Liquid storage solution for solar energy transport and release; results improved 100-fold

Researchers at Chalmers University of Technology in Sweden have demonstrated an efficient method for solar energy storage in a chemical liquid. The stored energy can then be transported and released as heat whenever needed.

One of the principal challenges with solar power is that it is difficult to store the energy generated and deliver it ‘on demand’. The research team has shown that it is possible to convert the solar energy directly into energy stored in the bonds of a chemical fluid – a so-called molecular solar thermal system.

The liquid chemical makes it possible to store and transport the stored solar energy and release it on demand, with full recovery of the storage medium. The process is based on the organic compound norbornadiene that upon exposure to light converts into quadricyclane.

“The technique means that that we can store the solar energy in chemical bonds and release the energy as heat whenever we need it,” said Professor Kasper Moth-Poulsen, leader of the research team. “Combining the chemical energy storage with water-heating solar panels enables a conversion of more than 80 per cent of the incoming sunlight.”

The research project was initiated at Chalmers over six years ago and the research team contributed to a first conceptual demonstration in 2013. At the time, the solar energy conversion efficiency was 0.01 per cent and the expensive element ruthenium played a major role in the compound.

Now, four years later, the system stores 1.1 per cent of the incoming sunlight as latent chemical energy – an improvement by a factor of 100. Also, ruthenium has been replaced by much cheaper carbon-based elements.

“We saw an opportunity to develop molecules that make the process much more efficient,” said Moth-Poulsen. “At the same time, we are demonstrating a robust system that can sustain more than 140 energy storage and release cycles with negligible degradation.”

The research is funded by the Swedish Foundation for Strategic Research and the Knut and Alice Wallenberg Foundation. The latest findings were presented in the scientific journal Energy & Environmental Science.

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