
334 Principles of Sustainable Energy Systems
© 2008 Taylor & Francis Group, LLC
nned heat pipe dissipation technique with the heat pipe attached to the bottom of the Ge
substrate to avoid shading from the sun. Cooling of such a device is important because the
efciency decreases at about 0.06% per °C increase in operating temperature.
Improvements in multilayer photovoltaic cells are continuing, and in April 2008, the
NREL announced that a world record in solar cell efciency of 40.8% had been achieved
at a concentration ratio of 326 suns with an inverted, metaphoric, triple-junction solar cell.
This new design used a composition of a galliu