Boffins from two UK universities believe they've figured a viable way to make space-based solar farms feasible, and it doesn't even require any new-fangled or expensive technology to accomplish.

The conclusion reached by the team from the University of Surrey and Swansea University comes after a first-of-its-kind experiment that sent four cadmium-telluride (CdTe) solar cell test panels into orbit on a cubesat way in September, 2016.

Now, in a recently authored paper, the team say their test cells showed exceptional resilience to ionizing solar radiation, haven't delaminated at all, and only showed degradation in their shunt resistance, which the scientists believe they have a solution for.

On top of that, they were only expected to work for a year, and six years on (the paper relies on data gathered through September, 2022) they're still working. 

"These detailed data show the panels have resisted radiation and their thin-film structure has not deteriorated in the harsh thermal and vacuum conditions of space," said Craig Underwood, professor emeritus of spacecraft engineering at the University of Surrey's Space Center. "This ultra-low mass solar cell technology could lead to large, low-cost solar power stations deployed in space, bringing clean energy back to Earth - and now we have the first evidence that the technology works reliably in orbit." 

Cadmium telluride solar cells aren't new technology. In fact, they're the second-most common type of solar cell deployed in the world behind crystalline silicon photovoltaic cells, albeit with just 5 percent of the market. Commercial CdTe solar cells, which are largely used in large commercial solar farms, have comparable efficiencies to silicon cells, and CdTe is the preferred material for most ultra-thin solar film products.

That said, the Surrey-Swansea study was the first effort to test CdTe cells in space, and their results suggest we might want to ditch the silicon cells for future space missions. 

As for the one drawback to CdTe use in space, the team noticed all four cells experienced a decrease in their fill factor, which is a measure of photovoltaic efficiency, in this case caused by the aforementioned decrease in shunt resistance. 

"We ascribe this to the diffusion of gold from the back contact into the CdTe layer forming micro-shunts along the grain boundaries," the team said. To address that issue "a new back contact architecture [needs] to be developed to realize the true potential of these cells for spaceflight."

The solution might be simple, though - the team said "methodologies more commonly employed for terrestrial CdTe modules" may be the needed tweak. 

To the team, "this flight has proven the basic soundness of [CdTe] for use in space." 

Great, now what about beaming the power back to Earth? 

It's encouraging to think a new, more efficient and long-lasting photovoltaic material usable for collecting solar energy in space has been found, but there's still the matter of getting all of that energy back to Earth. 

Researchers at the California Institute of Technology demonstrated beaming power from a satellite to Earth's surface for the first time over the summer in the form of microwaves, but it was more of a proof-of-concept able to light up a couple LEDs than any useful amount of energy. 

In contrast, the European Space Agency's calculations as part of its space-based solar power initiative called SOLARIS has determined that massive arrays - both on the ground and in space - would be needed to make beaming energy from space efficient. 

A single satellite, for example, would need to have so many solar cells that it would measure at least a kilometer across, while ground-based receivers would need to be around ten times that size.

We asked the Surrey-Swansea team whether CdTe cells would make space-based receivers more efficient or feasible, and will update this story if we hear back. ®

https://www.theregister.com//2023/10/25/brit_boffins_say_their_tech/