Europe is pursuing an aggressive programme to increase its share of renewable energy source (RES). However, the integration of intermittent RES (wind and photovoltaic) in the electrical system requires either maintaining in operation thermal backup systems or providing a substantial amount of electricity storage. We analyze the Italian electricity data for the year 2013 provided by the transmission system operator TERNA. The present level of intermittent RES power is scaled-up to a level at which it generates an amount of electricity equal to the annual demand. While a substantial reduction of the energy annually produced by fossil backup systems (and the associated CO2 emission) with respect to the no-RES case is possible in many scenarios considered here, the backup power is generally only marginally reduced below the value in the absence of RES. The strategy proposed is based on the combination of a modest amount of storage (0.5-5 TWh) and base-load power (6-15 GW, to be used during the seasons of low RES production). In this way the non-RES installed power can be reduced from similar to 50 GW to less than 15 GW and could be covered by a combination of biomass and nuclear energy without any CO2 emission.
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