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« Space Science Bull | Main | Bad News For NASA Funding? »

Give The Lunar Solar A Rest

One of the presentations at the Space Investment Summit was on Lunar solar power. Solar satellites were also referred to. One presentation noted that if a government agree to buy solar at $0.85/kwh (about a 900% subsidy) that space solar would pay. Great. You can make $50 billion if they give you a $70 billion subsidy. Hand me a glass of ethanol.

My previous best efforts on solar are here, here, and here.

I think there is a fairly simple case against. Grant that space solar is 4x as efficient per kilogram as Earth solar. Ignore the fact that people want more power during the day than at night. Grant that we can take raw silicon and turn it into solar cells with minimal remote human input. Grant that we can beam it. Ignore that if we import solar power in quantity that the price of coal and uranium will drop until they are competitive again as fuels.

Can't we just set one of the 'bots that will build the cells loose in an Earth desert? Doesn't it require the transportation cost to space be on the order of 4 times the manufacturing cost for space solar to be economically effective? Even if we are just talking about the regolith eating robot, don't we have to get transportation cost down to three times the cost of producing a sand eating robot and letting it loose in the desert? Am I missing something? I think this argument means space solar will never be competitive.

Posted by Sam Dinkin at April 18, 2007 02:28 PM
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Am I missing something?

Yes. Not to say that space solar is economically viable, but you are missing the fact that in space, there are no clouds and, more importantly, no night.

Desert solar panels can't provide baseload electricity, and you have to factor in the costs of energy storage. Space doesn't have this problem.

Posted by Rand Simberg at April 18, 2007 02:46 PM

I should add that, if you think that your statement that:

Ignore the fact that people want more power during the day than at night.

...obviates my comment about no power at night, consider the possibility of relaying the power to other areas.

Again, this is not necessarily to defend space solar power, but simply to clarify the issues and arguments.

Posted by Rand Simberg at April 18, 2007 02:53 PM

Lunar solar, otoh, makes absolutely no sense, if they're talking about beaming it back home. You've got a massively larger range to spread the beam over (meaning more waste and a much larger receiver)... aaaaand, you've got a two-week night.

Personally, I like nukes for basline (heck, for just about everything). I haven't fully drunk Kirk's koolaid yet, but I do think liquid fuel thorium sounds dang promising from an economic standpoint, and we have plenty of it for centuries.

Posted by Big D at April 18, 2007 04:01 PM

Rand, Sam did take cloud cover and such things into account. Remember that he said "Grant that space solar is 4x as efficient per kilogram as Earth solar" which covers your remarks (cloud cover, etc) in your first post as well as energy absorption from the atmosphere.

Posted by Karl Hallowell at April 18, 2007 04:54 PM

That solar power is far more valuable on the Moon to develop an industrial infrastructure and products that it would ever be worth to beam it back to the Earth.

Dennis

Posted by Dennis Ray Wingo at April 18, 2007 05:14 PM

I've never been a big fan of Dr. Criswell's Lunar-based solar power. It doesn't have the intuitive feel that GEO-based solar power does, but it does obviate a lot of the transport costs, and seems easier once you get to the Moon. His ideas are presented in the documentary "GaiaSelene".

I am okay with GEO-based solar power for a number of reasons:
1) It gets power generation assets up in space, away from the idiocies of humanity and the vagaries of nature. For the most part. It certainly serves to severely limit the range of threats to the functioning of those assets.
2) As far as we know the Sun is going to be around for about another four BILLION years. I've got your centuries right here.
3) Current terrestrial energy sources are not properly priced. Were they so, there would be no need for such things as EPA Superfunds, environmental remediation, and taxpayers paying for a long-term storage bunker for spent nuclear fuel. An abandoned GEO power sat would take something like 100,000 years for orbital decay, a fair chunk of it would vaporize in the atmosphere, and whatever remained would most likely end up in the ocean somewhere. I'll take those odds over more hydrocarbon spew.
3) The collection of SPS-delivered energy is simple,and can even co-function with other economic activities such as crops or livestock.
4) GEO-based power delivery would also provide an edge to our defense forces by ensuring the delivery of electricity to the troops via spot beams in the absence of any other means. Folks reacted with incredulity that I would suggest such a silly thing over at the Selenian Boondocks, but of course just recently a story was published at MSNBC that the military was looking at space-based solar power. I agree with Rand about the relays, which may be part of why the military is considering it.
5) The bulk components (arrays and support structure) are relatively simple and can easily be made from materials readily found on the Moon. Since I'd rather tear up the Moon than our Earth to create it. Though I'd rather tear up the asteroids than our Moon.

I'm not against nuclear, and prefer it over hydrocarbons, but I think that SPS is the way to go long-term, supported by fusion since it's still only 10 years away. Our entire prosperity is built on the delivery of energy in some way, shape or form, so we need something better than the next temporary solution. I consider four billion years to be an effectively permanent solution. It's sure going to take a lot of investment though.

