Researchers at the Chalmers University of Technology in Gothenburg, Sweden, have demonstrated efficient solar energy storage in a chemical liquid. The team has shown that it is possible to convert energy from the sun directly into energy stored in the chemical bonds of a chemical fluid — a molecular solar thermal system. That energy can be transported and released on demand, with full recovery of the storage medium.
Solar energy on demand
Professor Kasper Moth-Poulsen, who is leading the research, gives for consideration that the development of efficient methods for solar energy storage is a key challenge for a future society where the majority of the energy is derived from renewable energy. “In this context,” he says, “we are developing molecular solar thermal systems.”
The head of the Molecular Materials research group in Chalmers’ Department of Chemistry and Chemical Engineering explains that these systems are based on molecules that can absorb light and directly convert it into stored chemical energy though an isomerisation process that is based on the organic compound norbornadiene, which converts into quadricyclane when exposed to light. Furthermore, this process is reversible, so that the energy can be released as heat when needed and the molecule recovered to enable multiple solar energy storage and release cycles. The process is inherently a closed cycle, and there is no combustion or emission associated with it.
Most efficient molecules
“The molecules that we have developed are the most efficient we have worked with. They enable the conversion of 1.1% of incoming sunlight into stored chemical energy in our test device,” reveals the professor. “We further demonstrate for the first time that the chemical liquid can be combined with traditional low-temperature water heating, without compromising the efficiency of the water heating system.”
The professor notes that based on his team’s previously published estimates, they believe that it should be possible to reach 10–15% solar energy storage efficiency in the molecular solar thermal system, which he says could be used in domestic or industrial applications. Combined with water heating, a hybrid system might be able to make use of 85–95% of the incoming energy.
Advantages and promise for the future of solar energy
Moth-Poulsen points out several advantages of Chalmers’ molecular solar thermal system over previous solar energy storage solutions: “The heat is stored at room temperature without any need for insulation, the energy density in the storage medium is very high compared with traditional methods, and the used materials can potentially be fabricated at a low price, without the need of any precious metals or other limited resources.”
What promise does this innovative technique hold for the future of solar energy? “We hope that we — with further development — can develop a functional system that can contribute to an environmentally friendly energy transition towards a society where energy is produced from renewables,” the professor says.
Commercialization and outlook
Moth-Poulsen says he and his colleagues are currently exploring different strategies for making the pioneering solar energy storage solution commercially viable. The timeline to market will depend on specific applications and whether they will be able to attract the right type of collaborators outside academia.
“We will continuously work towards improving the performance of the system towards more efficient solar energy conversion, longer storage times and increased energy densities,” the expert concludes. “Also, we will be working on controlling the heat release process in an optimal way.”
The research is detailed in the article “Exploring the potential of a hybrid device combining solar water heating and molecular solar thermal energy storage," published in Energy & Environmental Science and featured on the journal’s cover.
Written by Sandra Henderson, Research Editor, Solar Novus Today.