32 gas for energy Issue 2/2018

REPORTS Sector coupling

Regionalized power supply at distribution grid level

by Peter Missal, Sina Hirschel, Thomas Kolb, Thomas Leibfried, Sören Hohmann, Joachim Walter, Doris Schmack

As part of the ”Energiewende“, the previously centralized power supply system is being replaced by a decentral-ized, volatile supply of renewable energies to the electricity grids, which shifts power supply from the transmis-sion to the distribution grid level. The KIBOenergy research project is based on this approach, exemplifying the way in which regionalization of power supply at distribution grid level can be achieved so as to reduce exchanges of electricity between the transmission grid and the distribution grid. Grid expansion necessary within the “Energiewende” can thus be reduced and manmade carbon dioxide emissions can be curbed. This enhances acceptance of the “Energiewende” by the public.

1. PROJECT BACKGROUND AND OBJECTIVES

The strategy pursued by the Federal Republic of Ger-many in environmental policy and climate protection is based on these four pillars: renewable energies, energy efficiency, energy storage technologies, intelligent grids, and the combined action of these energy technologies [1]. Moreover, the Federal Republic of Germany commit-ted itself to comply with the 2015 Paris Climate Agree-ment, and ratified the Global Climate Treaty in 2016 [2]. The KIBOenergy lighthouse project is built on these obli-gations. The purpose of the research project is to study the regionalization of energy supply at distribution grid level on the model location of Kirchheimbolanden so as to minimize exchanges of electrical energy between the transmission grid and the distribution grid. Kirchheimbo-landen is ideally suited to this purpose. This allows grid expansion to be reduced. The key to regionalization of the power supply system is storage and use of surplus eco-electricity. This can be achieved by optimum sys-tems integration of various energy subsystems (electri-city, gas, heat, mobility) (Figure 1). This is now described by the term “sector coupling,” more recently also referred to as “modal switch” [3]. Preliminary studies have shown that the KIBOenergy project needs long-term storage of renewable electricity [4]. For this reason, the project bases sector coupling on the power-to-gas technology (PtG). The KIBOenergy research project fully covers the German federal government’s concept underlying the

“Energiewende” and, in addition, makes a valuable contri-bution towards curbing manmade carbon dioxide emissions.

2. PROJECT PARTNERS

The project expense totals € 2.5 million and is financed by the German Federal Ministry for Economics and Energy (BMWi) within the framework of the “Power Grids” research initiative of the Federal Government to the tune of € 2.2 million. e-rp GmbH is responsible for project management. The DVGW Research Office with the Engler-Bunte Institute of the Karlsruhe Institute of Tech-nology (KIT) with three participating institutes (Engler-Bunte Institute (EBI), the Institute of Electric Energy Sys-tems and High-Voltage Engineering (IEH), the Institute for Control Systems (IRS)), the Bingen Transfer Agency for Efficient and Renewable Energy Use at the Bingen Tech-nical University, the Viessmann Group, and the town of Kirchheimbolanden are other partners cooperating in the research project.

3. KIRCHHEIMBOLANDEN MODEL LOCATION

Kirchheimbolanden is located in the state of Rhineland-Palatinate. It has approximately 8,000 inhabitants, 3,750 houses and buildings (state as of 2nd quarter 2017). e-rp GmbH is the local grid operator supplying electricity and gas to Kirchheimbolanden. This allows the use of real

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measured data for the lighthouse project with respect to both the generation of renewable energies and con-sumption by customers in households, trade and indus-try. The town of Kirchheimbolanden is also characterized by not only having a balanced distribution of power consumption by customers in households, trade and industry (approx. 30 % each), but also a sufficiently large capa-city of renewable energies (wind power, PV electri-city), installed capacity, and production volume for the most decentralized supply possible of eco-electricity to the town. Some data of the power supply situation of Kirchheimbolanden are shown in Table 1. It is seen that wind power (5.6 MWel) is currently being supplied to the medium-voltage grid and photovoltaic electricity (3.6 MWp) is being supplied to the low-voltage grid of the town. Moreover, some co-generation plants (0.3 MWel) are operated at Kirchheimbolanden, and there are also possibilities for demand-side management (DSM) with customers in trade and industry in Kirchheimbolanden. The respective companies were contacted by the project partners, and DSM possibilities were subsequently included in the project, which required implementation of a virtual power plant.

