Photovoltaic self-consumption in Germany - using lithium-ion storage to increase self-consumed photovoltaic energy

The new German Renewable Energy Sources Act (EEG) for the year 2009 provides a new tariff option: self-consumption (EEG §33,2). By economically favouring the local consumption of PV energy, the EEG incentivises the owners of PV systems to either shift their consumption to the time of production by load management or use storage options. Massive deployment of such energy management approaches may reduce the impact of PV energy in the grid and thus pave the way for a further rise of the number of installations. For maximizing locally consumed PV energy, a storage system based on lithium-ion batteries is developed in the French-German project Sol-ion. Fraunhofer IWES, INES, ISEA and ZSW developed models to analyse the energy flows in residential PV-battery systems installed in Germany and in France. The models are used to calculate the increase of PV self-consumption. Energy flow simulations show that PV battery systems as developed in the Sol-ion project increase the local consumption of PV energy at the point of common coupling without constraining the user in his consumption habits. Target battery costs were calculated in an economical assessment. The installation of a Sol-ion system will become economically interesting with specific battery costs below 350 e/kWh as expected by the manufacturers in the medium term. The integration of additional functionalities (e.g. backup power and grid support) can improve the benefit of the Sol-ion system significantly.