Powersphere: A Photovoltaic Cavity Converter for Wireless Power Transmission using High Power Lasers

PowerSphere (PS) is a high efficiency Photovoltaic Cavity Converter (PVCC) that is under development for Wireless Power Transmission (WPT) or Laser Power Beaming (LPB). The targeted power range is from 1 kW to 100 kW. In this paper we report the preliminary results in the 100 W to 200 W range that were obtained with a Nd:YAG laser operating at 1.064mum. As the receiver we used a modified solar PVCC prototype equipped with advanced Si concentrator cells. The overall "array" efficiency of the PowerSphere consisting of 22 internal mini-modules is over 14%. This result must be viewed with the understanding that: a) Si cells are not a good match for the 1064 nm wavelength, b) the flux density inside the sphere is 30% less than one sun, though the cells are optimized for 500 suns, c) the standard AR coating for the test cells inside the PowerSphere have a reflectance of ~15% at 1064 nm and, d) the cell population inside the cavity is only 24%. Given these facts the result is encouraging. If, corrected for these limiting factors, except item (a), PowerSphere equipped with advanced Si concentrator cells would allow conversion of Nd:YAG radiation at 40% efficiency. Our analytical studies predict that an array conversion efficiency of over 60% can be achieved if cells with perfectly matching bandgaps are used instead of Si cells