new registrations and a growing number of end-of-live vehicles may be

expected.

The quota of end-of-life vehicles is expected to rise in the coming years from 13.5 % to 19 %

of the total stock due to an ageing fleet. Without a significant increase in new registrations,

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projections for future trends are likely to predict low growth or virtual stagnation of the LPG

fleet.

The development of the CNG fleet is not characterised by such obvious trends. In contrast to

LPG, the market for conversion is very small. New registrations of CNG vehicles account for

about 0.2 % of the annual new registrations. The year 2012 saw a further decline in the

growth of the CNG vehicle stock. Evidently, increasing numbers of end-of-life vehicles and a

decrease in new registrations are equally relevant factors in the CNG fleet. Thus, the trend

points towards a stagnation of the CNG vehicle stock. However, future developments in the

range of models on the market or changes to the tax framework are likely to influence the

fleet growth. The factors are discussed in the following chapter (see Chapter 2.3.3).

2.3 Comparison of costs and perspectives for passenger cars

2.3.1 Methodology for full cost accounting

The calculations for the comparison of costs depending on the type of drive for new vehicles

are based on data from the ADAC car cost database (effective July 2012). Factors examined

include loss of value without interest, maintenance costs (e.g. oil changes and inspections

including common wearing parts and consumables, expenses for new tyres), insurance pre-

miums for collision damage waiver and comprehensive cover with a 50 % no-claims dis-

count, motor vehicle tax as well as fuel costs according to manufacturer data after ECE R841.

Fuel costs are assumed to remain constant over an operation period of four years. Energy

tax benefits in force until 31.12.2018 are included according to the German Energy Tax Act

of 15.07.2006 (EnergieStG), §2 (2)2. For the comparison of full costs under full taxation,

regular energy tax rates according to EnergieStG §2 (1) 7 and 83 and resulting higher VAT

levels are calculated. Biomethane is commonly sold at the same price as CNG, thus no dis-

tinction is made. To illustrate the influence of differences in taxation, the full costs of diesel

engines with a mineral oil tax similar to petrol are included.

To simplify comparisons, vehicles with available gas drive are structured in segments follow-

ing the classification of the German Federal Motor Transport Authority. Modelling of the av-

erage price per segment reduces the influences of price policies of individual manufacturers.

The small car segment presents the most diverse range on offer with 12 models or versions

from eight manufacturers. Thus, this segment exemplifies the actual market situation most

1 Fuel prices: Diesel 1.45 €/L, Normal/Super 1.60 €/L, SuperPlus 1.69 €/L, LPG 0.81 €/L, CNG

1.03 €/kg, Ethanol 1.15 €/L

2 13.90 €/MWh gaseous hydrocarbons; 180.32 €/t liquid gas

3 31.80 €/MWh gaseous hydrocarbons; 409.00 €/t liquid gas

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accurately.

In the full cost accounting of the present study, the probability density function of the annual

mileage in the respective vehicle segment interferes with calculation of the full cost. Hence,

the level of utilisation is reported for the purpose of assessing the comparison of cost in ref-

erence to the actual utilisation. In addition, the quartiles of the mileage distribution are re-

ported. These distributions are derived from data reported in the study [Mobilität in Deutsch-

land 2008].

2.3.2 Comparison of the full cost for new vehicles and conversions

The average full cost of the different types of drive in the B-segment is illustrated in Figure 2.

Cost differences for the average annual mileage are generally very slight. The full cost asso-

ciated with an annual mileage of 15,000 km for CNG and LPG engines in the small car seg-

ment over four years is approx. 300 € below petrol engine costs and approx. 150 € below

diesel. In case of full energy taxation, average CNG/LPG costs in the segment would exceed

the cost of diesel but not those of petrol.

Figure 2: Comparison of the average full cost depending on type of drive of new vehicles in the B-segment small cars

The comparison of costs between types of drive in individual cases is complicated by differ-

ing costs depending on engine model and size, but primarily obscured by the price policy of

the individual manufacturers. Different types of drive are positioned and promoted differently

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on the market. The surcharge for LPG may range between 5.5 % and 26 % of the petrol ve-

hicle price (list prices 07/2012). The purchase of an LPG vehicle is generally less expensive

than a diesel car. However, a competitive offer for a diesel vehicle may render the full cost

over four years more economical than the LPG engine. In contrast, LPG cars are generally

more economical over four years in comparison with petrol, except in isolated cases with

very low mileage. CNG vehicles are also subject to a highly variable price policy (2000 to

over 5000 € surcharge). Thus, the purchase costs of CNG engines in some cases exceed

those of a diesel car, yet CNG cars are more economical. However, the calculations further

reveal that for some models, the CNG version is currently less economical than the diesel

engine. The comparison of full costs associated with type of drive differs depending on man-

ufacturer, model and annual mileage. In consequence, diesel or petrol engines may compare

favourably in some cases. The buyer of a new vehicle may struggle to identify potential sav-

ings in the individual case.

Relevance of commercial registrations and company vehicle taxation

The German new vehicle market is dominated by commercial new registrations. In 2012,

almost 62 % of new registrations were commercial customers (see [KBA 2013]). It is com-

mon practice for the drivers of these company cars to select their vehicles. Current legislation

on the taxation of company cars includes the new vehicle list price, taxing 1 % of this price as

an employee fringe benefit in addition to taxable monthly income. Thus, the costs for the

driver are proportional to the original price, but not the running cost. In consequence, there is

an incentive to select inexpensive models, whereas economy of consumption is ignored.

Taxation of company cars according to consumption or emission levels could generate a

distinct shift towards the new registration of gas vehicles. The differences in commercial reg-

istrations depending on the segment are noticeable. Equal registration numbers of private

and commercial cars are reported only in the small car segment. In higher segments, the

proportion of commercial cars clearly prevails. In consequence, there are hardly any higher

segment gas vehicles on the market.

The conversion of petrol vehicles to LPG services a different market. The specific mileage

that renders conversion economically viable strongly depends on consumption and conver-

sion costs. Figure 3 illustrates the range of mileages to amortisation of an LPG system with

conversion costs between 1800 and 3500 € depending on fuel consumption. The vertical

range of the amortisation area reflects the conversion cost. For instance, the conversion of a

vehicle with a consumption of eight litres breaks even after a mileage between 33,000 and

65,000 km, depending on engine model and associated conversion cost. In this context, the

conversion costs of older, simpler engine models are lower than those for engines with so-

phisticated injection technology. It is evident that conversion is particularly beneficial in vehi-

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cles with high consumption. An analysis of the conversion potential of the German passenger

car fleet reveals that 20 % of the current petrol car stock would break even within two years4

of LPG conversion. The actual conversion rate of petrol cars, however, is as low as 0.3 %.

Thus, the cost advantages of conversion to LPG are practically ignored at present.

Figure 3: Range of amortisation of LPG conversion (1800-3500 €) depending on mileage and consumption

2.3.3 Future perspectives for the vehicle stock

The future costs of gas vehicles versus conventional passenger cars depend on a number of

factors. These include differences in fuel and technology costs, but also prevailing price poli-

cies and model ranges of individual manufacturers.

At present, fuel prices are strongly influenced by differences in energy taxation. Thus, subsi-

disation policy is going to define future fuel costs of CNG and LPG in comparison with con-

ventional vehicles. The current framework on average favours diesel engines for new vehi-

cles if no tax benefits apply. However, CNG and LPG may be more economical in individual

cases depending on manufacturer and mileage. Overall, the expiry of existing tax benefits is

going to put an end to the savings associated with gas engines for the driver. In conse-

quence, a decrease in new registration numbers may be expected. In contrast, LPG conver-

sion is going to retain its amortisation potential for a major proportion of the fleet regardless

4 The time period to amortisation was calculated based on mileage after [MiD 2008] and [Polk 2008]

depending on the type of engine (see Appendix I for details)

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of tax benefits. This particularly applies to vehicles with high consumption, high mileage and

simple engines. Future engines on the market are expected to be fuel-efficient petrol engines

with complex technology. Thus, the conversion potential is greatest in the midterm. Ultimate-

ly, developments on the global market for liquid and gaseous fuels are going to define future

fuel pricing. A prognosis for the global market is fraud with uncertainty and thus outside the

scope of the present study.

The comparison of full costs for new vehicles reveals a considerable range. Depending on

model and mileage, significant savings or additional costs for CNG/LPG in comparison with

other types of drive could be detected. In addition to fuel prices, future competitiveness of

CNG/LPG vehicles will depend on both the model range of offer and the price policy of the

individual manufacturer. The trajectory for the market is difficult to predict. However, existing

legislation on environmental aims may promote future benefits for CNG/LPG vehicles. In this

context, CNG vehicles offer a relatively convenient and technologically simple option for

manufacturers to significantly reduce CO2 emissions and comply with CO2 fleet targets. The

second half of 2012 saw the introduction of four new CNG models to the market with further

new releases announced. Greater variety and choice among CNG/LPG vehicles could sup-

port competitiveness with other types of drive, as well as attract customers to favour gas ve-

hicles.

Furthermore, the exhaust emission standard Euro 6 is going to come into force in 2015. In

consequence, exhaust emission control will have to be adapted to reflect stricter nitrogen

oxide regulations, in particular for diesel engines. The additional cost may be transferred to

the customer, potentially reducing or even cancelling out cost advantages of diesel vehicles

over gas drives.

However, perspectives for the future of gas vehicle stocks may not be reduced to considera-

tion of costs alone. To date, this has been demonstrated in the development of CNG/LPG

new registrations and the overall low utilisation of the LPG conversion potential in the fleet. In

other words, even energy tax benefits for gas fuels have not been instrumental in promoting

a major establishment of alternative fuels to date.

The user perspective reveals several potential reasons for the lack of acceptance. Among

those may be the limited availability of fuelling station infrastructure and an overall lack of

information and ignorance towards specific saving potentials. Ultimately, additional subsidi-

sation measures, e.g. development of the fuelling station infrastructure along major motor-

ways and through roads and improved information policy, may be required for the sustaina-

ble integration of LPG and CNG into road transport (see Chapter 4.2).

of 79

3 Environmental comparison and potentials for renewable ener-

gies

The comparison of costs shows that the full costs of CNG and LPG vehicles are fully compet-

itive with conventional engines while subject to energy tax benefits. Positive environmental

effects associated with CNG and LPG are a prerequisite for an extended subsidisation

through reduced energy taxes and additional measures (e.g. development of the infrastruc-

ture). A detailed environmental comparison considering present and future technologies is

presented in the next chapter.

For this purpose, the overall procedure is introduced (3.1) followed by a detailed description

of the baseline data on fuel supply (3.2) and vehicle operation (3.3). Chapters 3.4 and 3.5

illustrate and discuss the environmental impacts along the entire production pathway under

present and future conditions.

3.1 Structure of the environmental comparison

The environmental comparison of CNG and LPG vehicles includes two separate time hori-

zons, i.e. the present situation (2012) and a future scenario (2030). The vehicles, fuels and

supply pathways under investigation are presented in detail in chapters 3.2 and 3.3.

Figure 4: Schematic of the environmental comparison

The environmental comparison is focused on GHG emissions. These are reported in CO2

equivalents. A brief explanation of the methodology for the calculation of CO2 equivalents

associated with fuel supply may be found in Appendix II: Well-to-tank calculations. CO2 emis-

sions derived from the combustion of fuels may be inferred from the carbon content and the

heating values of the fuels. The fuel-specific emission factors reported in TREMOD [IFEU

2012] which are consistent with GHG inventories of the German Federal Environment Agen-

cy (Table 1), serve as standard values for the calculations.

2012 Passenger

car LPG Crude oil CO2eq

2030 City bus CNG

...

Natural gas NMVOC

…

Time horizon Vehicle Fuel Supply

pathway Emissions

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Table 1: CO2 emissions from fuel combustion

Fuel Petrol Diesel CNG LPG

g CO2 per MJ 72 74 56 65

Source: [IFEU 2012]

For fossil fuels, CO2 emissions derived from combustion during vehicle operation (TTW) are

included. In contrast, vehicle operation with renewable fuels is considered carbon neutral.

Therefore, only the proportion of fossil materials required for supply is factored in the calcula-

tions. GHG emissions from combustion of CH4 and N2O are always assigned to the TTW

portion of the model. As a rule, these emissions account for an overall low percentage of the

GHG emission total (see Chapter 3.3.3).

Parameters in addition to GHG emissions in the environmental comparison include:

Nitrogen oxides (NOX)

Non-methane hydrocarbons (NMHC)

Sulphur dioxide (SO2)

Renewable and non-renewable cumulative primary energy demand (CED)

The emission of the pollutants NOX, NMHC und SO2 contribute to air pollution in cities as well

as acidification and eutrophication. Therefore, their annual emission rates are limited for

each EU member state under the NEC Directive (2001/81/EC). At present, a future extension

of the NEC Directive to include particulate matter emissions (in the form of PM2.5) is being

discussed5. It was outside the scope of the present study to distinguish between fine and

coarse particulates (dust) generated during fuel supply (WTT). Therefore, the investigation

includes exhaust particles generated during vehicle operation (TTW) only (Chapter 3.3).

The cumulative energy demand (CED) is defined as the sum of all energies derived from

primary energy feedstocks within the system, including renewable energies and nuclear en-

ergy. Nuclear energy in particular is associated with very low GHG emissions.

5 http://www.umweltbundesamt.de/luft/reinhaltestrategien/nec.htm

http://www.umweltbundesamt.de/luft/reinhaltestrategien/nec.htm

of 79

3.2 Fuel supply – Well-to-tank (WTT)

Fuel supply is a central aspect of the environmental comparison due to the fact that fuel type

and supply pathway may significantly influence the associated environmental impacts. The

following chapter characterises the supply chains for CNG and LPG and the conventional

fuels petrol and diesel. An analysis of the environmental impacts including the emissions of

greenhouse gases (GHGs) and selected pollutants and energy consumption is carried out.

However, the focus is on prospective renewable supply pathways and their potentials for the

application in road transport.

