The accurate starting point
A “first space-based solar power system” in the full sense, a satellite that gathers sunlight and supplies electricity to people on Earth, has not been built. What exists is a long history of proposals, design studies and small tests of parts of the idea. This article covers that history and keeps clear which parts are demonstrated and which are not.
Note that ordinary artificial satellites have used solar panels since the late 1950s to power themselves. Space-based solar power is different: the aim is to send the energy to the ground.
Why anyone would try it
In orbit, a solar collector sits above the atmosphere and weather. In a suitable orbit, it can face the sun for most of the time, avoiding night for long periods. The sunlight is also somewhat stronger than at the surface. The attraction is therefore steadier output than ground-based solar. The difficulty is everything else: the power has to be sent to Earth, and the structure has to be built, launched and maintained in space.
Early ideas
The idea is often traced to the American engineer Peter Glaser, who described it in a 1968 article in the journal Science and later received a patent for a satellite system that would convert sunlight to microwaves and beam them to a receiving antenna on the ground. Fiction was there earlier. Isaac Asimov’s 1941 short story “Reason” features a space station that sends energy to planets by beam, though that was imagination, not engineering.
Glaser’s proposal rested on earlier work with wireless power. In the 1960s, William C. Brown demonstrated a small helicopter powered by microwave energy beamed from the ground, and in 1975 a larger transmission test at the Goldstone facility in California is reported to have delivered power over a distance on the order of a mile. These tests showed that microwave energy can be converted back to electricity at a receiver, which is the same principle the magnetron in microwave ovens makes familiar, though real power beaming is a much more precise matter.
The NASA and Department of Energy studies
In the 1970s, with energy prices in the news, NASA and the US Department of Energy ran a large evaluation. A reference design imagined satellites in geostationary orbit, covered with a very large area of photovoltaic cells, sending microwaves to ground receivers many kilometers across. The study found nothing fundamentally impossible, but the cost of launching so much material was a serious obstacle. The studies were never followed by construction, and funding declined as oil prices fell.
Later reviews in the 1990s and 2000s, including a NASA assessment in the late 1990s, proposed modular designs and cheaper launch, and Japanese agencies have supported research for many years. Interest has returned in the 2010s and 2020s as launch costs have dropped and solar panels have become cheaper, and agencies in Europe, Japan, China and the United States have studied or funded some form of the idea.
What has actually been tested
A few small experiments are reasonably well documented, though details should be checked against the agencies’ own reports.
- Ground-based beaming tests in the 1970s and later, described above, and some tests in Japan, which show power can be sent through the air to a receiver over a short distance.
- A US Naval Research Laboratory module was flown on an uncrewed spaceplane in 2020 to test converting sunlight into radio-frequency power in orbit.
- A California Institute of Technology demonstrator, launched in early 2023, tested lightweight solar modules, a flexible structure and a small wireless power transfer experiment. Reports from the team said that it transmitted a tiny amount of power in space and detected a signal on the ground.
These are experiments at a tiny scale. None provided useful electricity to the grid.
Open questions
The main hurdles are well known.
- Mass and launch cost. A system that delivers power on the scale of a conventional power station would be very large, and launching and assembling it would need cheap and frequent launches.
- Conversion losses. Power is lost at each step: sunlight to electricity, to radio waves, across the atmosphere and back to electricity.
- Competition. Ground solar farms, wind farms and batteries have become cheaper, which raises the bar for any space-based alternative.
- Safety, regulation and space debris. Beam designs spread energy over a wide area so that the density is low, but public acceptance and international rules would matter.
Where it stands
Space-based solar power is a real field of research with real test hardware, but it remains a concept for supplying electricity to Earth. Whether it will ever be economic is uncertain, and the honest summary is that the first true system is still in the future, if it is built at all.