University of Wisconsin-Madison

Another concern has to do with the fact that, in contrast to a GEO location where the SPS is always at a constant location to the rectenna on the Earth, there needs to be multiple receiving stations on the Earth as well. Locations at 120^o apart may solve this dilemma.
Other concerns have to do with the fact that fixed east-west facing solar cells on the surface of the Moon do not collect the maximum amount of energy because of shadowing during the morning or afternoon, the lower efficiency of Si cells (it is probably not cost effective to extract and make GaAs cells on the Moon), and the longer transmitting distance requires a larger transmitting antenna. The geometric problems of a rotating Moon and Earth system can be solved by placing orbiting microwave reflectors around the Moon and around the Earth.