Figure 2 provides an overview of the infrastructure existing at Kirchheimbolanden. As can be seen, Kirch-heimbolanden also has a gas accumulator with a geo-metric volume of 900 m3. Prior to the deregulation of energy markets, the gas accumulator had an important function in providing low-cost natural gas and now con-stitutes an important storage element in the sector coup-ling scheme of the project. The accumulator can store the synthetic “green gas” generated by converting sur-plus renewable energy, and is available for a variety of

Figure 1: Energy systems

integration by

sector coupling

with power-to-

gas

source: NUMAX3D – istockphoto.com

Table 1: Power economy data of Kirchheimbolanden (2nd quarter 2017)

inhabitants appx. 8,000

number of houses 3,750

number of electricity exit points 4,660

number of electricity gas points 2,620

consumed annual flow of electricity appx. 70 Mio. kWhel/a

consumed annual gas volume appx. 170 Mio. kWhth/a

cogeneration units 10 CHP (283 kWel)

wind power generation 5.6 MWel (2 x 1.8 MWel, 1 x 2.0 MWel)

photovoltaic electricity feed 3.6 MWp (155 PV-systems)

Pfalzwerke - 110 kV high voltage grid

wind farm Hungerberg35.2 MWel

PV power plant Ilbesheim 6.4 MWp

Pfalzwerke - 20 kV medium voltage grid

00

00

consumed anddelivered energy

Pfalzwerke

00PfalzwerkePV power feed

3.6 MWp

∑

FLEXexistingblock heatand power stations

cogenera-tion plants /new civilwind park

∑ ∑wind power feed

5.6 MWel

Pfalzwerke

industry

commerceand smallindustry

FLEX

0.3 MWel

biogas Bischheim 400 mn³/h

Gas storage900 m³ geom.

Figure 2: Kirchheimbolanden

project area

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applications, such as fuel or for being reconverted into electricity when electricity is needed. There is also a biogas plant on the outskirts of Kirchheimbolanden. This can be used to make available carbon dioxide for the power-to-gas plant. The supply of renewable energies to the power grid of Kirchheimbolanden can henceforth be expanded by more eco-electricity (35.2 MWel, 6.4 MWp) from the nearby Hungerberg wind park and the Ilbes-heim photovoltaic park so as achieve regionalization of power supply at distribution grid level at the Kirchheim-bolanden model location. EVO AG and STAWAG AG as the plant operators agreed to make available to the research project the load curves of the Hungerberg wind park and the Ilbesheim photovoltaic park. As a co nsequence, real-time data in terms both of power generation and power consumption are available to the project.

4. PROJECT STATUS

The lighthouse project started in June 2015 and will end in November 2018 after writing a final report. So far, all stu-dies to be conducted within a variety of work packages have been completed on schedule.

4.1 Modeling and validation of the electricity grid and the gas system

At the beginning, the power grid and the gas system of Kirchheimbolanden had to be modeled and validated. For this purpose, twenty measuring points were installed in the medium-voltage grid at selected nodes. All electric generation and feeding units and all electricity output units are connected to these measuring systems. A differ-ent approach was used for the gas system, where all gas

Figure 3: Electricity grid (left) and gas system (right): modeling and validation

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+PghlFigure 4: Building model

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output points were covered individually (cf. Table 1). This is due mainly to the fact that these data at the same time are entered into a building model determining the heat consumption of all users, but also taking into account electricity generation by co-generation plants in these houses. Meanwhile, modeling and validation of the elec-tricity grid and the gas system have been completed. Excellent agreement was found between the measured values and the results obtained in the models (Figure 3). The electricity grid was modeled on the basis of the MATLAB software program, while the gas system was modeled by means of the STANET program.

4.2 Modeling and validation of the building model and the building cluster

A building model is used in the research project which determines heat consumption of all users at Kirchheim-bolanden, but also takes into account electricity genera-tion by co-generation plants in the houses (Figure 4). In the building model, a difference is made between build-ings with gas heating, buildings with co-generation plants, buildings with heat pumps in place, by sizes of

the power plants (small, medium, large), and by types of buildings (single-family house, multifamily house, etc.). The studies also include other heating systems, e. g. oil heating systems, and energy stores installed in houses. The building model also allows measures of thermal insulation of individual houses to be considered. At the same time, a cluster of buildings of the town was estab-lished (Figure 5). The total of 3,750 houses and buildings in Kirchheimbolanden were logged by age and heat demand. The data determined in this way were also included in the building model. Also, field test units are to back up model calculations. In the meantime, a heat pump of the Viessmann group has been installed in a single-family house, and another bivalent heat pump has been installed in a multi-family house. Moreover, a co-generation plant with a gas burner was installed in a nursery school to cover peak load phases. In this way, the results of the building model can be harmonized with real-time data from the field test plants also in sce-narios of future power supply schemes in Kirchheimbo-landen, e. g. in 2030, because it is to be expected that present power plants will be replaced by modern power systems.

