Present day solar energy technology is designed to transform light, in the form of solar rays, into usable electrical energy. Solar energy technologies, such as photovoltaics, which capture photons, or solar-thermal collectors, which harvest heat, are not designed to store energy. When the sun is available, electricity is generated on the spot. Any extra sunlight which is not converted is lost as regular surface heat.
Most commercial units capture about 25% of the energy available. However, popular science news articles have noted several newly invented models, with prototypes available, which transform between 40% and 80% of the sunlight into usable energy. While these are important steps, they do not address the energy storage issues. For this to occur there needs to be an improvement in energy storage technology.
A new approach to the whole paradigm of solar energy is now being researched. An MIT research team has done some initial studies that could lead to an entirely new method for capturing and storing sunlight. It has the potential to make this renewable energy indefinitely storable and transportable.
The research is based on a molecule called fulvalene diruthenium. When a fulvalene diruthenium molecule absorbs sunlight, it changes shape into a semi-stable, but perfectly safe, formation. The molecule can stay in the new form indefinitely, without deterioration. When combined with a catalyst, the fulvalene diruthenium molecule snaps back into its original form, releasing the heat. When the energy is released, it can be used to heat a home or made to power appliances.
The research team believes there are many ways that fulvalene diruthenium could work at a systems level. One idea is that of a reusable liquid fuel. It could be placed in deep vats out in the sun and stirred, exposing as much of the liquid to solar heat as possible. Once charged it can be pumped and delivered through pipes, or by other means, to the point of use. Since energy in the fluid does not deteriorate, the point of use could be nearby or distant. Once used, the liquid can be recharged by the sun and reused. The process can be repeated over and over again without deterioration or loss of efficiency.
The drawback is that fulvalene diruthenium is derived from ruthenium, which is a rare, expensive hard white metal element of the platinum group. Estimated world reserves of the metal amount to 5,000 tons. Currently, only about twelve tons of ruthenium are mined each year.
However, it is also a byproduct of nuclear fission. There are industrial processes which can remove ruthenium from uranium waste and make it safely available for non-nuclear use. Currently, that process is very expensive. However, like other technologies, it could be made cheaper.