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PostPosted: Apr 21, 2007 8:48 pm 
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I would put this proposal
http://www.skywindpower.com/ww/index.htm
in with the 2 possibilities you note in #2.

I would note that all 3 of these work in only some parts of the world & would need some easy way of transporting energy over thousands of km to be usable in the other parts of the world. So if one of those works & no easy energy storage or transmission is developed, some sort of nuclear would still be needed in much of the world.

If solar power satellites become workable the receiving antennas will be cheaper near the equator since the power satellites will be over the equator & near the horizon for high latitude regions. So nuclear would have a competitive advantage at high latitudes.

If all of #2 energy sources or #3 are developed but no easy storage is developed, nuclear might become used only in the niche markets of ocean shipping & spaceships that go far from the sun.

Re: maglev. Is this the Maglev system using high strength permanent magnets described in an article in the January 2000 Scientific American?

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PostPosted: Apr 21, 2007 9:01 pm 
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I love you guys!

I worked space solar power in graduate school--I went to grad school basically funded by Mr. Space Solar Power, John Mankins. SSP doesn't work now or ever (economically) for reasons I will explain in depth. The tether technology Ray mentioned--well, that's me. I'm NASA's tether guy, and about the only one these days. It's not going to make SSP cheap enough.

I studied fusion at Georgia Tech and have little hope it will ever beat thorium on power density, economy, or proliferation resistance, for reasons I will explain in depth. Bussard's IEC concept is interesting and very well may work, but will have low power density like any other fusion concept and if it can run on P-Boron, it can run on D-T, which will produce 14 MeV neutrons that can be easily used to make weapons-grade plutonium from U-238.

I worked with Sea Solar Power to help push OTEC, which I think is fascinating, but for reasons I will also try to explain in depth, I have little hope it will ever be more than a niche application (but a very fun niche!) and the capital costs are exceptionally high.

And I am currently working with Sky Wind Power to help develop their concept--it's part of my day job. Great idea, I love it, but the FAA could have a thing or two to say about it if we try to get enough of these to displace coal. I know the principals at Sky Wind Power very well and communicate with them on a regular basis. I think it will have great niche applications, but again, don't see it displacing coal.


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 Post subject: Cool!
PostPosted: Apr 22, 2007 9:04 pm 
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I'd love to be wrong... I learn a lot that way.

The maglev technology is called "Inductrack",
and it's described here, with a link to scientific american...:
http://en.wikipedia.org/wiki/Inductrack

For tether-based launch, please see:
http://en.wikipedia.org/wiki/Space_Elevator

I really like Wikipedia for extreme engineering proposals,
because the articles tend to accumulate cool links.

In fact, one of my favorite ways to research stuff is to write a Wikipedia article as bait, and see what gets added to it.


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PostPosted: Apr 23, 2007 10:29 am 
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rgvandewalker: Thanks for the link. That is the version of Maglev I thought you meant.

Kirk: Is the problem with SPS, even granting cheap launches, in the transmission from space to ground? I would expect that that concentrating mirrors & a closed loop gas turbine would be the way to provide megawatts to any manned space facility.

As for OTEC I think the difficulty of getting the energy to the users would keep it in niche status. However, if the construction & operating costs were brought down to something similar to a good hydroelectric plant, then all the aluminum refineries & nitrogen fertilizer plants would be located in the equatorial oceans

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PostPosted: Apr 23, 2007 2:22 pm 
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Let me try to start with space solar power...

(going over this list is like remembering past girlfriends whose relationships didn't work out...it was all so wonderful in the beginning and then went south from there...)

Space solar power was a great passion of mine for many years. When I first learned about it I though "aha! here is the real reason to develop space!"

Of course, I wanted space to get developed, independent of everything else, so having an economic reason to do it was great. Unfortunately, like dating a really cute girl, you tend to overlook problems in the relationship for much longer than you should because she's so good-looking.

