Detailed information on energy research

Projektinfo 12/2012

Smart regulation of rural electricity gridsModern communications technology reduces the voltage fluctuations and regulates the storage of surplus electricity

In the “Smart Country” model project, researchers in Bitburg-Prüm were testing out the distribution network of the future. It is designed to respond flexibly to the increasingly decen-tralised generation of renewable electricity in the grid. For this purpose various operating resources were further deve-loped: an optimised biogas plant, which controls the electricity supplied by the grid, virtually stores surplus electricity with an efficiency of 98 %. In addition, voltage regulators double the usable output capacity in the grid. The Eifel project successfully passed the field test after around one year.

The existing electricity grid is not designed for the diverse manner of ways in which electricity is fed into the grid. This particularly applies to rural areas. Be-cause of the many decentralised grid injections and low local requirements, new grid solutions are necessary in order to meet future requirements. New distribu-tion grids – so-called Smart Grids – will provide the basis for sustained energy use. However, how these intelligent grids will (or should) actually look like is still not clear. With traditional electricity provision, the electricity only flows in one direction: from the power plant to the customers. With smart grids, there are additional small power plants. Wind turbines, solar power installations and biogas plants generate additional electricity that is fed into the grid. Because the energy is not constantly generated, this causes voltage fluctuations, particularly in rural electricity distri-bution grids.

This research project is funded by the:

Federal Ministry of Economics and Technology (BMWi)

The aim of the “Grids for Future Electricity Supply” re-search project (“Future Grids / Smart Country” for short) was to develop and demonstrate innovative grid con-cepts as a basis for smart grids and provide an econom-ic and technical analysis of them. “All measures are aimed at enabling more decentralised generation in the existing grid,” explains Torsten Hammerschmidt, head of the research project. The investigated grid concepts consider an increased use of information and communi-cations technology (ICT) as well as intelligent secondary technology. There are also new components analysed, ranging from voltage regulators based on power elec-tronics to approaches utilising flexible supply voltages in the grid, for example by providing the permissible voltage range for customer devices with inverters at house connection points. The construction of intelli-gent grid expansion is also indispensable for connect-ing decentralised generators, whereby the focus of the project ranged from the distribution grid to the custom-er connection. Together with plant manufacturer ABB, the consultancy company Consentec and the Techni-sche Universität Dortmund, RWE Deutschland tested the first smart grid in Germany of this kind in the Eifel region of Bitburg-Prüm in Rhineland-Palatinate. With just 32 inhabitants per square kilometre, the 173-square-kilo-metre test area is very sparsely populated, with more than 12 MW of electricity fed into the grid here from re-newable energies (Fig. 1).

Region acquires new gridsIn the Eifel region, the installed capacity of renewable energy generating systems in the low to medium voltage range currently exceeds the maximum load by more than 200 % (Fig. 1). This represents a challenge that could occur in many areas of Germany by 2030. Furthermore, the expansion of renewable generation has also not yet been completed in this area. Additional 50 % can be expected by 2030. The demonstration grid encompasses around 110 kilometres of medium-voltage distribution lines with around 100 stations. The following components have been used: data technology, information and communi-cations technology (ICT), a biogas storage system for balancing out electricity peaks, intelligent grid structures with powerful cable sections – effectively electricity high-ways – and voltage regulators that maintain the voltage in the grid at a constant level (Fig. 2).

Load balance in the demonstration gridWhen operating distribution grids without decentral-ised generation, the grid is sufficiently monitored by conducting electricity measurements in the medium-voltage terminations in the primary substations. How-ever, this is no longer the case with increasingly de-centralised generation. The grid must therefore be monitored with additional ICT. The actual load flows are recorded and transferred with the data transmission. In addition, individual status reports on operating equip-ment are continually checked and remote control con-cepts analysed in technical and economic terms, whereby switching commands are given and responses evaluated.