3.2.1 Overview of the emission factors under investigation

Table 2 illustrates the overview of pathways included in the analysis with the respective en-

ergy consumption and associated emissions. For the characterisation of the current situation

in 2012, a distinction was made between established (fossil only) and alternative fuel supply

chains (LPG from natural gas and biomethane). For the projection of the year 2030, a num-

ber of fossil and renewable options were considered due to the fact that the political frame-

work influencing the fuel mix in 2030 is not yet determined. From the present point of view,

the supply chains under investigation are expected to be available in 2030.

A brief description of the individual pathways may be found in the following chapters. Addi-

tional information on the methodology and assumptions for the calculation of well-to-tank

emissions and energy consumption including detailed descriptions of the pathways or cross-

references may be found in Appendix II: Well-to-tank calculations.

of 79

Table 2: Overview of energy consumption and emissions WTT

Fuel Supply pathway Cumulative energy

demand (CED)

CO2

eq

NMHC NOX SO2 CO2

eq

WTW*

MJ/MJ % renew-

able

g/MJ

Typical pathways in 2012

Petrol Crude oil 1.176 0.1% 14.4 0.053 0.037 0.028 86.4

Diesel Crude oil 1.196 0.1% 16.0 0.025 0.040 0.031 90.0

LPG Crude oil 1.163 0.2% 13.8 0.134 0.050 0.089 78.8

CNG Natural gas 4000 km 1.209 0.9% 17.3 0.012 0.045 0.004 73.3

Alternative pathways in 2012

LPG Natural gas 1.118 0.1% 8.1 0.015 0.041 0.027 73.1

Biomethane6 Biogas / biodegradable

waste

(electricity mix today)

2.24 69.2% 29 0.005 0.030 0.024 29

Biogas / renewable re-

sources / liquid manure

(electricity mix today)

2.99 79.6% 39 0.011 0.081 0.031 39

Additional pathways for 2030

Petrol Tar sands 1.422 0.7% 29.6 0.111 0.069 0.149 101.6

Diesel Tar sands 1.445 0.7% 31.5 0.084 0.071 0.154 105.5

CNG/ bio-

methane/

RE methane

Natural gas 7000 km 1.255 1.1% 20.9 0.016 0.064 0.003 76.9

Biogas / biodegradable

waste

(electricity mix 2030)

1.9 86.8% 8.9 0.003 0.020 0.007 8.9

Biogas / renewable re-

sources / liquid manure


2.80 87.5% 26 0.010 0.074 0.020 26

SNG / wood


2.20 87.3% 22 0.012 0.085 0.040 22

Electricity / H2-Electrolysis 1.856 99.1% 1.6 0.003 0.002 0.001 1.6

NB: Blending of biofuels to fossil fuels not considered

*equals CO2 eq including CO2 from the complete combustion of fossil carbon. CH4 und N2O generated during

combustion in the vehicle not included (see Chapter 3.3.3).

Source: own calculations. See Appendix II: Well-to-tank calculations

6 CO2 eq in this study were updated from [BMVBS 2013]. The data are representative for the common

range of the respective supply pathway.

of 79

3.2.2 Comments on fossil fuel production and supply

At present, petrol and diesel are predominantly produced from crude oil. LPG in Germany

arises as a byproduct during crude oil processing, although it may also be sourced as a by-

product during natural gas production. It is common practice to process LPG on site for sub-

sequent transport to Europe by ship, whereas natural gas for CNG is commonly transported

by pipeline (covering an average distance to the EU of 4000 km for marginal demand).

Future consideration of fossil fuel supply chains should seek to focus on demand and availa-

bility in particular. The average transport distance of natural gas for the supply of CNG is

expected to rise to 7000 km by 2030. In addition to production from crude oil, petrol and die-

sel could be supplied through extraction from tar sands. At present, this technique plays a

minor role in overall fuel consumption. However, the share of fuel derived from tar sands

could increase in the future due to the scarcity of conventional crude oil. An increase in tar

sand mining and processing would be associated with environmental impacts.

Blending of biofuels

It may be expected that fuels available at fuelling stations will contain a blend of biofuels, e.g.

- up to 7 vol. % biodiesel in diesel

- up to 5 vol. % (E 5), or 10 vol.% bioethanol (E 10).

The stipulations of the Biofuels Quota (§ 37 BImSchG) of 6.25 % (MJ/MJ) further allow the

offsetting of biomethane against the quota. Biofuels applied in the context of the quota

achieved an energetic proportion of 5.6 % or 5.8 %7 in 2011 and 2012. In 2012, this would

correspond to greenhouse gas (GHG) savings of approx. 2.9 % or 2.4 %, respectively, in

reference to typical or default values of the 2009/28/EC Directive compared to purely fossil

petrol or diesel.

Due to these minor GHG savings of biofuels, and the wide range of outcomes depending on

substrate and country of origin of liquid biofuels, the focus of the present study is restricted to

purely fossil fuel supply. For LPG derived from crude oil or CNG from natural gas, blending of

biofuels (e.g. biomethane) is equally excluded.

3.2.3 Comments on renewable fuel production and supply

In principle, the individual drive options under investigation (diesel, petrol, CNG, LPG) are

compatible with a multitude of fuels derived from renewable energy sources. One principal

focus of the present study was the investigation of renewable fuels applicable to the target

7 Calculation based on [BLE 2013]

of 79

drive options CNG/LPG, and the associated environmental impacts (see Table 2). In con-

trast, liquid biofuels are excluded from the present environmental comparison.

Renewable fuels for 2012 include compressed biomethane derived from biogas. In addition,

the projection for 2030 explores biomethane produced from the gasification of wood chips

with subsequent methanation (i.e. bio-SNG) and compressed methane derived from renewa-

ble electricity (RE methane). In theory, production of bio-LPG is equally conceivable, yet

there is little market relevance at present. Therefore, this option is introduced, but not includ-

ed in the environmental comparison scenario for 2030. In addition, liquefied biomethane

(LBG – liquefied biogas) is currently under consideration in countries like Germany and the

Netherlands, whereas Sweden and the United Kingdom are already establishing its applica-

tion. However, due to the scarcity of data, this pathway is excluded from the analysis.

Table 3 gives a broad overview of the renewable fuels included in the analysis. A detailed

characterisation may be found in the following paragraphs.

Table 3: Overview of the marketability of the renewable supply pathways under investigation

Pathway Brief description Feedstocks Technological

status quo

Market situation

Biomethane

from biogas

Fermentation, gas

processing

Renewable resources

(mostly maize)

Organic waste and

residues

(e.g. biodegradable

waste, sludge, distill-

ers grains, straw)

Commercial GER: major capaci-

ties based on re-

newable resources

(esp. electricity and

heat sector), minor

capacities based on

residues (currently

relevant for the

transport sector)

Biomethane

from syn-

thetic natu-

ral gas (Bio-

SNG)

Gasification, gas condi-

tioning, synthesis, gas

processing

Lignocellulosic bio-

mass

Pilot phase EU: Demonstration

plant in

Güssing/Austria,

commercial plants

in Sweden under

construction

RE-

Methane

Electrolysis of H2 with

renewable electricity

and subsequent

methanation

Electricity,

CO2

Pilot phase GER: ZSW/Stuttgart

(CO2 from air),

EWE/Werlte (CO2

from biogas upgrad-

ing)

Bio-LPG Byproduct of

HVO/HEFA produc-

tion; depending on the

concept also

BTL/Fischer-Tropsch-

Synthesis

Oil-based (HVO) or

lignocellulosic (BTL)

biomass

HVO/HEFA:

commercial

BTL/FT: to date

pilot phase

LPG utilisation

frequently plant-

integrated (e.g.

process energy)

HVO:

GER: no plant,

EU: Rotterdam,

Porvoo

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Biomethane

In 2010, approximately 10 PJ of gas fuels were utilised in Germany (Drucksache 17/9621

based on Energiestatistik). Biomethane may act as a supplement or substitute for natural

gas, thus representing a strategic resource for sustainable mobility in the coming decades.

Capacities for the supply of biomethane from biogas were substantially expanded in the past

five years. However, the establishment of gas-powered vehicles has been relatively slow. As

a result, biomethane sales targets in the fuel sector have been achieved to a limited extent.

The production of biogas via fermentation (anaerobic fermentation) with subsequent gas up-

grading and infeed into the grid represents the current state of the art. The plant capacity

installed by the end of 2012 of approx. 70,000 Nm3/h [DBFZ et al. 2013] equals an annual

production capacity of more than 20 PJ. Moreover, further 36 plants are under construction,

and 38 additional plants are in the planning stage [DENA 2013]. Throughout Europe, availa-

ble capacities amount to approx. 700 MW of biomethane in the key regions Sweden, Switzer-

land and the Netherlands [Green Gas Grids 2012]. More than 80 % of current facilities in

Germany are operated with renewable resources, i.e. predominantly maize and grass-based

silage, as well as animal waste like liquid manure. In the transport sector, biomethane is ap-

plied primarily from residues and waste materials. This may be linked to the fact that as of

2011, biomethane derived from residues and waste materials is eligible to receive double

credits within the quota framework according to § 37 BImSchG. In contrast to bioethanol and

biodiesel, there is no specific quota for biomethane. Moreover, natural gas as a fuel is not

subject to a quota. As a result, biomethane is only applied to the quota as a biofuel if there is

no alternative, or if available alternatives are cost-intensive in comparison.

Figure 5 presents biofuel utilisation in Germany in 2011 and 2012 according to an evaluation

report8 of the German Federal Office for Agriculture and Food (BLE) in contrast with the offi-

cial mineral oil statistics of the German Federal Office of Economics and Export Control

(BAFA). According to [BLE 2013], approx. 0.3 PJ biomethane were applied in road transport,

including one third not credited to the quota. In 2012, biomethane in road transport amounted

to approx. 1.15 PJ, representing more than 10 % of natural gas based fuels. The total includ-

ed 0.9 PJ (and 0.8 PJ thereof double credited) credited to the quota. The increase between

2011 and 2012 is based almost exclusively on biomethane from residues and waste materi-

als. Please note that in contrast to the relative growth, the absolute increase of biodiesel de-

rived from waste edible fats and oils is significantly higher than the increase of biomethane

from residues and waste materials.

8 Applies to certified biomass after Biokraft-NachV and BioSt-NachV

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Figure 5: Biofuels subject to energy tax benefits credited to the quota in 2011 and 2012 (DBFZ based on BLE 2013 and BAFA)

Sustainability certification is required for crediting9 to the biofuels quota. The German Bio-

kraft-NachV10 does not define a default value for biomethane from renewable resources.

Moreover, calculation methodology for the GHG balance complying with the legal framework

is not fully developed to date.

Stakeholder projections for 2013 assume that the absolute volume of biomethane utilised in

road transport will increase by a third in comparison with the previous year [DENA 2013].

Thus, the relative volume remains rather constant.

Verbio alone may supply biomethane from bioethanol production residues (distillers grains)

with a current capacity of 60 MW11 to both the road transport and cogeneration sectors. Un-

der the German Renewable Energy Act (EEG), biomethane from renewable resources is

primarily applied in the electricity and heat sectors.

9 In this case by transfer of compliance with obligations to a third party according to § 37a Satz 4 BIm-

SchG (German Federal Immission Control Act)

10 Biofuels Sustainability Ordinance

11 Source: verbiogas

(http://www.verbio.de/fileadmin/user_upload/verbio/02_Produkte/FactSheet_verbiogas_PR.pdf), cor-responding to approx. 1.8 PJ/a at full load

136 PJ

0

20

40

60

80

100

120

140

160

2011[BLE]

2011[BAFA]

2012[BLE]

2012[BAFA]

Bio

fuels

in P

J/a

Tax-exempt biofuels

Biomethane double (waste)

Biodiesel double (waste)

Biomethane (esp. waste)

Bioethanol (energy crops)

Hydrotreated oils

Biodiesel (waste)

Biodiesel (oil seeds)

Quota volume

Quota credit

BLE data

BAFA data

6.25% biofuels quota in 2012 equals approx. 136 PJ

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Furthermore, biomethane may be supplied through the gasification of lignocellulosic/ woody

biomass with subsequent methanation. In contrast to biomethane from biogas, this conver-

sion technology is not currently available on the market. Bio-SNG is successfully produced in

a pilot plant in Güssing (Austria) with a capacity of 1 MW biomethane. Additional plants in the

planning or construction stage are located in Sweden, Switzerland and Germany. However,

expectations for development of bio-SNG production facilities fall short due to economic chal-

lenges in competitiveness, although the technology is readily available. Nevertheless, the

production pathway remains promising for future utilisation of residues and waste materials

as well as lignocellulosic biomass (no immediate food/feed competition).

Synthetic methane from renewable electricity (RE methane)

Electricity may be converted to hydrogen through electrolysis, which in turn may be used to

synthesise methane in combination with CO2. The application of this procedure is being con-

sidered for wind and solar power plants at times of excess electricity and low demand. Thus,

the integration of fluctuating renewable power sources into the energy system would be facili-

tated [dena et al. 2012].

Excess electricity converted to RE methane may be stored in the existing natural gas infra-

structure. Thus, storage of large capacities over extended periods of time is feasible, and the

volumes in storage are available for a number of applications, including CNG fuel. However,

future quantities of so-called excess electricity are very sensitive to a number of parameters.

These include expansion of both the renewables sector and the grid, electricity storage, de-

mand side management and not least increasing the flexibility of existing conventional power

plants. Short-term gains from excess electricity are negligible compared to the total of elec-

tricity generated from renewable resources. Nonetheless, accelerated development of the

renewable energy sector would in all likelihood result in regionally significant quantities within

the present decade. Fluctuations in renewable electricity generation may reach proportions

of 70 %, 80 % or more in the annual energy balance. If no countermeasures like energy stor-

age are taken, the resulting excess electricity increases dramatically, as illustrated in Table 4

in scenario C 2023.