Space solar power has a bunch of fundamental problems. Power transmission being the biggest, in my mind. If you want to convert solar power to electrical power to microwave power, first you generate low voltage DC in a photovoltaic array. Then you convert it to low voltage AC. Then you transform it to high-voltage AC. Then you transmit it many kilometers to the transmitting antenna. Then you convert it back to low voltage AC. Then you convert it to DC to drive the microwave transmitter.

Then you beam it 36,000 km from geosynchronous orbit to the surface of the earth. Then you convert it from microwave energy back to low voltage DC. Then to low voltage AC. Then to high-voltage AC for inclusion into the grid.

You lose energy at each step. But let's not even worry about that right now. One of the real shockers to me about space solar power came when I spoke with Gordon Woodcock, who's one of these guys who's forgotten more than I will probably ever know. He described the physical process of transmitting power in a simple equation that involved the aperture of the transmitter, the aperture of the receiver, the wavelength of transmission, and the distance between them.

It was a simple relationship that showed that you can either make the transmitter big, the receiver big, the frequency higher, or the distance shorter, but that there was a relationship between all three that had to be satisfied. Now most SPS concepts already had huge transmitters with apertures on the order of a kilometer. And they had huge receivers (rectennas) with apertures on the order of 10 km. The distance between them was fixed at 36,000 km (GEO) and the wavelength was pretty much fixed at 2.45 GHz or thereabouts.

What was conspicuously absent in all this was the power transmission level itself! So I asked Gordon, "does the amount of power you're transmitting matter?" and he said "no, this applies to any level of power transmission."

So to my shock and amazement, I come to find out that whether you're transmitting a milliwatt or a gigawatt, the geometric relationship between transmitter and receiver aperture, wavelength, and distance must be satisfied. And the more I think about it, the more it makes sense.

I bring all this up, because for years I had held out the hope that by going to greater levels of concentration, that the rectenna size could be decreased. 10 km is simply too much area to try to gobble up, especially near populated areas.

Nope, for 2.45 GHz and GEO distance, that's how big it has to be. You could shrink it some by making your space transmitter bigger, but that makes your launch problem even worse.

This is one of the reasons why I think the lunar solar power concept is even nuttier than conventional SSP. If (36,000 km)^2 is out of control, imagine (384000km)^2! It's about 100 times worse!

On to launch costs....

This is what I worked as a graduate student at Georgia Tech in 1998-99. I was funded by a NASA program run by John Mankins to evaluate low-cost launch options for space solar power. For those of you who get in the "way-back" machine you'll remember that some of the original SSP proposals from folks like Gerry O'Neill anticipated the use of lunar materials, mass drivers, mass catchers, ion engine tugs, in-space fabrication, and so forth.

Mankins came along and essentially said "heck, let's not worry about all that--let's just launch it from the ground!"

Well, the whole theory of using lunar resources and in space fabrication was the potential for great reduction in cost, after you'd amortized the lunar base, mass driver, mass catcher, and in-space fabrication and transportation system.

So we were working on the launch part, and it was fun. We were considering "highly-reusable" vehicles that used scramjets and assembly robots and every other fun-under-the-sun technology you can think of.

The problem was, the economic case still wasn't closing.

And we were being very kind in our scenario. We were imagining some sort of energy-starved future world where electricity went for premium prices ($0.25 per kWh in today's dollars) and solar cells had amazing (~50%) efficiency and had practically no mass and experienced no radiation degradation. All the land we needed for the rectennas was free and carbon taxes made all our competitors exorbitantly expensive.

And it still wouldn't close, even with all these favorable considerations. We were postulating a launch cost of $200 per kilogram. One day, just to see if we could get it to work, we typed in $0/kg for the launch costs into the model. Now $0/kg is about as good as it gets...that's assuming it costs nothing to launch. That case encompasses a space elevator (since it will never be cheaper than free) or a fully-amortized lunar base, or asteroid mining, or whatever else you wanted to plug in.

