US military starts testing solar cells in orbit that beam electricity back to Earth

Recently I reported on how China and the US have both been dusting off some rather old concepts and are now planning to build solar power plants in space that beam Gigawatts worth of electricity back down to Earth as early as 2025.

Now, as a next step engineers at the US Naval Research Laboratory have announced they’ve launched PRAM, short for Photovoltaic Radio-frequency Antenna Module, aboard an Air Force X-37B Orbital Test Vehicle as part of a comprehensive investigation into “the prospective terrestrial use of solar energy captured in space.” In other words they’re now doing a small scale test of the concept to see how feasible it is to beam energy generated in space back to Earth, and the trial is a major milestone.

Credit: U.S. Naval Research Laboratory

“To our knowledge this experiment is the first test of in orbit hardware, designed specifically for solar powered satellites, which could play a revolutionary role in our energy future,” said Paul Jaffe, PRAM principal investigator.

The 12-inch square tile module will test the ability to harvest power from its solar panel and transform the energy to a radio frequency microwave that will then be used to beam the electricity back to a base station back on Earth.

“PRAM converts sunlight for microwave energy transmission. We could’ve also transmitted the energy using laser energy transmission,” said Chris Depuma, PRAM program manager. “Converting to [optical] might make more sense for lunar applications because there’s no atmosphere on the Moon. The disadvantage of optical is you could lose a lot of energy through clouds and atmosphere."

The use of solar energy to operate satellites began at the start of the space age with another NRL spacecraft: Vanguard I, the first satellite to have solar cells. This current experiment focuses on the energy conversion process and resulting thermal performance. The hardware will provide researchers with temperature data, along with PRAM’s efficiency in energy production. This information will drive the design of future space solar prototypes.

Depending on the results, the team aims ultimately to build a fully-functional system on a dedicated spacecraft to test the transmission of energy back to Earth. The development of a space solar capability could potentially help provide energy to remote installations like forward operating bases and disaster response areas.

This flight experiment enables researchers to test the hardware in actual space conditions. Incoming sunlight travels through the Earth’s atmosphere, both filtering the spectrum and reducing its brightness. A space solar system traveling above the atmosphere would catch more energy from each of the sunlight’s colour bands.

“There’s more blue in the spectrum in space, allowing you to add another layer to solar cells to take advantage of that,” Jaffe said. “This is one reason why the power per unit area of a solar panel in space is greater than on the ground.”

Over time, as the technology improves and then eventually gets deployed, it could end up playing a significant role in the world’s future energy mix as countries all around the world try to wean themselves off of fossil fuels and help turn back the clock on climate change.