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Optimum sizing of PV-attached electricity storage according to power market signals - A case study for Germany and Italy

This paper investigates the business case of power storage attached to PV generation from the perspective of an aggregator trading power on wholesale markets and possibly supplying household customers. The profitability and an optimum storage configuration are determined for two European regions: Baden-Wuerttemberg in Germany and Puglia in Italy. Under the assumptions made, adding storage to a portfolio of PV generators would not constitute a business case in Baden-Wuerttemberg. Profitability can be reached for Puglia; however the achievable return is below levels that would justify investments by companies with capital costs above borrowing costs of the state. Storage is financially more attractive in cases where severe grid constraints lead to significant levels of curtailment provided that the associated losses would not be financially compensated. This could pose a risk to any investor as grid upgrades would eventually erode the revenues. Restricting the storage to PV energy only (i.e. without the possibility to do arbitrage on markets) depresses the business case and is generally unprofitable, except but for situations of severe grid bottlenecks. The picture does not change significantly if a consumption portfolio is added. In order to reach profitability, the energy related CAPEX will have to fall to a range of 100-150 €/kWh. The optimal storage configuration depends on its usage and will not exceed 5 hours of discharge at full power with the discharging power limited to 40% of the nominal PV capacity.