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Look! Up in the sky! Proof of concept for satellites beaming energy to Earth!

They'd need to be a kilometer wide and point at even larger landside targets, so they won't fire up the renewables market

A recent demonstration has proven the feasibility of the European Space Agency's (ESA) plan to beam power to Earth from space, giving the astro agency some additional ammunition as it prepares to ask its governing body for more cash to fund solar energy research. 

The ESA's space-based solar power (SBSP) initiative created a preparatory program called SOLARIS to test beaming solar power from satellites to Earth via microwaves. SOLARIS was the agency's effort to investigate what technologies are needed to realize the idea, and the feasibility of using them. 

The ESA spent 2022 working on various aspects of SOLARIS, including publishing a pair of cost/benefit analyses and holding an industry day with presentations from the space agency and its commercial partners, including Airbus.

The ESA found SBSP feasible as a complementary power source to terrestrial renewables. And in September, Airbus demonstrated that it could use microwaves to transmit power at a distance of 36 meters (118 feet), which it used to light up a miniature city. It's not exactly Alderaan, but it's a start. 

Airbus's demonstration may be precisely what's needed to tip the scales in favor of more money for SBSP, if ministers aren't already convinced. 

"Now that we have successfully tested the key bricks of a future space-based solar power system on a small scale for the first time, we are ready to take Power Beaming to the next level", said Airbus research project leader Yoann Thueux. 

While those results are encouraging, SOLARIS can't do more without more funding from the ESA's Council of Ministers, which will soon stage its annual meeting at which it hears requests for cash. 

Using orbital solar panels to beam energy to Earth using microwaves isn't a new concept, either in fiction or reality. NASA has explored the idea, as have Japan's space agency, the US Navy, UK Space Energy Initiative, universities and private companies. 

So far, China appears to be leading the world in SBSP, having already tested the capabilities of a ground-based receiver using balloons floating at altitudes of up to 300 meters, and plans for higher altitude tests.

Space-based fantasy, or something more?

There are a lot of reasons why SBSP is exciting: It could help the world meet net zero goals, is able to deliver power 24 hours a day, captures solar energy far more efficiently since it's at a much higher altitude, and could minimize the amount of space needed to harvest energy in comparison to standard terrestrial solar arrays. 

But the ESA admits space-based solar power satellites are not currently feasible. Previous ESA studies and similar efforts from other agencies "have found no principal technical showstoppers but prohibitive challenges to make the concept economically viable due to high launch costs and engineering challenges."

Take solar-collecting satellites, for example. In order to make them efficient enough to be worth the hassle, a single satellite would need to be somewhere in the neighborhood of a kilometer or more across. It would be visible in the sky like a small moon – too big to be a space station. That would give the satellite the ability to beam around 2GW of power down to Earth – the same amount generated by a terrestrial nuclear power plant. 

But get this: In order to grab that amount of power, the receiver on the ground may have to be ten times that size. For a comparison, the 2GW Pavagada solar park in India occupies approximately 53 square kilometers.

However, unlike arrays of terrestrial solar panels, the SBSP microwave receiver would allow light and rainwater to pass through. That means the land underneath could still potentially be available for agricultural use.

Ground-based concerns aside, it's unlikely such satellites could be practically built with today's tech. Noting that it took dozens of launches to build the International Space Station, the ESA said it "would likely require an order of magnitude more launches to assemble a solar power satellite that weighs in at many thousands of tonnes." 

Rather than looking at that as a sign that SBSP is a waste of research funding, the ESA said that the necessary research would be a boon for the larger space industry. 

"Photovoltaic and power conversion efficiency, on-orbit manufacturing, assembly, and servicing, and deployable antenna developments" would all be developmental side-effects, the ESA said. 

For those worried these efforts could deliver wildfire-starting space lasers, it isn't. Microwaves, the ESA notes, operate at a non-ionizing frequency that won't cause cellular damage. Beyond that, models of microwaves designed for SBSP use have a maximum power density of approximately 250 watts per square meter at the center of the beam, while a person standing near Earth's equator at high noon would be blasted with four times that. 

Still, that's just one more thing the ESA said will be part of the many considerations and "further tests" needed to get the agency to the point where it sees SBSP as something that could meaningfully contribute to Europe's clean energy goals. "Only if, and when, these conclusions are reached would a proposal potentially be made to progress to an SBSP development project," the ESA said. 

In other words, don't start looking skyward for the makings of an Earth-orbiting Dyson swarm just yet. ®

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