Solar Energy as Liquid Fuel, targeting the Storage Conundrum

A team of researchers from the Chalmers University of Technology in Sweden, claim to have devised a way to store solar energy in a bottle. The team has developed a liquid fuel containing the compound norbornadiene, which when struck by sunlight, rearranges its carbon, hydrogen, and nitrogen atoms into an energy-storing isomer, quadricyclane, which consists of the same atoms but bound together in a different way.

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Quadricyclane holds onto the energy, estimated to be up to 250 watt-hours of energy per kilogram, even after it cools and for an extended period of time. For use, it’s passed through a cobalt-based catalyst, at which point the energy is released as heat. The catalyst acts as a filter, through which the liquid flows, creating a reaction which warms the liquid by 63 centigrades.  If the liquid has a temperature of 20°Celsius when it pumps through the filter, it comes out the other side at 83°Celsius. At the same time, it returns the molecule to its original form, so that it can be then reused in the warming system. The team has named the system MOST (Molecular Solar Thermal Energy Storage).

With all the recent advancements the team has made, the 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, leading to minimizing energy losses. When the energy is needed, it can be drawn through the catalyst so that the liquid heats up. It is envisioned that this warmth can then be utilized in, for example, domestic heating systems, after which the liquid can be sent back up to the roof to collect more energy – all completely free of emissions, and without damaging the molecule.

“The energy in this isomer can now be stored 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. We’ve run it through 125 cycles without any significant degradation. We have made many crucial advances recently, and today we have an emissions-free energy system which works all year round,” said Kasper Moth-Poulsen, Team Leader, Nano Materials Chemistry at Chalmers.