Luckily for the Earth, the world's supply of fossil fuels is limited. And for the past several decades, researchers have been looking for renewable energy resources to provide power to everyone without poisoning the Earth with atmospheric carbon dioxide from the burning of fossil fuels like oil and coal.
Some scientists think humans could get clean power collected from solar panels in space and beamed back down to Earth in our lifetime. Not only would the energy source be continuous, it would also be clean and unlimited. The only thing standing in the way is the astronomical cost.
But that's finally changing, and space-based solar power entrepreneurs are starting to see interest from private investors and potential customers.
Earth solar power versus space-based solar power
Roof solar panels on buildings convert sunlight into energy during the daytime. Which is great, but Earth-based solar panels have big drawbacks. They don't work at night or if the sky is too cloudy. Plus, our atmosphere shields the Earth's surface from much of the sun's energy - bouncing some of the light back into space.
Now imagine if we could put a solar panel in Earth orbit - around 22,000 miles up.
"If you put the solar panel in space, it's going to be illuminated 24 hours a day, seven days a week, 99% of the year," Paul Jaffe, a spacecraft engineer at the U.S. Naval Research Laboratory, said.
At 22,000 miles above the Earth, the sun is much brighter, so space-based solar panels could collect way more solar energy. They'd deliver up to 40 times the annual amount of reliable 24/7 energy that the same cell would generate on the Earth.
Scientists are calling the technology "stellar energy," because it would return so much more power than regular Earth-based solar energy.
Jaffe predicts that individual space-based solar arrays would be able to produce from 250 megawatts to 5 gigawatts of energy. But since the sun is a continuous, renewable resource the "total amount of power that could be produced is effectively infinite," he says.
Abd 250 megawatts is a ton of energy New York City, for example, which requires 20 gigawatts of power. By Jaffe's calculation, as few as four arrays [see picture below] - if each provided 5 gigawatts - would be able to power the entire city.
The cost of 'stellar energy'
The energy crises of the 1970s propelled the government to look into alternative energy sources as it started to become clear that oil was a limited resource and that its supply could be subject to the whims of international politics.
According to Jaffe, the conclusion at the time by NASA and the Department of Energy regarding space-based solar power technology was that it could be possible, but it would be very, very expensive - likely hundreds of millions of dollars. That's the reason the technology is stalled.
The reason it's so expensive is that it costs about $4,600 for each kilogram launched into low orbit. Stellar power can't compete with other kinds of renewable energy unless that cost drops to around $400 per kilogram, Discover Magazine reports.
Billionaire Elon Musk and his rocket company SpaceX are doing just that. Musk is working on a reusable rocket that would dramatically reduce the cost of launches - cut it about 100 fold. Instead of building an expensive rocket for every single launch and then throwing it away, you could use the same rocket over and over again.
Cheap rocket launches would bring down the overall cost of getting a solar panel into space. But that won't be enough if we don't figure out an efficient way to beam the solar energy back to Earth.
How space solar panels would work
While the technology needs some improvement, the basic idea is pretty clear: The sun sends out photons, energetic packets of light, in every direction. A regular solar panel converts those photons into electrons of direct current electricity. Then, in order to power an electronic device plugged into a wall outlet, the direct current is transformed into an alternating current and sent through the power grid.
In space, the big issue is how we would get that power to the grid.
With the solar farm in space, researchers needed to figure out the most efficient way to transfer the energy from the solar reflectors back to Earth. The answer: electromagnetic waves, like those used to transmit radio frequencies or heat up your food in the microwave.
"People might not associate radio waves with carrying energy because they think of them for communications, like radio, TV, or cellphones. They don't think about them as carrying usable amounts of power," Jaffe said in a statement.
Though we do know that microwaves (another subset of electromagnetic waves) carry power - their energy heats up our food!
Jaffe calls the technology he is working on the "sandwich" module. The image below shows mirror-like solar reflectors concentrating the sun's photons onto the array of sandwich modules. The top of the sandwich module array receives the solar energy. Antennas on the bottom side beam the radio waves to Earth.
