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Space-based solar power: How close to reality?

Artist’s concept of the transmission of space-based solar power. Image via JAXA.

The idea of capturing solar energy in space where the sun never stops shining and beaming it to Earth may seem far-fetched, but such technology is further along than most realize. In early 2018, scientists from the California Institute of Technology announced that they had succeeded in creating a prototype capable of harnessing and transmitting solar energy from space.

Their prototype is a lightweight tile that consists of three main components. Optical reflectors concentrate the sunlight, photovoltaic cells convert the sunlight to electricity, and an integrated circuit converts the electricity to radiofrequency energy that is transmitted through an attached antenna. Many individual tiles could be strung together to form large solar arrays in space. A ground-based microwave receiver on Earth would be used to intercept the incoming radiofrequency energy and convert it back into useable electricity.

Prototype for collecting space-based solar power. Image courtesy of Caltech.

The scientists demonstrated that their prototype works by subjecting it to space-like conditions in the laboratory and using it to power a light-emitting diode (LED) located about 20 inches (50 centimeters) away from the tile. You can view the prototype in action at the 2:26 mark in the video at the link here.

If you want to really geek out, you can access all of the exciting details about this new technology in their paper here. This paper was published in the proceedings of the American Institute of Aeronautics and Astronautics (AIAA) conference that took place January 8–12, 2018, in Kissimmee, Florida, and it was co-authored by 15 different scientists. Lead author Eleftherios Gdoutos is a research scientist at the California Institute of Technology (Caltech).

A key feature of the new tile design is that it is really lightweight — at 1.5 kilograms (3.3 lb) per square meter, it weighs a little more than a large pizza. Lightweight features are essential for keeping the launch and construction costs down. Moreover, the new tile design in which each unit is capable of generating and transmitting solar power individually is advantageous because this negates the need for a heavy power distribution system in space. Such a design also makes it easier to expand on missions and to make repairs without losing much functionality. In the future, the scientists plan on seeing if further weight reductions can be achieved by the incorporation of new lightweight materials.

Research on space-based solar power has been ongoing at Caltech, where professors Harry Atwater, Ali Hajimiri, and Sergio Pellegrino have received funding from the Northrop Grumman Corporation to study the potential of this source of clean energy.

Caltech scientists Sergio Pellegrino, Harry Atwater, and Ali Hajimiri. Image via Caltech.

Professor Atwater explained the reasoning behind this technology in an in-depth interview that was published in ENGenius in 2015. An excerpt of that article follows:

Solar arrays, no matter how efficient, only generate power when the [sun] is illuminating them. So if solar power is going to be the principal so-called “dispatchable” baseload source of power that replaces today’s fossil-fuel-powered electric-generating stations, inherently you have to have the generating source be available all the time. This is not possible for ground-based solar energy without some complementary form of electrical energy storage, which adds significantly to the cost of solar electricity generated on Earth. The great thing about space is that [orbits exist where] there’s no nighttime. And so we have the prospect of making dispatchable power, power that flows continuously and that can be instantly sent to where it is needed. The potential benefits are enormous. About a quarter of humanity has no electric power whatsoever. And so this is an enabling technology that could leapfrog the electric-power transmission grid on Earth, and have the same effect that the cellular phone system had on communications.

Besides technological know-how, there are still other barriers that must be overcome before space-based solar power becomes feasible. Interestingly, a good article published in The Smithsonian back in 2016 tackles the main barriers to space-based solar power – costs, safety, land for ground-based receivers – in such a way that leaves one thinking these barriers may not be that big of a deal. According to the article in The Smithsonian, one of the biggest barriers may be the amount of congestion encountered when transmitting radiofrequency waves, as these frequencies are the same ones we use for our radios, televisions and cellphones.

Other countries besides the U.S., including China, Europe, India and Japan, are working on this technology too. Presently, many designs for space-based solar power have been proposed.

The concept of space-based solar power is not new. In fact, this technology was mentioned way back in 1941 in the science fiction story “Reason” written by Isaac Asimov. Today, the technology for turning such science fiction into reality is developing rapidly and warrants additional attention.

Bottom line: Scientists from Caltech have developed a lightweight, functional prototype that could form the basis for future solar energy harvesting from space.

July 29, 2018

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