Virtual electricity storageTo enable the grid to be loaded more equally and thus enable additional decentralised generation units to be connected without grid enhancements, an intermediate

gas storage system was used at a biogas plant as part of a field experiment (Fig. 3). “To store the solar-generated electricity that is available in excess during the midday hours, we deployed a biogas storage system. It actually stores biogas, but is used as a PV storage system by shifting the generation of electricity from biogas from the midday hours to the evening,” explains Hammerschmidt. The biogas storage system is sized so that the PV feed-in is imitated in reverse, i.e. during the period with increased PV feed-in the electricity generated from the continually produced biogas is throttled down or stopped. The largest storage period for the biogas storage system is required during the summer months. In the winter months, on the other hand, this method of operation makes it possible to generate electricity from the biogas almost

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Fig. 2 Investigated voltage regulator in the low-voltage grid (left) and voltage regulator in the medium-voltage grid (right). Source: RWE Deutschland

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Fig. 1 Total decentralised generation in the Trier region (three rural districts, in total 3,900 km²: Bitburg-Prüm, Bernkastel-Wittlich and Trier-Saarburg). Depicted is only the decentralised generation fed into the medium and low voltage range. Source: RWE Deutschland

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without having to use the storage system. The 300 kWel produced at the site (160 Nm3/h raw biogas) has to be distributed during the day and year in such a manner that the biogas produced can also be completely used for generating electricity. Coupling the biogas storage system to the electricity injected by renewable energy sources such as photovoltaic and wind power balances out devia-tions in the electricity grid. The farm-produced biogas is used for generating electricity and heat in a CHP plant when insufficient photovoltaic or wind energy is available in the grid; conversely the production of electricity from biogas stops when the solar and wind energy can meet demand. With an efficiency of 98 %, this makes it possible to store renewable electricity pro-duced from wind, photovoltaics and biomass (Fig. 4).

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Fig. 3 Virtual PV electricity storage: Buffering of the PV electricity generation for grid- and needs-oriented feeding into the electricity grid. Source: RWE Deutschland

Fig. 4 Sketch of the implemented storage strategy: The biogas plant acts as photovoltaic storage system. Source: Ceno-Tec

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1,000

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Biogas

31.12.2010

Original grid transportationcapacity / max. load

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267

535

837

1.419

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967

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More flexible operational managementThe feed-in and load situation has reached a stage where the limits of the voltage range are now being reached at certain points. An analysis was therefore ini-tially conducted to examine the effectiveness of central (medium-voltage branch point), semi-central (second-ary station) or decentralised control (house connection point). For this purpose, a branch point, four local grid stations and two house connections were equipped with electronic voltage regulators. This minimised volt-age fluctuations, increased the voltage quality and, as a result, created capacity in the grid for other connections to decentralised generators.In addition, using 20-kV technology, a main supply axis has been laid in the demonstration grid that is more powerful and reliable than the surrounding 20-kV grid, since intelligently structured cable connections also form part of efficient smart grids. The increased short-circuit power of this main distribution line provides increased connection possibilities for decentralised generators. The main distribution line has been executed as a pow-erful dual cable in the demonstration grid, to which the rural overhead power lines are connected. The supply quality is supported by the use of break switches or re-mote-controlled load disconnectors between the over-head power lines and the main distribution line.

Successful first operating yearPractically throughout the entire trial year for the “Smart Country” project, a growing surplus of renewable energy-based electricity prevailed throughout the demonstration grid area – the generation there was almost constantly greater than the demand. After one year of testing, the project participants have drawn a positive balance. “This is the first time that we have deployed voltage regulators based on semiconductor technology in public energy distribution grids. These control the voltage pre-cisely to the set value,” summarises Torsten Hammer-schmidt. In this case the operational locations of the voltage regulators double the usable output capacity in the existing medium-voltage grid. The alternative meas-urement technology installed in another medium-volt-age grid enables the voltage fluctuations to be reduced by up to 38 %. “That is considerably important for rural supply tasks, since decentralised generation is devel-oping particularly rapidly in the countryside,” explains the project manager. The project results provide a basis for future grid plan-ning and for developing new strategies for managing the grid. Although the operating equipment used in the field test has provided very positive results, the opera-tional results will have to be further validated, since there is still no long-term experience. RWE Deutschland has therefore secured the validation of the operational equipment as part of a 3-year follow-up project.

