Fuel Comparison Calculator User Manual

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Fuel Comparison Calculator 2.0User Manual

November 26, 2013

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TABLE OF CONTENTS

Notation ........................................................................................... 1

Overview .......................................................................................... 2

Use Instructions .............................................................................. 2

Guide for Inputs .........................................................................2

Guide for Results .......................................................................6

Calculations and Assumptions ....................................................... 7

Trouble Shooting ............................................................................. 9

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NOTATIONAbbreviationsFuels: gas = gasoline CNG = compressed natural gas LPG = liquidized petroleum gas (propane) E85 = 85% ethanol B100 = 100% bio-diesel HEV = hybrid electric vehicle BEV = battery electric vehicle PHEV = plug-in hybrid electric vehicleGGE = gasoline gallon equivalentGHG = greenhouse gas LHV = lower heating valueWTW = wheel-to-well

EquationsAs a convention for cost related variables, a lower-case c represents annual costs, and lower-case subscripts represent per vehicle costs. For example, cF represents the total annual fuel cost while Cv represents the incremental cost per vehicle with no time dependence. This convention also holds for fuel use, savings, mileage, payback, GHG emissions, and petroleum consumption.

cF = total annual cost of fuel ($/year) cµ = total annual cost of maintenance ($/year)Cr = grants, incentives, or other revenue per vehicle ($/vehicle) Cv = incremental cost per vehicle ($/vehicle)e = annual WTW GHG emissions (tons of CO2 equivalent)E = total WTW GHG emissions (tons of CO2 equivalent)ef = WTW GHG emissions factor (short tons CO2 equivalent / gallon of fuel use)LHV = lower heating value (grams/btu) m = annual vehicle miles traveled (mi/year)M = total vehicle miles traveled (mi) or simple payback miles (mi)MPG = fuel economy (mi/gal)MPGgain = fuel economy gain (%)MPGloss = fuel economy loss (%)µ = maintenance cost per mile ($/mi) µsavings = maintenance savings per mile (%)N = simple payback years (years) p = annual WTW petroleum consumption (barrels of petroleum)P = total WTW petroleum consumption (barrels of petroleum)pf = WTW petroleum consumption factor (barrels of petroleum /gallon of fuel use)Pfuel = price of fuel ($/gal) from those listed above (e.g. Pgas is the price of gasoline)s = annual savings per vehicle ($/year/vehicle) sTOT total annual savings ($/year)U = total fuel use (gal)u = annual fuel use (gal/year)Uincrease = fuel use increase (%)Ureduction = fuel use reduction (%)V = # of vehicles

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OVERVIEWThe Fuel Comparison Calculator was developed by Clean Energy Coalition as a part of our fleet consulting service, Fuel Forward. Fleet managers can insert their gasoline or diesel fleet data into the calculator to generate dynamic alternative fuel scenarios. The calculator displays the potential savings and simple payback period of switching to alternative fuels in a side-by-side comparison. The calculator also takes fuel price uncertainty into account by displaying the variation of the results with short-term fuel price fluctuations and long-term fuel price projections. In addition, the calculator estimates the potential displacement of greenhouse gas emissions on a WTW basis with each alternative fuel option to allow fleet managers to calculate their current emissions and develop successful emission reduction plans. Petroleum consumption displacement is also reported on a WTW basis to allow fleet managers to gauge their potential impact on the energy security of our nation.

