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29 October 2008

Solar Power on the Moon

A new type of solar cell that doesn't use silicon in their construction has been developed. According to New Scientist, the new design is dye based and sprayed onto a substrate of titanium dioxide. Titanium dioxide (TiO2) is found on the lunar surface. It is concentrated in the maria. Aside from free samples of TiO2 in the maria, it is locked up in ilmenite - TiO3. This is significant because ilmenite is a major source of lunar oxygen. Hydrogen reduction of ilmenite is one of the simplest processes for in-situ production of oxygen for fuel and life support.

FeTiO3+H2 ---->Fe+TiO2+H2O

The reduction produces free iron, titanium dioxide and water. The water can be cracked into its constituents through electrolysis.

The dye is used to coat TiO2 grains, which sit in an electrolyte in the solar cells. The whole mixture is sandwiched between two electrodes; a transparent glass sheet doped with tin oxide to make it conducting and an opaque rear panel. This allows a current to flow when the cell is placed in sunlight

But the efficiency of dye-sensitised solar cells designed for outdoor conditions is currently about 6%. That's light years from the 42.8% efficiency reached by some silicon solar cells and well below the 15% standard for many silicon designs.

Michael Grätzel of the Swiss Federal Institute of Technology in Lausanne, Switzerland – who co-invented dye sensitised solar cells in 1991 – had thought it may be possible to double the efficiency of his low-cost cells simply by designing one that collects light from both sides simultaneously.

Now Grätzel's team, working with Seigo Ito of the University of Hyogo, Japan, has done just that. Their new dye-sensitised solar cell is almost as efficient at converting light into energy when it strikes the rear side as when it strikes the front.

To achieve the trick, Grätzel's team first replaced the opaque back panel with a second sheet of glass, making the entire device transparent.

The new panel is also coated with tin oxide and acts as the second electrode, donating electrons back to the electrolyte to complete the circuit. But because it is transparent, it lets light into the system from the rear.

Robert Hertzberg, chairman and co-founder of G24 Innovations, a company based in Cardiff in the UK that manufactures dye-sensitised solar products. "This technology allows you to capture power in low light, even rainy conditions," he says. "Silicon cells only allow you to capture power during a short window [when light is intense]." That means the cells give a better performance over the whole day even if they are less efficient under ideal conditions.