The idea of space-based solar power (SBSP) – using satellites to collect energy from the sun and “beam” it to collection points on Earth – has been around since at least the late 1960s. Despite its huge potential, the concept has not gained sufficient traction due to cost and technological hurdles.
Can some of these problems now be solved? If so, SBSP could become a vital part of the world’s transition away from fossil fuels to green energy.
We already harvest energy from the sun. It’s collected directly through what we generally call solar power. This comprises different technologies such as photovoltaics (PV) and solar-thermal energy. The sun’s energy is also gathered indirectly: wind energy is an example of this, because breezes are generated by uneven heating of the atmosphere by the sun.
But these green forms of power generation have limitations. They take up lots of space on land and are limited by the availability of light and wind. For example, solar farms don’t collect energy at night and gather less of it in winter and on cloudy days.
PV in orbit won’t be limited by the onset of night. A satellite in geostationary orbit (GEO) – a circular orbit around 36,000 km above the Earth – is exposed to the Sun for more than 99% of the time during a whole year. This allows it to produce green energy 24/7.
GEO is ideal for when energy needs to be sent from the spacecraft to an energy collector, or ground station, because satellites here are stationary with respect to the Earth. It’s thought that there’s 100 times more solar power available from GEO, than the estimated global power demands of humanity by 2050.
Transferring energy collected in space to the ground requires wireless power transmission. Using microwaves for this minimises the energy lost in the atmosphere, even through cloudy skies. The microwave beam sent by the satellite will be focused towards the ground station, where antennas convert the electromagnetic waves back into electricity. The ground station will need to have a diameter of 5 km, or more at high latitudes. However, this is still smaller than the areas of land needed to produce the same amount of power using solar or wind.
Evolving concepts
Numerous designs have been proposed since the first concept by Peter Glaser in 1968.
In SBSP, the energy is converted several times (light to electricity to microwaves to electricity), and some of it is lost as heat. In order to inject 2 gigawatts (GW) of power into the grid, about 10 GW of power will need to be collected by the satellite.
A recent concept called CASSIOPeiA consists of two 2km-wide steerable reflectors. These reflect the sunlight into an array of solar panels. These power transmitters, approximately 1,700 metres in diameter, can be pointed at the ground station. It is estimated that the satellite could have a mass of 2,000 tonnes.
Another architecture, SPS-ALPHA, differs from CASSIOPeiA in that the solar collector is a large structure formed by a huge number of small, modular reflectors called heliostats, each of which can be independently moved. They are mass-produced to reduce cost.
In 2023, scientists at Caltech launched MAPLE, a small-scale satellite experiment which beamed a tiny amount of power back to Caltech. MAPLE proved the technology could be used to deliver power to Earth.