USE INSTRUCTIONSThe calculator consists of two Microsoft Excel sheets; one for gasoline vehicles and one for diesel vehicles. The user first decides how many vehicles they would like to consider switching to alternative fuels. Secondly, the user should input the average annual miles traveled and average fuel economy of these vehicles into table (1) of the appropriate sheet (for either gasoline or diesel fueled vehicles). Inputting actual or averaged values into the calculator will yield more accurate and useful results as opposed to estimated or default values. Third, the user should select the alternative fuels that they would like to consider from table (2). At this point, the calculator will display graphics and charts representing the potential savings, simple payback period (in both years and miles), WTW GHG emissions reduction, and WTW petroleum consumption reduction. However, the user should take the time to specify the additional inputs available which tailor the results to better match how switching to alternative fuel vehicles will play out in the real-world. These additional inputs include maintenance costs, fuel prices, payback goals, incremental conversion costs, grants or incentives for alternative fuels, alternative fuel vehicle fuel economy, and alternative fuel vehicle maintenance costs. For a detailed discussion of the inputs and results of the calculator, see the “Guide for Inputs” and “Guide for Results” sections below.

Guide for InputsInput table (1) Fleet Profile contains all of the inputs pertaining to the vehicles (Number of Vehicles) that the user would like to convert to alternative fuels. The best candidates for conversion are vehicles that consume significant amounts of fuel on an annual basis either

through driving many miles in a year (Annual Miles Traveled /Vehicle) and/ or suffering from bad fuel economy (Gasoline Fuel Economy). These vehicles will achieve greater annual savings and thus a quicker payback. While a vehicle’s rated fuel economy can be used as input, the rated fuel economy reflects unrealistically ideal driving conditions such that the actual fuel economy of vehicles on the road will always be less.

A more accurate fuel economy can be determined if one knows the amount of fuel consumed over a known distance. Fuel consumption can be tracked at the pump and mileage from the odometer. Fuel economy can then be calculated using the following equation:


(1)

If several vehicles are being considered, the ideal fuel economy input would be an average calculated value from the combined annual mileage and fuel use of these vehicles.

The maintenance cost input (Maintenance Cost /Mile) is on a per mile basis in order to reflect the dependence of the total maintenance cost on vehicle wear-and-tear. Thus, vehicle wear-and-tear is assumed to be correlated with mileage, which is a reasonable assumption if the vehicle inspection schedule is determined by the odometer. The Alternative Fuels Data Center offers industry average maintenance costs per mile for various vehicle types, which is preferred to using fleet data unless the fleet data captures maintenance costs averaged across the entire lifetime of vehicles. One can set the maintenance cost to $0 per mile if they would like to consider only fuel costs and not combined fuel and maintenance costs.

The payback goals (Payback Goal (Years), Payback Goal (Miles)) affect the display of the payback charts in the calculator. By default, the payback goal in miles is equal to the payback goal in years multiplied by the annual miles per vehicle. Alternatively, one can set the payback goals to represent an expected vehicle lifetime, and the results will then display payback accordingly. This may be desired if one cares more about reducing emissions and petroleum consumption and, thus, is concerned more with breaking even than profiting from the implementation of alternative fuels.

The price of gasoline or diesel (Gasoline Price, Diesel Price) should ideally be set to the average fuel price that the fleet has paid over the past year. Alternatively, regional and national average gasoline and diesel prices can be found on the Energy Information Agency’s website, eia.gov.

Table (2) Select Scenarios allows the user to select the scenarios of their interest. The calculator will only display results for scenarios that have been selected. To choose a scenario, select “yes” from the drop-down list next to the scenario name, or type the word “yes” into the cell and press enter. For the screen-shots that follow, the scenarios Natural Gas, Propane, Ethanol, HEV, and New Efficient Vehicle were selected as examples.

The price of scenario fuels in table (3) Scenario Fuel Prices only needs to be set for the scenarios that have been selected. Current alternative fuel prices can be found on the Alternative Fuels Data Center website, afdc.com, but these prices tend to be higher than the

deals that fleet managers can often procure.

Table (4) Scenario Assumptions allows the user to further customize the results to match their real-world options. For example, some fuels (such as CNG and LPG) are better for the engine than gasoline and thus have the potential to reduce maintenance costs (Maintenance Savings). Electric vehicles achieve maintenance savings by eliminating the need for a combustion engine all-together. The default maintenance savings values reflect what one can expect from our


experience with other fleets switching to alternative fuels. Alternatively, if one believes maintenance costs may increase from alternative fuels, the maintenance savings can be set to a negative value, or zero if one believes the maintenance costs will stay the same.

