Most forms of energy we use ultimately come from the sun in one way or another. Even fossil fuels are the end product of millions of years of plant life that captured solar energy. The advantage fossil fuels have over direct solar power is that they are, in fact, fuels and therefore can be stored for use when needed.
Scientists in Sweden have now developed a specialized fluid that absorbs some of the sun’s energy, holds it for months or even years, and then releases it when needed. This solar thermal fuel is like a rechargeable battery for heat rather than electricity.
The special fluid is pumped through transparent tubes where ultraviolet light from the sun excites its molecules into an energized state. A compound called norbornadiene is converted into quadricyclane. The quadricyclane is a quite stable substance until it is passed over a cobalt-based catalyst, which causes it to turn back into norbornadiene and release copious amounts of heat.
Such a solar thermal fuel could be stored in uninsulated tanks in homes or factories or piped or trucked to where it was needed. It could then be used for water heaters, dishwashers, or clothes driers. The room temperature fluid quickly warms to about 183 degrees when passed over the catalyst, plenty warm enough for heating a home or office. Both the fuel and the catalyst are damaged very little by the reactions, so the process can be recycled many times.
There is much development work needed to optimize shelf life, energy density, good recyclability and other properties before this technology can be commercialized but there are at least 15 groups around the world now studying this intriguing way to get liquid fuel from the sun.
Photo, posted August 17, 2009, courtesy of Hiromichi Torihara via Flickr.