There are a few articles floating around on the green news sites about space based satellites that could potentially gather solar power and beam it back to Earth as microwave energy. On Earth it is re-converted back into electrical power to help solve the carbon-intensive power generation issues and possibly provide a source of cheap alternative energy. While it is admirable to think laterally and evaluate all possible solutions for the greenhouse gas problem, we should also remember to concentrate only on those possibilities that truly have a realistic chance of actually delivering on what they promise.
Using some of the data in the references, one can quickly see that this space based solar satellites’ proposal is not feasible. The proposed antenna (rectenna) design of 50,000m2 would generate 10MW, weigh 10,000-15,000kg and need about 35% of the payload volume of the shuttle. The weight and magnitude of such an antenna drives the enormous challenge to actually launch such devices. The estimates also do not consider the mass of the spacecraft itself, nor of any solar panels, all of which is likely to be of the same order of magnitude or greater.
The work performed in the study (Rectenna Technology Program, ref.1) was actually for a microwave link from earth to power the satellite in orbit and not vice-versa. Many unaddressed technical problems with the proposed rectenna for space-based applications were also identified in the same article. Other recent studies, such as the report for the European Space Agency (ref. 4), also identify the technical problems and seems to conclude that space based power generation is technically feasible but likely to be 3 to 5 times more expensive than ground based solar generation.
Evaluating the actual energy needs also shows it to be an implausibly gigantic undertaking. The peak US demand for summer power in 2005 was around 790GW which would mean that 79,000 of these satellites would be needed to supply all this power requirement and assuming 100% antenna efficiency which is obviously not possible. It seems an equivalent sized area on Earth is also needed as the receiving rectenna. Can you imagine the enormous cost and environmental damage caused by 30,000 shuttle-like launches? Some references talk about putting these in geo-synchronous orbit so even larger launch vehicles would be required.
The cost to launch a shuttle is around $600million and about $8billion to build each one. The 5 shuttles have only flown approximately 120 times in over 35 years, with the loss of two, so you can imagine the enormous fleet of shuttles, or rockets, required to launch a space based power generation fleet. A rocket launch to geosynchronous orbit would be around $100-120million each and have similar enormous environmental and technical hurdles to overcome.
There are a myriad of other mind-boggling issues such as the impacts of gigawatts of microwave energy passing through the atmosphere, the risk of failures and the possibility of using it as a weapon with a little tweak of the power settings and a re-point, it could be used to frazzle electronics and people. While it makes for fanciful eco-science fiction, it certainly cannot readily translate into science fact and would probably never reach a stage of engineering, budgetary, nor political possibility quick enough to solve any of our immediate problems.
Let’s tackle the real issues with tangible solutions such as wind, terrestrial solar, ocean and geo-thermal renewable energy. We can continue to reduce our energy consumption, maybe turn off our lights at night and gaze at the stars in the night sky, rather than the additional hundreds of thousands of pieces of space junk that would otherwise be floating up there if we attempted pursued this concept.
References
1) http://www.nss.org/settlement/ssp/library/1987-NASACR179558-RectennaTechnologyProgram.pdf
2) http://greenupgrader.com/4233/solar-satellites-in-space-beam-endless-energy-to-earth/
3) http://www.nss.org/settlement/ssp/index.htm
4) Earth & Space-Based Power Generation Systems A Comparison Study, performed for the European Space Agency.
Note: 1 gigawatt = 1000 megawatts = 1,000,000 kilowatts = 1,000,000,000 watts.
Trevor Williams is a University of Victoria Mechanical Engineering PhD candidate specialising in renewable energy, power grid modelling and plug-in hybrid electric vehicles. He has a bachelors in Aeronautical Engineering, a Masters in Management Science and over 23 years international experience in the space industry, having worked on Earth observation and telecommunications satellites
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