The fuel economy loss (Fuel Economy Loss) represents the different energy densities of the fuels and effectiveness of the vehicle technology to capture that energy upon combustion. If the initial and final fuel economies are known, fuel economy loss can be calculated using the following equation,

(2)

where the prime denotes the final fuel economy (i.e. that of the scenario versus the initial gasoline or diesel value). The fuel’s energy density (i.e. how much energy is stored in a gallon of fuel on an atomic level) is represented by the lower and higher heating values (LHV and HHV respectively). The range in energy density from LHV to HHV is the result of a range in energy released on combustion depending on whether the product of water is formed as a liquid or vapor. The LHV is used in the calculator’s computations to provide conservative fuel use estimates. The achievable fuel economy may be better than the chemistry would suggest as a result of fuel specific technologies. Therefore, the fuel economy loss from energy density should be adjusted based on conversion kit specifications, and can be determined using


the following expression:

(3)

Equation 3 was derived from the relationship between fuel economy and fuel use, which is an important relationship to understand in the context of considering alternative fuels. The relationship can be stated as follows from equation 1 assuming that the mileage remains the same:

(4)

Hence, a fuel economy loss corresponds to an increase in fuel use, and a fuel economy gain corresponds to a reduction in fuel use, which are defined as follows:

(5)

(6)

(7)

From these equations, one can derive an expression to go straight from fuel economy loss to fuel use increase, fuel economy gain to fuel use reduction, or vice versa.

(8a)

(8b)

(9a)

(9b)

An equation can also be derived to calculate final fuel use or fuel economy given a single initial condition and a percentage change as follows:

(10a)

(10b)

Fuel economy gets its name from its inherent relationship with fuel prices and costs. Improvements in fuel economy work to directly counteract the rise in fuel prices. The sample problem (specifically question #4) in the “Calculations and Assumptions” section details this relationship explicitly.

Not all scenarios require a fuel economy loss input. For example, CNG is sold in units of GGE which has the same per unit energy as a gallon of gasoline. Thus, there is no fuel economy loss. The HEV, BEV, PHEV, and New Efficient scenarios require a fuel economy (Fuel Economy) input instead of a fuel economy loss percentage, since this is the information that will be available when looking at these types of vehicles. Equation 8b with the help of equations 2 and 5 are especially useful for these scenarios in order to calculate the equivalent fuel use reduction that you can expect from switching to a better fuel economy.

Other inputs in table (4) include incremental costs (Incremental Costs) and grants or incentives (Grants or Incentives). Both should be entered on a per vehicle basis. The incremental cost represents a conversion costs, or the cost of a conversion kit. This can be found on the manufacturer’s website. Alternatively, Clean Energy Coalition can assist you in finding specific suitable conversion options for your fleet.


In addition, some of the inputs in table (4) are scenario specific. For example, the bi-fuel scenarios allow the user to estimate what share of their miles they expect to run on alternative fuels (Percentage of Natural Gas Miles, Percentage of Propane Miles). The BEV and PHEV scenarios ask the user to estimate how many days in the year (Days Driven in a Year) and the all-electric range of the vehicle in miles (All-Electric Range). The calculator then uses the annual miles traveled to estimate the average miles driven per day. If this value exceeds the all-electric range, a BEV will require charging throughout the day, and a PHEV will consume gasoline. This is taken into account for all of the results on BEVs and PHEVs.

Guide for ResultsTable (5) Results - At a Glance is the first results table, and is located directly to the right of the inputs. It contains all of the calculated values as graphics. These graphics were designed to clearly depict the value that they contain so that results can be quickly and easily understood at a glance.

