Solar farms in space move one step closer

A breakthrough in power transmission is just the latest step towards readily available, continuous solar energy.

Solar power has one big problem: it's only available when the sun is shining. But what if it could be generated 24/7, whatever the weather?

That's the premise behind several projects, now starting to show real results, that involve building huge solar farms in space.

These initiatives are based on the same general principles. Rockets deliver components to an orbit 22,000 miles up, where they are assembled by robots which will also carry out servicing and maintenance. Once in operation, solar reflectors direct the sun's rays onto vast arrays of solar panels, which then convert them to high-frequency radio waves that can be beamed to a ground station on Earth.

Transmission breakthrough

The latest advance comes courtesy of Oxfordshire, UK-based Space Solar, which has now successfully demonstrated its Harrier wireless power transmission system. This allows the microwave energy beam to point in all directions, keeping the power supply stable and continuous, regardless of orientation.

The team reckons it should be possible to deliver its first commercial power within the next nine years, with gigawatt-scale power generation within twelve years.

"Space-based solar power offers a compelling solution to our energy needs while mitigating the environmental impacts of traditional energy sources," says Mini Rai, professor of space robotics at the University of Lincoln and a member of Space Solar's advisory board.

In the US, the Air Force Research Laboratory (AFRL) is working on a similar project, the Space Solar Power Incremental Demonstrations and Research Project (SSPIDR). Last spring, the team successfully transmitted power in space and beamed detectable power to Earth for the first time.

Meanwhile, the European Space Agency is in the early stages of an initiative called Solaris, exploring the technical feasibility, benefits, implementation options, commercial opportunities, and risks of space-based solar power.

"We are really starting from a blank sheet of paper to get an up-to-date design for what working solar power satellites could look like, sourcing promising ideas from everywhere we can, and leveraging the latest advancements in space and terrestrial technologies," says Sanjay Vijendran, ESA’s lead for the project.

"The studies will look at as wide a range of options as possible, including investigating all the different ways to move the energy, safely and efficiently, down to Earth: radio frequency transmission, lasers, and simply reflecting sunlight down to solar farms on the ground."

Such developments would require enormous numbers of expensive rocket launches. However, the cost is falling, partly thanks to the advent of reusable commercial heavy-lift launch vehicles from SpaceX. Overall, says Space Solar, this means that the cost of a launch has fallen by 90%.

A report from engineering consultancy Frazer Nash and London Economics found in 2022 that a space-based solar power station could be built for around £21 billion and could generate 800 TWh a year – much the same cost-efficiency as a nuclear power plant.

Some hurdles remain

There are, though, other problems. Rocket launches aren't exactly good for the environment, and such projects would also create a huge amount of debris at the end of their lives.

However, an environmental analysis of the Cassiopeia project by the University of Strathclyde has found that overall, including launch, the carbon footprint of a space solar plant could be as little as half that of terrestrial solar, at about 24g of CO2 per kilowatt-hour.

There would be major maintenance issues, as solar panels would degrade much faster in space than on Earth – as much as eight times faster – thanks to strikes from micrometeorites and other harsh conditions such as the high levels of radiation. As a result, the efficiency of panels could degrade by as much as 10% per year.

And current robotics may not be good enough for the initial assembly of the solar plant nor for the regular maintenance required.

Perhaps one of the biggest hurdles, though, may be gaining public acceptance. As we've seen, plans depend on beaming microwaves down to specialized base stations on Earth.

The maximum power density at the center of the Space Solar beam is 230W/m2 – less than a quarter of the intensity of the sun at noon – and has been shown to represent no danger to humans, wildlife, or aircraft. However, in a world where conspiracy theorists are convinced that 5G represents a risk to human health, the idea of microwaves from space is unlikely to go unchallenged.

There seems no doubt, though, that solar power generation in space is going to happen. Governments are throwing their weight behind the concept, with the UK government last year pledging £4.3 million in funding for the sector through its Space Energy Initiative. Japan and the US, too, have said they are committed to the development of space-based solar power. Technology and economics are now at the point where it's now just a matter of time.