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Space-Based Solar Power

17 Mar

Left of the above diagram: Part of the solar energy is lost on its way through the atmosphere by the effects of reflection and absorption.

Right of the above diagram: Space-based solar power systems convert sunlight to microwaves outside the atmosphere, avoiding these losses, and the downtime due to the Earth’s rotation.

Space-based solar power (SBSP) is the concept of collecting Solar Power in Space for use on Earth. It has been in research since the early 1970s.

SBSP would differ from current solar collection methods in that the means used to collect energy would reside on an Orbiting satellite instead of on Earth’s surface. Some projected benefits of such a system are:

  • Higher collection rate: In space, transmission of solar energy is unaffected by the filtering effects of atmospheric gases. Consequently, collection in orbit is approximately 144% of the maximum attainable on Earth’s surface.
  • Longer collection period: Orbiting satellites can be exposed to a consistently high degree of solar radiation, generally for 24 hours per day, whereas surface panels can collect for 12 hours per day at most.
  • Elimination of weather concerns, since the collecting satellite would reside well outside of any atmospheric gasses, cloud cover, wind, and other weather events.
  • Elimination of  plant and wildlife interference.
  • Redirect-able power transmission: A collecting satellite could possibly direct power on demand to different surface locations based on geographical base load or peak load power needs.

SBSP also introduces several new hurdles, primarily the problem of transmitting energy from orbit to Earth’s surface for use. Since wires extending from Earth`s surface to an orbiting Satellite are neither practical nor feasible with current technology, SBSP designs generally include the use of some manner of wireless power transmission. The collecting satellite would convert solar energy into electrical energy on-board, powering a microwave transmitter or laser emitter, and focus its beam toward a collector (rectenna) on the Earth’s surface. Radiation and micro meteoroid damage could also become concerns for SBSP.

A laser pilot beam guide the microwave power transmission to a rectenna.

Advantages

The SBSP concept is attractive because space has several major advantages over the Earth’s surface for the collection of solar power.

  • There is no air in space, so the collecting surfaces could receive much more intense sunlight, unobstructed by weather.
  • A satellite could be illuminated over 99% of the time, and be in Earth’s shadow on only 75 minutes per night at the spring and fall equinoxes.
  • Relatively quick redirecting of power directly to areas that need it most.
  • Higher collection rate: In space, transmission of solar energy is unaffected by the filtering effects of atmospheric gasses. Consequently, collection in orbit is approximately 144% of the maximum attainable on Earth’s surface.
  • Longer collection period: Orbiting satellites can be exposed to a consistently high degree of solar radiation, generally for 24 hours per day, whereas surface panels can collect for 12 hours per day at most.
  • Elimination of weather concerns, since the collecting satellite would reside well outside of any atmospheric gasses, cloud cover, wind, and other weather events.
  • Elimination of plant and wildlife interference.
  • Redirectable power transmission: A collecting satellite could possibly direct power on demand to different surface locations based on geographical base load or peak load power needs.

Disadvantages

The SBSP concept also has a number of problems.

  • The space environment is hostile; panels suffer about 10 times the degradation they would on Earth. System lifetimes on the order of a decade would be expected, which makes it difficult to produce enough power to be economical.
  • Space debris are a major hazard to large objects in space, and SBSP systems have been singled out as a particularly hazardous activity.
  • The broadcast frequency of the microwave downlink (if used) would require isolating the SBSP systems away from other satellites. GEO space is already well used and it is considered unlikely the ITU would allow an SPS to be launched.
  • Only about half the power generated by the SSP would be delivered to the grid, once all losses are factored in. These losses are on the same order as modern fossil fuel plants.

Space-based solar power essentially consists of three elements:

  • a means of collecting solar power in space, for example via solar cells or a heat engine
  • a means of transmitting power to earth, for example via microwave or laser
  • a means of receiving power on earth, for example via a microwave antenna (rectenna)

The space-based portion will not need to support itself against gravity (other than relatively weak tidal stresses). It needs no protection from terrestrial wind or weather, but will have to cope with space hazards such as micrometers and solar flares.

Two basic methods of conversion have been studied: photovoltaic (PV) and solar dynamic (SD). Photovoltaic conversion uses semiconductor cells to directly convert photons into electrical power. Solar dynamic uses mirrors to concentrate light on a boiler. The use of solar dynamic could reduce mass par watt. Most analyses of SBSP have focused on photovoltaic conversion (commonly known as “solar cells”).

Wireless power transmission was proposed early on as a means to transfer energy from collection to the Earth’s surface, using either microwave or laser radiation at a variety of frequencies.

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Posted by on March 17, 2012 in RENEWABLE ENERGY

 

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