A single kilometer-wide band of geosynchronous Earth orbit experiences enough solar flux in one year to nearly equal the amount of energy contained within all known recoverable conventional oil reserves on Earth today. - U.S. Pentagon's National Security Space Office, 2007
Most people think solar energy is best collected on the Earth. Actually, it makes more sense to collect sun power in Earth orbit and then beam the energy home via microwaves.
Orbiting comsats, even manned spacecraft, have used solar power since the 1960s. However, if you're going beyond the orbit of Mars, it makes much more sense to use nuclear power sources, but we'll corral our discussion to collecting the vast amount of sunlight falling on near Earth space with orbiting solarsats.
The idea of solarsats has been around since the 1950s, but with the price of oil rising steadily and fears of peaceful nuclear power generation here on terra firms, the 21st century may become the century of solarsats.
According to Jeff Keuter, president of the George C. Marshall Institute, space-based solar power developing a string of solar satellites around the Earth is technically feasible today, "It will require a great deal of money," he said, "but it is certainly possible."
An average of 341 watts of solar energy falls on every square meter of Earth. This includes both Earth's night side and north and south poles. Unfortunately, our atmosphere blocks a lot of the Sun's energy which is where solarsats come in to save the day. Free of Earth's blanket of air, an orbiting fleet of solarsats could collect up to 5 kilowatts of energy per square meter.
A recent U.S. government study suggests that a large solarsat, providing enough energy to light several large cities the size of Burlington, would cost $10 billion. The price tag excludes ground-based infrastructure to collect the solarsat's beamed microwaves and distribute the electricity, etc.