Despite many challenges, space-based solar power (SBSP) technology, which generates solar energy in space and transmits it back to Earth via microwave beams, could help humanity break free from fossil fuel dependence.
The concept of space-based solar power (SBSP), which involves using satellites to collect energy from the Sun and transmit it to receiving stations on Earth, has existed since at least the late 1960s, according to Science Alert. Despite its enormous potential, this idea has not garnered significant attention due to high costs and technological hurdles. If these issues can be resolved, SBSP could become a crucial component in the global transition from fossil fuels to green energy.
Humans have long harnessed solar energy through various technologies such as photovoltaics (PV) and solar thermal energy (STE). Solar energy can also be collected indirectly, such as through wind energy, which is generated by the uneven heating of the atmosphere by the Sun. However, these forms of green energy production have limitations. They occupy extensive land areas and are constrained by the availability of sunlight and wind. For instance, solar farms cannot collect energy at night and generate less power during winter or cloudy days.
Simulation of the space-based solar power system SPS-ALPHA. (Image: NASA).
PV systems in orbit are not limited by nighttime. A geostationary satellite (GEO), which orbits at a height of 36,000 km above Earth, is exposed to sunlight for over 99% of the time throughout the year. This allows it to produce green energy 24/7. GEO is ideal for transmitting energy from spacecraft to receivers or ground stations, as satellites at this position remain stationary relative to Earth. Researchers believe that the solar energy available from GEO is 100 times greater than the estimated global electricity demand for humanity by 2050.
Transmitting energy collected in space back to Earth requires wireless power transmission. Using microwaves to transmit electricity helps minimize power loss in the atmosphere, even on cloudy days. The microwave beams transmitted by the satellite will focus on the ground station, where antennas convert the electromagnetic waves into electricity. The ground station will need to have a diameter of 5 km or larger if positioned at high latitudes. However, this area is still smaller than the land required to generate an equivalent amount of electricity through solar or wind energy.
Researchers have proposed various SBSP designs since Peter Glaser’s initial concept in 1968. In SBSP, energy is converted multiple times (light – electricity – microwave – electricity), with some energy lost as heat. To deliver 2 gigawatts (GW) to the grid, the satellite would need to collect approximately 10 GW.
A recent design called CASSIOPeiA features two steerable reflectors that are 2 km wide. They reflect sunlight onto a series of solar panels. Subsequently, a 1,700 m diameter generator can be aimed directly at the ground station. It is estimated that the satellite will weigh 2,000 tons.
Another design, SPS-ALPHA, differs from CASSIOPeiA in that its solar light collector consists of a large structure made up of many small modular reflectors called heliostats, each of which can move independently. These are mass-produced to reduce costs.
In 2023, scientists at the California Institute of Technology launched MAPLE, a small-scale satellite experiment that transmits small amounts of electricity back to the institute. MAPLE demonstrates that this technology can be used to transmit electricity to Earth.
Currently, the European Space Agency is assessing the feasibility of SBSP through 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 Earth by 2025, with a transition to larger systems within two decades.
The main limitation of SBSP is the enormous mass that needs to be launched into space and the cost per kilogram. Companies like SpaceX and Blue Origin are developing heavy-lift launch vehicles, focusing on reusing many parts of the vehicle after flight. This approach could help reduce launch costs by 90%. Even using SpaceX’s Starship, which can launch 150 tons to low Earth orbit, SBSP satellites would still require hundreds of launches. Some components are designed to be expandable and can be 3D printed in space.
The SBSP mission will be very challenging and requires a thorough assessment of risks. While the electricity produced is entirely green, the environmental impact from hundreds of launches is difficult to predict. Additionally, controlling such a large structure in space will require significant fuel, forcing engineers to work with hazardous chemicals. Solar panels will be affected by degradation, with efficiency declining over time, ranging from 1 to 10% each year. However, maintenance and refueling could extend the satellite’s lifespan. A microwave beam strong enough to transmit to the ground could harm anything in its path. For safety reasons, the energy density of the microwave beam must be limited.
