Solar Power Satellite (SPS)
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Solar Power Satellite (SPS)

All current efforts of collecting solar energy take place on earth. There are other options however...

The human population keeps increasing, the demand for energy does the same. But the fossil fuel supplies are declining. No wonder a lot of research is being performed on alternative energy sources. One of the largest energy sources in our vicinity is incredibly large and will be staying around for a couple billion years. The sun. Many efforts are being done on converting solar radiation to usable energy. Most of these efforts take place on the earth’s surface. But what if we can capture solar energy in space, without interference of the atmosphere? That is where the idea of a solar power satellite (SPS) comes from.

A What?

A solar power satellite is basically a regular satellite, but one with solar panels on it. These satellites should be in geostationary orbit, so that the antenna geometry can remain constant and a nearly continuous power supply is available. Some have proposed a low earth orbit, as a means to make it less costly, but it would also mean frequent changes in antenna geometry, an increased change of being hit by debris and more power stations to receive power continuously. In both cases, the power should be transmitted to earth wirelessly through microwaves.

These satellites will also have to be quite large. The collector area (panels and mirrors) will have to be several tens of square kilometers, the antenna for sending the power to earth will have to be about one kilometer in diameter and the rectenna (or ground antenna) probably ten kilometes in diameter. However, this is based on current technology. As the efficiency of the technologies involved increases, these numbers can greatly decrease (for example, with state-of-the-art solar panels, the collector area could be reduced by nearly two-thirds).


Obvious difficulties are the cost and construction. But there are also those who state that the transmission of the gathered power through microwaves can be quite dangerous. They question the safety of these microwave transmissions, as concentrated microwaves can have harmful effects, such as a carcinogenic influence and burning of deeper, moisture-rich tissues.

The microwave safety level determined by the Occupational Safety and Health Act (OSHA), is 10 mW/cm². The beam coming from the satellites would be 23mW/cm² in the centre and a maximum of 1 mW/cm² at the edges of the rectenna. So, this should not be a problem since the rectenna will be a ‘no-go’ zone. Outside the edges of the rectenna, the microwave intensities will rapidly decrease, posing no problems to nearby towns.


  • Goldsmith, J. R. (1997). Epidemiologic evidence relevant to radar (microwave) effects. Environmental Health Perspectives. 105, pp. 1579 – 1587.
  • Landis, G.A. (2004). Reinventing the Solar Power Satellite. NASA/TM – 2004-212743. pp. 1 – 35.
  • Nagatomo, M.; Sasaki, S. & Naruo, Y. (1994). Conceptual of A Solar Power Satellite, SPS 2000. Proc. of the 19th Int. Symp. on Space Tech. and Science. pp. 469 – 476.
  • United States Department of Labor: Occupational Safety and Health Administration:

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Comments (2)

Very interesting!

Any advancement has its externalities.