Space-Based Solar Power

How Space-Based Solar Power Works

Space-based solar power combines several established technologies: photovoltaic electricity generation, electromagnetic energy transmission, antenna systems and electrical power conversion.

The core concept is to collect solar energy above Earth's atmosphere and transmit it wirelessly to a receiving station on the ground.

Collecting Solar Energy in Orbit

Large arrays of photovoltaic solar cells would convert sunlight into electricity, much like conventional solar panels on Earth.

One proposed location is geostationary orbit, approximately 35,786 kilometres above Earth's equator. At this altitude, a satellite orbits at the same angular rate as Earth's rotation, allowing it to remain approximately above the same location on the ground.

A solar power satellite in a suitable geostationary orbit could receive sunlight for most of the year, although periods of eclipse would still occur.

The electricity generated by its solar arrays would power the satellite's transmission equipment.

Converting Electricity into a Microwave Beam

One proposed method uses radio-frequency energy, particularly microwaves, to transfer power from orbit to Earth.

Electrical energy from the solar arrays would be converted into microwave radiation using specialised electronic equipment.

Large transmitting antenna arrays could then direct the energy towards a designated receiving station.

Microwaves are electromagnetic waves, like radio signals, but at higher frequencies than many conventional broadcasting services.

Frequencies around 2.45 GHz and 5.8 GHz have been investigated for wireless-power transmission because of their propagation characteristics and the availability of suitable electronic technologies.

The transmitting system would require accurate beam steering and control to keep the energy directed towards its intended receiver.

Receiving the Energy on Earth

The ground-based receiving station would use a rectifying antenna, commonly called a rectenna.

A rectenna combines antenna elements that receive electromagnetic energy with electronic rectifiers that convert the received alternating electrical signal into direct-current electricity.

That electricity could then be conditioned and converted into a form suitable for distribution through the electrical grid.

Rectenna technology has already been demonstrated in terrestrial wireless-power experiments.

However, efficiently receiving large quantities of energy transmitted from geostationary orbit would require substantial receiving infrastructure and careful engineering.

Alternative Transmission Using Lasers

Laser-based power transmission is another proposed approach.

Instead of converting electricity into microwaves, a satellite could use electrically powered lasers to direct energy towards photovoltaic receivers designed for the laser's wavelength.

Laser beams can be focused more narrowly than microwave beams using comparatively smaller optical systems.

However, atmospheric clouds, absorption, scattering and the need for precise alignment present significant challenges.

For these reasons, microwave transmission remains a prominent option in many large-scale space-based solar power proposals.

Converting Orbital Energy into Usable Electricity

The complete process would involve several energy conversions:

Sunlight → Solar Cells → Electricity → Microwave Transmission → Ground Rectenna → Electricity Grid

Each stage introduces energy losses.

The overall efficiency would therefore depend on the performance of the solar cells, transmission electronics, antenna systems, atmospheric propagation, receiving equipment and electrical conversion systems.

A successful orbital power station would need to deliver enough usable electricity to justify its construction, launch, maintenance and operating costs.