PG&E, one of the , has an unusual deal on its books. It has pledged to buy all the solar power produced by a tiny, secretive California start-up. But you won’t find these panels laid out in orderly rows across a baking desert – they will be in orbit 36,000 kilometres above Earth. There, they will collect the sun’s limitless energy and beam it down to power grids.
This isn’t just California dreaming. A surprising number of space solar projects are under way around the world, with some heavyweight backers. China is in on the act, and aims to have prototypes in orbit in the 2020s. Russia has already built a prototype, and Japan is so committed to the idea that it has launched a national space solar programme and plans to have operational satellites by the 2030s. The US Navy and several aerospace firms are interested too. So are we seeing the start of a second space race?
It’s not hard to see the appeal. In space, solar power overcomes three obstacles that frustrate terrestrial producers. There are the obvious issues of night and clouds, but also a less discussed problem. Namely, even on the clearest, longest, brightest day, the atmosphere scatters and absorbs the sun’s incoming energy until only a fraction of its original strength remains. “How much it’s reduced depends on your location,” says Paul Jaffe, who is working on space solar modules at the US Naval Research Laboratory in Washington DC. Once through the atmosphere, the power intensity can be anywhere between three and 20 times less (see graph).
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All three problems go away if you park solar panels in orbit. Out there, vast photovoltaic solar arrays could harvest the sun’s undiluted energy almost constantly, offline for just a few hours per year. They would convert this energy to microwaves, which can slice through Earth’s atmosphere, rain or shine, sending enough power into terrestrial grids to rival coal and nuclear, but without their environmental drawbacks (see illustration).
That’s the theory, anyway, and it was first in 1968. A decade later, when the oil crisis threatened the US with a future devoid of fossil fuels, NASA and the US Department of Energy collaborated on a into how to make it work in practice.
Their findings were not encouraging. Supplying electricity just for the north-eastern part of the US would have required solar panels many kilometres wide, feeding a microwave antenna 2 kilometres across. Built from the technology available at the time, this monstrosity would have weighed 81,000 tonnes. Back when it cost $50,000 to send a single kilogram of cargo into space, the launch costs alone came in at $4 trillion. When the oil crisis ended shortly after, nascent space solar plans were scrapped.
A few decades on, worries about fossil fuels have compelled several countries to take a fresh look at space solar. China, beset with choking levels of fossil-fuel smog, is studying space solar as part of a much larger renewable energy programme. Roscosmos, Russia’s federal space agency, has built a small Earth-based prototype.
At the forefront of space solar research, however, is Japan. It makes sense; the country has no fossil fuel resources of its own, insufficient land mass for wind and solar, and the Fukushima nuclear disaster is still fresh in citizens’ minds. Japan’s space agency, JAXA, along with the Universities of Tokyo and Kobe, as well as Japan Space Systems have developed a rigorous road map for space solar. Orbital tests are scheduled for the 2020s, in readiness for fully operational satellites delivering 1 gigawatt in the 2030s.
These optimistic schedules reflect a growing global consensus that the prospects for space solar are brighter this time around. “It’s not like antigravity,” says George Whitesides, CEO of Virgin Galactic and a former executive director of the US National Space Society, a space solar advocacy group. “It’s just a question of whether you can get it to work, and make sense financially.”
They are starting to get it to work, thanks in part to half a century of technological advances. Take wireless power. In 1975, NASA beamed 34 kilowatts to light an array of 300-watt lamps 1.5 kilometres away. By 2008 they had increased the distance more than 100 times, beaming between two islands in Hawaii. A Kobe University project has even beamed power to an Earth-based receiver from space. “The most important thing is not the power but learning how to steer the beam,” says Kobe researcher Nobuyuki Kaya. Last year, aerospace contractor Mitsubishi, working with JAXA, set a new record for precision.
Solar cells have also seen steady improvements. Peak efficiencies for the best space-based solar cells crept up from 6 per cent in the 1950s to hover around 30 per cent, says Gary Spirnak, CEO of Solaren, the start-up in Manhattan Beach that’s in league with PG&E. “But that’s just for one sun,” he says. Reflecting the sun’s intensity onto them many times over, using dynamic arrays of mirrors, doesn’t merely yield more energy from more radiation. “If we can get 400 to 500 suns on them,” he says, “their efficiency actually improves to .”
That still leaves an enormous structure to get into space – unlike solar and wireless technology, launch costs have not improved significantly with time. According to most analyses, they still need to drop by at least two orders of magnitude for space solar to become viable – to $150 per kilogram.
That won’t happen in any hurry, so the only other option is to put space solar satellites on a strict weight loss regime. This is what much of the new research is focused on. Last year, the on a three-year, $17.5 million research programme. The aim is to “attack every aspect of the weight,” says Harry Atwater, a photovoltaic materials scientist at Caltech: “the solar energy generation layer, the wireless microwave transmission system and the spacecraft structures”.
But reducing launch costs isn’t just about weight – it’s also a matter of folding the design into as few launches as possible. Kaya says he has found a way to tuck the photovoltaic layer, the electricity-to-microwave conversion electronics and the Earth-facing antenna into one lightweight sliver less than 1 centimetre thick. Similar plans are afoot at Solaren. While Spirnak is keeping details under wraps, he says their satellite will be placed into orbit in as few as three large rocket launches.
And those rocket launches are set to get a lot cheaper thanks to another ongoing space race – the race to build reuseable rockets. Several companies are vying for dominance, having demonstrated successful tests. When it is no longer necessary to throw away an entire rocket with every launch, there will be major boosts for space solar’s bottom line.
