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Solar photovoltaic (PV) is one of the fastest growing energy sources. The mismatch between the solar supply and power demand is one of the major challenges which need to be overcome.

Recent research at Aalto University shows that PV systems could benefit even from small energy storage. A storage unit of 2 kilowatthours of storage for each kilowatt of PV is the optimum to compensate for the daily mismatch. With this capacity a PV system could reach a yearly power self-consumption level of 60–70% in a northern climate and 80–90% in a southern climate, respectively. The study was recently published in Journal of Energy Storage.

As a practical example of the study, a Finnish household with a PV system (without storage) sized to the yearly electricity demand (3,700 kWh) could directly use some 30% of the solar energy produced, the rest would be surplus and need to be curtailed or fed into the power grid. Adding a 8 kWh storage to the 3.8 kW of PV, which corresponds to less than 1/4 of a Nissan Leaf EV battery, the self-consumption of PV would increase to 70% of the yearly demand. During the winter months with less solar insolation, the system would not be able to deliver much solar power.

More information: Lund, P.D., Capacity matching of storage to PV in a global frame with different loads profiles. Journal of Energy Storage 18 (2018) 218-228. Full article can be downloaded from