In the previous post I mentioned space-based solar power (if you prefer SBSP) as the future of photovoltaic. Does it seem too fictional? DOE (Department of Energy) thinks it's not. The first time space-based solar power was mentioned was in a novel of Isaac Asimov. Now it has become a possible alternative for the future.

Let's hear what DOE has to say: every hour, more solar energy reaches the Earth than humans use in an entire year and 30% of energy is reflected back into space. Solar panels collect a high intensity uninterrupted solar radiation, thanks to huge mirrors they reflect it to the satellite that transform it into energy and then send it to the Earth as either a microwave or a laser beam.

Obviously in space there aren't cloud and day and night, so space solar panels are able to capture and transmit substantially more solar energy than solar panels on Earth.

SBSP presents more options: the two most commonly discussed designs for SBSP are a large, deeper space microwave transmitting satellite and a smaller, nearer laser transmitting satellite.

Microwave transmitting satellites

Microwave transmitting satellites orbit Earth in geostationary orbit (GEO), about 35,000 km above Earth’s surface. Designs for microwave transmitting satellites are massive, with solar reflectors spanning up to 3 km and weighing over 80,000 metric tons.

The long wavelength of the microwave requires a long antenna, and allows power to be beamed through the Earth’s atmosphere, rain or shine, at safe, low intensity levels hardly stronger than the midday sun.

The estimated cost of launching, assembling and operating a microwave-equipped GEO satellite is in the tens of billions of dollars. High price but it worth it. On Earth, the rectenna used for collecting the microwave beam would be anywhere between 3 and 10 km in diameter, a huge area of land, and a challenge to purchase and develop.

Laser Transmitting Satellites

Laser transmitting satellites orbit in low Earth orbit (LEO) at about 400 km above the Earth’s surface. This satellite, with its 10 metric tons, is just a fraction of microwave one and is cheaper too; a laser-equipped SBSP satellite would cost nearly $500 million to launch and operate. It would be possible to launch the entire self-assembling satellite in a single rocket, drastically reducing the cost and time to production.

At its smaller size, there is a correspondingly lower capacity of about 1 to 10 megawatts per satellite. Therefore, this satellite would be best as part of a fleet of similar satellites, used together.

A huge cost, a huge work and it seems an impossible and useless project, someone would say. It's true: a lot of money and work but fifty years ago who would have thought that today 20% of global energy comes from the Sun, the wind and the water? If we continue to repeat that something it's impossible we'll never reach our targets so we have to believe and to support these ideas that can become real facts that will improve our world.

For more information go to Energy.gov

Photo from NASA.