Water storage tanks are the most widely-used storage systems for solar power, but researchers at the Fraunhofer Institute for Organic Electronics, Electron Beam and Plasma Technology (FEP) are working on “adsorption” storage concepts that have a higher storage capacity than water. The novel heat exchange storage system is based on nanoporous zeolite granules, a sorbent material which interacts with H20. They are coated with aluminium to improve heat conduction.

“When water vapour-laden air flows through the storage material, it adsorbs water, releasing heat that can be used in heating circuits," explains Heidrun Klostermann, from the Fraunhofer FEP research team in a press release. Conversely, the zeolite granulate expels water when the tank is loaded with heat from solar or other renewable sources to be stored. As the zeolite itself does not have good thermal conductivity, aluminium layers are pre-applied to ensure good heat transport and transfer at the exchanger.

At the present time, hybrid materials like zeolite – which have the capacity to absorb and release water – are not yet manufactured on an industrial scale. But the manufacturers of thermal storage systems will be watching this field of development closely because thermo-chemical storage offers the distinct advantage of higher storage density and smaller storage volumes.

Beyond solar, adsorption storage applications could also be used to harness waste heat in vehicles such as fuel cell drives and there’s potential for adsorption chillers to be used for refrigeration.