Tracking beam
However, even amid all this optimism, some of the more ambitious programmes have already stumbled. Solaren was originally supposed to start transmitting power this year, but quietly shifted the schedule to 2025. And Japan, which had plans to test a small solar satellite in low-Earth orbit in 2018, now seems to be redrafting its timeline. Is this a temporary hitch or the beginning of another slide back into obscurity?
There’s plenty of money on the latter. Some of the biggest criticisms come from Elon Musk, the high-profile founder of commercial space-flight firm SpaceX, and also of solar panel maker Solar City. His objection is that multiple conversions between energy types – solar to electricity, then to microwaves and then back to electricity – is inefficient and will waste power, quashing any advantage gained from a 24/7 power source.
If the steady pace of improvement keeps up, Musk’s objection will eventually be resolved. John Mankins, a physicist and NASA veteran who now advocates for space solar, doubts that such setbacks will keep nations like Japan, at the mercy of imported energy prices, from driving the technology forward. Then there’s climate change. Unlike the oil crisis of the 1970s, it’s not going away.
The Paris Agreement aims to hold anthropogenic warming to “well below” 2 °C. Most climate scientists agree that existing technologies . Transformative technologies are needed, says Mankins.
A more damning objection is whether space solar can even produce useful amounts of power. Most entities pursuing space solar have chosen 1 gigawatt as their goal. But even if one massive satellite can provide that, the number pales compared with existing solar .
However, Mankins says 1 gigawatt is just the start. His estimates suggest the satellites can be scaled up to 10 gigawatts each.
What’s more, Glaser’s original plans had the satellites in geostationary orbit, hovering above the same spot on Earth’s surface to make beaming power as simple as possible. But there is no reason to keep them confined to an increasingly crowded orbital belt. Equip them with widely available beam-steering equipment, and they could spread into the wider area of geosynchronous orbit. Here, they would need to adjust their beam to keep it trained on the receiver back on Earth. This would add cost, but makes room for 1000 satellites. The long-term potential of space solar now climbs to 10 terawatts – more than half of Earth’s present capacity.
“Whoever gets space solar to work will be the Saudi Arabia of clean energy“
But Jaffe wonders if comparison with nation-scale energy supply misses the point. Beamed continuously 24 hours a day, space solar will never need to be stored, eliminating batteries. And a beam that can be sent anywhere in the world can deliver power to places without transmission lines. That’s an attractive prospect, albeit only for high-end niche concerns to start with. US navy ships, for example, are becoming floating data centres, so the organisation is keen to find alternative ways to provide them with extra power. Tracking a ship with an orbital power beam fits the bill.
And that’s just on Earth. Using lasers to transmit power would be dangerous for terrestrial applications (see “Myths and Realities“), but it opens up a wealth of possibilities in space. JAXA thinks they could be useful for beaming power from one spacecraft to another, or from space to the moon. There aren’t many other options for getting power to asteroid mining and lunar operations.
Whatever the killer app, Jaffe says, the first successful demonstration of the technology will likely spark a new space race. “Whoever gets this technology to work first,” he says, “becomes the Saudi Arabia of clean energy.”
No wonder California wants in.
Space solar: Myths and realities
Will it fry birds?
Unlikely. This question is probably a hangover from the days when lasers were earmarked as the delivery system for beaming space-generated power to Earth – the vast majority of today’s projects aim to use microwaves (see main story).
The most intense sunshine on Earth – a clear, sunny day at the equator – hits you with 1000 watts per square metre. If you were standing at the centre of a 10-kilometre-wide microwave beam from space, it would hit you with one tenth of that, says Paul Jaffe, who works on space solar at the US Naval Research Lab in Virginia. This is the internationally agreed . The birds will probably be fine, too. A study trained a microwave beam two and half times more intense . “It showed no harmful effects,” Jaffe says.
Will it down planes?
No. None of an aircraft’s instruments operate on the frequencies being considered for space solar transmission. However, passengers’ in-flight Wi-Fi might suffer for a few moments as the plane passes through the beam. That’s if Kobe University in Japan has its way and space solar transmits via the 2.4 gigahertz frequency. That’s not a guarantee – the Japanese Space Agency prefers the industrial 5.8 gigahertz frequency. The final say will go to the UN’s International Telecommunications Union, the body that polices frequency allocations. If it chooses the industrial frequency your Wi-Fi will be fine.
Will it change the weather?
Solaren, a space solar start-up in California, has filed a patent that indicates a microwave beam directed from space onto the eye wall of a hurricane could dissipate its destructive energy. The patent was not granted, but does it suggest that one – or many – directed energy beams could seed clouds or otherwise interfere with the world’s weather. Should we worry?
Jaffe thinks not: the frequencies of any future space solar beam will be chosen explicitly to minimise interference with meteorological systems, letting all the energy pass through unimpeded. Otherwise, the beam would be an unreliable power source.
In any case, getting a solar power beam to change the weather, he says, “is probably harder than making a space solar power system, which is already pretty hard”.
Will it be used as a death ray?
Could there be geopolitical ramifications for the first nation to beam power from orbit? Would it be seen as an act of war? It will only be a problem, says Jaffe, if an operator opts for laser delivery. “A big laser in space presents more of a weapon threat than a giant radio wave transmitter in space. With microwave beams, the physics works against you,” he says. In other words, very weak heating is a very poor weapon.
This article appeared in print under the headline “Star power“