Table 4: ‘Dumped energy’ according to German Network Development Plan [NEP 2013, p. 64, Table 9]

of 79

The simulations informing the German Network Development Plan show that the accelerated

development of the renewables sector according to the energy plans of the German Federal

States (NEP scenario C 2023) would significantly increase the proportion of renewable elec-

tricity lost to the grid (7.0 TWh in scenario C 2023, compared to 0 TWh and <0.1 TWh in the

scenarios A 2023 and B 2023, respectively). This sensitivity is distinctly obvious in the com-

parison of the loss of 7.0 TWh of dumped energy under accelerated renewables develop-

ment in the year 2023 (NEP scenario C 2023) with the loss of 0.8 TWh in 2023 under renew-

ables development following the BMU Leitstudie (NEP scenario B 2023).

Even in the case that the quantities of so-called excess electricity could be contained with

measures like grid expansion, electricity storage etc., the production of electricity-to-methane

could accommodate relatively high technical potentials of renewable electricity in Germany.

A strategic decision to produce RE methane with significant (renewable) energy input in or-

der to utilise the product in combustion engines with relatively low energy conversion effi-

ciency should be discussed in the context of various visions for mobility.

The production of hydrogen through water electrolysis could further develop into a relevant

electricity consumer in the energy sector with significant potential to provide grid services,

such as demand side management and demand response.

Figure 6 illustrates the underlying principles of the process electricity-to-methane (RE me-

thane) exemplary for the utilisation of CO2 from biogas upgrading.

Figure 6: Methanation of H2 from electricity utilising CO2 from biogas upgrading

At the end of 2012, about 120 biomethane plants with an installed capacity of approx.

140,000 m³/h crude biogas, or an entry capacity of approx. 70,000 m³/h biomethane [DBFZ

et. al. 2013], were in operation in Germany. The upgrading of biogas to natural gas quality

entails the removal of CO2 with physico-chemical processes. The processing generally in-

of 79

creases the methane content from 40 – 75 % in crude biogas to over 90 %. In compliance

with § 36 of the Gas Grid Access Ordinance (Gasnetzzugangsverordnung - GasNZV), the

resulting gas is required to comply with the stipulations in work sheets G 260 and G 262 of

the German Association for Gas and Water e.V. (DVGW, Version 2007), both at the feed

point and during the infeed. According to these stipulations, of the original CO2 content of 25

– 55 %, a maximum of 6 % may remain in the resulting biomethane. The arising CO2 may be

utilised for the supply on synthetic methane. For a biomethane production of 560 Mio. m³/a12,

a volume of approx. 300 Mio. Nm³/a CO2 is expected. In theory, these quantities could be

utilised to produce approx. 3 TWh (10.8 PJ) of synthetic methane annually. The resulting

methane is equal to the current consumption of natural gas in the transport sector, and cor-

responds to 0.46 % of the total fuel consumption in road transport in 2012. In theory, addition

of CO2 extraction facilities to existing biogas production plants would be possible. Moreover,

CO2 may be extracted from air. Thus, the supply of CO2 does not present a major limitation

for the production of RE methane. The energy demand according to Sterner [2009] amounts

to approx. 8.2 MJ electricity per kg CO2, resulting in an additional electricity demand of ap-

prox. 0.45 MJ per MJ methane.

LPG from renewable feedstocks

The production of BTL (Biomass to liquid) fuels (HVO/HEFA) with hydrotreating of vegetable

oil generates approx. 0.06 MJ gaseous products per MJ HVO according to the manufacturer

[IFEU 2006]. For the most part, these products consist of LPG. An LPG content of energetic

5 % HVO of the total fuel consumption would result in a proportion of 0.35 % LPG from HVO

production of the total fuel consumption.

The extent of market relevance remains to be seen. However, major market shares appear

currently unlikely. Thus, the present study does not consider LPG from renewable feed-

stocks.

12 Capacity at the end of 2012 for 8,000 equivalent full load hours annually

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3.3 Vehicle operation – tank-to-wheel (TTW)

The operation of vehicles is associated with pollutants and GHG emissions generated during

the combustion of fuels. There is a strong correlation between energy consumption and CO2

emissions on the one hand and the overall efficiency of the drive concept on the other

(3.3.2). However, exhaust emissions are strongly dependent on the employed technologies

for exhaust emission control, or the prevailing emission limits (3.3.3).

3.3.1 Vehicles under investigation

The vehicles included in the models were generic new vehicles of the medium size range per

vehicle category according to TREMOD [IFEU 2012]:

Medium-size passenger car13

City bus (total weight 15-18 t)

In this context, all possible drive concepts and fuel options were applied to a typical vehicle

without further consideration of model-specific features. Thus, additional technological ad-

vances unrelated to engine or fuel type were excluded from the analysis.

Relevance of the vehicles included in the model

Passenger car transport is responsible for approx. 85 % of the mileage and 60 % of the GHG

emissions in road transport [IFEU 2012]. In consequence, passenger cars were the focus of

a number of recent studies comparing the drive concepts CNG and LPG (e.g. [JEC 2007],

[DVFG 2010], [LBST 2010], [DENA 2011]). City buses, however, represent a special case of

established CNG engines in the heavy commercial vehicle sector. Although buses do not

feature strongly in the overall GHG balance, the air quality in inner city areas is strongly de-

pendent on their emissions. Potentials may arise in this context for the overall integration of

CNG into road transport through a dedicated development of the fuelling station infrastruc-

ture for fleets. Furthermore, the freight transport sector could benefit from the continued de-

velopment of alternative engine technologies. A separate study in the context of the Mobility

and Fuels Strategy investigated potentials of CNG and LNG (liquefied natural gas) for

transport by lorry (see study on catenary hybrid trucks).

13 Defined as a passenger car with 1.4-2.0l engine displacement, according to TREMOD, representa-

tive of approx. 70 % of the vehicle sectors ‘lower middle class’ and ‘middle class’ registered with the Federal Motor Transport Authority.

of 79

3.3.2 Fuel consumption

Due to the different specific CO2 emissions (per MJ) associated with CNG, LPG and conven-

tional fuels (see Table 1 in 3.1), the energetic fuel consumption represents the most im-

portant factor in the comparison of GHG emissions. In this context, fuel consumption is

strongly dependent on the individual features of the vehicle and the manner of operation,

which should be representative across all engines in an environmental comparison. Con-

sumption levels were derived from previous work carried out by the JEC group

(JRC/Eucar/Concawe). Further data sources included the Manual for Emission Factors

(HBEFA) and specific vehicle type-test data of recent vehicle models. The analysis and cal-

culation of consumption levels is described in the following chapters.

Data sources and sensitivities

The difference between fuel consumption in CNG/LPG vehicles and petrol cars is dependent

on a number of parameters. The energy conversion efficiency in the engine may be improved

by the utilisation of fuels with a higher anti-knock capacity/ octane rating compared to petrol.

The specific design of the vehicle plays a vital role and may differ significantly. The installa-

tion of LPG tanks and especially CNG tanks adds to the overall weight of the vehicle. Moreo-

ver, engines of gas vehicles are frequently larger to compensate torque losses [JEC 2011].

Individual adaptations are ultimately part of the strategy of the individual manufacturer, how-

ever, they may influence fuel consumption significantly.

JEC 2011

The [JEC 2011]14 report took the adaptations described above into consideration for CNG

vehicles, thus simulating comparable consumption levels aided by the ADVISOR model15 for

the New European Driving Cycle (NEDC). However, for LPG vehicles, vehicle design was

kept constant apart from a slight increase in the weight of the tank. The results of the model

for new vehicles in 2002 were consistent with recent vehicle type-test data for new petrol

cars.

The resulting consumption levels for present and future vehicle generations16 are presented

in Table 5. According to JEC data, the fuel consumption of CNG and LPG of 187-190

MJ/100km in the generation ‘2010 advanced’ is comparable to petrol direct injection engines.

Future concepts employing hybrid engine technology promise a significant improvement of

14 An update of the JEC report (Version 4, 2013) was carried out simultaneously to the present study,

and could thus not be incorporated

15 A tool developed by the National Renewable Energy Laboratory (NREL) for the simulation of fuel

consumption and driving quality (http://www.nrel.gov/vehiclesandfuels/vsa/related_links.html#advisor) 16

Defined as a generic ‘Golf class’

http://www.nrel.gov/vehiclesandfuels/vsa/related_links.html#advisor

of 79

efficiency. CNG hybrids are expected to specifically benefit due to the fact that their inherent

efficiency advantage at high speeds is superior to petrol cars [JEC 2011]. Hybridisation of

bivalent cars was not considered in the study, so data for the hybridisation of LPG remains

unavailable.

Table 5: Fuel consumption of a small family car (Golf class) in the NEDC after JEC 2011

Generation

Petrol Diesel CNG LPG

(Direct injec-

tion)

(with particulate

filter) (Dedicated) (Bi-Fuel)

MJ/

100km

MJ/

100km

Diff. to petrol

MJ/

100km

Diff. to petrol

MJ/

100km

Diff. to petrol

“2002 conventional“ 209 183 -12% 223 +7% 224 +7%

“2010 advanced“ 188 166 -12% 187 -0,4% 190 +1%

“2010 ad-

vanced+hybrid“ 154 133 -14% 139 -10% n.a.

Source: JEC 2011, data rounded to integers

Comparison with recent type-test data

In the following paragraph, type-test data for three recent vehicles of the manufacturer VW

with LPG and CNG models are compared with data for new vehicle reported in the [JEC

2011] report. This serves the purpose of verification of assumptions and sensitivities on the

parameters fuel consumption and vehicle design. The vehicles included for comparison are:

VW up 44 kW (petrol) with VW eco up 50 kW (CNG),

VW Golf Plus 1.2 l TSI 77 kW (petrol) with Golf Plus 1.6 l BiFuel 75 kW (LPG),

VW Caddy 1.2 l TSI (Petrol) with VW Caddy 2 l Erdgas (CNG) and 1.6 l BiFuel

75 kW (LPG)

The JEC vehicle is associated with lower CO2 emission both as a CNG or LPG engine com-

pared to petrol models (Figure 7, top). ). A look at the three sample vehicles reveals that the

CNG and LPG engines showed CO2 emissions that were equal or higher compared to petrol

cars. The reason for this may be the larger engine displacement, and the associated elevat-

ed consumption. In contrast, the VW Eco Up (CNG) was the only vehicle in which the engine

displacement was held constant, and its CO2 emissions were reduced by 27 % compared to

a petrol vehicle.

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Source: own calculations based on manufacturer data and [JEC 2011]

Figure 7: Exemplary comparison of CO2 emissions and relevant vehicle design of selected passenger cars

All gas-powered vehicles, especially CNG vehicles, carry additional weight in comparison

with petrol models. However, at least in the case of the VW Eco Up (i.e. with a constant rela-

tive engine displacement) there are no negative impacts on CO2 emissions. All recent LPG

models included in the analysis are fitted with a larger engine displacement, thus resulting in

a higher weight and slightly higher CO2 emissions compared to the JEC model. The assump-

tions in the JEC report are primarily derived from converted LPG cars originally operated with

petrol (see Chapter 2.2). In this case, drivers may be content to accept a certain loss of driv-

ing quality in the LPG mode and forego modification of the engine displacement if the petrol

mode still delivers high performance. However, in this case the CO2 benefits of the LPG

mode assumed in the [JEC 2011] report cease to apply.

In the present context, the analysis of type-test data may serve as an exemplary comparison.

Beyond that, the interpretation of test-type data as representative and comparable levels of

consumption is not valid due to the low number of models included, and the range of tech-

0%

-30%

-25%

-20%

-15%

-10%

-5%

+0%

+5%

+10%

+15%

+20%

CNG LPG CNG LPG CNG LPG

VW Up VW GolfPlus

VW Caddy JEC ("Golf class"2010+)

CO2 emissions per km (NEDC combined)

-20%

+0%

+20%

+40%

+60%

+80%

CNG LPG CNG LPG CNG LPG

VW Up VW GolfPlus

VW Caddy JEC ("Golf class"2010+)

Engine displacementEngine powerVehicle weight

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nical modifications versus the petrol engine.

The JEC data, however, offer a consistent generic database for energetic consumption (in

MJ). The applicability of the data is plausible under the assumed vehicle parameters.

Fuel consumption in TREMOD/HBEFA

In contrast to previous data sources, the HBEFA [INFRAS 2010] reports consumption for

specific traffic conditions reflecting actual traffic. The TREMOD model ([FEU 2012] is also

based on these data, thus allowing the weighting of specific traffic conditions and the calcula-

tion of consumption for typical segments of the German vehicle fleet. Consumption data for

CNG and LPG cars is based on fewer actual measurements than petrol and diesel vehicles.

For this reason, TREMOD/HBEFA data are not immediately applicable. They rather serve for

the standardisation of consumption levels of the average German fleet of petrol and diesel

vehicles in actual traffic. Furthermore, the consumption for new vehicle registrations in the

years 2012 and 2030 may be inferred based on scenarios. For this purpose, TREMOD in-

cludes a trend scenario in which the CO2 fleet limit for passenger cars is reached in 202017,

and projected to decrease annually by 1.2 % from there.

Consumption levels for passenger cars

Table 6 illustrates the consumption derived for WTW comparisons for passenger cars in

2012 and 2030. Due to the fact that differences between the individual consumption rates of

the “2010advanced” generation in the JEC 2011 report were non-significant, the same ener-

getic fuel consumption is assumed for CNG/LPG and petrol cars for simplification.

Efficiency increases of the new vehicle fleet in 2030 for petrol and diesel engines correspond

to the values of the TREMOD trend scenario (see above). This scenario reflects the likeli-

hood of a (part) hybridisation. In a conservative approach, it is expected that half of the CNG

new vehicle fleet will be at an advantage of 10 % relative to petrol hybrid vehicles according

to [JEC 2011]. Thus, the overall fuel consumption of CNG vehicles in 2030 is projected to be

5 % lower compared to petrol cars. Due to the fact that there are no data available for LPG,

the consumption is assumed to be equal to petrol cars.

17 The European average limit for passenger cars is 95 g CO2/km, the German level in TREMOD is at

108 g/km

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Table 6: Fuel consumption of average passenger cars in 2012 and 2030

TREMOD data Projected data in reference to JEC 2011

Generation

Petrol Diesel CNG LPG

MJ/

100km

MJ/

100km Diff. to petrol

MJ/


MJ/


2012 238 198 -17% 238 - 238 -

2030 163 139 -15% 155 -5% 163 -

Diff. to 2012 -32% -30% -35% -32%

Source: TREMOD [IFEU 2012], own calculations based on [JEC 2011]

Consumption levels for city buses

City bus consumption (see Table 7) is calculated analogous to passenger cars. For diesel

buses, the consumption is modelled as the average commercial vehicle in the German fleet

for the years 2012 and 2030 in a typical inner-city traffic situation according to

TREMOD/HBEFA.

