Placing solar panels in space, then using it to beam energy wirelessly to any point on Earth would be among the greatest engineering projects of all time. Is it possible? Is it ever going to happen?
Space-based solar power has been a dream since April 1941, when the idea was proposed by Isaac Asimov in a short story called "Reason." The concept has been researched by the Department of Energy since the mid-1970s, and, more recently, proposed by Japan as an alternative to nuclear power. Still, there are very real roadblocks standing in the way of the space solar power dream.
There's not a whole lot of people who have actually worked on orbital solar projects, but onMonday at the Satellite 2015 conference in Washington, DC, three of them discussed how much we've progressed, and how far we have to go.
"Nobody has ever built a system that's the size of a dozen aircraft carriers for use here on Earth, let alone put them in space"
Paul Jaffe, a scientist at the US Naval Research Lab, has been working on the underlying components of space solar power, namely wireless power transmission. Patrick Rayermann is director of business development at Airbus's satellite division, a company that has actually poured money into developing space solar power. And Edward Horowitz is the director of US Space LLC, a company that's constantly making decisions about whether or not a technology is actually worth investing in.
Why should we put solar panels in space?
As sci-fi as it sounds, the arguments for orbital power are pretty straightforward: solar panels are estimated to be about 10 times more efficient in space, and they can be pointed at the Sun 24/7. If you have a power plant in space, you can beam that energy to any point on Earth, including remote, poor areas or war zones. In theory, it's clean and efficient.
"It can be done, the question is to what end?"
So why haven't we done it yet?
To be useful, we'd need the equivalent of several miles-worth of solar panels sitting in orbit, a proposition that, as it stands, would require dozens or hundreds of launches. Getting all of that material to space is expensive (like, many billions of dollars expensive), and assembling it in orbit is at the limits of our current technological capabilities.
"Nobody has ever built a system that's the size of a dozen aircraft carriers for use here on Earth, let alone put them in space," Rayermann said.
It's not science fiction
The science of space solar power is sound. We can obviously generate solar power here on Earth using panels, we can transmit it wirelessly via microwaves or lasers, and we can launch things to space. This is doable. But that doesn't mean we're there yet, and it doesn't mean it's ever going to happen.
"I think it can be done, the question is to what end?" Horowitz said. "When I ask investors what they want to see, they can't see 50 years from now, they can see maybe two, so you have to present the story in chapters."
"If you're going to do this commercially, the business case has to make sense"
Horowitz said that those developing the tech have to start pitching the incidental technology that will develop out of this, whether it be robots that can work in space, better wireless power transmission that leads to televisions you don't have to plug in, cheaper space launch technology, and better sunlight-to-power conversion.
Who's going to pay for this?
The US government spent $50 million researching the idea between 1978 and 1981, during the height of the 70s oil crisis. Since then, it has cut funding drastically, but Jaffe and other researchers at the US Naval Research Lab continue to work on the underlying technology that'll be necessary to put this in space.
Airbus also has researchers looking into space solar power, but it's not going to happen anytime soon.
"If you're going to do this commercially, the business case has to make sense," Rayermann said. "Saying to investors, 'you'll start getting a return on investment in a couple decades' does not work, you have to do it faster than that."
The military wants orbital power
The most convincing narrative, from an investment standpoint, that Rayermann or Horowitz can think of is one that protects troops' lives, not one that provides power for those in underdeveloped or remote areas. It'll probably be like other space technologies, which start out as military projects and eventually trickle down to the masses.
It's unlikely that space power is going to be cheap at first, even after it's actually built. To get a return on the price of building a space power plant, Rayermann said we're looking at prices of something like $5 per kilowatt hour of power.
Right now, the US average is 12 cents per kilowatt hour—in other words, this isn't going to be powering New York City anytime soon. But the military pays something like $10 per kilowatt hour of power in battlefields, where fuel-based generators have to be used. That makes the tactical and safety advantages of space solar power attractive.
