Space photovoltaics closer to shining some light on earth

An array of small solar panels that are part of the Space Solar Power Project integrate photovoltaics, power transfer circuitry, and incorporate beam steering. (Image courtesy of Caltech).

A team of researchers at the California Institute of Technology is working to deploy a constellation of modular spacecraft that collect sunlight, transform it into electricity, then wirelessly transmit that electricity wherever it is needed—including to places that currently have no access to reliable power.

According to the scientists, harnessing solar power in space relies on breakthrough advances in three main areas:

The first key aspect involves the design of ultralight high-efficiency photovoltaics that are optimized for space conditions and compatible with an integrated modular power conversion and transmission system.

The second area refers to the development of the low-cost and lightweight technology needed to convert direct current power to radio frequency power and send it to earth as microwaves. Despite how it sounds, the process is safe as non-ionizing radiation at the surface is significantly less harmful than standing in the sun. In addition, the system could be quickly shut down in the event of damage or malfunction.

Finally, the third area involves inventing foldable, ultrathin, and ultralight space structures to support the photovoltaics as well as the components needed to convert, transmit, and steer radio frequency power to where it is needed.

The basic unit of the system the researchers envision is a 4-inch-by-4-inch tile that weighs less than a tenth of an ounce. Hundreds of thousands of these tiles would combine into a system of flying carpet-like satellites that, once unfurled, would create a sunlight-gathering surface that measures 3.5 square miles.

“This concept was, in the past, truly science fiction. What made it possible for us to consider taking it from the realm of science fiction to the realm of reality was the combination of developments happening in photovoltaics in Harry Atwater’s lab, in structures in Sergio Pellegrino’s lab, and in wireless power transfer, which is happening in my lab,” Ali Hajimiri, one of the researchers leading the project, said in a media statement.

“We realized that we can now pursue space solar power in a way that is becoming both practical and economical.”

Hajimiri noted that one of the first questions that anyone asks is, “Why do you want to put photovoltaics in space?” To what he replies that in space, where there is no day and night or clouds, it is possible to get about eight times more energy than on earth.

“The vision of this program is to be able to provide as much power as you need, where you need it, and when you need it,” he said.


In terms of progress toward making this project a reality, the researcher explained that over a period of two years, the group built and demonstrated a prototype tile. This is the key modular element that captures the sunlight and transmits the power.

Through that process, they learned how to design highly integrated and ultralight systems of this sort. They then developed a second prototype, 33% lighter than the first.

A series of tiles are to be mounted on a very flexible structure that can be folded to fit in a launch vehicle. Once deployed, the structure expands, and the tile works in concert and in synchronization to generate energy, convert it, and transfer it exactly where it is needed.

Speaking about the next steps, Hajimiri and his colleagues said that soon, the time to test things outside the lab will come.

“Most spacecraft today have solar arrays—photovoltaic cells bonded to a carrier structure—but not with this type of material and not folded to the dimensions we’ve achieved,” Pellegrino said. “By using novel folding techniques, inspired by origami, we are able to significantly reduce the dimensions of a giant spacecraft for launch. The packaging is so tight as to be essentially free of any voids.”