Seasonal storage of hydropower
Up to now, hydrogen has generally been stored in a gaseous state – both in the mobile and stationary sectors. But there are other possibilities: For example, a group of companies has applied the same technology to a South Tyrolean residential building that is also used in fuel cell-powered submarines: Metal hydride storage. With their help, a seasonal energy transfer of hydropower from summer to winter is being tested as part of a demonstration project.
Instead of storing hydrogen at high pressure (gaseous hydrogen, GH2) or at low temperatures (liquid hydrogen, LH2), the H2 molecules can also be incorporated into metal compounds. The volumetric storage density in such metal hydride storage tanks is relatively high compared to compressed gas cylinders.
In 2019, a 10 kW energy system with such a metal hydride storage system was installed in the Miner’s house in Prettau and has since been tested. If the metal hydride is filled with hydrogen, heat is released (exothermic). If the storage system is to release H2 gas, it must be heated (endothermically) so that the molecules break away from the lattice structure. The thermal energy for desorption (H2 release) is taken from the fuel cell system to desorb the stored hydrogen from the lattice structure of the metal hydride. In addition, a wood pellet stove for heat supply and four lithium iron phosphate accumulators with around 10 kWh storage capacity for uninterruptible electricity supply are installed.
The Miner’s house in the Ahrntal is located at 1,400 m above sea level and has no public electricity connection. Instead, the extensively renovated and expanded building in the Italian Alps is supplied with energy via a Pelton water turbine (8 kW). However, since the water inflow is lower in winter due to frost, there used to be an oil generator for which an alternative should be found.
With the solid storage facility realised in 2019, hydrogen can now be produced by electrolysis from the purified spring water using electricity from the turbine and stored in the metal pellets (iron-titanium alloy). On demand – especially in winter – the chemically stored energy can then be converted into electricity and heat with the help of a polymer electrolyte membrane fuel cell. The compact unit is throttled to around 6 kW of electrical power and supplies electricity and heat with an efficiency of around 50 percent.
… Read more in the latest H2-International e-Journal, Aug 2021
Author: Sven Geitmann