Saving solar energy for years? We’re almost there

Sun rays are a cheap and abundant source of energy, ready to be harvested by solar panels. Storing all that energy is another matter, however. Most storage technology in use can store solar power only for shorter spells and even that at relatively high costs. That has long been a drawback to solar power, especially in countries with intermittent periods of sunshine.

Enter solar thermal fuel. Developed by a team of researchers at Chalmers University of Technology in Sweden, a country where sunshine is AWOL much of the year, the fuel can store solar power for almost two decades so that solar power is available long after the sun has stopped shining.

Based on a molecule in liquid form, the fuel is composed of carbon, hydrogen and nitrogen. When the liquid is soaked in sunlight, the bonds between atoms within it are realigned so that the liquid becomes an energy-rich isomer, which captures and stores some of the power contained in sunshine.

“The energy in this isomer can now be stored for up to 18 years,” says Kasper Moth-Poulsen, a professor at the university’s Department of Chemistry and Chemical Engineering who led the research team. “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 adds.

The liquid is stored in a solar thermal collector designed by the team. It is a concave reflector with a pipe in its middle, which tracks the sun’s path across the sky and focuses its rays to just where the liquid leads through the pipe.

For controlling the release of the stored energy thus obtained, his team has developed a catalyst, which acts as a filter that creates a reaction that warms the liquid by 63 degrees Celsius. Simultaneously, it returns the molecule to its original form so that it can be reused in the warming system, the team explains.

“During the same period, [we] 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,” they say. “This was a crucial improvement, as the focus of the project is primarily chemical energy storage.”

It works even at room temperature with minimal losses of energy. The liquid captures energy from sunlight in a solar thermal collector placed on a roof. When energy is needed, the catalyst is activated whereby the liquid heats up.

The resultant heat from it, meanwhile, can be used in domestic heating systems. Once the process of drawing energy from the liquid is completed, the liquid returns to collecting more energy from sunshine without suffering any damaging, which means it won’t have to be replaced regularly.

“We have made many crucial advances recently, and today we have an emissions-free energy system which works all year around,” Moth-Poulsen says.

His team’s work isn’t done yet. “There is a lot left to do. We have just got the system to work. Now we need to ensure everything is optimally designed,” Moth-Poulsen stresses, adding that the technology could be made commercially available within a decade.