Orbital Power Plant Dummies' Guide

Professor John Mankins wants to harness solar energy directly from space in an effort to end our dependence on fossil fuels. The power of the sun will be harnessed by a kilometer-wide series of geostationary solar panels in space, beaming an inexhaustible amount of energy back to Earth by either microwave or laser.

Test 1: Investigate the Fresnel lens, a large, commercially available technology that can concentrate the power of the sun and melt glass.

Test 2: Design and launch a weather balloon carrying solar radiation meters, to a height of 90,000 feet.

Test 3: Test a pilot beam system using microwave-beaming technology.

Test 4: A shorter-range demonstration of of the final test in which low-power microwaves will be transmitted across an airfield.

Final Test

The team will beam power from one Hawaiian island to another over a distance of 100 miles. Low-power microwaves will be transmitted from one island, and collected on the other. These microwaves will not be harmful in any way to humans, or animal or plant life; and they do not interfere with radio or mobile phone communications.

Equipment will be set up close to the summit of peaks on each island, each of which is an extinct volcano with good road access (and with observatories near the top).

Experiment Assumptions

* The plan calls for huge arrays of solar panels to orbit the Earth, collecting pristine solar radiation, free from the day/night cycles, weather and atmospheric effects that limit solar radiation down on the ground. The energy collected will be "beamed" down to power stations on the surface, either by microwave (or an alternative system, by laser) — and then distributed as normal power across the grid.

* A 1 kilometer band of satellites orbiting the equator could provide energy equivalent to all known remaining hydrocarbon reserves in a single year.

* Microwaves should also be a very efficient way of getting power back to the surface.

* The team proposes a novel system for collecting solar energy using "Stretched Lens Arrays," which are light enough to put into space, and which focus the sun's rays onto tiny photovoltaic cells. The efficiency of the arrays jumps by approximately 15 percent at high altitudes, where there is less atmosphere to scatter the rays. The ultimate aim would be to put these arrays in space and hope for an even greater jump in efficiency.

* On the ground, the energy is collected by a "rectenna" (rectifying antenna) which converts the energy into DC current.

* Why go into space to collect solar energy? Because three things limit the potential of solar panels on the Earth's surface:

• 1. Weather — Clouds block sunlight very easily. One key benefit of beaming power from space via microwaves is that they are not affected by the weather in the same way.

• 2. Altitude — Weather blocks sunlight, but even on a clear day, the particles and gases in the atmosphere absorb solar radiation and stop it from getting through. This is a good thing in some ways (since the ozone filters out a lot of harmful UV radiation), but not if you want to collect solar energy. At 25 kilometers (the height at which the highest reconnaissance planes fly), the sun is 25 percent stronger.Go to 100 kilometers and you're outside the Earth's atmosphere. Here, the sun is up to 40 percent stronger.

• 3. Day/night — You can't collect solar energy when it's dark, which is, on average, about half the time. If you're on the equator, you lose 12 hours a day, every day; if you're at the poles, you effectively lose six months of light every winter. Either way, we lose half the sunlight that would otherwise have reached us.

* By putting a solar panel in space (preferably in a geostationary orbit, at 36,000 kilometers), we can avoid all these problems. We could collect 40-percent stronger sunlight, 24 hours a day, regardless of the weather or any other atmospheric effect.