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Better energy distribution in smart grids According to the German Federal Environment Agency, approximately 600 TWh of electrical energy are consumed each year in Germany, of which roughly 25 % is lost during the energy transmission and conversion. By developing the electricity networks to form an intelligent grid – the Smart Grid, it should be possible to use the available energy much more efficiently and therefore considerably reduce energy losses.The aim of the 3-year “Energy to Smart Grid” (E2SG) research project is to reduce the losses created when distributing the energy by 20 %. The focus of interest is on smart electricity meters and the interfaces (communications processes and voltage converters) between the end devices (household peripherals, lamps, etc.) and the Smart Grid.In order to reduce the energy losses on route from the energy generators to the consumers, the German E2SG project partners are focussing their research on components for the secure, cost- and energy-efficient networking of devices. The devices include electricity meters that have particularly secure communications processes for transmitting the electricity consumption from the households to the energy provider and smart power supply units that take into account the grid load for domestic appliances, internal and external lighting and energy storage systems. It is also intended to take into account when the consumers want to use the energy, for example to operate domestic appliances during low-tariff periods or when the local PV installation is currently providing electricity – without sacrificing comfort or reducing the accustomed safety and invoicing standards.Under the management of Infineon, 31 partners from business and research from 9 countries are working on the European E2SG research project. In addition to Infineon, the German E2SG partners include the Fraunhofer Institute for Integrated Systems and Device Technology (IISB), Insta Elektro, NXP Semiconductors Germany, RWTH Aachen and Telefunken Semiconductors GmbH. A total of 34 million euros is being spent on the research project throughout Europe, of which the German partners are contributing 4.9 million euros and the German Federal Ministry of Education and Research is funding 4.4 million euros.

Project participants >> Project management: RWE Deutschland AG, Essen, Germany, Torsten Hammerschmidt,

torsten.hammerschmidt@rwe.com>> Operating resources: ABB AG, Mannheim, Germany, Dr. Thomas Benz, thomas.benz@de.abb.com>> Evaluation methods: Consentec GmbH, Dortmund, Germany, Dr. Wolfgang Fritz, fritz@consentec.de>> Scientific monitoring: Technische Universität Dortmund, Dortmund, Germany, Dr. Christian Rehtanz,

christian.rehtanz@tu-dortmund.de

Links and literature>> www.zukunftsnetze.de | www.smart-country.de>> Grid integration of decentralised power generators. BINE-Projektinfo brochure 02/2008

More from BINE Information Service>> This Projektinfo brochure is available as an online document at www.bine.info under

Publications/Projektinfos. Additional information in German, such as other project addresses and links, can be found under “Service”.

>> BINE Information Service reports on energy research projects in its brochure series and newsletter. You can subscribe to these free of charge at www.bine.info/abo.

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Project organisationFederal Ministry of Economics and Technology (BMWi) 11019 Berlin Germany

Project Management Organisation Jülich Research Centre Jülich Dr. Ralf Eickhoff 52425 Jülich Germany

Project number 03KP101 A-D

ImprintISSN0937 - 8367

Publisher FIZ Karlsruhe · Leibniz Institute for Information InfrastructureHermann-von-Helmholtz-Platz 1 76344 Eggenstein-LeopoldshafenGermany

AuthorAnna Durst

Cover imageGerhard Hirn, BINE Informationsdienst

CopyrightText and illustrations from this publication can only be used if permission has been granted by the BINE editorial team. We would be delighted to hear from you.

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