Renewable sources are intermittent and volatile by nature, and the energy they make available does not match demand moment by moment.
Even when their total TWh generation over the year is in line with electricity request, production can exceed the demand in certain periods and fail to meet it in others – thus exposing the grid to the risk of instability.
To match production and demand energy must be stored for some time (time shifting).
Short-term storage can be provided by conventional batteries – which have the drawback of limited lifespan, and need to be carefully (and costly) disposed of at the end of life.
Long-term power storage can also be based on power-to-gas technologies (e.g. transformation of renewable energy into hydrogen) or on thermodinamic storage, with new-generation closed-cycle systems such as the CO2 batteries offered by Ansaldo Energia.