Saving the summer sun’s energy for the winter

Technology News | October 8, 2018

By Christoph Hammerschmidt

Batteries / Power Supplies Power Management

Solar energy is available in almost inexhaustible quantities – but not at all times. The switchover to renewable energy sources would have been much more advanced if it were possible to store these energies in larger quantities and over a longer period of time. Researchers from Sweden have now taken a big step towards such storage technologies.

A research group from Chalmers University of Technology, Sweden, has made great, rapid strides towards the development of a specially designed molecule which can store solar energy for later use. Around a year ago, the team presented a molecule that was capable of storing solar energy. The molecule, made from carbon, hydrogen and nitrogen, has the unique property that when it is hit by sunlight, it is transformed into an energy-rich isomer – a molecule which consists of the same atoms, but bound together in a different way. This isomer – the researchers named it MOST (Molecular Solar Thermal Energy Storage) – can then be stored for use even after longer periods- for example, at night or in winter. In the meantime, the research group achieved further progress.

According to research team leader Kasper Moth-Poulsen from the Department of Chemistry and Chemical Engineering at Chalmers, the isomer can now store its energy for up to 18 years. “And when we come to extract the energy and use it, we get a warmth increase which is greater than we dared hope for”, he said.

The research group developed a catalyst for controlling the release of the stored energy. The catalyst acts as a filter, through which the liquid flows, creating a reaction which warms the liquid by 63°C. If the liquid has a temperature of 20°C when it pumps through the filter, it comes out the other side at 83°C. At the same time, it returns the molecule to its original form, so that it can be then reused in the warming system.

During the same period, the researchers also learned to improve the design of the molecule to increase its storage abilities so that the isomer can store energy for up to 18 years. This was a crucial improvement, as the focus of the project is primarily chemical energy storage. What’s more, the researchers also succeeded in modifying the composition of the molecule so that it is no longer flammable.

Taken together, the advances mean that the MOST energy system now works in a circular manner. First, the liquid captures energy from sunlight, in a solar thermal collector on the roof of a building. Then it is stored at room temperature. The researchers claim that during the storage period, the system only has minimal energy losses. When the energy is needed, it can be drawn through the catalyst so that the liquid heats up. In the future, such systems could be utilised in domestic heating systems, after which the liquid can be sent back up to the roof to collect more energy. And the best of all: the entire energy circle is completely free of emissions.

The next steps for the researchers are to combine everything together into a coherent system.

The group is satisfied with the storage capabilities, but more energy could be extracted, Kasper believes. He hopes that the research group will shortly achieve a temperature increase of at least 110°C and thinks the technology could be in commercial use within ten years.

The results of the research have been presented in several scientific articles this year, with the most recent being published in the highly ranked journal Energy & Environmental Science. The research is funded by the Knut and Alice Wallenberg Foundation and the Swedish Foundation for Strategic Research.