Space-based solar power

Space solar power (SSP) is the conversion of solar energy into power, usable either in space or on earth, at a location outside of the near earth's atmosphere and gravitational field. Using space-based systems to collect the sun's energy and turn it into usable power generally may include locations such as man-made satellites or space probes, the moon or other planets. Photovoltaics (PV) is generally utilized for energy conversion and microwave technology for transmission through space. In space, sun shines constantly and has greater intensity than on earth. Problems with weight and atmospheric corrosion are eliminated. On earth, diurnal rotation and the associated change from day to night necessitates collection only during daylight hours. Generally, ten times as much average energy per unit area is available in near earth space than on earth. Considering both atmospheric and diurnal effects, the energy available to an earth based solar power system would produce only a third as much energy for the associated capital investment.

Future space solar power has the potential to solve global socioeconomic and environmental problems associated with reliance on finite fossil fuels and nuclear energy. It promises to use space outside of the earth's ecology system and has essentially no by-product waste, once established.

Solar power applies many methods of harnessing energy from the light of the Sun. Nearly 100% of the Sun's energy is radiated into space in directions other than that of earth's cross sectional area. The Sun is the Earth's ideal nuclear energy (fusion) generator. It utilizes a type of stellar nucleosynthesis particular to its spectral type (type G stars have the sun's characteristic yellow color and include stars such as Capella and Alpha Centauri A).

History

1865: James Clerk Maxwell publishes his paper A Dynamical Theory of the Electromagnetic Field, in which Maxwell's equations demonstrated that electric and magnetic forces are two complementary aspects of electromagnetism. He showed the associated complimentary electric and magnetic fields of electromagnetism travel through space, in the form of waves, at a constant velocity of 3.0 × 10⁸ m/s. He also proposed that light was a form of electromagnetic radiation and that waves of oscillating electric and magnetic fields travel through empty space at a speed that could be predicted from simple electrical experiments. Using available data, he obtained a velocity of 310,740,000 m/s and stated "This velocity is so nearly that of light, that it seems we have strong reason to conclude that light itself (including radiant heat, and other radiations if any) is an electromagnetic disturbance in the form of waves propagated through the electromagnetic field according to electromagnetic laws." Also see his "A Treatise on Electricity and Magnetism, 1873."

1881: Nikola Tesla conceived of wireless power transmission and stated "Throughout space there is energy. If kinetic, it is a mere question of time when men will succeed in attaching their machinery to the very wheelwork of nature."

1968: Dr. Peter Glaser introduced the concept of a large "solar power satellite" in geostationary Earth orbit (GEO) for collection of sunlight, and generation of an electromagnetic beam to transmit usable energy to the Earth.

1999: Axel Roth of NASA stated that "Ultimately, we'd like to put a power generation station into space... The power station would harness the Sun's energy for use on Earth and by spacecraft traveling through the solar system."^[1]

2001: Dr. Neville Marzwell of NASA stated "We now have the technology to convert the sun's energy at the rate of 42 to 56 percent... We have made tremendous progress. ...If you can concentrate the sun's rays through the use of large mirrors or lenses you get more for your money because most of the cost is in the PV arrays... There is a risk element but you can reduce it... You can put these small receivers in the desert or in the mountains away from populated areas. ...We believe that in 15 to 25 years we can lower that cost to 7 to 10 cents per kilowatt hour. ...We offer an advantage. You don't need cables, pipes, gas or copper wires. We can send it to you like a cell phone call -- where you want it and when you want it, in real time." ^[2]

Solar Power Satellites (SPS)

Solar Power Satellites would be vast assemblies of large solar modules for producing large scale space solar power. Energy generated from sunlight could be converted into microwaves and beamed to a rectifier-antenna, called a rectenna on earth, where the microwave power is rectified and converted to electric power.

A 1996 estimate^[3] for the production of 5 billion watts (equivalent to five large nuclear power plants) would require several square km of solar collectors (weighing approximately 5 million kg) and an earth-based antenna 5 miles in diameter.

Terrestrial Solar Energy

An average of approximately 0.1 and 0.2 kW/m2 of solar energy can be received from the Sun on the Earth's surface. Solar energy striking the earth's surface consists of 2 components^[4], direct and diffuse (diffuse light may be further subdivided into several other categories). Due to influences of the atmosphere (reflection, absorption and scattering), including man made gases and particulates only 10% to 13% of the total incident energy approaching the earth's cross sectional area from the sun is available on earth.

Extraterrestrial Solar Energy

Extraterrestrial solar power is that collected outside of the earth's atmosphere. In near Earth space the average quantity of energy that can be collected is approximately ten times as much, that is, around 1 to 2 kW/m². (Earth's orbit causes varying extraterrestrial S flux between approximately 1329 and 1421 W/m². 1370 W/m² is the solar constant, i.e., mean flux perpendicular with the solar beam in outer space, at the mean distance from the Earth to the Sun.^[5]) Unaffected by atmospheric gases, particulate matter and cloud cover, photovoltaic arrays in a geostationary Earth orbit (at an altitude of 22,300 miles) would receive, on average, eight times as much sunlight as they would on Earth's surface. ^[6] In addition, they would be unaffected by the Earth's day-night cycle.

Extraterrestrial Intelligence

In the search for extraterrestrial intelligence, some speculations state that the harnessing of a significant portion of this type of "lost" energy from a star might be a detectable indicator of a quantum leap in the energy available to a stable, high energy consuming, advanced civilization. It is very difficult to identify planets outside of the solar system which are capable of sustaining intelligent life, but identifying a star with light modified by a civilization's large scale application of space solar power might be feasible.