Posted by Ken Murphy at April 18, 2007 05:37 PM

Karl: yes, thanks. The 4x comes from near 100% daylight in many orbits and no atmospheric absorption or clouds. Doesn't that mean we still need the price of transport to make space solar more economically efficient to have the transport cost be less than 3x of the manufacturing cost? If solar costs $45 per kilogram, don't we need transport to be $145/kg for the economic case to close? If a regolith eating solar fab costs $10,000/kg delivered, doesn't it need to be competitive with a $2,500/kg sand eating solar fab to be economical?

Ken: It is certainly an elegant art project to do space solar, but if it is not cost effective, aren't we better doing Earth based solar until we run out of remote Earthbound locations? Solar receivers can look like rectennas and be not that displeasing even if they take up real estate. We can use the money we save to buy tourist flights to view the pristine Moon unmarred by Earth industry.

Rand: thanks for cleaning up the links.

Posted by Sam Dinkin at April 18, 2007 05:45 PM

4) GEO-based power delivery would also provide an edge to our defense forces by ensuring the delivery of electricity to the troops via spot beams in the absence of any other means.

So, instead of using a diesel generator, methanol fuel cell, or CIGS thin film panels (low efficiency, but they weigh almost nothing and you can sew the sheets onto tents), they want the military to build a giant two square kilometer rectenna.

Have they at all thought this ludicrous scheme through?

Posted by Adrasteia at April 18, 2007 06:13 PM

Oops, just found the article. It was at Space.com, and by a staff writer at Space News. The exact quote is:

"The Pentagon's National Security Space Office (NSSO) may begin a study in the near future on the possibility of using satellite to collect solar energy for use on Earth, according to Defense Department officials."

The MSNBC story was "Space station builder lays out business plan". Sorry 'bout that.

Posted by Ken Murphy at April 18, 2007 08:06 PM

on the contrary, lunar solar makes LOTS of sense .. on lunar surface. What i am saying, that the Space Vacuum Epitaxy centers ( A. Ignatiev and A. Freundlich ) project of manufacturing sheets of thin-film solar cells directly on the surface of moon is a great idea for continously expanding available power output of the lunar outpost, without delivering more mass.
Whether it will be economical to export that produced power to GEO, or even earth, remains for future bean counters to work out.

Posted by kert at April 18, 2007 11:04 PM

"So, instead of using a diesel generator, methanol fuel cell, or CIGS thin film panels (low efficiency, but they weigh almost nothing and you can sew the sheets onto tents), they want the military to build a giant two square kilometer rectenna.

Have they at all thought this ludicrous scheme through?
Posted by Adrasteia at April 18, 2007 06:13 PM"

If the electricity for the base/post/position is a 2 km(sq) mesh rectenna, that could probably be basically air-dropped and unfurled in descent; once on the ground and hooked up, the enemy can't take out the power with a lucky shot to the generator. (And no IR signal from a generator for homing in on.) Parts of the grid could be damaged without taking down the system as a whole. Such a small-scale power distribution net would be invaluable in many situations, I would think. Plus the civilian spinoff/adaptations would be immense.

Posted by Stewart at April 19, 2007 04:21 AM

Have they at all thought this ludicrous scheme through?

Posted by Adrasteia at April 18, 2007 06:13 PM

Yeah they probably have but have to justify the study anyway

Robert

Posted by Robert G. Oler at April 19, 2007 05:57 AM

How much and how often? If we only have 12 folks at a base on the Moon, we don't need a huge power research project to support them. How often are we fighting wars where our diesel is at risk?

Posted by Sam Dinkin at April 19, 2007 06:29 AM

Klauss Heiss has written a chapter in an upcoming book on spacepower theory regarding the emplacement of 1 gigawatt of power on the Moon to be used in-situ as a jump start to lunar industrialization.

I like the argument. The book will be out this summer and we can publish some of our work on the internet for discussion then. (I have a chapter in the book as well as Bob Z pushing for Mars)

Dennis

Posted by Dennis Ray Wingo at April 19, 2007 11:25 AM

I think you are making two major mistake, beyonds those mentioned already, which mak your 4X estimate is way off.

First, you are considering only total solar flux, thereby presuming that weight / square meter of receiver is the same in orbit as on the ground. It seems very reasonable to me that this value is much smaller in orbit, due to lack of gravity and weather. For instance, reflectors only have to be thick enough to reflect, not thick enough and braced enough to withstand gravity and wind. That's not a small difference.

The other mistake is presuming the use of silicon based solar panels, as opposed to such things as nitrogen cycle turbines. These work much better in space than on the ground because you have a 4K heat sink in orbit.

SPS isn't just big ground based installations in orbit, it depends strongly on the fact that you can build very differently in orbit.

Posted by Annoying Old Guy at April 19, 2007 01:46 PM

Actually Rand isn't an the 4x is part of the calculation.

