Earlier in the Photo of the Week series, we saw how Vortex Bladeless is offering a radical new way to harvest wind energy. But in the solar energy sector a lot of innovation is going on as well. The Swedish firm Ripasso is building what it claims to be the most efficient solar electricity system. In the South African Kalahari desert, giant parabolic mirrors follow the track of the sun and focus the rays in a small point where it drives a Stirling motor. That’s an invention dating back to 1816, but up to now it has mainly been used in military submarines although it can have much higher inefficiencies than classical combustion motors. It has no exhaust or inlets and works solely on the heating and cooling cycle of an internal fluid. Ripasso took this Stirling motor to South Africa where it is now able to convert solar energy to electricity with an efficiency of 34%, significantly higher than the 23% at best of other solar systems available today. Although it was not easy to convey banks their technology can fulfill its promises, Ripasso has now enough funding to start its first commercial-scale installation.