Table (6) Results - Comparison Summary contains slider comparison charts. All of the scenarios selected are displayed on a single line so that one can quickly identify the best and worst scenario for each calculated value. Scenarios are ordered from worst on the left to best on the right.

Table (7) Results - Price Fluctuations displays the variation one can expect in the results from price fluctuations. The price ranges extend from the price inputs plus or minus three times the average standard deviation across ten years of fuel price data from the Alternative Fuels Data Center. If fuel prices in a given year can be considered normally distributed, then the fuel price range captures 99.7% of all fuel prices one will observe in the next year. Fuel prices are not normally distributed since they result from a complex system and tend to increase from year to year. So while one may observe fuel prices outside of the range, the charts are still useful in providing a level of certainty that one will achieve annual savings and a reasonable payback period.

Table (8) Results - Price Projections calculates projected prices from the payback target in years input and displays the results according to these projected prices. The calculator uses a high and low projected annual growth percentage of fuel prices as reported in the Energy Information Agency’s Annual Energy Outlook 2013 (table A3). These charts can be used to estimate how savings and simple payback may change from the base year to the target payback year.


CALCULATIONS AND ASSUMPTIONSAnnual savings (equation 11) accumulate as a result of reduced operating cost from decreased fuel and/or maintenance costs. If the maintenance cost per mile input from table (1) is set to zero, savings will represent fuel costs. A negative annual savings indicates increased operating costs as a result of switching to the scenario fuel or vehicle.

(11)

where,

The payback years (equation 12) calculation is considered simple because it does not account for the time values of money. The calculator is meant to provide a starting point for alternative fuel considerations, and thus the simple payback calculation is sufficient. It is a useful as a point of comparison between the various scenarios.

(12)

The simple payback in miles (equation 13) removes the time dependence of the payback years and allows for variable yearly mileage that one encounters in real life. One can use the payback miles charts to determine a range of odometer miles that represent the alternative vehicle paying for itself. Any additional savings from miles driven beyond this odometer reading can be considered profit. However, the time value of money is not taken into consideration, so one must be aware of this when using the numbers in this way.

(13)

The calculator estimates GHG emissions (equation 14) and petroleum consumption (equation 15) on a WTW basis directly from the amount of fuel used. In actuality, vehicle emissions increase with vehicle age and bad driver behavior (such as idling and hard starts and stops) which are not accounted for by the calculator. Therefore, the results of the calculator are conservative estimates. The calculator does however account for different fuel sources. For example, the emissions factor for North American CNG is nearly thirty-three times larger than the emissions factor for CNG from land-fill gases. In later editions of the calculator, the user will be able to explore different alternative fuel sources by changing an input in table (4) to the available drop-down choices.

(14)

(15)

The following page includes a sample problem that can be used to test ones comprehension of the equations above.


Assume you drive 15,000 miles annually and your fuel economy increases from 12.64 mpg to 15.59 mpg.

1. How much money will you save annually in fuel costs by switching one gasoline vehicle to the better fuel economy if the price of gasoline increases correspondingly from $3.50/gal to $3.60/gal? [Hint: use equation 11 to calculate annual savings]

2. How much money does the increase in the price of gasoline take away from your savings?

3. If you were to stick with the old fuel economy, how much would the increase in the price of gasoline cost you?

4. What effect if any does the fuel economy gain have regarding the increase in fuel price?

5. At what new gasoline price would your annual savings drop to zero (i.e. the break even price) with the given fuel economy increase?

Sample Problem

Solution


TROUBLE SHOOTINGIf you have any issues regarding the calculator, please contact us by phone or email as detailed below. We would greatly appreciate you taking the time to make us aware of your issue. Feedback and recommendations are also greatly appreciated.

Doug KripkeFall Associate | Clean Energy Coalition734.585.5720 [email protected]

Fuel Comparison Calculator User Manual

Automotive

Transcript of Fuel Comparison Calculator User Manual