In contrast to passenger cars, no type-test data is available for consumption of CNG city

busses. However, based on recent data, the following assumptions may be made: the ener-

getic consumption of a modern CNG bus with EEV standard according to HBEFA exceeds

that of a diesel bus by 24 %, whereas [VTT 2012] quantifies the excess consumption be-

tween 32 % and 39 %. The discrepancy may be due to calculations based on differing inner-

city driving cycles (VTT: ‘Braunschweig Cycle’ versus HBEFA: Weighting of specific inner-

city traffic situations). For the environmental comparison in the present study, the excess

consumption is simplified to an average of 30 % in 2012.

Similar to passenger cars, hybrid engines are assumed to be the key technology for city bus-

es in 203018. Thus, the trend could equally apply to CNG buses. A number of sources ex-

pect CNG engines to reap more benefits from increasing efficiency through hybridisation

than diesel engines:

Spark-ignition engines utilising CNG or petrol are expected to benefit more strongly

from hybridisation than compression-ignition engines such as diesel ([VTT 2012],

[JEC 2011]).

CNG engines operated in the part-load range are less fuel-efficient, yet operation in

this particular range is the rule in city traffic (JEC 2011). Thus, city buses are ex-

pected to benefit more strongly from hybridisation than passenger cars.

18 Since 2011, hybrids are the most common alternative drives among new registration motor buses

[KBA 2011]

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Preliminary data for the Hyundai ‘Hybrid Blue-City’ report a 30-40 % decrease in con-

sumption compared to non-hybrid CNG buses19. Thus, the results exceed the predic-

tions of 20-30 % for diesel buses after [VTT 2012] by approx. 10 %.

Additional reductions in consumption for CNG city buses could be achieved through the du-

al-fuel technology that is currently being considered for commercial vehicles. With this ap-

proach, CNG may be employed in compression-ignition engines with a projected efficiency

equal to diesel engines20.

Thus, the scenario for 2030 assumes a relative decrease of consumption of 20 % for diesel

and 35 % for CNG city buses, resulting in a reduction of the excess consumption of CNG

buses to 5 %.

Table 7: Fuel consumption of average city buses in 2012 and 2030

Generation Diesel CNG

MJ/100km MJ/100km Diff. to diesel

2012 1210 1573 +30%

2030 970 1022 +5%

Diff. to 2012 -20% -35%

Source: TREMOD [IFEU 2012], [VTT 2012], own assumptions

3.3.3 Greenhouse gas and pollutant emissions

In addition to CO2, vehicles with combustion engines emit GHGs in the form of CH4 (me-

thane) und N2O (nitrous oxide). In contrast to the linear correlation between CO2 emissions

and fuel consumption, the emissions of methane, nitrous oxide and other air pollutants are

influenced by engine technology and exhaust gas aftertreatment measures. The Handbook

‘Emission Factors for Road Transport’ (HBEFA) supplied data for modelling based on actual

typical traffic conditions. Thus, in addition to distinction according to vehicle type and fuel

type, the factors road category and exhaust technology may be included. Assignments were

made for the following emission factors:

Passenger car:

Average distribution of mileage in all road categories

Exhaust emission standard Euro 5 for 2012, Euro 6 for 2030

Fitting of diesel cars with particulate filters

19 http://www.hyundai.com.au/About-Hyundai/News/Articles/Hyundai-continues-its-Blue-Drive-push-

with-CNG-Hybrid-Bus/default.aspx

20 http://cleanairpower.com/duel-technology.php

http://www.hyundai.com.au/About-Hyundai/News/Articles/Hyundai-continues-its-Blue-Drive-push-with-CNG-Hybrid-Bus/default.aspx

http://www.hyundai.com.au/About-Hyundai/News/Articles/Hyundai-continues-its-Blue-Drive-push-with-CNG-Hybrid-Bus/default.aspx

http://cleanairpower.com/duel-technology.php

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City bus

Mileage in inner city areas only

Exhaust emission standard diesel: Euro V incl. exhaust gas recirculation for 2012, EURO

VI for 2030

Exhaust emission standard CNG: EEV (Enhanced Environmentally Friendly Vehicle)

Table 8 illustrates the GHG emissions factors under investigation. GHG emissions generated

during vehicle operation are highest for petrol vehicles and lowest for CNG. The GHG ad-

vantage of CNG and LPG is mainly based on the low carbon content. The advantage of die-

sel, however, is related to the higher energy efficiency of the engine. For this reason, the

GHG emissions of CNG city busses with lower efficiency in 2012 are marginally lower than

those of the diesel buses. In 2030, however, increased efficiency of CNG engines is ex-

pected to result in a pronounced GHG advantage. The GHGs N2O and CH4 account for a

minor proportion of the GHG emission total (max. 2.6 %).

Table 8: Emission factors for greenhouse gases TTW

Vehicle/

Emission Standard Engine

CO2 equivalents N2O CH4

Diff. to petrol car/

Diesel bus

part

N2O+CH4 g/km mg/km mg/km

Passenger car 2012

(Euro 5)

Petrol - 0.2% 172 0.4 7

CNG -22% 0.3% 134 0 15

LPG -9% 0.6% 156 2.0 15

Diesel -14% 1.1% 148 4.7 10

Passenger car 2030

(Euro 6)

Petrol - 0.2% 118 0.4 6

CNG -26% 0.4% 87 0 13

LPG -9% 0.9% 107 2.0 13

Diesel -11% 1.5% 104 4.7 9

Bus 2012

(Euro V)

Diesel 0.2% 895 0 77

CNG 0% 1.7% 881 0 623

Bus 2030

(Euro VI)

Diesel 0.1% 718 0 35

CNG -18% 2.6% 572 0 623

Source: Own calculations. HBEFA 3.1

The resulting differences between actual air pollutant emissions of the engines under investi-

gation are slight according to HBEFA. As a rule, the emission limits according to Euro 5/V

and Euro 6/VI are complied with under actual traffic conditions. An exception may be found in

LPG and diesel cars with NOX emissions that exceed emission limits derived from test cycles

in actual traffic conditions. For the 2030 scenario, this assumption of the HBEFA has not

of 79

been adopted. Compliance with the limit under actual traffic conditions in 2030 is anticipated

instead.

The emission performance of CNG buses with respect to PM emissions is superior to Euro V

diesel buses. However, the introduction of the Euro VI standard will render these differences

negligible. It is expected that the associated requirements for exhaust gas aftertreatment

technologies, e.g. SCR and particulate filter systems, will result in additional costs and the

need for more sophisticated maintenance and monitoring measures. CNG buses will be ex-

empt from these requirements.

Table 9: Emission factors for air pollutants TTW

Vehicle/

Emission Standard Engine

NOx PM NMHC CO SO2*

g/km mg/km mg/km g/km mg/km

Passenger car 2012

(Euro 5)

Petrol 0.06

1.9

6.8 0.56 0.87

CNG 1.2 0.48 0

LPG 0.1 11.5 0.90

Diesel 0.53 1.5 9.5 0.02 0.74

Passenger car 2030

(Euro 6)

Petrol 0.05

1.6

5.9 0.44 0.60

CNG 1.0 0.38 0

LPG 0.08** 9.9 0.71

Diesel 0.06** 1.4 8.5 0.03 0.52

Bus 2012

(Euro VI/EEV)

Diesel 3.37 44.8 74.8 1.03 0

CNG 0.83 1.5 49.8 1.18 4.51

Bus 2030

(Euro VI/EEV)

Diesel 0.62 5.5 33.9 1.32 0

CNG 0.83 1.5 49.8 1.18 3.61

* based on a sulphur content of 8 ppm for petrol/diesel ** in contrast with HBEFA, compliance with the limit is assumed Source: HBEFA 3.1. Own calculations

Research on converted LPG engines in Euro 4 passenger cars showed that emissions may

in some cases rise significantly compared to the original petrol vehicle [EMEP/EEA 2012].

These results could not be verified in the following environmental comparison for present and

future commercial vehicles. However, the findings should be incorporated in the evaluation of

present LPG passenger cars, as the majority of the present LPG fleet has undergone con-

version.

of 79

3.4 Well-to-wheel (WTW) comparison 2012

3.4.1 Greenhouse gas emissions

Passenger car

Given the present fuel supply pathways, the comparison of GHG savings in reference to a

petrol engine shows that CNG cars generate the highest GHG savings with 15 %, followed

by diesel with 13 % and LPG with 9 % (Figure 8). ). The differences illustrate the relevant

GHG savings potentials of the individual fossil fuels for a generic average passenger car.

However, the considerable range associated with individual car models should be kept in

mind (see Chapter 3.3.2). Yet, significantly higher GHG savings may be achieved with re-

newable fuels. The GHG emissions of CNG vehicles operated with biomethane produced

from biodegradable waste are 66 % lower compared to a petrol vehicle. The utilisation of

biomethane derived from renewable resources/ liquid manure WTW may save 55 % of GHG

emissions.

Figure 8: WTW Greenhouse gas emissions for passenger cars in 2012

0

50

100

150

200

Petrol car Diesel car LPG car CNG car LPG car CNG car CNG car

WTW Greenhouse gas emissions for passenger cars in 2012

WTT TTWIn g CO2 eq / km

Crude oil Crude oil Natural gas

Natural gas(4000 km)

Biomethane –biodegradable

waste*

Biomethane –renewable resources /

liquid manure*

Crude oil

-13% -9% -15% -15% -66% -55%

Established pathways Alternative pathways

*Update on biomethane [BMVBS 2013] (see Chapter 3.2)

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Comparison with other studies

Recent work on the comparison of LPG and CNG vehicles employ a range of methods and

show considerable variation in the input data. Thus, findings may significantly differ between

studies. In the following, the underlying assumptions and methodology of the present study

are compared to the study of the German LPG Association [DVFG 2012] and the study of the

Association Erdgas Mobil [LBST 2010].

Distinctions between the studies

The study of the German LPG Association investigates CNG, LPG and petrol vehicles. In

contrast to the present study and [LBST 2010], renewable fuel supply pathways are not con-

sidered. Therefore, only CO2 emissions21 of recent passenger cars operated with fuels pro-

duced from fossil supply pathways are included. Moreover, only the status quo is presented,

as the [DVFG 2012] study does not include future scenarios.

Table 10: System boundaries and fundamental assumptions of recent studies on environmental comparisons of CNG/LPG with other fuels

Study [DVFG 2012] [LBST 2010] Present Study

Location WTT: EU

TTW: Germany

EU Germany

Period of

investigation

Status quo (2010) 2010

2020

2012

2030

Vehicle type Passenger car Passenger car

(Qualitative assessment

of commercial vehicles)

Passenger car

Bus

WTT Specific pathways Ranges Specific pathways

Renewable energies ex-

cluded

Renewable energies

examined (CNG)

Renewable energies ex-

amined (CNG)

TTW Variety of vehicles (Stock

Germany according to

DAT).

Means (cohorts)22

Generic vehicle “Golf

class”

Ranges

Generic vehicle (car 1.4-2l

engine displacement).

Means

21 CO2 equivalents from CH4 and N2O are excluded from the model, thus the comparison is based on

CO2 only. This is a valid simplification due to the low proportion of CH4 and N2O (see Chapter 3.3.3)

22 Calculation of TTW GHG savings in Table 7, line 4 in DVFG 2012 inexplicable

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Results WTW, WTT and TTW

Figure 9 illustrates the differing results for CO2 emissions of CNG and LPG cars. Thus,

[DVFG 2012] finds that the CO2 emissions per km of an LPG car are 4 % lower than those of

a CNG car across the entire causal chain (WTW). However, both the present study and

[LBST 2010] report higher GHG savings for CNG (-7 % and -16 %, respectively).

Figure 9: Comparison of the CO2 benefits of CNG and LPG from fossil supply pathways for motors cars in 2010/2012 in recent studies

The reasons for the discrepancies may be explained with differences in the underlying as-

sumptions for WTT and TTW.

Analogous across all studies, the CO2 parameters for fuel supply (WTT) are based on data

reported in the JEC studies [JEC 2011]. However, differing assumptions for the origin of fos-

sil fuels in Germany were made:

[DVFG 2012]: LPG from natural gas (transport by ship). CNG per pipeline, distance 4000

km

[LBST 2010]: LPG from crude oil. CNG from the North Sea, distance 1000 km

Present Study: LPG from crude oil. CNG per pipeline, distance 4000 km

The resulting differences between the supply pathways are considerable, and may result in

favourable CO2 emissions for LPG (DVFG and present study) or CNG (LBST) depending on

the assumptions.

In the present study, the fuel supply was specifically adapted to the status quo in Germany.

-200 -100 0 100 200

LBST 2010

DVFG 2012

This study

g CO2/km - WTW

-7%

-4%

-16%

LPG CNG-200 -100 0 100 200

LBST 2010

DVFG 2012

This study

g CO2/km - TTW

-14%

-6%

-13%

LPG CNGEqual engine efficiency

LPG more energy-efficient

Similar engine efficiency

-200 -100 0 100 200

LBST 2010

DVFG 2012

This study

g CO2/km

-20%

-45%

-32%

LPG CNG

1000km

4000km

4000km

Crude oil

Crude oil

Natural gasWTT

TTW

WTW

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Thus, the present results and the reported CO2 emission advantage of -20 % for LPG are

likely to be plausible. However, the influence of the (fossil) fuel supply on WTW emissions

was revealed to be minor (below 50 g CO2/km).

In contrast, the influence of the assumptions concerning fuel consumption, or rather the GHG

emissions generated during vehicle operation (TTW), is highly significant. The present

study and the Erdgas Mobil study are based on JEC data [JEC 2011]. Thus, the underlying

assumptions for CNG, LPG and petrol were similar, revealing a CO2 advantage of CNG over

LPG between -13 % and -14 % (Figure 9). In contrast, DVFG (2010) inferred average CO2

savings from a number of type-test data, resulting in CO2 savings of only -4 % for CNG com-

pared to LPG. In this case, the energetic fuel consumption in LPG vehicles would be approx.

