Could we use solar panels in space?
If solar panels were put in space, how could the energy produced be sent back to earth?
John C. Mankins - In space near Earth, sunlight has roughly 30% more energy than the sunlight we see, because of weather and haze in the atmosphere. When one adds the impact of the day/night cycle and the natural changes between summer and winter, in some locations, the difference between Earth-based and space-based solar power grows to a factor of 20 or more.
It is possible that in the future, space solar power could deliver hundreds of thousands of megawatts - enough to power tens of millions of homes around the world.
First, just as on earth, sunlight in space will be converted into electricity by solar rays, that in turn power used electronic devices that produce radio waves in what is known as the "microwave" region - a wavelength of about one to ten centimeters.
This microwave energy is then transmitted from many thousands of small antennas, very much like thousands of musicians all playing the same note on their instruments. By orchestrating the individual transmitters - like an orchestra conductor with his baton guiding many musicians a coherent beam can be formed, and the converted solar energy directed to a desired location on Earth.
Radio waves of this size have virtually no interaction with our atmosphere, and very little with our weather; in other words, the atmosphere is almost invisible to them. As a result, more than 90 percent of the radio wave energy from space will reach Earth in a low intensity, but precisely pointed transmission.
Once there, the microwave energy is converted back into electricity by a large but simple receiver known as a rectifying antenna, or "rectenna" which will look a lot like mesh fencing, just like one of the goals in International football, but laid out flat, like a semi-transparent ceiling.
And that's it - that's how solar energy collected in space can be transmitted efficiently and safely back to Earth for our benefit.