Solving seasonal storage with aluminum cycling

• Scientists at Switzerland’s University of Applied Sciences Rapperswil have demonstrated an aluminum conversion process which could be valuable for long-term renewable energy storage. Simulations suggest that by employing the process, a new multi-family building in Switzerland could meet all its energy demand from a 7-11 kWp solar system.

One of the remaining obstacles to the universal adoption of solar power is the fact that in many parts of the world, electric demand peaks during the least sunny seasons.

While energy storage is being deployed rapidly alongside intermittent renewables, the majority of commercial solutions address the shorter-term demand shift from midday to evening, rather than seasonal disparities.

Scientists at the University of Applied Sciences Rapperswil, in Switzerland, may have found the answer in the form of an oxidization process which produces heat and hydrogen using aluminum.

Energy density

The process, described in the paper Seasonal energy storage in aluminium for 100 percent solar heat and electricity supply, published in Energy Conversion and Management, ‘charges’ by using electricity to convert aluminum oxide or aluminum hydroxide into elemental aluminum. The aluminum, which can be stored safely for any period of time, is discharged by oxidizing it to release hydrogen, heat and aluminum oxide.

The researchers note the reaction can produce as much as 0.11kg of hydrogen and 4.3 kWh of heat per kilogram of aluminum, ensuring it outperforms the energy density of hydrogen. “With this process, a solid material (Al) is obtained directly and can be stored without losses as long as desired,” reads the paper, “with much less safety concerns than for hydrogen or hydrocarbons.”

Application

The group conducted simulations based on systems at four Swiss locations and found an aluminum storage system combined with a hydrogen fuel cell and heat pump could meet the full energy demand of a multi-family building with 350-530kg of aluminum and a rooftop PV system with a generation capacity of 7-11 kWp, depending upon location.

The study included a cost estimate – based on forecast prices for 2030 when the researchers estimate large scale application of such technology could be more widespread – which indicated the potential affordability of such systems.