What is the difference between microwave and laser power beaming for SBSP?

Microwave and laser power beaming are the two primary transmission pathways studied for space-based solar power, each with distinct advantages and constraints. Microwave beaming uses radio frequencies in the microwave range (typically 2.45 GHz or 5.8 GHz) to transmit energy. It passes through clouds and rain with relatively low atmospheric attenuation, which makes it more reliable in varied weather conditions. The receiving rectenna can be relatively permeable to sunlight and rain, allowing dual-use of the land area. However, microwave beams spread significantly over the GEO-to-Earth distance, requiring large apertures at both the transmitter and receiver. The receiving area can be tens to hundreds of square kilometers for a large system. Laser power beaming uses concentrated light in the near-infrared spectrum. It achieves a much smaller beam and smaller receiving footprint. But laser beams are strongly affected by clouds, atmospheric turbulence, and aerosols, making reliable delivery more complex. Pointing accuracy over 36,000 km is also more demanding for lasers. Most of the major SBSP programs (NASA, ESA, JAXA) have historically focused primarily on microwave beaming, though laser WPT has attracted increasing research interest.