space-based solar power
space-based solar power, the collection in space of solar energy, which is then transmitted as a microwave or laser beam to the ground and converted into electrical energy.
The idea of space-based solar power predates the space age. Konstantin Tsiolkovsky proposed in 1923 that space-based mirrors could beam sunlight to the ground. American science-fiction writer Isaac Asimov’s story “Reason” (1941) was set on a solar power satellite that beamed energy around the solar system. American engineer Peter Glaser proposed the idea of collecting solar power and transmitting it to Earth with microwaves in 1968.
Collecting solar power in space has several advantages. Unlike Earth-based installations, solar arrays in geostationary orbit would not have to stop collecting because of nighttime or bad weather. Moreover, it is estimated that space-based installations would feed several times more electricity to consumers than solely Earth-based installations, which cannot collect the portion of solar radiation blocked by Earth’s atmosphere. Power satellites in Earth orbit would be a source of plentiful clean energy that would help the world transition to a carbon-free future. In cases of natural disaster, power could be quickly beamed to the affected area without having to wait to rebuild power plants and transmission lines.
U.S. government studies of Glaser’s concept in the late 20th century found no great technological hurdles with the efficiency of the system or the transmission of the power to Earth. However, the large size required for the solar power satellites, which together would measure about a kilometre across, would require hundreds of launches per year, each carrying hundreds of tons of material. For most of the space age, the cost of launching 1 kg to Earth orbit has been $10,000. However, with the advent of SpaceX’s reusable Falcon rockets, that cost has gone down to about $1,000, and it is estimated that SpaceX’s proposed Starship would bring the cost down to $200.
The first test of space-based solar power occurred in 2023, when the Microwave Array for Power-transfer Low-orbit Experiment (MAPLE), on board Caltech’s Space Solar Power Demonstrator (SSPD-1) satellite, beamed solar power in the form of microwaves to a receiver on Earth. There the microwaves were converted into electricity, which was used to light a pair of LEDs (light-emitting diodes). MAPLE consists of solar radiation receivers and an array of flexible lightweight microwave power transmitters. Through a small window, those transmitters can beam power to a precise location on Earth—specifically, to a receiving array at Caltech in Pasadena, California.
Several countries are conducting or planning experiments in space-based solar power. The U.S. Naval Research Laboratory launched an experiment to the International Space Station in 2023 that has used a laser beam to transmit power over a distance of 145 cm (57 inches) for months. The European Space Agency’s Project Solaris is studying the feasibility of space-based solar power with the aim of deciding in 2025 whether to proceed with further development. China hopes to build a one-megawatt solar power satellite by 2030.