trade-/industrialarea

Caption [amount]buildings [3750] heat required [MWh(th)/a]

Detached houses [729) 3.630Multiple dwelling units [634] 25.730Large multiple dwelling units [60] 6.250End terrace houses [554] 8.320Mid terrace houses [241] 10.790trade, industry, service not specified

RegEnKibo – Kirchheimbolanden - scheme

trade area (old)trade area

area

Figure 5: Build-

ing cluster

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4.3 Modeling and simulation of the PtG plant and the PtG test facility

Regionalization of power supply at distribution network level requires assessment of the complete system includ-ing sector coupling. In this way, the two power subsys-tems, namely electricity and gas, can be interconnected meaningfully and renewable energies can be used com-pletely and efficiently in the sense of “Energiewende.” As mentioned initially, the KIBOenergy project falls back upon the power-to-gas technology (PtG). Together with the Karlsruhe Institute of Technology (KIT), a three-phase methanization reactor was developed at the DVGW Research Office of the Engler-Bunte Institute. It is charac-terized by good heat transfer properties [5]. The reactor is integrated into the research project and is modeled also in its control aspects. In the meantime, hydrodynamic

calculations have been conducted, and the materials transport and reaction kinetics aspects of the methaniza-tion reaction have been studied. A first reactor design has also been completed. A schematic process flowsheet of the reactor with its potential operating conditions is shown in Figure 6. A test run was performed within the overall simulation environment by coupling to the build-ing model.

At the same time, the Engler-Bunte Institute at Karlsruhe runs a PtG test facility for steady-state as well as dynamic experiments. These studies serve to check whether the volatility of renewable energies has an impact on the degree of conversion in exothermic chemical methaniza-tion of hydrogen with carbon dioxide into methane and water (Sabatier reaction). For this purpose, the electric sig-nals are run from the control center of e-rp GmbH to Karlsruhe. In electrolysis preceding methanization, the research project uses extensive published data and find-ings made in other projects, e.g. the data of the “electricity-to-gas facility” of the Thüga Group, in which e-rp GmbH had been one of the partners in that research project. The KIBOenergy project also investigates to what extent con-version of the surplus eco-current up to the level of hydro-gen is sufficient without restricting the gas technology and combustion technology characteristics of the natural gas used at Kirchheimbolanden (in this case, H natural gas).

4.4 Optimized control of the overall energy system and virtual power plant

One focus of the lighthouse project is on the combina-tion of the two energy subsystems by sector coupling so

Simulation-Workspace

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overall energy

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three-phasemethanasation

20 bar300 °C

H2CO2

CH4 (SNG)

H2O

boiling water(e.g. 300 °C, 22 bar)

gas bubbles

liquids + catalysor

liquids:silicon oildibenzyltoluolIonic liquid

Figure 6: Process

flowsheet of the three-

phase methanization

reactor

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as to establish one overall energy system interconnected for control. This is to consume optimally on the spot the renewable energies generated at Kirchheimbolanden and allow regionalization of energy supply at distribu-tion network level. Control of the overall energy system is to be model-based predictive (MPC). The optimization algorithm of the overall energy system includes all meas-ured data and, in addition, for instance also meteorologi-cal data, weather forecasts, and DSM measures. For this reason, a virtual power plant is one component of the project integrated into the overall energy system. This allows more energy efficiency to be exploited in the interest of the “Energiewende.” There is also a break-down of loads into SLP customers (standard load profile) without recording power measurement, and RLM cus-tomers (recording power measurement) in such a way that all households, trade, and industrial customers and their load profiles are taken into account. All their data are stored in databases. Other components entering the “simulation workspace” are shown in Figure 7. Control time is to be organized in one-minute steps. During that time, all input quantities must be entered, processed, assigned a quality mark, and connected with control quantities acting on the overall energy system as output quantities by way of the MPC controller. The first results about model-predictive control are promising, as is shown in Figure 8. Thus, 1 MWel power of the PtG con-verter already allowed a substantial reduction of the power flow to the transmission grid to be achieved. The simulation calculation was conducted in a model with 192 time steps (of 15 min. each) within the optimization horizon (np = 192). In the meantime, all preconditions have been established to allow the control optimization algorithm to be further handled and started.

