Thread: Space based solar power

On SBSP/SSP/SPS, GEO stationary orbit will likely be best when we have a million megawatts of SBSP. In the meantime, solar synchronous semi polar orbit has numerous advantages. Even far Northern countries can receive the beam during, and a few hours before, the evening peak demand period. With rare exceptions they won’t pay more than 4 cents per kilowatt hour for electricity at other times of day as their own generators are adequate, and not practical to shut down for a few hours. Other advantages are international companies and/or governments can share the start up costs, ship propulsion and the SPS is considerably closer than GEO but still in continuous sunlight. GEO satellite owners will be unhappy about megawatts, being transmitted near by.
Economies of scale likely run out at less than 100 megawatts, making many SPS practical. This is because 100,000 volts dc at 100 amps = 10 megawatts. More volts or more amps creates rapidly rising costs in space, so logically we build many medium size SPS. The Sun delivers about 1300 watts per square meter, but following the numerous conversions, and losses perhaps only 130 watts per square meter is delivered to the grid. Thus one square kilometer of solar panel in space, puts 130,000,000 watts = 130,000 kilowatts = 130 megawatts on the grid. That may be a billion solar cells in series parallel. That many connections presents a reliability problem, especially for open cells which are likely to reach temperatures of thousands of degrees as the very high voltage arcs across the open circuit. Solutions, especially at one million volts, get very complicated, heavy and expensive.
Almost a million laser diodes connected in series to use the million volts DC produce similar potential arcing which will damage nearby diodes.
Laser diodes are superior as they can focus on to existing solar farms (or ships at sea) with dimensions as small as 60 meters by 100 meters = about 5000 square meters = one megawatt if the beam is 200 watts per square meter. Microwaves cannot produce that small a spot except from LEO = low earth orbit, which is shaded by Earth about 40 minutes out of each 100 minute orbit. Neil

SPS = solar power satellite. SBSP = Space based solar power. SSPS = ? An early satellite will have a 2000 square meter solar panel. Perhaps 20 million solar cells in series to produce 10 million volts at 1/10 amp = one million watts. The low current means low copper loss, even if we use #26 wire. For best results the panel must turn to face the sun. That should be comparatively easy. Thermal couples mounted on the back of the cells can provide auxiliary power for the satellite electronics and miscellaneous. The panel will be optimised for watts per kilogram, and long life in space rather than watts per square meter or efficiency, so the about 40% efficiency may be optimistic. The transmitting antenna needs to point at a single square kilometer on Earth's surface, so extreme precision is needed to keep the beam that narrow and centered on the rectenna on Earth's surface. Even using 10,000 megahertz (3 centimeter wavelength) The transmitting antenna is bigger than the solar panel. Likely much bigger from 36,000 kilometers away = GEO altitude. We should seriously consider solar synchronous semi polar orbits for the early satellites to reduce the altitude, make the energy available, occasionally to all the nations of Earth and permit a much smaller transmitting antenna, with less energy spilled outside the rectenna. A dozen such satellites can supply power to all the nations (who build a rectenna) every evening during the peak electricity demand period when electricity is worth up to 50 cents per kilowatt hour. Electricity is worth much less during most of the rest of the day and night. So far we have one megawatt at the solar cells. 990 kilowatts at the input to the 99 klystrons in series running off the almost ten million volts. Klystrons are good as they can be modulated with wide band data which may be far more valuable than the electricity. Most locations on earth and through out the inner solar system will be able to receive the data due to several kilowatts which is scattered from the beam by earth's atmosphere and imperfections in the transmitting antenna. I'm guessing the rectenna will produce 1/2 megawatt of low voltage direct current. perhaps 400 kilowatts that goes on the grid as high voltage 60 hertz 3 phase electricity or million volt HVDC = high voltage direct current. Is there any practical way to connect ten million dipole rectifiers in series so we can avoid another energy transformation which loses several more percent?
I suggest a flexible power line tethering the transmitter and antenna satellite to the giant solar panel, thus allowing both to aim independently. Concentrating mirrors can be added later to boost the beam power by perhaps ten times. The thermocouple units will then become active cooling devices to prevent heat damage to the solar cells. The ten million volts will no longer be optional when a 1000 amp solar panel is built in space = ten gigawatts at ten million volts. Most of the above is applicable if we use millions of laser diodes instead of klystrons or magnetron's. Neil

We need to pursue all promising alternative energy sources faster than seems prudent except nuclear which has extreme down side if we fast track. The main objection to thorium nuclear reactors is even massive funding would require more than a decade to get to the second gigawatt except at high risk. This is especially true as powerful people want thorium to fail.
If the properties of liquid nitrogen super conductors can be optimised, they are likely practical for long distant power lines. Near term, HVDC = high voltage direct current power lines are operational and superior to 60 hertz three phase power lines for up to about 1500 kilometers. We could build a town that uses dc instead of ac appliances, as avoiding the conversion back to ac may reduce losses if not improve cost effective. Can dc wind turbines be operated in series to produce a million volts dc? Likely, but it may be impractical for several reasons. Yes, electric vehicles can help stabilize a dc grid, but the concept is not well established for ac nor for very high voltage dc. The cost is unknown and vehicle owners who decide at the last minute to take a trip will be unhappy, if the grid just halved the range of their vehicle. This will upset most consumers even if it happens rarely.
For SBSP = space based solar power, I like sun synchronous orbit as the satellite can stay over the sunshine terminator, and thus be able to beam power approximately straight down to cities that are experiencing peak demand. (Ten degrees above the horizon, in all possible directions means the rectenna must have lots more area than for a beam coming from directly above) Early evening is when the power is worth up to 25 times the midnight price. Other advantages are the satellite is at lower than GEO orbit so the aiming is less critical and the transmitting array can be smaller and all the nations of Earth can be served at least rarely by a single solar synchronous satellite in a semi polar orbit. About 12 satellites are needed to power hundreds of rectennas every late afternoon and every early evening.
Lasers may be available soon as an alternative to micro waves. Existing solar sites can receive, up to several megawatts of laser energy, as small as 4000 square meters = a 64 meter square, while rectennas need to be much larger because microwaves illuminate a larger spot. A receiving site dedicated to the transmitted frequency/wave length will be about twice as efficient, but we can tolerate reduced efficiency for demonstration purposes. Neil

Originally Posted by neil

We need to pursue all promising alternative energy sources faster than seems prudent except nuclear which has extreme down side if we fast track. The main objection to thorium nuclear reactors is even massive funding would require more than a decade to get to the second gigawatt except at high risk. This is especially true as powerful people want thorium to fail.

That and the fact there's not enough thorium to go around here on Earth.

Still, there's enough sun hitting the surfaces of our deserts to make solar concentrating Stirling engines a reality, and more practical (economnically) than putting the collectors in space.