11 % lower than in CNG vehicles (and approx. 4 % lower than in petrol cars). The caveats of

type-test data for generalised calculations have been introduced in Chapter 3.3.2. Test-type

data may be useful to illustrate ranges and sensitivities. However, simple calculation of the

mean will not ensure the delivery of consistent consumption rates for similar vehicles.

Conclusions

The CO2 emissions of CNG and LPG passenger cars are strongly dependent on underlying

assumptions. The most significant factor is the vehicle fuel consumption (TTW). As a rule,

CO2 emissions of CNG compare favourably due to the low overall carbon content. Even the

most favourable assumptions for LPG regarding fuel supply and consumption will not fully

close the gap in the CO2 advantage of CNG over LPG. Moreover, it is essential for the as-

sessment of environmental benefits of CNG and LPG to include renewable fuel supply path-

ways. A comparison of supply from solely fossil feedstocks is thus incomplete.

of 79

City bus

The GHG emissions of a city bus are illustrated in Figure 10. Due to the significantly elevated

energetic fuel consumption of CNG buses, the GHG emissions of a CNG bus operated with

natural gas are even higher than those of a diesel bus. However, the actual difference of 7 %

is relatively minor. Moreover, the application of biomethane may decrease GHG emissions

significantly in comparison with purely fossil diesel (42 % reduction for renewable resources/

liquid manure, 57 % for biodegradable waste). As an alternative to CNG, biodiesel may be

utilised. However, in this case disadvantages resulting from pollutant emissions similar to

those of conventional diesel may be expected (see following chapter).

Figure 10: WTW greenhouse gas emissions of city buses in 2012

0

200

400

600

800

1000

1200

1400

Diesel bus CNG bus CNG bus CNG bus

WTW greenhouse gas emissions of city buses in 2012

WTT TTWIn g CO2 eq / km

Crude oilNatural gas

(4000km)

Biomethane -biodegradable

waste

Biomethane –renewable resources /

liquid manure

+7%

-57% -42%

Established pathways Alternative pathways

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3.4.2 Primary energy consumption and pollutant emissions

Passenger car

Figure 11 reveals that diesel cars are associated with the lowest primary energy consump-

tion relative to established fuel supply pathways. The range between petrol, LPG and CNG

(approx. 4 %) is smaller compared to that of the GHG emissions. The primary energy con-

sumption of CNG based on biomethane is considerably higher than that of the fossil path-

ways. However, the high consumption is offset by the fact that the consumption of fossil

(non-renewable) energies is low.

Source: HBEFA 3.1. own assumptions and calculations

Figure 11: WTW pollutant emissions of passenger cars in 2012

The emissions of the pollutants NMHC and SO2 are generated primarily during fuel supply

(WTT). These are highest for LPG as a byproduct of crude oil processing.

012345678

Pet

rol –

cru

de

oil

Die

sel –

cru

de

oil

LPG

–cr

ud

e o

il

CN

G –

nat

ura

l gas

LPG

–n

atu

ral g

as

Bio

met

han

e –

bio

deg

rad

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was

te

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e –

ren

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eso

urc

es

Renewable

Non-renewable

In MJ/km

Primary energy consumption

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

Pet

rol –

cru

de

oil

Die

sel –

cru

de

oil

LPG

–cr

ud

e o

il

CN

G –

nat

ura

l gas

LPG

–n

atu

ral g

as

Bio

met

han

e –

bio

deg

rad

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was

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met

han

e –

ren

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urc

es

NOX

TTW

WTT

In g/km

0.00

0.05

0.10

0.15

0.20

0.25

0.30

0.35

Pet

rol –

cru

de

oil

Die

sel –

cru

de

oil

LPG

–cr

ud

e o

il

CN

G –

nat

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LPG

–n

atu

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as

Bio

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han

e –

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deg

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was

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eso

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NMHC

TTW

WTT

In g/km

0.00

0.05

0.10

0.15

0.20

0.25

Pet

rol –

cru

de

oil

Die

sel –

cru

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oil

LPG

–cr

ud

e o

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CN

G –

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LPG

–n

atu

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as

Bio

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SO2

TTW

WTT

In g/km

of 79

NOx emissions in significant quantities arise during operation (TTW). These are highest for

diesel vehicles compared to the alternatives available. For air quality control purposes, the

substitution of diesel cars with CNG promises several benefits, as CNG cars are associated

with GHG savings in addition to lower NOx emissions. Substitution with LPG, however, is

disadvantageous with respect to NMHC and SO2 emissions. Moreover, converted vehicles

could generate additional actual emissions compared to petrol cars (see Chapter 3.3.3).

of 79

City bus

Diesel buses are associated with the lowest total primary energy consumption. The result

reflects the low energetic fuel consumption of diesel buses compared to CNG (Figure 12).

Operation with biomethane also requires a primary energy consumption significantly exceed-

ing that of fossil fuels. Yet, the quantities of fossil energy consumed are much lower.

The principal advantage of a CNG-powered city bus lies in the low actual pollutant emissions

(TTW) of NOX (also PM, see Chapter 3.3.3) which are beneficial to local air quality. From the

WTW perspective, pollutant emissions are also lower for biomethane compared to diesel

buses with the exception of SO2.


Figure 12: WTW pollutant emissions for city buses in 2012

0

10

20

30

40

50

Die

sel –

cru

de

oil

CN

G –

nat

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l gas

Bio

met

han

e –

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deg

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was

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han

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ren

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eso

urc

es

RenewableNon-renewable

In MJ/km


0

1

2

3

4

5

Die

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CN

G –

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Bio

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NOX

TTW

WTT

In g pro km

0

0.1

0.2

0.3

0.4

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CN

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NMHC

TTW

WTT

In g/km

0

0.1

0.2

0.3

0.4

0.5

0.6

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SO2TTW

WTTIn g/km

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3.5 Well-to-wheel (WTW) comparison 2030

3.5.1 Greenhouse gas emissions

Passenger car

The scenario 2030 assumes significant reductions in fuel consumption for all vehicles (-30 %

to -35 % MJ/MJ). As a consequence, GHG emissions for all included alternatives decrease

considerably. For instance, emission from a petrol vehicle operated with crude oil-derived

fuel are projected to fall from 206 g CO2 eq/km in 2012 to 141 g CO2 eq/km in 2030 (Figure

8, Figure 13). For the established fossil fuel supply pathways, the relative changes in GHG

emission rates between 2012 and 2030 in reference to petrol cars are minor. For CNG cars,

the ratio of GHG emissions is slightly shifted towards the fuel supply stage (WTT) due to the

longer transport distance (7000 km instead of 4000 km). However, the shift is compensated

by the additional reduction in consumption associated with CNG hybrid vehicles. GHG sav-

ings of CNG cars versus petrol cars remain constant at 15 %.

Figure 13: WTW greenhouse gas emissions for passenger cars in 2030

A key topic for future evaluations will be the shift of fuel supply pathways. In the event that

the enormous demand for petrol and diesel fuel cannot be met with crude oil anymore, other

sources such as tar sands may be exploited for fuel supply. In consequence, the GHG bal-

ance of these fuels would deteriorate (for petrol from 141 g/CO2 eq/km to 166 g/CO2 eq/km).

For LPG, the consequences are harder to predict. In the case that LPG was produced from

0

20

40

60

80

100

120

140

160

180

WTW greenhouse gas emissions for passenger cars in 2030

WTT TTWIn g CO2 eq/ km

Petrolcar

Dieselcar

LPG car CNG car (Natural gas/methane)

Crude oil Crude oilNatural gas

Natural gas(7000 km)Crude oil

-9% -15% -15% -90% -76%

Additional WTT proportion for extraction from tar sands

-98%

Biomethane/SNG – wood

Biomethane -biodegradable

waste RE-Methane-wind energy

of 79

fossil natural gas deposits like CNG, the GHG emission would remain constant. In fact, the

GHG advantage compared to petrol and diesel would grow more pronounced.

For CNG vehicles, renewable resources would continue to be available in 2030. Biomethane

(from biogas produced from waste or bio-SNG) and RE methane derived from wind energy

electrolysis could potentially achieve GHG savings between 76 % and 98 %. The supply of

biomethane from biodegradable waste is associated with significantly lower GHG emissions

compared to 2012.

City bus

Heavy commercial vehicles such as city buses could also benefit from CNG engines for fu-

ture GHG emissions savings compared to diesel-powered vehicles. These savings are asso-

ciated with efficiency increases of the vehicle (TTW), e.g. hybrid or dual-fuel engines. These

advanced technologies would close the gap in consumption efficiency between diesel and

CNG. In addition, a shift in fuel supply pathways towards renewable methane or diesel from

tar sands could result in GHG benefits for CNG buses (Figure 14).

Figure 14: WTW greenhouse gas emissions for city buses 2030

0

200

400

600

800

1000

1200

WTW greenhouse gas emissions of city buses in 2030

WTT TTWIn g CO2 eq/ km

Diesel bus

Crude oilNatural gas

(7000km)

-8% -74%

Additional WTT proportion for extraction from tar sands

-98%-88%

Biomethane/SNG – woodBiomethane -

biodegradable waste RE-Methane-

wind energy

CNG bus (Natural gas/methane)

of 79

3.5.2 Primary energy consumption and pollutant emission

Passenger car

In analogy to GHG emissions, primary energy consumption and WTW pollutant emissions

are expected to decrease significantly in absolute terms with improved efficiency in reference

to 2012 (Figure 15). In this context, the primary energy demand of biomethane and RE me-

thane may be met with 80 % to 100 % renewable energies.


Figure 15: WTW pollutant emissions for passenger cars 2030

NOx emissions continue to arise in relevant quantities TTW. However, compliance with the

Euro 6 standards considerably reduces differences between the individual fuel types. The

WTT angle reveals significant differences between the fuel supply pathways. The NOx emis-

sions of LPG and CNG (with the exception of RE methane) exceed those of petrol and diesel

0

1

2

3

4

5

Pet

rol –

cru

de

oil

Die

sel –

cru

de

oil

LPG

–cr

ud

e o

il

LPG

–n

atu

ral g

as

CN

G –

nat

ura

l gas

Bio

met

han

e –

bio

deg

rad

able

was

te

Bio

me

than

e/SN

G -

wo

od

RE-

Me

than

e-el

ectr

icit

y


In MJ/km


0.00

0.05

0.10

0.15

0.20

0.25

0.30

Pet

rol –

cru

de

oil

Die

sel –

cru

de

oil

LPG

–cr

ud

e o

il

LPG

–n

atu

ral g

as

CN

G –

nat

ura

l gas

Bio

met

han

e –

bio

deg

rad

able

was

te

Bio

me

than

e/SN

G -

wo

od

RE-

Me

than

e-el

ectr

icit

y

NOX

WTT (Tar sand)

TTW

WTT

In g/km

0.00

0.05

0.10

0.15

0.20

0.25

Pet

rol –

cru

de

oil

Die

sel –

cru

de

oil

LPG

–cr

ud

e o

il

LPG

–n

atu

ral g

as

CN

G –

nat

ura

l gas

Bio

met

han

e –

bio

deg

rad

able

was

te

Bio

me

than

e/SN

G -

wo

od

RE-

Me

than

e-el

ectr

icit

y

NMHC

WTT (Tar sand)

TTW

WTT

In g/km

0.00

0.05

0.10

0.15

0.20

0.25

0.30

Pet

rol –

cru

de

oil

Die

sel –

cru

de

oil

LPG

–cr

ud

e o

il

LPG

–n

atu

ral g

as

CN

G –

nat

ura

l gas

Bio

met

han

e –

bio

deg

rad

able

was

te

Bio

me

than

e/SN

G -

wo

od

RE-

Me

than

e-el

ectr

icit

y

SO2

WTT (Tar sand)

TTW

WTT

In g/km

of 79

from crude oil, yet the NMHC and SO2 emissions of CNG tend to be lower, particularly in

comparison to petrol and diesel extracted from tar sands. In line with GHG emission results,

the most favourable overall pollutant balance may be observed for CNG passenger cars op-

erated with RE methane from renewable electricity sources.

of 79

City bus

Reduced consumption levels of both CNG and diesel buses are going to decrease future

primary energy demand. Moreover, a considerable drop is expected in the demand for fossil

energy for renewable methane versus diesel from crude oil compared to 2012 (Figure 16).


Figure 16: WTW pollutant emissions for city buses in 2030

The differences in actual pollutant emissions (TTW) of CNG and diesel are negligible after

introduction of the Euro VI standard. However, diesel engines may be subject to additional

exhaust gas aftertreatment measures associated with additional costs. For pollutant emis-

sions generated during fuel supply (WTT), a picture similar to the passenger car scenario

emerges, i.e. the lowest emissions are associated with RE methane. In the case of bio-

methane, NOX and SO2 emissions may exceed those of diesel produced from crude oil.

However, low to no additional pollutant emissions are associated with the operation of CNG

buses, particularly if future diesel fuel will be extracted from tar sands.

0

5

10

15

20

25

30

35

Die

sel-

Ro

hö

l

CN

G-N

atu

ral g

as

Bio

met

han

e –

bio

deg

rad

able

was

te

Bio

me

than

e/SN

G -

wo

od

RE-

Me

than

e-el

ectr

icit

y


In MJ/km


0.00

0.50

1.00

1.50

2.00

Die

sel-

Ro

hö

l

CN

G-N

atu

ral g

as

Bio

met

han

e –

bio

deg

rad

able

was

te

Bio

me

than

e/SN

G -

wo

od

RE-

Me

than

e-el

ectr

icit

y

NOX

WTT (Tar sand)TTWWTT

In g/km

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

Die

sel-

Ro

hö

l

CN

G-N

atu

ral g

as

Bio

met

han

e –

bio

deg

rad

able

was

te

Bio

me

than

e/SN

G -

wo

od

RE-

Me

than

e-el

ectr

icit

y

NMHC

WTT (Tar sand)

TTW

WTT

In g/km

0.00

0.30

0.60

0.90

1.20

1.50

1.80

Die

sel-

Ro

hö

l

CN

G-N

atu

ral g

as

Bio

met

han

e –

bio

deg

rad

able

was

te

Bio

me

than

e/SN

G -

wo

od

RE-

Me

than

e-el

ectr

icit

y

SO2

WTT (Tar sand)

TTW

WTT

In g/km

of 79

4 Perspectives for the promotion of CNG and LPG in road

transport

4.1 Benefits from an environmental perspective

Both CNG and LPG offer advantages over crude oil-based petrol and diesel fuels. Although

(actual) pollutant emissions are similar to petrol engines, both CNG and LPG show a more

favourable GHG balance. Due to the fact that climate change mitigation represents one of

the major political challenges, a favourable GHG balance may be well received in support of

an extension of subsidies.