"There's a huge military interest in this kind of capability, you can deliver energy anywhere on the battlefield if you need it, where now you need to truck in fuel past roadside bombs and risk having people die," Rayermann said. "From there, you can extrapolate to [the earthquake] in Haiti and the typhoon that hit the Philippines. The satellite industry likes to say how quickly we can get communications back online. Well, imagine if we could reestablish power in these areas immediately."
What about Japan?
Japan has made a lot of waves lately in the space solar power space. It says it wants to have a gigawatt power station in space by 2025. It's the only country that really has a plan for a space power plant, and its ambition should be lauded. But it's still a long shot: Last week, Mitsubishi and Japan demonstrated wireless power transmission technology in which it delivered 1.8 kilowatts of power from a base station to a receiver 55 meters away. It was impressive because of how accurate the microwaves were, but the technology itself is not unprecedented.
"NASA sent 34 kilowatts over 1.5 kilometers in 1975," Jaffe said. "A lot of great work has been done, but much of it is in the past. Japan and China have studies and small efforts at tech development, but it's not a program on track to become a flight program."
"There's lots of concepts, and the number only seems to grow over the years," he added.
Microwave or laser?
There are two ways to send the power back to Earth: microwaves and lasers. Microwaves can, generally, go through clouds, which is a major drawback of lasers. But microwaves are less accurate and could generate radio interference with cell phones and other communications devices. Lasers, on the other hand, have pinpoint accuracy—a receiver station can be much smaller, potentially even portable. Laser-based power is potentially more flexible in deployment, and at a price point that may be cheaper because of the smaller form factor required.
One large power station, or many satellites?
The biggest holdup, at this point, is getting a huge solar farm into space. A single large power station would seem like the easiest solution to manage in orbit, but then there's another issue: you have to assemble it in space.
"When the US looked at this in the 1970s, it imagined huge colonies in space of astronaut construction workers. That's a nonstarter for cost and other reasons," Jaffe said. "We're working with DARPA on space robotics, which will allow you to assemble these pieces in space, which seems like it'd be unavoidable."
But what if you launched a whole bunch of solar power satellites into space, then used lasers to transmit the power between each individual satellite to an in-orbit base station, which could then beam it to the Earth? The worry here is that power would have to be transmitted wirelessly twice, which could reduce efficiency. But, hey, it might work.
What about giant blimps in the stratosphere?
Why use satellites at all? Instead, it may be possible to launch giant aerostats, drones, or blimps into the stratosphere but below orbit. It'd probably be cheaper and would afford you at least some of the benefits of a space solar plant (you could beam power to remote areas, as long as the blimp could see it).
The big downside here is that, in the stratosphere, blimps would deal with this downside called "nighttime," where they couldn't generate any power at all.
"One idea proposed that overcomes the downfalls of night and overcomes the problem of clouds is sending the power from a satellite to a high-altitude platform above the clouds and then to the ground," Jaffe said. "The potential downside is, you might make it less efficient, and you still have to get it from the stratosphere to the ground."
Space junk and the environmental impact
On the periphery, there are some other concerns with space solar power. The odds of a piece of space debris hitting a normal-sized satellite isn't negligible, but it's much less likely than a piece of space junk hitting a target that's the size of several aircraft carriers. It's not a good look to spend many years and billions of dollars creating a solar power plant, only to have it destroyed by a decommissioned satellite hurtling through orbit.
We've already mentioned cloud cover, but there's also the concern of what blasting the atmosphere with constant microwaves might do.
"It seems green, but maybe there's something going on that will harm the atmosphere in ways that we can't imagine today," Rayermann said.
Monday's talk was given by three people who believe very much that space solar power is a viable option—and even they have major reservations. But that's not to say it won't happen. It just might not happen soon.
If someone (maybe Elon Musk) can figure out how to get to space cheaply, one major piece of the puzzle will be solved. In the meantime, maybe someone will figure out a better way to create power here on Earth, and we won't ever even need to worry about space solar power.
"I don't think we can know what it's going to look like today, this is going to take at least until the middle of the century to mature," Rayermann said. "It's not impossible that cheap fusion energy will be readily available when we figure out space-based solar. If we can do it here on Earth, maybe space is not as attractive."