5. FURTHER PROCEDURE AND OUTLOOK

The KIBOenergy lighthouse project fully covers the “Energiewende” concept adopted by the German Fed-eral Government. The results obtained so far are promis-ing. In the next few weeks, the optimization calculations of the overall energy system are to be refined. For this purpose, also real-time operation of individual plant components is planned. This is to show the practical applicability of the model results elaborated by the pro-ject team. In addition, scenario assessments are carried out for the years 2030 and 2050. They will subsequently

be included in the overall energy system assessment, and will show the resultant changes in regionalization of power supply at distribution network level. In particular, efficiency measures will have increasingly stronger impacts on energy supply, which should be taken into account.

The regionalization of power supply at distribution network level on the model location of Kirchheimbolan-den can be considered an individual cell. These individual cells will be combined with other individual cells to establish renewable energies within the framework of the “Energiewende.” The individual cells may differ in size, ranging from the quarter solution to regional power sup-ply and on to metropolitan dimensions. Moreover, in the design of cells, a distinction must be made between a power supply system more rural in character and power supply in conurbation areas. The KIBOenergy lighthouse project is a rural power supply system. Especially plants for producing renewable energies are classified under this heading. It is thus a purpose of the “Energiewende” to consider all these boundary conditions and find technical solutions and economic schemes for interconnecting the energy cells. For this reason, the lighthouse project is to be continued after completion in order to interconnect several cells of different sizes and test the control charac-

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Figure 8: Model-based predictive control of load flow

(PtG converter: 1 MWel)

FIND THE FILM ON THE RESEARCH PROJECT UNDER:

www.youtube.com/tch?v=5Ywiaub0QVk (KIBOenergy: renewable energies – regional and efficient) orwww.meine-e-rp.de/region/kiboenergy-so-wird-strom-in-gas-verwandelt

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teristics of this overall energy system, which is larger than the KIBOenergy project, with sector coupling as the key element and its called EnergyCells.

Calculations have shown that regionalization of power supply at the Kirchheimbolanden model location on the basis of renewable energies will reduce manmade car-bon dioxide emissions by some 30,000 t/a; additional switching from natural gas to synthetic natural gas (SNG) will make this approx. 80,000 t /a.

REFERENCES

[1] BMU: Das Energiekonzept der Bundesregierung 2010 und die Energiewende 2011. Berlin, Status October 2011

[2] BMU: Bundesumweltministerin Barbara Hendricks unterzeichnet das Pariser Klimaabkommen. Press release dated April 22, 2016

[3] DVGW: Der Energie-Impuls – ein Debattenbeitrag für die nächste Phase der Energiewende. Bonn, Status May 2017

[4] Missal, P.: Dezentrale Energieversorgung mit Wind-strom – Modellbetrachtung und Wirtschaftlichkeit-sanalyse. Masterarbeit, FernUniversität in Hagen, Fakultät für Wirtschaftswissenschaft, 2012

[5] Götz, M; Graf, F.; Lefebvre, J.; Bajohr, S.; Reimert, R.: Speicherung elektrischer Energie aus regenerativen Quellen im Erdgasnetz – Arbeitspaket 2a: Drei-Phasen-Methanisierung. DVGW energie-wasser-praxis 65 (2014) Nr. 11, pp. 41-43

AUTHORS

Prof. Dr.-Ing. M.Sc. Peter MissalManaging Director e-rp GmbHAlzey, GermanyPhone: +49 6731 405-238Email: peter.missal@e-rp.de

Sina Hirschel LL.M.Law, special projects, community managemente-rp GmbHAlzey, GermanyPhone: +49 6731 405-351Email: sina.hirschel@e-rp.de

Prof. Dr.-Ing. Tomas KolbHead of InstituteKIT, DVGW Research Office and Engler-Bunte Institute Karlsruhe, GermanyPhone: +49 721 608-42560Email: thomas.kolb@kit.edu

Prof. Dr.-Ing. Thomas LeibfriedHead of InstituteKIT, Institute of Electric Energy Systems and High-Voltage EngineeringKarlsruhe, GermanyPhone: +49 721 608-42520Email: thomas.leibfried@kit.edu

Prof. Dr.-Ing. Sören HohmannHead of InstituteKIT, Institute for Control SystemsKarlsruhe, Germany Phone: +49 721 608-43180Email: soeren.hohmann@kit.edu

Dipl.-Ing. (FH) Joachim WalterManaging DirectorBingen Transfer Agency of ITGg GmbHBingen, GermanyPhone: +49 6721 98424-250Email: Walter@tsb-energie.de

Dr. Doris SchmackManaging Director MicrobEnergy GmbH/Viessmann GroupSchwandorf, GermanyPhone: +49 9431 751-281Email: doris.schmack@microbenergy.com