However, a comparison of CNG/LPG and petrol from fossil supply pathways23 reveals the

limited cost efficiency of relative GHG savings in correlation with financial losses associated

with energy tax benefits (see Figure 17). Due to moderate GHG savings of -9 % to -15 %,

diesel is currently the most cost-efficient fuel apart from pure biomethane. In addition, energy

tax losses for diesel are largely compensated with an overall higher motor vehicle tax. In the

cases of fossil CNG, and LPG derived from crude oil in particular, subsidisation with energy

tax benefits may not be justified with GHG savings or superior cost efficiency (in this context,

rebound effects, such as improved mileage through lower costs, are not taken into consid-

eration).

Figure 17: Energy tax losses and GHG savings in relation to a petrol vehicle in 2012 (Calculation in Appendix III)

23 Blending of biofuels not considered

0%

10%

20%

30%

40%

50%

60%

70%

0 500 1000 1500 2000 2500

Re

lati

ve G

HG

sav

ings

pe

r ve

hic

le k

m

Energy tax losses in EUR per ton CO2 savings

LPG

CNGDiesel*

CNG - 100% Biomethane (from biodegradable waste)

*increased motor vehicle tax rate not considered

of 79

In addition to the relative GHG savings, a number of arguments in favour of a strategic sub-

sidy extension of CNG or LPG exist. The scope of the present study is limited to a qualita-

tive assessment of these factors:

Diversification of fuels – crude oil-independent fuels should be promoted to ensure

security of supply. Both CNG and LPG qualify when derived from natural gas.

Integration of renewable energies – the road transport sector should seek to utilise

renewable energies in the long-term. At present, there are perspectives for CNG but

not for LPG.

Thus, LPG has a strategic potential to contribute to diversification only, whereas CNG is may

be expected to also facilitate the integration of renewable energies and future technologies

into road transport.

The distribution of CNG and the associated development of the required infrastructure may

further offer opportunities to exploit additional potentials for the diversification of fuels and

integration of renewable energies in the commercial vehicle sector. For instance, the CNG

infrastructure could be instrumental in the establishment of renewable methane not only in

the car sector, but also in additional areas (e.g. LNG for long-distance freight transport).

4.2 Potential subsidy framework

From an environmental perspective, the application of CNG is more profitable than LPG. This

should be taken into account during the design of an extension of current energy tax bene-

fits. Renewable supply pathways should be the particular focus of the extension. Alternative

applications of biomethane may be restricted to small-scale utilisation schemes (cogenera-

tion applications), or they may be associated with significantly reduced GHG savings (heat

applications). Therefore, available biofuels should be promoted to find broad application in

the near future, including utilisation in road transport. Support to this scheme could come

from an additional, or exclusive, subsidy of renewable methane through energy taxation as a

prerequisite for tax benefits. Further, statutory quotas assigning renewable methane for utili-

sation as CNG fuel could be defined.

LPG is associated with fewer environmental benefits at present, and projected to hold less

potential for the reduction of environmental burdens. Moreover, the implementation of re-

newable LPG components appears unlikely given the present development trajectory. These

facts should be considered in the debate over an extension of subsidisation. However, the

contribution of LPG to the diversification of the fuel market should be given proper regard.

As an alternative to the present energy tax benefits, subsidies in Germany could be modelled

on the EU alternative fuels strategy. In this case, energy taxation would follow the emissions

of CO2 or GHGs per MJ fuel. A specific distinction of the existing fuels and the respective

of 79

supply pathways would thus allow accounting for the differences in GHG emissions for CNG

and LPG from fossil and renewable pathways.

However, the low overall integration of new CNG and LPG vehicles to date indicates that

measures beyond benefits in energy taxation may be required. These measures should in-

clude aspects such as the development of the fuelling station infrastructure (for CNG in par-

ticular) and detailed consumer information, thus addressing multiple stakeholders. In this

context, the ‘Initiative Natural Gas Mobility – CNG and Biomethane fuels’ should be noted as

a source of information. The initiative was coordinated by the dena with support of the

BMVBS, and targeted the development of measures in collaboration with key players in the

energy industry and the road transport sector (see http://www.erdgasmobilitaet.info).

Table 11: Supporting framework for the subsidisation of CNG and LPG

CNG LPG

Extension of the reduced energy tax. distinction be-

tween fossil and renewable CNG/methane as appro-

priate

No extension. or adapted rate of the reduced

energy tax

Blending quotas for renewable methane

GHG=based energy tax following EU alternative fuels strategy

Development of service station infrastructure de-

pendent on demand

Revision and update of consumer information regarding fuel pricing and service station labelling

Expanded supply and improved communication on new motor vehicles on the market

http://www.erdgasmobilitaet.info/home.html

of 79

Appendix I: Amortisation potential of LPG conversion for the Ger-

man petrol vehicle fleet

Figure 18 illustrates the potential of an LPG conversion for the German petrol vehicle stock.

The vehicles in stock were assigned model-specific individual mileages based on empirical

data after [MiD 2008] and [Polk 2008]. Calculations were carried out considering consump-

tion and annual mileage. The individual conversion costs depend on the specific engine

(characterised by engine displacement, year of manufacture and exhaust emission standard)

with a discounting of 2 %. The assumed maximum mileage to end-of-life of the vehicle is

200,000 km. Vehicles include models built from 1995.

Figure 18: Potential of conversion to LPG for the German vehicle fleet

Thus, 20 % of the German vehicle will redeem conversion expenses within two years, as-

suming current operation levels and tax benefits. Without tax benefits, only 10 % of the fleet

will break even within two years of conversion. Amortisation is most readily achieved for ve-

hicles with high mileage or fuel-intensive cars with simple engines (and inexpensive conver-

sion). The figure illustrates the immense potential for cost reduction through LPG conversion

in the actual fleet. For the majority of the fleet, it is evident that conversion costs are re-

deemed within a few years. Despite the obvious benefit, an annual percentage of only 0.3 %

of the fleet is actually converted from petrol to LPG.

In the case of a short period of ownership, conversion may still break even due to a higher

resale value of the vehicle. In this case, the added value is transferred to the next owner

through the residual value.

of 79

Appendix II: Well-to-tank calculations

Methodology

Well-to-tank calculations were carried out according to established LCA standards, i.e. ISO

14040 and ISO 14044.

Physical energy content method

In compliance with international organisations (IEA, EUROSTAT, ECE) and the AG Energie-

bilanzen (AGEB), the calculation of primary energy consumption was carried out with the

‘physical energy content method’.

In this method, hydroelectricity and other renewable energy carriers that cannot be attributed

with a heating value (e.g. wind and solar electricity) are assigned ‘heating values’ that equal

the amount of electric energy generated in the process. Thus, an ‘energy conversion effi-

ciency’ of 100 % is assumed.

Furthermore, in the case of nuclear electricity production, heat from the nuclear reaction is

the primary energy form. The energy conversion efficiency assumed for the generation of

electricity from nuclear energy is 33 %.

Allocation of byproducts

In the case that several products arise in the process, energy consumption and emissions

have to be allocated to the individual products, respectively.

In the case of cogeneration of heat and power plants (CHP), such as the supply of electricity

from the electricity mix after [Nitsch et al 2012], the partial substitution method according to

RED 2009/28/EC and [JEC 2011, 2013] is applied.

For the supply of biomass-based fuels, allocation of energy consumption and emissions is

carried out in compliance with the stipulations of the RED 2009/28/EC in reference to the

lower heating value of the primary product and byproducts. In the case that biofuel plants

produce electricity as a byproduct, compliant with the RED 2009/28/EC the partial substitu-

tion method is applied. In this case, the byproduct electricity is substituted by electricity gen-

erated from the same energy carrier.

For the supply of petrol and diesel after [JEC 2013], a marginal approach is carried out, i.e.

the calculation of the efforts required to provide an additional amount of fuel.

For LPG from natural gas processing, allocation was carried out according to energy content.

For LPG derived from crude oil (refinery), allocation factored in the energy content of the

refinery products (petrol, kerosene, diesel, LPG etc.) in reference to the respective refinery

of 79

process after [ETSU 1996].

Embodied energy

The energy consumed in the construction of processing plants and vehicles (so-called em-

bodied energy or grey energy) and the associated greenhouse gas emissions are not con-

sidered. Analyses with a similar scope, e.g. well-to-wheel analyses conducted by

JRC/EUCAR/CONCAWE at the European level [JEC 2011] or the EU Renewable Energy

Directive (RED 2009/28/EC) for the calculation of typical values, have adopted a similar poli-

cy. Embodied energy may be considered negligible in the electricity and fuel supply in gen-

eral. As the proportions of renewable electricity and renewable heat increase, the energy

emissions associated with the construction of plants, infrastructure und vehicles decrease.

Exceptions to this general trend may be found when considering non-energetic environmen-

tal impacts, such as depletion of raw materials (mining).

Other impact categories

The environmental impacts investigated here include energy consumption, greenhouse gas

(GHG) and pollutant emissions (Chapter 3.1).

As the proportion of fuels derived from biomass, tar sands and shale gas in the fuel mix in-

creases, additional environmental impacts such as biodiversity, soil quality, water intensity

and area demand become increasingly relevant. The analysis of these highly complex rela-

tionships is beyond the scope of the present study. This may serve as a cautionary tale to

illustrate that a single environmental indicator, such as the GHG emissions frequently ad-

dressed in politics, science and society, reveals but a glimpse of the full picture. From a

mathematical perspective, every single indicator is required, yet insufficient in isolation due to

the associated risk of collateral damage to other environmental sectors.

Fossil fuels

Petrol and diesel from crude oil

For petrol and diesel produced from crude oil, the assumptions underlying the conclusions

followed [JEC 2013], which updates [JEC 2011]. The pollutant emissions were adopted from

[ETSU 1996]. The following tables illustrate the energy flows and emissions associated with

the production of crude oil.

of 79

Table 12: Energy flows and emissions from crude oil production

I/O Unit Amount

Crude oil from field Input MJ/MJ 1.058

Crude oil Output MJ 1.000

Emissions

CO2 - g/MJ 3.8

CH4 0.0384

NOx - g/MJ 0.0097

Dust/PM - g/MJ

SO2 - g/MJ

NMVOC - g/MJ 0.0112

CO - g/MJ 0.0015

Crude oil is exported to Europe for processing. Table 13 illustrates the energy flows and

emissions arising from crude oil transport to the refinery.

Table 13: Energy flows and emissions from crude oil transport

I/O Unit Amount

Crude oil Input MJ/MJ 1.000

Heavy fuel oil Input MJ/MJ 0.010


Emissions

CO2 - g/MJ 0.8

NOx - g/MJ 0.015

Dust/PM - g/MJ 0.001

SO2 - g/MJ 0.015

NMVOC - g/MJ 0.001

CO - g/MJ 0.002

The consumption of heavy fuel oil (HFO) is linked to the supply of HFO.

Crude oil is processed to petrol and diesel in a refinery. The associated energy consumption

and GHG emissions follow [JEC 2011], whereas the pollutant emissions are reported from

[FEA 1999].

of 79

Table 14: Energy flows and emissions from the production of petrol and diesel in oil refineries

I/O Unit Petrol Diesel

Crude oil Input MJ/MJ 1.08 1.10

Diesel Output MJ 1.00 1.00

Emissions

CO2 - g/MJ 7.0 8.6

NOx - g/MJ 0.0072 0.0089

Dust/PM - g/MJ 0.0006 0.0006

SO2 - g/MJ 0.0103 0.0131

NMVOC - g/MJ 0.0094 0.0117

CO - g/MJ 0.0039 0.0047

The products petrol and diesel are transported to a fuel depot via pipeline, inland waterway

vessel (distance 500 km) or rail (distance 250 km). The percentage of fuel transport modes is

distributed as follows: via pipeline 60 %, via inland waterway vessel and rail 20 % each. Elec-

tricity consumption for pipeline transport amounts to approx. 0.0002 MJ per MJ fuel. Fuel

transport via ship requires about 0.012 tkm per MJ petrol and diesel over a distance of 500

km. Table 15 illustrates the energy consumption and GHG emissions of a typical inland wa-

terway vessel derived from [EDU 1996]. Fuel calculation is based on a return trip (empty) per

transport via inland waterway vessel.

Table 15: Fuel consumption and GHG emissions of an inland waterway vessel

I/O Unit Amount

Diesel Input MJ/tkm 0.50

Distance Output tkm 1.000

Emissions

CO2 - g/tkm 36.9

CH4 - g/tkm 0.03

N2O - g/tkm 0.00

NOx - g/tkm 0.30

Dust/PM - g/tkm 0.03

SO2 - g/tkm 0.031

NMVOC - g/tkm 0.04

CO - g/tkm 0.17

Fuel transport over a distance of 250 km by rail requires approx. 0.0058 tkm per MJ pet-

rol/diesel in transport. Rail electricity consumption amounts to approx. 0.21 MJ per tkm cov-

of 79

ered by the EU electricity mix (10-20 kV level).

The electricity consumption of a fuel depot totals at approx. 0.0008 MJ/MJ fuel which is sup-

plied by the EU electricity mix (0.4 kV level).