AM0 (Air Mass Zero) insolation standard conditions

1358 watts/m2
25 degrees c.

AM1 (Air Mass 1) standard conditions

1000 watts/m2
25 degrees c.

Considerable difference.

I have a set of solar panels operating at 3600 ft altitude right now and they put out about 14% more power than the same ones at sea level (they are on a mobile trailer so I have checked this.

Posted by Dennis Ray Wingo at April 19, 2007 02:44 PM

The other mistake is presuming the use of silicon based solar panels, as opposed to such things as nitrogen cycle turbines. These work much better in space than on the ground because you have a 4K heat sink in orbit.

Yeah, but what's the thermal conductivity of a vacuum? Zip. It's not easy to get rid of heat quickly by pure radiation loss. This is why ISS has those giant cooling fins and expensive ammonia refrigeration system.

Posted by Carl Pham at April 19, 2007 03:43 PM

Old guy: this says Earthbound is about $80/kg. So let's say you need half the structure in orbit and it's 4x as efficient. Let's further say it's still only $80/kg. So that's 8x as efficient per kg. So that means we need launch costs to be less than $560/kg for space solar to be competitive with Earth solar. Right now, you can buy a SpaceX Falcon IX for only $2800/kg. That leaves you -$2240/kg to buy rectennas.

Posted by Sam Dinkin at April 19, 2007 10:17 PM

If I were to plan an SPS launched from the ground, I would not use PV modules with the same mass/power as terrestrial ones. After all, the space units would not have to put up with wind or hail. Thin films (CIS absorbs in less than 1 micron, for example) deposited on thin plastic sheeting would seem to be a better bet to me.

The lunar proposal effectively did this, vacuum depositing micron-thick a-Si layers directly on smoothed regolith, a technique not practical on terrestrial soil.

Posted by Paul Dietz at April 20, 2007 09:13 AM

Solar in the desert is stupid, it would never get past the environmentalists. Better to give some kind of tax benefits to people that install solar on their roof and pass laws saying that power companies have to buy back extra power (reversable meters). Set a time line so that if you bootstrap the industry it doens't get a permenant subsidy and let the market take over from there.

The big advantages are that the roofs are currently unused space. That a terrorist attack couldn't take out the grid since it becomes very decentralized. The power is clean and silent and might create jobs.

The disadvantages. Well only sunny states get the advantages. Sucks to live in Alaska.

Posted by rjschwarz at April 20, 2007 01:33 PM

Another way to bootstrap the distributed solar is to have the government put solar panels on school buildings (in areas that are reasonable) thus cutting power bills at those schools. In some cases those schools might actually have enough surface area to get a check back from the power company.

Jails and other government buildings are also options. This should probably be done at the State level though. California would be a great place to start with our Environmentally conscious Governator and lots of sunshine and schools that are never satisifed with their budgets.

Posted by rjschwarz at April 20, 2007 01:37 PM

RJS: Solar on the Moon is also an environmental issue. There are plenty of desert sites that are private property.

Paul: One cannot do vapor deposition of solar cells onto flat regolith on Earth, but one can till soil with a diesel tractor. And a person and unroll a sheet of cells produced in a factory in China. The trick to making the Moon competitive is to get the delivered cost low enough to pay the interest on the development cost and a 10x return in 10 years (26% interest) given the high risk. The $ per watt all in has to be cheaper in space for it to make sense. And even if it is cheaper, it has to be risk adjusted.

Posted by Sam Dinkin at April 22, 2007 08:26 AM

Some of the comments above are slightly flawed. ie if 4X is correct for GEO altitude then 2X is about right for the Moon which has night that lasts two weeks. We can partially correct for this by building a power line that circles all the Equator of the Moon. With present power line technology this will provide a little power for Equitorial moon colonies and outposts during the long night. Surplus power can be sent to Earth, except there will rarely be a surplus and the transmitting antenna needs a diameter of 12 kilometers if one kilometer is the correct size for a GEO transmitting antenna.
In GEO the solar panel array can be aimed at the sun with very little energy or initial cost, but on the moon steerable solar panels are perhaps as costly as steerable solar panels on an Earth desert or on the roof of a Walmart store. Steerable helps a lot at GEO, and on the Moon but only increases average output about 15% in December and early January in the middle of the North Temperate Zone of Earth. Neil

Posted by Raymond Neil Cox at June 28, 2007 05:42 AM

There are some problems with roof instalation. Typical roofs are not pitched toward the sun sufficiently. There are chimneys, vent pipes, sometimes heat exchangers scattered here and there. These cast moving shadows on the photovoltaic panels which reduces the panel output more than you would think. Also how do you repair a roof covered with solar panels? One partial solution is to mount the solar panels on a frame about 2 meters = 7 feet above the roof. Now we have added a wind loading problem, which existing buildings likely cannot tolerate. We likely should not mandate solar panels on roofs except for new construction. Neil

Posted by Raymond Neil Cox at June 28, 2007 06:25 AM


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