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© Fernwasserversorgung Elbaue-Ostharz GmbH
With virtual power plants, load management, new market platforms
Projektinfo 13/2012

Fig. 1: The Druiberg wind farm on the edge of the Dardesheim energy model town is the largest in the rural district of Harz.
© Windpark Druiberg GmbH u.Co KG
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Rural district of Harz tests electricity supply of the future

Regions with a large proportion of renewable energies offer particularly good prerequisites for testing out future decentralised supply systems. In the rural district of Harz, one of six model regions in the German government’s E-Energy programme, more than 20 partners from various sectors of the electricity industry have developed technologies and business models for smart grids. Four municipal utility companies and two distribution network operators were involved in their implementation. The four-year RegModHarz research project, which is funded by the German Federal Ministry for the Environment, will be completed at the beginning of 2013.

“The rural district of Harz can export electricity from renewable sources” – this realisation formed the starting point of the project. In the first stage, the already existing renewable energy generation capacities and the regional potential were determined. For example, renewable energy generation provides a good third of the overall annual electricity consumed within the rural district, which amounts to 1.2 billion kWh (basic scenario 2008); the German average in the first six months of 2012, on the other hand, was around 25 %. Around one third of the electricity consumed by the more than 240,000 inhabitants in the rural district of Harz is already produced from renewable sources. The potential is, however, considerably greater: the region still has many unused reserves in the generation, storage and load transfer fields, whereby wind energy provides the most area-efficient and, currently, the most cost-effective form of renewable energy. If all designated wind power sites were to be optimally used, the annual wind power volume could be doubled. If 0.5 % of the rural district’s surface area were used, already half of the electricity requirement would on balance be met by wind energy. Solar energy also has considerable potential. In contrast, however, hydropower currently only provides around 2 % of the electricity supply and there is little potential for its expansion.


Pumped storage power plant as enormous battery

In order to balance out fluctuations in the volume of wind and solar energy, storage systems will play an increasingly important role in future. Pumped storage power plants are suitable for this purpose, since they can store large volumes of energy for longer periods of time. Therefore an important component of the Harz Renewable Energy Model Region is the Wendefurth pumped storage power plant at Rappbode dam, which has a storage capacity of 600 MWh. This can theoretically supply the rural district with at least four hours of electricity. This plant is indispensable for the future electricity supply system, since it balances out output fluctuations in the grid very quickly. The Rappbode dam system can store surplus renewable electricity like a giant rechargeable battery. The valley reservoir at Wendefurth dam acts as the lower reservoir for the pumped storage power plant, whereas the upper reservoir is situated on a nearby hill. The surplus electricity can be used to pump water from the lower reservoir up into the upper reservoir. When electricity is required again, for example because there is currently no wind available, this water can flow back into the valley where it drives two 40-megawatt turbines. This enables the stored electricity to be used again when required.

The mobile storage possibilities provided by batteries in electric cars were also investigated. The controlled “tanking” of electric cars provides enormous potential for shifting consumption in the household sector, which would also enable fluctuations in the production of wind and solar power to be balanced out in future. Calculations based on a field test have shown that 46% of the electricity consumption in households can be currently shifted by, for example, starting the washing machine two hours later when the wind blows more strongly or the sun shines more intensely, which means that more regional renewable energy is available.

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