From the fuel depot, fuel is distributed to the fuelling station across a distance of 150 km. For

this purpose, fuel is transported by lorry with a gross vehicle weight of 40 t and a transport

capacity of 26 t petrol or diesel. The fuel consumption of the lorry is 35 l per 100 km.

The electricity consumption of the fuelling station amounts to 0.0034 MJ/MJ petrol or diesel.

Petrol and diesel from tar sands

The production of synthetic crude oil (SCO) from tar sands includes the mining of the bitumi-

nous sand, extraction of bitumen and refining into synthetic crude oil fit for processing in con-

ventional oil refineries.

The energy flows and emissions from the production of SCO from tar sands were adopted

from [Renewbility 2009], and are based on data from Syn-Crude and SunCor in Canada.

Bitumen from tar sands is applied as a feedstock for upgrading. To date, Syn-Crude is ex-

tracting tar sands exclusively through strip mining on the surface, whereas SunCor employs

surface mining as well as in situ application of solvents.

Table 16: Energy flows and emissions from the production of synthetic crude oil (SCO) from tar sand deposits in Canada

I/O Unit Amount

Tar sands Input MJ/MJ 1.279


Emissions

CO2 - g/MJ 19.1

CH4 - g/MJ

N2O - g/MJ

NOx - g/MJ 0.042

Dust/PM - g/MJ

SO2 - g/MJ 0.115

NMVOC - g/MJ 0.065

CO - g/MJ

Additional environmental impacts associated with the mining and processing of tar sand de-

posits include water pollution with toxic substances, hazards to drinking water and the altera-

tion of large natural areas with consequences for biodiversity.

Bitumen extraction consumes between 2 and 4 barrels of water per barrel crude bitumen.

of 79

Residues from SCO production are stored in open surface ponds (so-called tailings). The

residues contain toxic components. Leakage may result in pollution of surface and ground

water [Pembina 2009].

The SCO is transported to the coast via a 5000 km pipeline. The electricity consumption of

the pipeline transport is approx. 0.0082 MJ per MJ SCO after [GEMIS 2005]. From the coast,

the SCO is shipped to the EU per tanker over 6000 km. The oil tanker is operated with HFO

with a sulphur content of 3.5 %. The specific energy consumption and emissions of an oil

tanker (Table 17) were derived from [ESU 1996].

Table 17: Fuel consumption and GHG emissions of an oil tanker

I/O Unit Amount

Heavy fuel oil (HFO) Input MJ/tkm 0.056


Emissions

CO2 - g/tkm 4.3

CH4 - g/tkm

N2O - g/tkm

NOx - g/tkm 0.086


SO2 - g/tkm 0.086

NMVOC - g/tkm 0.003

CO - g/tkm 0.011

In the EU, SCO is processed in a refinery close to the entry port. For refinery and distribution

of the fuels petrol and diesel, the same assumptions were applied as for petrol and diesel

produced from conventional crude oil (see previous chapter).

CNG from natural gas

Natural gas is extracted and processed in remote gas fields. The associated energy con-

sumption and GHG emissions were estimated according to [JEC 2013]. Air pollution was

derived from [ETSU 1996] and [Ecoinvent 2007].

of 79

Table 18: Energy flows and emissions from the production and processing of natu-ral gas

I/O Unit Amount

Natural gas Input MJ/MJ 1.024

Natural gas Output MJ 1.000

Emissions

CO2 - g/MJ 1.65

CH4 - g/MJ 0.083

N2O - g/MJ 0.000

NOx - g/MJ 0.005


SO2 - g/MJ 0.001

NMVOC - g/MJ 0.004

CO - g/MJ 0.001

The energy input is calculated in reference to the lower heating value, i.e. the energy input is

inversely proportional to the efficiency.

Natural gas is conveyed from the gas field to the EU via a pipeline. Two pathways were in-

cluded in the analyses:

Transport distance 4000 km

Transport distance 7000 km

Natural gas transport via pipeline across distances of 4000 km, or 7000 km, is associated

with mechanical work of approx. 0.36 MJ/tkm [JEC 2013]. The lower heating value of natural

gas is approx. 50 MJ/kg. Loss of natural gas through leakage along the transport route is

estimated after [Wuppertal 2004]. Methane loss during long-distance natural gas transport is

minor (< 1 % over 7000 km). The assumptions of [JEC 2013] approximately correspond with

data from [Wuppertal 2/2008].

Table 19: Energy flows and emissions from transport of natural gas over great dis-tances

I/O Unit 4.000 km 7.000 km

Natural gas Input MJ/MJ 1.0052 1.0092

Mechanical work Input MJ/MJ 0.028 0.051

Natural gas Output MJ 1.0000 1.0000

Emissions

CH4 - g/MJ 0.104 0.184

of 79

The mechanical work associated with natural gas transport in pipelines is performed with gas

turbines operated with natural gas. The energy conversion efficiency of the turbine is esti-

mated to be approx. 30 %. Energy consumption and emissions from mechanical work for

natural gas transport are derived from [GEMIS 2011]. In [GEMIS 2011], natural gas transport

from Russia to Germany in 2020 is assumed to be performed with a gas turbine efficiency of

32 %, which is similar to the 31.5 % assumed by [Wuppertal 2/2008] for 2030 (scenario with

low natural gas production and low investment). The present study assumes a gas turbine

efficiency of 32 % for the time horizon from 2020.

Table 20: Natural gas consumption and emissions from gar turbines of natural gas compressors

I/O Unit 4000 / 7000 km

(2010)

4000 / 7000 km

(2020)

Natural gas Input MJ/MJ 3.333 3.125

Mechanical work Output MJ 1.000 1.000

Emissions

CO2 - g/MJ 183.6 171.9

CH4 - g/MJ 0.028 0.026

N2O - g/MJ 0.009 0.008

NOx - g/MJ 1.114 1.044

Dust/PM - g/MJ 0.028 0.026

SO2 - g/MJ 0.001 0.001

NMVOC - g/MJ 0.070 0.065

CO - g/MJ 0.557 0.522

Analogous to [JEC 2013], the regional fuel distribution is assumed to cover 500 km (high

pressure natural gas pipeline), whereas the local distribution will not exceed 10 km (local

natural gas grid) to the CNG fuelling station. Methane loss during distribution along the high

pressure network amounts to approx. 0.0006 % according to [GEMIS 2006]. The required

mechanical work of 0.003 MJ per MJ natural gas is performed with a gas turbine with an en-

ergy conversion efficiency of 31 %.

The electricity consumption of the CNG fuelling station is 0.026 MJ per MJ CNG in 2010, and

0.024 MJ per MJ CNG in 2020. Electricity is supplied by the grid.

LPG from crude oil/natural gas

In addition to methane (CH4), the gases extracted from a natural gas field contain portions of

fuel gases such as ethane (C2H6), propane (C3H8) and butane (C4H10). During natural gas

processing, propane and butane are isolated and traded as LPG (Liquefied Petroleum Gas).

of 79

Energy demand and emissions for the production of LPG from natural gas processing are

derived from ETSU [1996]. The data in [ETSU 1996] are reported in reference to the higher

heating value (HHV) and were converted to the lower heating value (LHV)24. Table 21 illus-

trates the inputs and outputs for the extraction of LPG. The LPG input is equal to the LPG

escaping from the gas field.

Table 21: Energy flows and emissions for the production and processing of LPG

I/O Unit Amount

Natural gas Input MJ/MJ 0.053

LPG Input MJ/MJ 1.000

LPG Output MJ 1.000

Emissions

CO2 - g/MJ 3.1

CH4 - g/MJ 0.015

N2O - g/MJ 0.000

NOx - g/MJ 0.009


SO2 - g/MJ 0.000

NMVOC - g/MJ 0.011

CO - g/MJ 0.001

For transport of LPG with small transport vessels, LPG is shipped in a compressed state. For

transport of LPG in large transport vessels, LPG is liquefied through cooling to -48°C and

stored in a cryogenic storage tank on board (the boiling point of LPG at a pressure of

0.1013 MPa is at -42°C).

Liquefaction of LPG through cooling requires 130 MJ of electricity per ton LPG [ETSU 1996].

Electricity is supplied by a combined cycle gas turbine plant (CCGT) operated with natural

gas with an energy conversion efficiency of 58 %.

In the United Kingdom, LPG consists of a blend of approx. 90 % propane (volumetric) and

10 % butane (vol.) [ETSU 1996]. In Germany, LPG in the winter season consists of 60 %

propane (vol.) and 40 % butane (vol.), whereas in the summer the ratio is reversed to 40 %

propane (vol.) and 60 % butane (vol.). Thus, the average annual mix in Germany is 50 %

propane and 50 % butane (vol.). This corresponds to 47 % (ener.) propane and 53 % (ener.)

butane in reference to the lower heating value (LHV) in Germany.

24 LHV (Propane) = 50.0 MJ/kg; LHV (Propane) = 46.4 MJ/kg

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Table 22: Fuel qualities of LPG

Unit Propane Butane

Lower heating value

(LHV)

MJ/kg 46.35 (1)

46.33 (2)

45.74 (1)

45.62 (2)

Density at 15°C liquid kg/l 0.51 0.59

Composition in Germany

Winter % vol. 60 40

Summer % vol. 40 60

Mean % vol. 50 50

% energetic 47 53 (1)

Calculated; (2)

[LBST 2010]

With an estimated LHV of 46.0 MJ/kg for the German propane/butane blend, the electricity

consumption for liquefaction purposes amounts to approx. 0.0028 MJ per MJ LPG. The elec-

tricity demand is commonly met with a CCGT plant operated with natural gas with an energy

conversion efficiency of 55 %

The capacity of the LPG transport vessel ‘Djanet’ by Kawasaki is 84,000 m³ LPG [Kawasaki

2000]. Another LPG transport vessel by Kawasaki, the ‘Grace River’, has a similar capacity

of 79,200 m³ LPG (~45,000 t LPG) [Kawasaki 1/2002].

The majority of Japanese ports are equipped to discharge cargo from such LPG transport

vessels [Kawasaki 2/2002]. The data for the vessel ‘Djanet’ were employed in the calculation

of energy consumption and emissions in [JEC 2011].

Table 23: LPG transport vessel “Djanet“ [Kawasaki 2000]

Transport capacity (LPG) 84,310 m³

Speed 16.8 kn (31 km/h)

Driving power (Kawasaki-MAN B&W 5S70MC Mk VI) 13,646 kW

Fuel Heavy fuel oil (HFO)

At -42°C and 0.1 MPa, the density of propane is approx. 0.58 t/m³. At -48°C and 0.1 MPa,

the density of propane is approx. 0.59 t/m³. The maximum fill factor is 0.98. Thus, with a

nominal transport capacity of 84,310 m³, the ‘Djanet’ may ship approx. 47,900 t of LPG. The

specific fuel consumption for the main engine system of the vessel (fitted with a two-stroke

diesel engine) amounts to approx. 169 g per kWh of mechanical work ( 5 %) operated with

fuel with a LHV of 42.7 MJ/kg hat. The total energy conversion efficiency amounts to 49.9 %

[MAN 2003].

of 79

Two options were included for the transport distance:

LPG from remote natural gas fields. One-way distance for LPG transport by ship:

5,500 nautical miles (10,186 km).

LPG from natural gas fields in the North Sea. One-way distance for LPG transport by

ship: 1,000 km.

Large volumes of LPG are commonly stored in fuel depots under cryogenic conditions, i.e. at

< -42°C [ETSU 1996]. The transport distance for lorry transport of LPG is assumed to aver-

age 500 km to the fuelling station.

Lorry transport of LPG is pressurised to retain liquid LPG. According to [SeAH 2003], the

geometric volume of an LPG tanker lorry is approx. 43.5 m3. With a maximum filling factor of

0.85 and an LPG density of 0.5 t/m3, the total LPG to be loaded in one tanker comes to ap-

prox. 18.5 t LPG. The mass of the LPG tank amounts to approx. 8.6 t.

The estimated specific fuel consumption depending on payload is based on an assumed fuel

consumption of 35 l diesel per 100 km. According to [KFZ-Anzeiger 2003], the average fuel

consumption of a Mercedes-Benz Actros 1844 is 31.6 l diesel per 100 km. The preceding

model, the Mercedes-Benz Actros 1843, had a fuel consumption of 34.9 l diesel per 100 km.

The average fuel consumption of a different lorry, the MAN TG 510 A, is reportedly 37.0 l

diesel per 100 km [KFZ-Anzeiger 2001]. The fuel consumption of a lorry with a payload of

25 t amounts to 32.8 l diesel per 100 km according to [ETSU 1996]. This corresponds to a

specific consumption of 0.936 MJ/tkm assuming empty return. Thus, the estimate of 0.936

kWh/tkm is considered a realistic assumption for the present study.

Table 24 illustrates the fuel consumption and the emissions of a lorry with a gross vehicle

weight of 40 t and a payload of 27 t, representing typical conditions for LPG transport by lor-

ry. The lorry is classified Euro 4. The emission limits for heavy-duty vehicles are reported in g

per kWh mechanical work. For the conversion in g/km, a cycle conversion efficiency of

37.5 % is assumed for diesel engines based on lorry manufacturer data.

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Table 24: Fuel consumption and emissions of a 40 t lorry

I/O Unit Amount

Diesel Input MJ/tkm 0.936


Emissions

CO2 - g/tkm 68.6

CH4 - g/tkm 0.005

N2O - g/tkm 0.000

NOx - g/tkm 0.341


SO2 - g/tkm 0.000

NMVOC - g/tkm 0.040

CO - g/tkm 0.146

LPG from the tanker lorry is transferred to a stationary pressure tank by simple overflow due

to a pressure gradient. Thus, no additional electricity demand for compression arises. The

electricity consumption of an LPG fuelling station is assumed to equal that of a regular diesel

or petrol fuelling station. The electricity consumption of a diesel/petrol fuelling station

amounts to approx. 0.0034 MJ per MJ diesel or petrol according to [TotalFinaElf 2002]. Anal-

ogous to [JEC 2013], it is assumed that the electricity is supplied from the EU electricity mix,

i.e. attributed emissions of 489 g CO2 equivalent per kWh electricity. Operation with the

German electricity mix (approx. 575 g CO2eq/kWhel after [UBA 2010a]25, or estimate LBST for

2011 approx. 596 g CO2eq/kWhel) would result in slightly higher GHG emissions. With in-

creasing percentages of renewable electricity in the German electricity mix, future GHG

emissions from electricity supply are expected to decrease (LBST estimate based on BMU

Leitstudie 211 CO2eq/kWhel in 2030).

