Orbital solar power: beaming the sun’s rays back down to Earth

JP Casey 27 May 2019 (Last Updated May 28th, 2019 15:10)

China has invested $15m in a test for a “solar space station”, a craft that will orbit the Earth, absorbing solar rays, converting them into electricity, and beaming them back down to the planet; but it remains to be seen if this ambitious project can overcome the significant technological hurdles it faces.

Orbital solar power: beaming the sun’s rays back down to Earth
The proposed station would orbit 22,000 miles above the Earth, and provide a constant supply of energy, collecting and returning energy 99% of the time.

In 2017, China invested $125.9bn into renewable energy sources, almost half of the global total, as the country looks to the Earth’s winds and waters to satisfy its vast energy needs. Perhaps its most ambitious project, however, is not on Earth at all, but in space, where scientists aim to launch a “solar space station” that can absorb the sun’s rays, convert them to electricity, and beam them back down to Earth.

The project faces a number of technological and logistical challenges, but with clear potential and significant financial backing, the developers hope to complete the world’s first outer space solar station by the middle of the century.

The orbital solar power process

The process is simple in theory. A power generation device in space would convert solar energy into electrical energy, just as solar panels do on Earth. The device would then either convert the energy into microwaves or lasers to beam back to a receiving station on Earth, which would then convert the transmission back into electrical energy and deliver it direct to a power grid.

The proposed station would orbit 22,000 miles above the Earth, and provide a constant supply of energy, collecting and returning energy 99% of the time, as the sun’s rays would not be intercepted or blocked by gases, as happens to 30% of the rays as they pass through the Earth’s atmosphere.The device would be unaffected by the changes from night to day, or season to season, as solar panels are on Earth.

The project would fulfil a key energy need for China, which has consumed more coal than the rest of the world combined since 2011. The country has invested considerably in renewable energy sources in recent years, becoming the world leader in hydroelectric power in 2014 after increasing its hydroelectric capacity by 408% in the first 15 years of the millennium.

Testing at 1,000 metres

Researchers from Chongqing University, Xidian University and the Xi’an branch of the China Academy of Space Technology are developing a test facility in Chongqing. The project has received $15m in funding, and over two years will see the launch of six tethered balloons to an altitude of one kilometre above sea level. The balloons will be tied to each other and the ground, and be fitted with solar panels, which will be used to capture solar rays, convert them into microwaves, and beam them down to Earth. The test project is identical to the planned final project, but on a much smaller scale.

The team plans to complete its power transmission tests within the next ten years, before completing a larger test facility, one that will be sent into space and is capable of transferring metawatts of energy, by 2030. This will coincide with a government plan to see 20% of China’s energy come from non-fossil fuel sources. China then plans to build a commercial space station before 2050.

Technological and logistical challenges

Any project of this scale faces a number of technical challenges, and one of the main difficulties for this plan is simply getting the station into orbit to begin with. The station is expected to weigh 1,000 tonnes, more than double the weight of the International Space Station. Researchers are exploring a number of alternatives to launching the craft from Earth, including sending a separate facility into space that would use 3D printing technology to construct robots that would then build the station directly in space.

The researchers will also have to decide whether to use lasers or microwaves to transfer the energy back to Earth. While lasers can function at an orbit of just 250 miles above Earth, they cost around $500m to produce, and can only beam fewer than 10 megawatts per satellite, making them an inefficient solution. Microwaves can transfer more energy, but need to be around 22,000 miles above the planet, causing concern over how the station will be placed that far from Earth, and raising concerns that it will be almost impossible to manage once in orbit.

With tests only currently able to transfer energy over 100 metres, the scientists have considerable work to do to realise this lofty ambition.