It may seem like a lot of work to collect solar energy in space, but there could be considerable advantages to doing it. For one, the sun never sleeps in high orbit, so energy is generated continuously. Space-based panels also aren’t vulnerable to weather and seasonal changes as on the ground.
More to the point, building a platform may not be as difficult as you think. It’s certainly possible. In 2011, the International Academy of Astronautics looked at three designs that can collect energy, convert it to beam-able form, and transmit it to Earth. It concluded: “Solar Power Satellites appear to be technically feasible as soon as the coming 10 to 20 years using technologies existing now in the laboratory.”
Several groups are now pursuing the idea. Here are three projects we came across recently:
IEEE Spectrum reports on the work of the Japan Aerospace Exploration Agency. It’s long-term goal is to build a commercial one gigawatt system “weighing more than 10,000 metric tons and measuring several kilometers across.”
The Japanese have two designs, one that sits in stable position, another with two huge solar panels floating in formation. And the focus is on how on to transmit power wirelessly to Earth–the most difficult of all the challenges involved. Their proposed solution is to send microwaves using a “phase-adjusting” system. The rectifying antenna (a rectenna) sends a pilot signal from the ground. “As each individual antenna panel on the satellite received the pilot signal, it would calculate the necessary phases for its microwaves and adjust accordingly,” the IEEE piece explains.
JAXA hopes to do the “first microwave power transmission in space experiment” in 2018, with a 100 kilowatt demonstration in 2020. Its vision for the 2030s is massive rectenna receiving stations a few miles from major cities (say on a purpose-built island outside Tokyo).
“Arrays of rectennas would convert the microwave power to DC power with an efficiency greater than 80%. Then the DC power would be converted to AC and fed into the electrical grid.” the article says.
The U.S. Naval Research Laboratory is working on a satellite module folded like a sandwich. There are three layers: solar panels, electronics to convert the energy to a radio frequency, then, on the other side, an antenna to beam it back to Earth. The leader of the project, Paul Jaffe, a spacecraft engineer at the lab, envisions a one-kilometer array of modules followed by “auxiliary sun reflectors” that concentrate the light on to the panels (See the slideshow for pictures). He already has a small prototype which he’s tested in space-like conditions in his lab. The next step is space itself.
In 2009, Solaren became the first company in the world to agree a contract to supply solar from space. The deal was with PG&E, a California utility. It planned to set up a radio frequency receiving station in Fresno, and to start delivering power by 2016. But that doesn’t seem likely now. The founders have found it hard to the millions required for rocket launches and module development.
“While investors are usually impressed with and excited about the concept of space solar power, when we discuss it with them, many are still reluctant to make an investment,” admits Cal Boerman, vice president of sales and delivery.
“It turns out that raising capital is much harder than any of the technical designs we are working on,” he adds. “Not what we expected.”
PG&E is still waiting for its power. But other projects seem more promising.