LPG is further produced in a number of processes during crude oil refining. For instance,

LPG is extracted from light fractions resulting from atmospheric distillation, cracking process-

es (hydrocracker, FCC cracker) and visbreaking and coking, further as a byproduct of cata-

lytic reforming (improvement of octane number) and subsequent processes.

25 [UBA 2010a] considers CO2 emissions only; emissions of CH4 and N2O may results in additional

GHG emissions of 30 g/kWhel.

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Figure 19: Crude oil refinery

In a refinery, crude oil is converted to petrol, diesel, LPG and a number of other products.

Refinery data was derived from [ETSU 1996].

Table 25: Energy demand and emissions from LPG production in a crude oil refin-ery

I/O Unit Amount

Crude oil Input MJ/MJ 1.087

LPG Output MJ 1.000

Emissions

CO2 - g/MJ 7.0

CH4 - g/MJ 0.000

N2O - g/MJ 0.000

NOx - g/MJ 0.015


SO2 - g/MJ 0.067

NMVOC - g/MJ 0.100

CO - g/MJ 0.001

Analogous to the assumptions for LNG in [JEC 2011], the average distance for LPG lorry

transport to the fuelling station is assumed to be 500 km. LPG transport assumes the same

HDS

HDS

Atm. residue

Vaccuum residue

Visbreaker

FCC

Crude

oil

10 MtHydroCracker

H2

H2

Propane: 0.5 Mt

Atm.distillation

Isomerization

Catalyticreformer

Reformatefractionation

and hydrogenation

H2

Diesel

Heavy naphtha

Light naphtha

Visbreaker

diesel

Diesel

DieselHeating Oil

Gasoline

Visbreaker

kerosine

Kerosene

Polymerisate

Isomerate

Isomerate

FCC naphtha

Butane

iC4/nC4

To naphtha HDS

To kerosin HDS

To diesel HDS

Diesel

GasSep. plant

C4 & lighter

H2

C4 & lighter

C4 & lighter H2

Reformate

FCC naphtha

C3/C4

C1/C2

Visbreaker

NaphthaLt. naphtha

Lt. naphtha

Heavy naphtha

Source: FZJ 1994, Acurex 1996, Scanraff 2002

HDS

H2H2S

C1/C2

H2S

H2S

Vacuumdistillation

HDS

H2H2SVacuum

distillate

C4 & lighter

C4 & lighter

Diesel

Heating Oil

3.6 Mt

Gasoline

2.8 Mt

Heavy fuel oil, Bunker C:

1.1 Mt

40%

Claus plant

H2S

S: 0.041 MtVaccum gas oil (0.1-0.7% S):

0.8 Mt

Butane: 0.6 Mt

C3

Kerosene

Low sulfur fuel oil (0.1% S):

0.6 Mt

HDS

HDS

Atm. residue

Vaccuum residue

Visbreaker

FCC

Crude

oil

10 MtHydroCracker

H2

H2

Propane: 0.5 Mt

Atm.distillation

Isomerization

Catalyticreformer

Reformatefractionation

and hydrogenation

H2

Diesel

Heavy naphtha

Light naphtha

Visbreaker

diesel

Diesel

DieselHeating Oil

Gasoline

Visbreaker

kerosine

Kerosene

Polymerisate

Isomerate

Isomerate

FCC naphtha

Butane

iC4/nC4

To naphtha HDS

To kerosin HDS

To diesel HDS

Diesel

GasSep. plant

C4 & lighter

H2

C4 & lighter

C4 & lighter H2

Reformate

FCC naphtha

C3/C4

C1/C2

Visbreaker

NaphthaLt. naphtha

Lt. naphtha

Heavy naphtha

Source: FZJ 1994, Acurex 1996, Scanraff 2002

HDS

H2H2S

C1/C2

H2S

H2S

Vacuumdistillation

HDS

H2H2SVacuum

distillate

C4 & lighter

C4 & lighter

Diesel

Heating Oil

3.6 Mt

Gasoline

2.8 Mt

Heavy fuel oil, Bunker C:

1.1 Mt

40%

Claus plant

H2S

S: 0.041 MtVaccum gas oil (0.1-0.7% S):

0.8 Mt

Butane: 0.6 Mt

C3

Kerosene

Low sulfur fuel oil (0.1% S):

0.6 Mt

of 79

lorry data applied for the transport of LPG from natural gas processing, including the same

assumptions for the fuelling station (see above in this chapter).

Renewable fuels

Biomethane

Methodology

The results for biomethane included in the present study are based on a number of published

studies examining potential environmental effects of production and utilisation of biomethane

as a fuel [Biogasrat 2011], [CML 2001]. The reported GHG emissions were derived from the

Renewable Energies Directive [EU RED, 2009/28/EC] and the German Sustainable Biofuels

Ordinance (Biokraft-NachV).

In principal, the calculation steps were uniform across the impact categories and selected

pollutants (i) cumulative energy demand (CED), (ii) nitrogen oxides (NOX). (iii) non-methane

hydrocarbons (NMHC) and (iv) sulphur dioxide (SO2). The cumulative energy demand was

calculated employing the CML Impact Assessment Method [CML 2001]. The additional pollu-

tants included are excerpts from the inventory results of the biomethane concepts under in-

vestigation.

Results

Table 26 summarises data for major environmental parameters of biomethane supply via

biogas in contrast with future supply via gasification (bio-SNG). The inference of universal

statements for entire fields of technology (e.g. biomethane production) remains difficult due

to the fact that LCAs generally present specific case studies. The data for biomethane from

renewable resources and waste materials reported in the table represent averages for typical

plant concepts in new facilities operated with state-of-the-art facilities. For the examined

pathways, the reduction potential for GHG emissions primarily depends on the utilised feed-

stocks, the supply of process energy and the extent of methane emissions during conver-

sion.

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Table 26: Overview of data for ecological parameters of biomethane supply

Assumptions and references

An overview of the concepts for biomethane supply from renewable resources/liquid manure

or biodegradable waste examined in the present study is presented in the following. A de-

tailed description may be found in [Biogasrat 2011].

Supply concepts biomethane via biogas from renewable resources/liquid manure or biode-

gradable waste:

The size selected for conversion plants for the supply of biomethane from renewable re-

sources/liquid manure and biodegradable waste was 1.2 MWel eq.

The renewable resources/liquid manure plant applied 64 % maize, 8 % cereal silage, 8 %

grass and 20 % liquid manure.

The concept for biomethane production from biodegradable waste applied 50 % biodegrada-

ble waste and catering waste/residues from the food industry, respectively. For the purpose

of maintaining a conservative calculation approach, supply of external process energy (ex-

Concept Category Unit

Scenario

Electricity mix today

Electricity mix 2030

Biomethane via biogas from renewable resources/liquid manure

GHG g CO2 eq/MJ fuel 39 26

CED non-renew. MJ/MJ 0.61 0.35

CED total MJ/MJ 2.99 2.80

NHMC g/MJ fuel 0.01072 0.009726

NOx g/MJ fuel 0.080646 0.074362

SO2 g/MJ fuel 0.030723 0.020197

Biomethane via biogas from bio-degradable waste

GHG g CO2 eq/MJ fuel 29 8.9



NHMC g/MJ fuel 0.004571 0.00300

NOx g/MJ fuel 0.03027 0.0203

SO2 g/MJ fuel 0.02420 0.00739

Biomethane via gasification (SNG 380 MW)

GHG g CO2 eq/MJ fuel 29 22



NHMC g/MJ fuel 0.013 0.012

NOx g/MJ fuel 0.089 0.085

SO2 g/MJ fuel 0.05 0.04

of 79

ternal electricity supply, heat supply via natural gas boiler) was assumed. Methane emissions

from biogas production and upgrading were an estimated 2 % factored in the balance. Addi-

tional relevant data on the examined production facility concepts are illustrated in Table 27.

Table 27: Parameters of the examined concepts for biomethane production from renewable resources/liquid manure and biodegradable waste [Biogasrat 2011]

Unit Biomethane from renewable resources/liquid manure

Biomethane from biodegradable waste

Substrate volume (renewable resources/biodegradable waste) incl. silage losses

t/kWh Hsbiomethane

0.00099 0.00096

Liquid manure volume t/kWh Hsbiomethane

0.00021

Transport distance substrate km 15 15

Biogas volume Nm³biogas/a 4973317 4722262

Electricity demand biogas plant kWhel/kWh Hs bio-methane

0.0242 0.0804

Heat demand biogas plant kWhth/kWh Hs bio-methane

0.0949 0.1185

Biomethane volume Nm³biomethane/a 2703495 2703495

Electricity consumption pressur-ised water washing

kWhel/kWh Hs bio-methane

0.0514 0.0488

Full load hours h/a 8100 8100

Supply concept biomethane via gasification (bio-SNG):

The thermo-chemical conversion process of biogenic solid fuels into biomethane is struc-

tured in five successive stages: (i) drying, (ii) gasification, (iii) gas cleaning and conditioning

(iv) methanation and (v) gas upgrading. In this process, dried biomass is converted into a

flue gas consisting of CO2, CO, H2O, H2 and – depending on the conversion process – CH4 in

a gasifier under application of a gasification medium (e.g. steam, oxygen). The resulting gas

contains impurities including particulate matter, tars, sulphur and nitrogen compounds and

halogens. These impurities have to be removed in a purification step before methanation. In

the subsequent step, the hydrogen and carbon monoxide content in the purified gas is con-

verted to methane and water in a synthesis reactor supported by a catalyst (methanation).

The gas escaping during synthesis is high in methane. However, before infeed into the gas

grid, gas upgrading, i.e. drying and removal of CO2, is required.

The bio-SNG concept examined in the present study is an advanced theoretical model based

of 79

on the concept applied at the pilot plant in Güssing, Austria. The concept assumes a thermal

input of 500 MW. Fuels in this concept include 65 % short rotation coppice, 25 % logging

residues and 10 % cereal straw. A detailed description of the concept may be found in [DBFZ

2009].

Synthetic methane from renewable electricity (RE methane)

Electrolysis of water has been employed for the production of hydrogen for about 100 years.

The first major electrolysis plant was established by Norsk Hydro in Norway in 1927 [Ullmann

1989]. Today, caustic potash (KOH) or proton exchange membranes (PEM) are used as

electrolytes. In the first plant constructed in 1927, caustic potash served as electrolyte. Alka-

line water electrolysis remains the most common technology. Advances in the field of PEM

electrolysis technology include innovations by Siemens, currently developing PEM electro-

lysers with multi-MW output [Waidhas 2011].

Electricity consumption including all auxiliary power units (rectifiers, pumps, compressors,

control units, gas processing if applicable) of recent electrolysers ranges between 4.3 and

5.2 kWh per Nm3 hydrogen. This corresponds to an energy conversion efficiency of 58 to 70

% in reference to the lower heating value of the resulting hydrogen. The present study as-

sumed an electricity consumption of 4.5 kWh per Nm3 hydrogen. Hydrogen is supplied with a

pressure exceeding 2 MPa (high-pressure electrolysis).

Methanation with CO2 is carried out in the subsequent step. The generation of methane from

hydrogen involves the following reaction:

4 H2 + CO2 CH4 + 2 H2O (gaseous) H = -165 kJ

This is an exothermic reaction. The catalytic methanation is carried out at temperatures be-

tween 200 and 400°C in the presence of a catalyst based on Ni or Ru, Rh, Pt, Fe, and Co

[Lehner 2012].

CO2 is assumed to be supplied by a biogas upgrader. Purification of biogas to pure methane

produces high-purity CO2 during pressurised water washing and pressure swing adsorption

(PSA). The only prerequisite required in this case is the compression of hydrogen from am-

bient pressure (0.1 MPa) to the pressurisation level for methanation (0.5 MPa). Electricity

consumption for CO2 compressions amounts to approx. 0.04 kWh per kg CO2. The CO2 de-

mand of approx. 0.198 kg per kWh methane thus results in an electricity consumption of ap-

prox. 0.008 kWh per kWh methane associated with CO2 supply.

of 79

Table 28: Input/output data for the production of methane from CO2 and hydrogen (incl. CO2 supply)

I/O Unit CO2 from biogas upgrading

CO2 Input kg/kWh 0.198

Electricity Input kWh/kWh 0.008

H2 Input kWh/kWh 1.200

CH4 Output kWh 1.000

An electrolysis energy conversion efficiency of 67 % in reference to the lower heating value

of hydrogen results in the overall energy conversion efficiency of 56 % for CO2 derived from

biogas upgrading.

In comparison, [Sterner 2009] state an energy conversion efficiency of 60 % in reference to

the lower heating value for the production of methane from renewable electricity. However,

the energy conversion efficiency of the electrolyser is reported at 76 % in reference to the

lower heating value (LHV). This corresponds to approx. 87 % in reference to the higher heat-

ing value (HHV). The result appears to be rather high given the fact that the electricity de-

mand of all associated auxiliary power units (pumps, ventilation, rectifiers etc.) and transfer

losses due to ohmic resistance are supposedly factored in the calculation.

The resulting methane is transferred to CNG fuelling station via the natural gas grid. The

electricity consumption of CNG fuelling stations amounts to 0.026 MJ per MJ CNG in 2012

and 0.024 MJ per MJ CNG in 2030. Electricity is supplied by the grid.

of 79

Appendix III: Energy taxation for fuels

Table 29: GHG savings costs for energy tax benefits in comparison to petrol

Fuel Energy tax

in ct/kWh

GHG emissions

in g CO2 eq/km

GHG savings costs in

comparison to petrol

in €/t CO2 eq

Petrol 7.3 206 -

LPG 1.3 188 2.256

CNG

1.4

175 1.263

Biomethane from biode-

gradable waste 69 286

Diesel 4.7 180 547

Source: Energy Tax Act. Values converted to ct/kWh. Own calculations.

of 79

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