Solar panels on Earth cannot make power at night, and they are weak on rainy days. In space, there is no night or rain for most of the time.

So scientists want to put solar panels in space. The power would be sent to Earth as radio waves. In 2023, a satellite sent power through space, and people on the ground found the waves. But a real space power station would be huge and expensive.

Solar power on Earth has two weaknesses: it stops at night, and it becomes weaker on cloudy or rainy days. Space-based solar power aims to solve this by placing solar panels in orbit, where there is almost no night and no weather. The idea was first proposed in 1968 by Peter Glaser, an American engineer.

Electricity generated in space would be converted into microwaves, beamed to receiving antennas on the ground, and then turned back into electricity. In 2023, a Caltech satellite transmitted power wirelessly in space, and its signal was also detected on the roof of the university. However, a real power station would need panels and antennas kilometers wide, and launching such huge structures would be very expensive.

Ground-based solar panels face unavoidable limits: they produce nothing at night and little under heavy cloud. Space-based solar power proposes to bypass these limits by collecting sunlight in orbit, particularly near geostationary orbit, where a station would be in darkness only briefly and never affected by weather. The concept was first set out in 1968, when engineer Peter Glaser argued in Science that a large orbiting power station could beam energy to Earth as microwaves. The process involves three conversions: electricity is turned into microwaves, transmitted as a narrow beam to ground antennas tens of thousands of kilometers away, and converted back into electricity.

In 2023, Caltech's demonstration satellite steered a microwave beam in space and its signal was detected on a campus rooftop, while Japan's JAXA has conducted ground-based kilowatt-class transmission tests. These were proofs of concept, however, delivering only tiny amounts of power. A practical station would require kilometer-scale structures assembled in orbit, each conversion step would lose energy, and public acceptance of the beams would be essential. Falling launch costs have revived interest, but some analyses conclude that spending the same money on ground solar plus storage would be cheaper.