Technology to transmit solar power from space to Earth

Despite many challenges, the technology to generate solar power in space and transmit it to Earth via microwave beams could help people break free of fossil fuels.

Simulation of the solar power generation system in the SPS-ALPHA universe. Photo: NASA

The idea of ​​space-based solar power generation (SBSP), which uses satellites to collect energy from the Sun and transmit it to collection points on Earth, has existed since at least the late 1960s, according to Science . Alert . Despite the huge potential, the idea did not attract much attention due to cost and technological obstacles. If the problem can be solved, SBSP will become an important part of helping the world transition from fossil fuels to green energy.

Humans have long gathered energy from the Sun, through various technologies such as photovoltaics (PV) and solar thermal (STE). Solar energy is also collected indirectly, such as wind energy, due to the wind generated by the uneven warming of the atmosphere under the influence of the Sun. But these forms of green energy production have limitations. They take up a lot of ground space and are limited by the available light and wind. For example, the solar farm cannot collect energy at night and collect less in winter or cloudy day.

PV in orbit is not restricted by night. A satellite in geostationary orbit (GEO), in circular orbit 36,000 km above Earth, is in contact with the Sun more than 99% of the time throughout the year. This allows it to produce green energy 24/7. GEO is ideal when it is necessary to transmit power from a spacecraft to a receiver, or ground station, because the satellite at that location is in the same place relative to Earth. The researchers say that the solar energy available from the GEO is 100 times more than the estimated global electricity demand of humanity in 2050.

Transferring the energy collected in space to the ground requires wireless power transmission. Using microwaves to transmit electricity helps to reduce electricity loss in the atmosphere, even when it's cloudy. The microwave beam transmitted by the satellite will focus on the ground station. There, the antenna converts electromagnetic waves into electricity. The ground station would need to be 5 km in diameter or larger if at high latitudes. However, this area is still smaller than the land needed to produce the same amount of electricity with solar or wind energy.

Researchers have proposed many SBSP designs since the first idea of ​​Peter Glaser in 1968. In SBSP, energy is converted several times (light - electricity - microwave - electricity) and some is lost. in the form of heat. To bring 2 gigawatts (GW) to the grid, the satellite will need to collect about 10 GW.

A recent design called CASSIOPeiA includes two directional reflectors 2 km wide. They reflect sunlight into a series of photovoltaic cells. Then, the generator system 1,700 m in diameter can be pointed directly at the ground station. The satellite is estimated to have a mass of 2,000 tons.

Another design named SPS-ALPHA differs from CASSIOPeiA in that the solar collector is a large structure made up of many small modular reflectors called heliostats, each of which can move independently. They are mass produced to reduce costs.

In 2023, scientists at the California Institute of Technology launched MAPLE, a small-scale satellite experiment that delivered small amounts of electricity to the institute. MAPLE demonstrates that this technology can be used to transmit electricity back to Earth.

Currently, the European Space Agency is assessing the feasibility of SBSP with the SOLARIS initiative, followed by a plan to fully develop the technology by 2025. Other countries have also recently announced plans to transmit electricity to the region. Earth in 2025, and transition to a larger system within two decades.

The main limitations to SBSP are the huge volume required to launch into space and the cost per kilogram. Companies like SpaceX and Blue Origin are developing heavy-duty launch vehicles that focus on reusing many vehicle parts after flight. This way can help reduce the cost of launching by 90%. Even using SpaceX's Starship vehicle, which can launch 150 tons of cargo into low Earth orbit, the SBSP satellite still requires hundreds of launches. Some parts are designed to be scalable, 3D printed in space.

The SBSP mission will be very challenging and requires a full risk assessment. While the electricity produced is purely green, the pollution impact from hundreds of launches is difficult to predict. In addition, controlling such large structures in space would require large amounts of fuel, forcing engineers to work with hazardous chemicals. Photovoltaic batteries will be affected by degradation, the efficiency of which decreases over time, from 1 to 10% per year. However, maintenance and refueling can prolong the life of a satellite. A microwave beam strong enough to reach the ground can harm anything in its path. For safety reasons, the energy density of the microwave beam needs to be limited.