Space-based Solar

The sun is an amazing source of energy.  Fusing around 620 billion kilograms (that’s 683 million tons)  of hydrogen per second into helium nuclei, it produces about 38,400,000,000,000,000,000,000,000,000 Watts of power per second.  You know how really big explosions are measured in kilotons or megatons of TNT?  The largest nuclear device ever exploded on Earth was 100 megatons .  The sun produces 90 million times that energy every second.

 Just to give another comparison, the entire energy usage of humans in 2008 was a mere 15 terawatts (15,000,000,000,000 Watts).  If we could capture 1 million billionth of one second of the sun’s output, we could run our planet for an entire year.

The Earth is very, very small compared to the sun, so the Earth directly receives only about 174 petawatts (174,000,000,000,000,000 W) from the sun.  Still, if we could capture 1 ten thousandth of that, we could supply the entire planet for a year.  Of course, some of that energy is reflected back into space (about 30%), and about 20% is absorbed by the atmosphere and clouds before it even reaches the surface.  Just over 50% actually hits the surface of the Earth.  Still, if we could capture that, even at an efficiency of about 20% (actually high for current solar panels), we’d have more electricity than we knew what to do with.

Now, plants need some and other photosynthetic critters need some (corals, some clams, etc) so we can’t take all of the light.  In fact, we need the energy from the sun to keep the Earth warm.

But, as I mentioned, the Earth is very, very small.  What if we could catch some of the solar energy that would never hit Earth anyway?

What if we could direct the direct source of solar radiation, without all the annoying clouds and weather and even atmosphere to get in the way?

Well, that has been a idea since Isaac Asimov wrote about it in 1941 Reason .

 The idea is simple.  Put the largest photovoltaic panels you can make into orbit.  As the panels collect the unfiltered sunlight, the satellite will transform that electricity into microwave radiation and send that to a receiving station on Earth.  That station will convert the microwaves back into DC electricity which can then be fed into the grid after rectification (DC to AC conversion).

 How likely is this?  Well, I was reminded that at least one company, Solaren (about which I have requested additional information), has pledged to do this.  Their goal is to have a 200MW of delivered power to Pacific Gas and Electric Company of California at 12.9 cents per kilowatt hour, starting in 2016.

 I honestly don’t know if that’s an even reasonable goal or not.  It sounds good, but (and this is why I asked for more info)…

 An Earth based solar array of a mere 80 MW has a surface area of almost 1 million square meters (that’s about 1 million standard PV panels).  Solaren will be in space, where there is 100% more sunlight available.  Of course, they want to produce over 100% more electricity too.

 Then there is the steps to get the power from orbit to Earth.  Losses will occur during each of these steps.  The first is converting panel generated electricity to microwaves.  Beaming the microwaves to Earth will cause some losses too (scatter, absorption by water molecules in clouds, etc).  Then the conversion from microwaves back to electricity.  A million panels is the minimum they would need.

 Then they have to get a million solar panels, plus the microwave convertor and the reflector and the trusses to keep everything in place and the wiring, into space.  Then, somehow, they have to get it assembled.  Unless this goes up as once, very carefully packed system, then it will have to be assembled by humans. 

 It costs a lot to get a human into space.  With the space shuttle, one launch costed between 450 million and 1.7 billion dollars.  Of course, the space shuttle is gone, but so is America’s ability to put people into orbit.

 Finally, and I’m not an expert on this, but I think we must consider the effect of the microwave radiation hitting the Earth.  That’s a lot of energy plowing through the atmosphere.  If the beam is off by even 1%, then it will be microwaving something that it’s not supposed to.  I doubt that it would be a suburban neighborhood, but it sure won’t do animals and plants any good.  I have heard, but cannot confirm, that some of the US Navy’s most powerful radars can cook birds in flight.  A bird flying into this beam, may not make it out again.

 I love the idea of this, but I think that the 2016 is very optimistic.  I also think there are some significant hurdles to overcome.

 As I said, I’ve requested more information.  We’ll see what is forthcoming.

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4 Responses to Space-based Solar

  1. jonolan says:

    You left out the climate effects. 😉 Somebody is going to claim that these microwaves are changing the world’s wind and rain patterns and causing “climate disruption.”

    You also left out the odds on bet that the power generation system would be weaponized…

  2. bill says:

    I’ve was curious how much mass is converted to power in a nuclear energy plant. From your 15 terawatt figure I calculated that comes to 0.17 grams of energy per year using e=mc2. So I’m guessing the change in mass of nuclear fuel would probably not be measurable.

    The total solar energy of 174 petawatts would be about 1.9 kg of energy. I’m not totally sure about my calculations but it seems in the ballpark.

    Interesting blog! I was looking up the asinine Texas HB2454 and found it.

  3. ogremkv says:


    The 15 Terawatts is electrical energy developed by all sources, not just nuclear.

    As far as 0.17 grams of energy, I haven’t done the calculation, but that seems reasonable. One thing to keep in mind, fission reactors use U-235 and (civilian models at least) have fuel rods that are only 5% U-235. So, even in reactors, the amount of material actuallly fissioning is around 1/20 of the total volume of the fuel rods.

    Of that amount, only about 3% actuallly undergoes fission in the fuel rod’s life cycle in the reactor. The majority of the energy in a nuclear reactor comes from the fast moving neutrons. They were bound in the nucleus. After fission, they are released (and without getting into the strong nuclear force and quantum level science), they now have a fair bit of energy.

    The amount of mass lost in a nuclear reactor is miniscule. If only we could convert mass directly into pure energy… well we’d probably blow ourselves up.

    Jon, yeah, I didn’t talk about weaponization, but any beam of concentrated energy could be a weapon. Even using it as a soft kill (electronics) would work fine.

    I’m thinking that the satellite would have to be in geosynchronus orbit, so would only be able to target our hemisphere. A 200MW beam of microwaves would very, very tempting to use as a threat.

  4. David Evans says:

    This idea was explored in the 1970’s, notably by Gerald O’Neill in his book “The High Frontier”. He proposed getting around the launch costs by building the satellites in orbit from lunar materials. In his design the energy density of the microwave beam was too low to threaten life – the antennae would be large open-work structures the land under which could be used for farming – and could not be increased enough to make a useful weapon. I wish we had put some money into the concept back then.

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