Brief Thought: Space Solar Power

In the spirit of trying to blog a little more, I just wanted to throw out one that I didn’t have a chance to post as a comment to a recent Transterrestrial post by Sam Dinkin. In his post Zero Divided By Zero = Space Solar Power, Sam wrote:

To focus on one link in this chain, it will require launch prices to fall below three times manufacturing costs of solar for space solar to be competitive with Earth solar which would require launch costs of less than $500/kg given solar manufacturing of about $170/kg now (and that is falling at 5%/year so it might be $150/kg that is the moving target to beat terrestrial solar in the 2030s).

While I agree with Sam’s basic point that Space Solar Power has far from proved its case, I did want to mention something. In all the discussions I see about space solar power vs. terrestrial solar power, many people rip on how for space solar power to be competitive, it has to be only three times more expensive then terrestrial solar power. And this is because space solar power on average only receives about three times as much power as a terrestrial station. The problem is that little word there–average. One of the major benefits of space solar power is that it is extremely consistent. No need to worry about clouds or other inclement weather, no night-time (especially in the right orbits you can supposedly eliminate even very brief earth-caused shadows), 24-7 consistent power output. Terrestrial solar isn’t constant enough to serve provide baseload power. Terrestrial solar also doesn’t do a lot of good during primetime (which is long after the sun has set). But space solar power can handle both of these situations. Which means its value is greater than the simplistic case made before.

Not that I think that this makes space solar power the best thing since sliced bread or anything. Just thought that the line of argument being used wasn’t entirely fair or accurate.

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Jonathan Goff

Jonathan Goff

President/CEO at Altius Space Machines
Jonathan Goff is a space technologist, inventor, and serial space entrepreneur who created the Selenian Boondocks blog. Jon was a co-founder of Masten Space Systems, and is the founder and CEO of Altius Space Machines, a space robotics startup in Broomfield, CO. His family includes his wife, Tiffany, and five boys: Jarom (deceased), Jonathan, James, Peter, and Andrew. Jon has a BS in Manufacturing Engineering (1999) and an MS in Mechanical Engineering (2007) from Brigham Young University, and served an LDS proselytizing mission in Olongapo, Philippines from 2000-2002.
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12 Responses to Brief Thought: Space Solar Power

  1. Karl Hallowell says:

    You also have to compare SPS to an orbital microwave relay. I have heard it claimed that the loss for microwaves from orbit to Earth can be as low as 15%. Presumably that is the same for going the reverse direction. So even if SPS systems are competitive with alternate Earth-based power sources at a given location, it’s doubtful that they are competitive with Earth-based power plus a 17% markup within a few thousand miles of the target region.

    For example, if you have some isolated region in the Canadian Northwest Territory, it could be powered by cheap hydroelectric beamed from British Columbia to a constellation of microwave relays in LEO and down to a target antenna.

  2. Karl Hallowell says:

    Jon, I know this isn’t the place for it, but I’m consistently getting silly posting problems with this blog and I don’t know if it’s a blog configuration problem or blogspot that is causing the problem. A glance through blogspots help didn’t help, it’s too much effort for the moment.

    I have to type in captchas every time I preview or post. My profile doesn’t appear by default (so if I do nothing, “karl” will appear instead of “karl hallowell”). It’ll remember my profile for the session, but next time I’ll be back to square one.

    But now it’s giving what is probably the most annoying behavior to date. Various commands are ignored the first time (and a new captcha test issued). For the post I just did, I had to enter about 8-10 captchas to preview, set my profile, preview, and then post.

    I don’t have your email address (I think), Jon, otherwise I’d just email you about it. Feel free to delete this. Email is “khallow” with the usual hotmail suffix.

  3. Sam says:


    We need launch costs to be 3x if the space solar is 4x as much power. Still have to manufacture the one going to space too.

    Your argument about variability is sensible for wind power, but not solar. Peak electricity usage tends to be on hot sunny days when solar panels are working so the variability problem actually works against space solar–night time power isn’t worth as much as day power–perhaps 1/3 as much in some parts of the world.


  4. Jon Goff says:

    I thought there was another peak in power usage in the early evening when everyone gets home from work? While I agree that hot sunny days would probably correlate fairly well with good terrestrial solar, it isn’t always the case. And the shear fact that there is as much variability in the supply has been an issue with terrestrial solar all along. I was under the understanding (though I might be wrong) that for power generation sources that don’t meet the requirements of base power, that they couldn’t sell their power back to the grid for as much. Now, I could be wrong on that account, but if I’m right, that would imply that a consistent solar power source that didn’t have the variability and thus could sell into a different higher value market would be worth more per kW of output than a given terrestrial source.


  5. Monte Davis says:

    A 1999 paper by Geoff Landis goes into some detail on the potential economic advantage of “following the peak” — i.e., redirecting transmission to the moving target of highest-valued power sales.

    Karl — good point on orbital relay, but it’s not necessarily a stark either-or; one can imagine a scenario in which orbital relays are part of the path to — or continuing adjuncts to — classic ” SPsats

  6. Jon Goff says:

    Yeah, it looks like I had my information backwards. I remember reading that a while back and must have got the concepts jumbled.


  7. Karl Hallowell says:

    Good point, Monte. Long ago I used to think that most space projects were monolithic. You either had SPS or you didn’t, Same goes for orbital launch vehicles, space elevators, etc. But as we see, there are potentially profitable intermediate steps that one can do. This makes bootstrapping a possibility.

  8. Monte Davis says:

    Karl — a dozen times I’ve seen quarrels between advocates of the “beanstalk” space elevator and rotating orbital tethers (rotovators, bolos, whatever).

    It makes me want to tear my hair out: jeez, guys, don’t you think any reasonable program aiming at a beanstalk would include space exposure tests of shorter segments anyway? And if you ever had a beanstalk up and operating, wouldn’t a rotovator be a handy rocket-free way to step from GEO to LEO or any other orbit?

  9. Jon Goff says:

    You aren’t possibly suggesting that the Space Tethers Front of Judea could ever possibly speak with the Judean Space Tethers Front, are you? 😉


  10. Monte Davis says:

    Splitter! Heretic! STONE HIM!!!

  11. Jon Goff says:

    Unbeliever? Persecute him, PERSECUTE HIM!!!

    Ah, that’s the funniest movie I never should’ve watched 30-45minutes of.


  12. Sam says:


    The power company has to follow loads (throttle system power) all the time. There are good and bad ways to do so. A big battery on a solar panel is a bad way just today. Solar nearly completely overlaps with the time that gas cyclers and intermediates are turned on if not the peakers that come on around 5:00 when air conditioners are going full blast at home and at work.

    Green solar power is commanding a substantial premium in the market as a differentiated, heavy quota good. That is, states are requiring solar be a fraction of generation and customers are buying extra through their utility. So solar is trading at a premium to the power generated via other methods whatever its load shape. When solar starts being 20-50% of the installed capacity, that’s when we start needing to design more efficient plants to complement the load shape of solar. Not at 1% which is still 10x away.

    For GEO space solar, the load shape is 23 hours on which picks up an hour or two of peak, but 10 hours of off peak. Again, it’s economic value is only about 1.5 having the terrestrial half-day solar. This leaves out the co-sine for fixed terrestrial solar because of the angle of incidence of the sun so space solar could be closer to 3x the economic value and more considering you shine it where it’s most expensive to produce power.

    Rand’s talking about hundreds of dollars per pound to GEO in bulk so it might be economically feasible anyway.

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