Solar Power From Space
The Washington Post had an intriguing article on Sunday, titled An Energy Fix Written in the Stars:
Solar energy is a favorite of environmentalists, but it works only when the sun is shining. But that’s the trick. There is a place where the sun never sets, and a way to use solar energy for power generation 24 hours a day, 365 days a year: Put the solar cells in space, in high orbits where they’d be in sunshine all the time.
You do it with the solar power satellite (SPS), a concept invented by Peter Glaser in 1968. The idea is simple: You build large assemblages of solar cells in space, where they convert sunlight into electricity and beam it to receiving stations on the ground.
The solar power satellite is the ultimate clean energy source. It doesn’t burn an ounce of fuel. And a single SPS could deliver five to 10 gigawatts of energy to the ground continually. Consider that the total electrical-generation capacity of the entire state of California is 4.4 gigawatts.
Conservative estimates have shown that an SPS could deliver electricity at a cost to the consumer of eight to 10 cents per kilowatt hour. That’s about the same as costs associated with conventional power generation stations. And operating costs would drop as more orbital platforms are constructed and the price of components, such as solar voltaic cells, is reduced. Solar power satellites could lower the average taxpayer’s electric bills while providing vastly more electricity.
They would be big — a mile or more across. Building them in space would be a challenge, but not an insurmountable one: We already know how to construct the International Space Station, which is about the size of a football field. And the SPS doesn’t require any new inventions. We have the technology at hand.
The SPS was granted a pantent in 1973, according to Wikipedia:
In 1973 Peter Glaser was granted U.S. patent number 3,781,647 for his method of transmitting power over long distances (eg, from an SPS to the Earth’s surface) using microwaves from a very large (up to one square kilometer) antenna on the satellite to a much larger one on the ground, now known as a rectenna.
A rectenna is a rectifying antenna, a special type of antenna that is used to directly convert microwave energy into DC electricity. Its elements are usually arranged in a multi element phased array with a mesh pattern reflector element to make it directional.
A simple rectenna can be constructed from a Schottky diode placed between antenna dipoles. The diode rectifies the current induced in the antenna by the microwaves. Schottky diodes are used because they have the lowest voltage drop and highest speed and therefore waste the least amount of power due to conduction and switching.
Rectennas are highly efficient at converting microwave energy to electricity. In laboratory environments, efficiencies above 90% have been observed with regularity. Some experimentation has been done with inverse rectennas, converting electricity into microwave energy, but efficiencies are much lower—only in the area of 1%.
Here’s a good article from last July’s Scientific American on SPS in Japan, which also cites the Japanese animated series "Mobile Suit Gundam," which has humanity turning to space-based solar power in the year 2307:
Want to learn more? Check out the Citizens for Space Based Power blog.
