On the optimal mix of renewable energy sources, electrical energy storage and thermoelectric generation for the de-carbonization of the Italian electrical system

The integration of intermittent renewable energy sources (RES) requires a substantial amount of electrical energy storage and significant increase of the grid capabilities. To keep these upgrades within reasonable limits, strategies maintaining a moderate but flexible thermoelectric power have been investigated. Based on the experimental loads for Italy in 2013, the implications of increasing the contribution of scalable RES, particularly wind and photovoltaic, are investigated in detail. The optimal value of the storage depends on its round-trip efficiency (1.3 TWh for hydroelectric storage and 6 TWh for power to gas). For RES producing 100% of the annual demand, the use of the optimal storage and of about 10 GW of thermoelectric power allows a substantial de-carbonization (more than 90%) of the electricity production still maintaining a capacity factor of the thermoelectric generators above 40%. Avoiding thermoelectric generation is possible but it requires overproduction by RES, between 120 and 200% of the annual electricity demand, depending on the storage technology and the mix between wind and photovoltaic generation. The calculations have been performed for realistic values of the storage round-trip efficiency and for various combinations of photovoltaic and wind powers. The capital costs required are also estimated at current costs of present day technologies.