Photovoltaics, in short PV, is the technology that can convert (solar) light into electricity. This technique is based on the photoelectric effect. In the technical equipment of buildings, individual modules of the same type are connected in strings. Depending on the technical type of the modules, they can convert up to about one fifth of the incident solar energy into electrical energy. Often there are confusions with the solar thermal technology, because the modules used are visually similar.

photography by Medl GmbH

According to Prof. Dr. Volker Quaschning (04/19) there is an installed capacity of 46 GW throughout Germany. The specified power of PV systems always applies to the maximum expected solar radiation, the so-called “peak”, and is therefore stated as kWp (kilowatt-peak). The majority of the operating hours, the PV provides a lower yield than in the case of maximum solar radiation, because the photovoltaic power (like wind power) is highly weather dependent. This requires intermediate storage for the electrical energy gained in order to be able to use energy from PV systems even in the case of low solar radiation or in the dark.

The following link of the company “SMA Solar Technology AG” shows the actual PV power in Germany:

In order to accelerate the development of renewable energies, state subsidies have been paid for high feed-in tariffs for electricity from PV systems in the past, some of which were even significantly above the subscription price for private-end-customers. As a rule, the producers of solar power have therefore purchased grid power and at the same time fed solar power into the public grid. Since this subsidy for some of the German PV systems will be expired or , there is the problem of unprofitable PV systems. Profitability for new PV systems is only possible in the case of a self-consumption rate of the electrical energy generated by the PV system.

Battery storages are storage systems in which (renewable electricity) can temporarily be stored. This can significantly increase the self-consumption rate of the consumers connected to the PV system and thus make a significant contribution to economic operation. Battery storage is expensive, so an exact dimensioning of the memory size is required.

photography by Medl GmbH
installed battery storage
photography by Medl GmbH

In the GreenEnergyFirst project, a PV system with 26 kWp and a battery storage with a capacity of 30 kWh were integrated in the technical building equipment. If possible, the yield of the PV system is used directly by the residential units connected in the district. In the case that the yield of the PV system exceeds the demand of the connected residential units, the battery storage is charged with the excess solar power. Only when the battery storage is fully charged and the yield of the solar system is higher than the demand of the connected apartment, this surplus will be fed into the public grid.

The project will use digital meters to determine the demand profile of the connected costumers in order to develop and test optimized charging and discharging strategies for the battery storage.