EVEN THOUGH solar panels have improved over the years they are still not very efficient at doing their job. Standard panels using silicon-based solar cells typically convert 17-19% of the sun’s energy into electricity. It is possible to use more exotic solar cells to make panels that are some 40% efficient, but these can cost around $300 a watt compared to just under $1 for some silicon versions. Hence the better panels are used in specialist roles, such as powering spacecraft.
Now, a middle way seems to have been found. Insolight, a startup from the Swiss Institute of Technology in Lausanne, has developed a panel that uses expensive high-efficiency solar cells, but does so in such a fashion that should make its panels competitive with the standard silicon variety. The new panel has been confirmed in independent tests to be 29% efficient.
Insolight employs so-called multi-junction solar cells, which are similar to those on spacecraft. These capture energy from a much broader spectrum of sunlight by using a stack of different materials, such as gallium arsenide and gallium indium phosphide. Fabricating such cells is complex and costly.
Insolight, though, is extremely parsimonious in their use. Instead of spreading them across an entire panel, they are spaced well apart in a grid that covers just 0.5% of the...