The German pilot focuses on both building up a centralised energy storage device as well as examining new business models for distributed energy storages.
The Green City Freiburg in the south-western corner of Germany has about 200.000 inhabitants. Freiburg is one of the sunniest regions in Germany, experiencing a great penetration of Renewable Energy Sources. Further development and use of renewable energies is not only limited by a lack of resources, but also by the lack of capacity in power lines leading to the outskirts of the city. Due to the relatively high sun radiation in the south-west compared to other regions in Germany, many PV plants are installed. They are mainly connected to the low voltage network. Feed-in peaks during the day require new strategies to cope with congestion management and occurring voltage peaks.
Therefore, it suggests itself to select an application for the centralised energy storage dealing with this problem in a network area operated by the local distribution system operator bn-Netze, which is a subsidy of badenova. The selected spot is located at an end-feeder in the rural area of Freiburg-Opfingen, which is a community pretty remote from the main city of Freiburg and located at the outer rim of the electricity network. Nevertheless, this region is predestined for PV-systems, because it’s settled with many farm houses coming along with barns and extended roofs, perfectly suitable for the configuration with PV-modules.
In the selected case, a farmer’s house is located at the end of a feeder, including four PV plants with a total installed power of 30.5 kWp. All four PV plants are connected via one single grid connection point to the low voltage network. The pilot test site is located at the end of a feeder which length amounts to 840 m until the next substation. In some cases on sunny days, voltage limits at the grid connection point are violated by the local generation of electricity. The voltage on the grid connection point rises up nearly 7.5% above the regular level on a day with maximum feed in from the PV-Systems and regular load. 3% are allowed at maximum. Due to the geographical distance of the PV plants to the grid connection point the voltage increases further on the property. It may happen, that at the connection point of the inverters the acceptable voltage tolerance of 10% is exceeded. In this case, the inverters shut down automatically and the PV-systems are no longer able to generate electricity. In consequence the PV-system owner loses the guaranteed feed-in tariff for the not produced energy. A strong interest on the side of the PV-system owner exists, that this case is avoided in any case.
By using a battery storage system, the PV plant shall fully feed-in into the local distribution grid even during peak production periods. The energy is not transported over the weak line but is stored within the battery temporarily. During night time, this energy is transported without causing any problems over the low stressed line. So the battery is foreseen to solely work as a grid-friendly component exclusively operated by the local DSO. Due to regulatory issues, it is not attended to increase the self-sufficiency of the farm house at the same time.
This case is an excellent example illustrating that a battery storage device can help to secure full generation of renewable energies without expensive grid enforcement. At the same time, new potentials to expand existing PV-plants on the roofs with more panels as well as installing of new PV-systems which are connected to the weak feeder are tapped.
Hybrid pilot implementation – Distributed energy storage
The connection of distributed energy storages is the second part of the hybrid pilot implementation in Germany. Overall in Germany there is a trend to intensify the utilization of distributed energy storage technologies. Until end of 2018, for example, badenova will have sold more than 150 PV storages to private households, and there are already several hundred battery storage installations of private individuals in the entire supply area of bnNetze. Under existing market conditions these batteries could be connected and marketed as virtual power plants. However, this approach can even lead to additional network load if marketing does not take into account the capacity of the network. INVADE could be the first step to solve these issues through a network of battery storages that help to balance production and consumption. For this reason, algorithms shall be developed and tested in INVADE that enable a balance between the interests of the market and the grid. The affected parties shall both experience a financial benefit or that could turn out to be financially beneficial due to adjustments of the regulatory/market framework.
Within badenova’s market area at least ten households that are already equipped with PV systems and small batteries with individual capacities of around 10kWh will be identified and connected to the INVADE platform. In parallel a strong effort is set on the economic examination of marketing opportunities. In this context applications like provision of auxiliary power as well as avoidance of imbalance costs for the balance group operator – in addition to the possibilities of intraday-trading – will be examined.
The pilot for distributed energy storage focuses on examining various business models as well as testing the technical feasibility of the most promising one.
Since SMA is the market leader in Germany for solar hardware, badenova seeks a strong cooperation with this company. On the other hand, SMA provides already a home management system calls “Sunny Home Manager”, which is capable to make forecasts of PV-generation and load consumption and to calculate on this basis an operation scheme for the local battery. Main target of the system is to minimize the energy consumption from the grid, as the tariffs are nearly twice as high as the production costs from the own PV-system. But: The optimization algorithm in the Sunny Home Manager focus only on the building. A connection to a higher optimization level is not realized right now. Exactly at this point badenova and SMA want to create a benefit for a potential flexibility operator as well as for the private customer. Additional market opportunities shall create a financial benefit which can be shared between the parties. By implementing a comprehensive control algorithm, the private household still optimizes its own consumption via the Sunny Home Manager and can participate at the same time in a large scale community. This approach seems to be technically feasible, as many battery storages on household level are dimensioned to big and still hold capacity-reserves, which are not used.