Seasonal Energy Storage in Aluminium for 100 Percent Solar Space Heat, DHW and Electricity

For climates with large amounts of solar energy in summer and buildings with significant energy consumption for space heating in winter, solutions are needed to store and transfer solar energy from summer to winter. In this paper, a seasonal energy storage based on the aluminium redox cycle (chemical reduction and oxidation of aluminium) is proposed. For charging, electricity from solar or other renewable sources is used to convert aluminium oxide or aluminium hydroxide to elementary aluminium (chemical reduction: Al3+ -> Al). In the discharging process, aluminium is oxidized (chemical oxidation: Al -> Al3+), releasing hydrogen, aluminium hydroxide and heat. Hydrogen is used in a fuel cell to produce electricity. The heat produced in the fuel cell and in the aluminium oxidation process is used for domestic hot water production (DHW) and space heating. The system proposed uses 480 kg of aluminium, 11 kWp of photovoltaics and a battery of 11 kWh useable capacity to achieve 100% solar heat and electricity coverage of a single family home with a total heat demand of 5.2 MWh and an electricity demand of 3.3 MWh for all seasons of the year.