Do we really need a seasonal energy storage? Results for photovoltaic technology in an unfavourable scenario

Energy storage systems play a crucial role in the transition to renewable energy. Short-term storage (STS), e.g., batteries, has a capacity of a few hours, meant to compensate the energy deficit due to day-night cycle or short-term fluctuations. Long-term storage (LTS), e.g., renewable fuels, can compensate seasonal variations. The importance of STS is undisputed; the need for LTS is much more debated. Here we compare two photovoltaic systems, one (A) endowed only with STS, and another (B) equipped also with unlimited LTS, in a scenario unfavourable to (A) because of high seasonal variability of irradiation and high heating load in winter. We show that (A) requires only a moderate oversize of the peak power (about 20%) w.r.t. (B) when both systems are sized to supply 85% of the whole electrifiable load, which includes domestic heating and transport. Therefore, the current lack of clear routes towards grid-scale LTS should not be considered as a reason to delay the transition to renewables.