Back on Earth, the energy-containing radio frequencies from the space-based solar panels would be received by a special antenna known as a "rectenna," which could be as big as six miles in diameter.
"It would look like a field full of wires sticking up. The rectenna elements receive incoming radio waves and convert it back from that high frequency radio wave into electricity," Jaffe said.
The power beam of radio waves could be sent to a wide variety of locations on Earth, because the direction of the beam can be changed by a method called "retrodirective beam steering." According to Jaffe, "This works by sending up a small 'pilot signal' from the center of the ground receiving station. The satellite sees this signal and adjusts its transmitter to send the radio waves to the ground station." For example, the same beam would be able to provide power to Seattle and redirected to provide power to Rio de Janeiro in Brazil.
An advantage for the military, as well as civilians, would be that they could build receivers at remote operating bases and locations where it is logistically difficult and incredible costly to deliver diesel fuel.
A giant beam of energy from space
A giant beam of radio waves coming down from space to Earth may sound a little scary and dangerous, like something an alien ship would use to explode our precious planet. But really, you wouldn't even be able to see the radio beam with the naked eye - radio signals are flowing around us at all times.
Though these radio signals contain more energy than an AM or FM signal you'd pick up in your car radio, the power density of the signal would still be quite low and wouldn't threaten people, airplanes, or birds that would fly through it. Of course, the technology hasn't actually been tested outside of the laboratory yet, so there's no real-world proof the installation would be problem-free.
The biggest impediment so far to space-based solar power isn't safety or regulation or design: It's cost. And this problem affects all parties involved, whether government-, private-, or commercial-funded research.
It's hard to say what exactly the full-scale implementation of a space-based solar power system would cost, but it would likely be hundreds of millions of dollars. There is a limit to how big of an object can be launched into space, and strapping the components to rockets doesn't come cheaply. For example, the International Space Station had to be built in space part by part because there wasn't a rocket big enough or strong enough to launch the completed apparatus into space.
Jaffe's research was funded by the Office of Naval Research, and he had funding to produce prototypes of one section: the sandwich module, but not to see the project to completion. He also tested the modules in space-like conditions to ensure they could withstand (and continue to work in) the incredible heat of the sun in space, which hadn't been done before. "The work that we did demonstrates the state of the art and suggests the path forward," said Jaffe.
He is trying to find sponsors to secure funding for continuation of his project. But he stressed that it is hard to sell long-term energy projects, especially when he can't show people the technology in action, aside from prototypes.
He thinks the real motivator will be foreign competition, like in the 1950s when the Russians developed Sputnik and launched the U.S. into the space race. This time it's likely that the Japanese government may launch the technology first.
The way forward
But even without government funding, small startups like California-based Solaren are looking to make space-based solar power a reality in the next few years. Gary Spirnak, CEO of Solaren, had a long career in space engineering for both the government and private industry. He had watched for years as government funding for space-based solar power waxed and waned and private industry seemed to take little interest.
Spirnak told us that he saw a "system problem" he thought he could engineer his way out of by building lighter versions of the prototypes already being tested. And, in 2009, he convinced Pacific Gas & Electric that his design (which is different from Jaffe's explained above but based on similar concepts) for space-based solar power was viable, and they awarded him the "first power purchase agreement in the world for space solar power," meaning that the electricity company would buy the solar energy that he was collecting from space and deliver it to some of their California customers.
The original terms of the contract were to provide energy from space starting in 2016. The start date has now been pushed back because of funding issues.
Other companies have found an alternative way to get investors interested: creating satellites that can collect solar energy and beam TV, radio and telephone signals. The space energy plant would double as a giant communication satellite. This set up might get big investors like DirecTV or Verizon on board.
Then we'd finally see this unlimited energy technology take off.
Katie Jennings contributed to an previous version of this story.