Resumen de Large scale battery systems in distribution grids
The main objective of the thesis is to quantify the extent to which grid expansion measures can be avoided by the use of batteries and to what extent the balancing act between an economic and grid supportive operation is possible. As part of the project, that is investigated in this thesis, a large-scale vanadium redox flow battery storage prototype system was integrated into the power grid of a German distribution grid operator for the first time.
A preliminary analysis of possible business cases for large battery systems shows that the application of batteries in the primary control power market is by far the most lucrative application in the current German framework. It is followed by an application for cost reduction where self consumption of PV power is favoured over grid power. Both business cases are analysed in further detail.
The thesis is mainly focused on the grid supportive primary control application. The grid supportive behaviour of the analysed battery has been ensured by regulating the voltage in the low voltage grid via a reactive power control and thus increasing the grid capacity. The developed battery system was tested in the field during a one-year field test. The battery prototype and the grid of the pilot region was modelled based on measurement data. Furthermore, a method to derive an optimal operating strategy for electricity storage was developed and implemented. The strategy was developed with the aim to identify a self-sufficient operation mode which ensured the highest possible profit and validated in a field test. Albeit being the most lucrative battery application in Germany today, economic calculations have shown that the average cost of vanadium redox batteries would have to fall by about 60% to achieve profitable operation. Nonetheless, since this is a new technology, both the expectations and potential for cost reduction are high.
The second most promising application, the maximisation of self-consumption, is also analysed through the means of a simulation for the pilot region, but without a implementation in the field. For this purpose a battery model for a vanadium redox flow battery based on measurement data is applied. To ensure grid supportive behaviour, an autonomous reactive power control based on a Q(V)-characteristic and peak shaving is implemented. The technical and economic assessment of this operation strategy is compared with a lithium-ion battery providing the same service. It is shown that this business case could already be profitable, with a more favourable legal framework in place. However, at present the investment costs of the vanadium redox flow battery has to fall by at least 77% to break even for this operation strategy. Nonetheless, it could be demonstrated that it has almost no negative economic impacts if the battery storage system is operated in a grid supportive way in addition to its primary purpose.
Finally, a technical and economic assessment of the impact of the two large scale battery applications on distribution grid planning is conducted. Additional flexibility options such as a cosf(P) and Q(V)-control of PV systems and the use of residential storages are considered as well. For this purpose, a future PV expansion pathway was developed for the pilot region, as well as an automatic (traditional) grid expansion without flexibility option as a reference scenario. The PV expansion pathway is based on the identification of suitable roof areas for PV systems using aerial photographs. It has been shown that the hosting capacity for renewable energy installations increases in all cases compared to the scenario without flexibility options, sometimes by up to 45 %. In addition, it was found that from the perspective of grid operators it is more profitable to apply the presented flexibility option instead of a traditional grid expansion.
