Solar power has been a key part of humanity's clean energy repertoire. We spread masses of sunlight-harvesting panels on solar fields, and many people power their homes by decorating their roofs with the rectangles.
But there's a caveat to this wonderful power source. Solar panels can't collect energy at night. To work at peak efficiency, they need as much sunlight as possible. So to maximize these sun catchers' performance, researchers are toying with a plan to send them to a place where the sun never sets: outer space.
Theoretically, if a bunch of solar panels were blasted into orbit, they'd soak up the sun even on the foggiest days and the darkest nights, storing an enormous amount of power. If that power were wirelessly beamed down to Earth, our planet could breathe in renewable clean energy, 24/7.
That would significantly reduce our carbon footprint.
Against the backdrop of a worsening climate crisis, the success of space-based solar power could be more important than ever. The state of the climate is in the spotlight right now as world leaders gather in Glasgow, Scotland, for the COP26 summit, which has been called.
CNET Science is highlighting a few futuristic strategies intended to aid countries in cutting back on human-generated carbon emissions. Next-generation tech like space-based solar power can't solve our climate problems -- we still need to rapidly decarbonize our energy systems -- but green innovation could help achieve the goals of the Paris Agreement: Limit global warming to well below 2 degrees Celsius (3.6 degrees Fahrenheit) by the end of the century.
An unlimited supply of renewable energy from the sun might help us do that.
From science fiction to fact
For decades, space solar power has lived in the minds of science fiction lovers and scientists alike.
In the early 1900s, Russian scientist-mathematician Konstantin Tsiolkovsky was steadily churning out a stream of futuristic designs envisioning human tech beyond Earth. He's responsible for conjuring things like space elevators, steerable rockets and, you guessed it, space solar power.
Since Bell Labs invented the first concrete "solar panel" in the '50s, international scientists have been working to make Tsiolkovsky's sci-fi fantasy a reality. They include Japanese researchers, the US military and a team from the California Institute of Technology spearheading the Space Solar Power Project.
Space solar power "was investigated extensively in the late 1960s and the 1970s, sort of in the heyday of the Apollo program," said Michael Kelzenberg, senior research scientist on the project.
Unfortunately, due to the materials' weight and bulk, the era's technology wasn't advanced enough to cost-effectively achieve the feat. It would've been exceptionally difficult to send classic solar panels to space via a rocket without breaking the bank.
"The distinctively unique and defining feature of the Caltech approach is a focus on reducing the component mass by 10 to 100 times," said Harry Atwater, the project's principal investigator. "This is essential to reducing both the manufacturing and the launch costs to make space solar power economical."
A sky full of solar panels
Instead of rocketing traditional solar panels to space, the Caltech team advocates a new type of panel that's lighter, more compact and foldable. They suggest dispatching into orbit a large number of these airy, mini solar panels resembling tiles.
Each individual tile has everything it needs, like photovoltaics, to harvest solar energy. When connected in space, the little squares essentially make a giant renewable energy mine floating around Earth.
Though the team has been looking at a range of composites to create the ideal ultralight structure, some are actually less effective when compared with Earth-based solar panels. But Kelzenberg notes that in space, "effectiveness" earns a new meaning.
"The increase in effectiveness really comes from the fact that by putting them in space, they get plenty of intense sunlight because the sunlight doesn't have to come through the atmosphere," he said. "They also get sunlight, basically, 24 hours a day."
When the sun shines on these panels, they'd absorb bundles of direct current, or DC, energy. In the team's mechanism, that energy would get translated into radio frequencies. The next step would be to bring that power down to Earth.
That would happen, according to the team, through microwave radiation. Radio frequency energy would be beamed toward our planet onto areas reminiscent of solar fields in the desert. But in place of what are typically solar panels, these regions would contain receivers with antennas that collect the harvested energy.
It's basically wireless energy transfer, something Nikola Tesla famously alluded to in the late 19th century.
Using such radiation, Kelzenberg says, allows the system to operate in rain and fog, at night and during gentle storms, only risking disruption by the most severe weather. However, one question often raised about wireless radiation patterns is whether they would adversely impact vegetation or features of the land.
Atwater says that isn't a concern.
"The power density received on Earth would be equivalent to the power density in sunlight on a sunny day," he explained. "And systems for space solar power can be designed to be intrinsically safe in this regard."
As an extra safety precaution, Kelzenberg says, familiar measures can be taken, like cordoning off the receiver zone. Cellphone towers, which use a similar form of wave communication, do the same.
After the Earth-planted receivers retrieved the energy in the form of radio frequencies, they'd work with a ground station to convert it back to DC energy, which would then be transformed into alternating current power, or AC power, fed into the utility grid, Atwater said.
It's a complex process, but that last bit, the AC power, is the regular old electricity that runs through your house's sockets to charge your iPhone and give life to your laptop. Voila.
Beam the Earth up, Scotty
"Our first space flight to demonstrate space solar power component technology is now scheduled for late 2022, on a commercial spacecraft," Atwater said.
Though the team won't be launching the real deal, they'll be conducting an experiment that'll demonstrate the feasibility of the technologies on a smaller scale. It'll be a makeshift, simpler form of the invention. They'll even be sending a number of solar cells that've never seen the vacuum of space before.
But one day, if space-based solar power becomes a reality, it could change the world.
Not only would it help power remote areas and balance out the power grid to prevent outages, it could also send energy to mining operations on other planets.
"Space solar power can be deployed to remote areas on Earth where there is not an existing utility grid; it could also be used to generate baseload power on the moon or Mars via a similar scheme of orbital power generation and beaming to the surface," Atwater explained.
Most importantly, the energy humans could generate via 24/7 sun power would be enough to meet the climbing demands of our planet and even replace nuclear or coal power. "It represents a source of 'baseload' power that is continuously available, unlike solar panels on Earth," said Atwater.
Added Kelzenberg, "That's why we think that it can play an important role in going to a fully carbon-neutral power grid in the future."
Of course, there's a long road ahead. Even if the team's 2022 experiment is successful, there are manufacturing costs to consider, as well as legal questions about taking up orbital space (there may be governmental restrictions). Questions around the practicality of replacing known power grids with space-solar power plants will also remain.
But at the end of that path, we may find something golden.
"I think certainly we can agree that getting a cheap solar panel and putting it on the ground is going to cost a lot less than launching one into space," Kelzenberg said. "But the real virtue of space solar power is the ability to deliver solar energy day and night."