Space-based Solar Power or Dyson Specks

There has been a bit of buzz around space-based solar power (SBSP) and when a friend chatted me up about it today, I decided to organize my opinions about the technology and share them here.  SBSP is not a new idea.  They amount to the smallest useful Dyson Sphere.  SBSP is ugly so I’ll rename them Dyson Specks for the remainder of this essay.

The idea, as you can read in more detail from the links, is that a geostationary satellite captures some energy from the sun and beams it down to earth where collectors gather it and convert it to electricity.  Sustainable, carbon neutral, green energy.  A veritable panacea and a damn sexy concept for anyone who’s ever turned their eyes skyward in wonder.

As a bit of an aside, the media coverage mentions “beam” and “microwave” when it concerns getting the energy to the ground.  I will call this “beam” what it is by referring to it as a “laser” from here forward.

Other articles discuss the engineering difficulties so I’ll ignore them here.  Let’s take a flight of fancy and say we can wave a magic wand and construct our Dyson Speck out of thin air.  What do we now have?  We have a pretty stellar (sorry) source of energy.  But there are side effects I haven’t heard mentioned yet.  I’ve heard that the laser could be some 10 km in diameter when it gets to the surface of the ground.  So we have a 10+ km diameter section of the earth permanently dedicated to receiving this energy safely.  This is not an insignificant alteration of the biosphere.

We also have a column of air 10 km in diameter and 120 km high that will be continuously heated by this microwave laser.  That’s a lot of air.  We may not be producing greenhouse gases anymore but now we’re heating the atmosphere directly with bonus solar radiation that would have otherwise sped out to the cosmos.  We’ve effectively increased the surface area of the earth.  This sounds like a great recipe for global warming to me.  If this technology becomes popular and we someday have 1000 of these satellites powering population centers all around the globe, how many watts of power will we be feeding directly into the atmosphere and what effect will that have on surface and ocean temperatures?  What about the impact on weather patterns?  One small benefit, I suppose would be the surreal and beautiful photos of the way these lasers would perforate clouds and otherwise manipulate atmospheric moisture.  But at what cost?

In order to keep the solar panels pointed at the sun, the satellite will have to expend a fair amount of energy to remain in position.  It will have to have fairly powerful propulsion to achieve this.  This subtle artifact leads me to my biggest concern about Dyson Specks.  The powerful propulsion mechanism required to keep the laser focused on the right spot while keeping the arrays pointed at the sun will make retargeting the laser swift and accurate.  What if the laser were fitted with a lens or mirror that it could use to focus its laser to, say 10 meters wide.  Now we have a weapon of mass destruction that can quickly target any point on half the globe with a push of a button.

The military says they are interested in this technology for providing power to tactical field operations, and I’m sure that is part of their motivation, but I think this is Strategic Defense Initiative (aka Star Wars) Redux.  What better way is there to furtively reinstate a controversial program than to greenwash it?

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2 Responses

  1. Hi Ken! So, a couple things I think I might be able to clear up here:

    1) it’s not really a “laser”; I think it’s not even a maser (which is a laser in the microwave bandwidth); it’s just a focused beam of microwave radiation, but it’s not coherent, even if it might be just one wavelength.

    2) The atmosphere is fairly transparent to microwave radiation, which is why you’d choose it as your carrier frequency (you want as much of that energy to reach the receiver as possible). This means that as long as the air column through which the beam travels is dry, it won’t get heated. Put your receiver at the top of an equatorial mountain, and you minimize atmospheric effects.

    2a) The receiving array can be optically transparent and microwave-opaque, just like the viewport on a microwave oven. You could have plants growing underneath it.

    3) You don’t actually need to expend fuel to keep proper orientation. If your overall shape is long and narrow, you can use tidal gravity to keep it pointed at the Earth. This provides a stable platform against which regular electric motors, powered by solar cells, can push to keep the panels pointing at the sun. Some fuel is needed to keep the station in position (all orbits are unstable when you get down to it). But the thrust required is extremely low, so high-efficiency/low-thrust motors like ion rockets and the like can be used.

    4) The smaller the focal area, the larger the transmitting antenna. To get a 10km receiving area, the transmitter has to be dozens of km in diameter. Even using phased array techniques to steer the beam (meaning, you don’t have to physically re-point the transmitter), actually increasing the power density at point of receipt (by decreasing the area) is not really feasible.

    5) The gigawatts of power coming the SPS (solar power satellite) would offset megatons of carbon that would otherwise have been released by being burned for energy. I’ve not done the math, but my gut feeling is that this would be a net win for the environment.

    Something tells me, though, that this is essentially video vinyl: a technology that is technically possible, but obsolete before it’s even practically feasible. With mobile autonomous solar-cell minifactories, deserts and highways could be converted into power stations; check out these graphs:

    http://www.informationisbeautiful.net/2009/surface-area-required-to-solar-power-the-world/

    See also

    And personally, I’m still betting on fusion:

    http://www.askmar.com/Fusion.html
    http://en.wikipedia.org/wiki/Dense_plasma_focus
    http://www.generalfusion.com/

    • I appreciate your thorough response. I feel somewhat reassured that we may not be greenwashing defense technology. You have obviously done more thinking about this technology than I have and you’ve given me a lot of food for thought (and a lot of reading assignments!) 🙂 Thank you and warm regards,

      Ken

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