10. Renewable power-to-hydrogen systems and sector coupling power-mobility

The transition of the energy infrastructure toward decarbonization requires an increasing deployment of nonprogrammable renewable energy sources (RES) [1], with issues in controlling the power balances and guaranteeing the reliability of the electric grid. Renewables are nowadays allowed in most countries to generate and inject electricity into the grid without a constrained profile, deviating from the scheduled dispatch which is instead typical of conventional power plants. The resulting mismatch between generation and consumption of electricity is traditionally compensated using appropriate ancillary resources, which include dispatchable power generators (e.g., fossil-fuel based) or conventional storage systems like pumped-hydro plants. However, the situation is expected to change rapidly in the future, in particular in the EU, where the pursue of decarbonization will mandate a substantial increase in the deployment of fluctuating RES, like wind and solar photovoltaic (PV), making more and more difficult to manage the stability of the electric grid. One way to solve the issue is using “power-to-hydrogen” (P2H) systems that are able to draw electricity from the grid at the most suitable times and produce hydrogen, which can be delivered on a different time schedule (including storage in gas, liquid or other form [2–5]) to a range of final users, which include mobility (with hydrogen vehicles), industrial processes, as well as generic residential and power uses directly or by injection into the natural gas (NG) grid. The latter is also labeled “power-to-hydrogen-to-gas” or simply “power-to-gas” (P2G). When the P2H system relies exclusively on RES, for example, PV or wind, it enables a fully green and sustainable energy conversion chain, which is increasingly supported by the environmental policies in the EU and in various countries.