And guess what, it still wouldn't close.

Now, I still loved SSP at this point, and I really wanted it to work. I tried to imagine some sort of tech development that would change this number, but everything we could possibly use to make it look better was already in the model. Horribly expensive power? Check. Super advanced super high performance power conversion? Check. Free launch? Check.

What more could we do? But it still didn't make economic sense. And that was when I begin to slowly abandon the idea that SSP would ever be a contender for a future energy source. Several years would pass before I found out about thorium and the fluoride reactor.

I've seen nothing in the last 10 years to make me think that there's a more attractive version of SSP than the one we modeled. I'd be happy to learn more, but I'm not holding out much hope. Before you tell me about laser power transmission, you should just know that we didn't even entertain that for practical political reasons that involve something like the Death Star. Yes, I know it makes the apertures much much smaller but it also doesn't work in bad weather.


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PostPosted: Apr 23, 2007 8:10 pm 
Okay, well I was just going to post some opinions on SSP, but I think Kirk did a much better job than I could have. I will say that when I took Energy Conversion as an undergraduate in 1980, we studied this to some degree to come to the conclusion that the economic case just wouldn't close, even under very favorable circumstances. I haven't seen anything since that changes my mind. And actually the projected launch costs for "future" vehicles as seen from the rosey glasses of 1980, hasn't panned out. As I recall, we used the then thrown-around launch costs for Shuttle (a year before the first launch) of about $100/lb. It wouldn't close at that price and we were way off - as you all know, it turns out to be around $10,000/lb. Not to mention the difficulties of transmitting the power to Earth.

As for wave electricity producing devices in the oceans; they're neat ideas, but I'm skeptical. Not that they will not work or that they can be economical, but I have trouble believing that the public will go along with these monstrously large devices (some would call them eyesores) off our shores. This could be construed as no better solution than the offshore oil rigs by the coastal populations. They could also have some unforseen consequences like the giant wind turbines in Europe. There are "green" groups that are opposing the placing of these large turbines because they have shown to chop up the local birds. A lot of the locals don't like them because of the eyesore factor.

I'm always very interested in these innovative types of energy producing devices and ideas, but to date, I haven't seen anything that can compete with nuclear when a total systems approach is examined.


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PostPosted: Apr 23, 2007 8:14 pm 
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BTW one thing I wondered about proposed SPS designs is why did they usually used photovoltaics rather than concentrating mirrors & heat engines. Aluminized plastic would be cheaper per square meter than P-N junctions with any imaginable technology & heat engines can achieve 30 to 50 percent efficiency compared to maybe 20 percent for solar cells. The heat radiator at the low temperature end might be the most expensive part, but still likely cheaper than solar cells.

Also the heat engine turning a generator would make AC which would remove the need for a DC to AC conversion step.

Your previous post however,tells me that none of that would be near enough to out weight the unreasonable antenna size required.

The laser power transmission would be blocked by clouds but it might be a good way to provide power to a moon base.

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PostPosted: Apr 23, 2007 8:29 pm 
Could it be that photovoltaic designs are more robust in that they employ much fewer moving parts and thus increase the reliability of the system? If one considers the backup systems required to provide a heat engine system with the same level of reliability, it could drive the costs up significantly.


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PostPosted: Apr 23, 2007 8:31 pm 
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Jim Baerg wrote:
BTW one thing I wondered about proposed SPS designs is why did they usually used photovoltaics rather than concentrating mirrors & heat engines. Aluminized plastic would be cheaper per square meter than P-N junctions with any imaginable technology & heat engines can achieve 30 to 50 percent efficiency compared to maybe 20 percent for solar cells. The heat radiator at the low temperature end might be the most expensive part, but still likely cheaper than solar cells.

Also the heat engine turning a generator would make AC which would remove the need for a DC to AC conversion step.

Woodcock proposed a solar-dynamic version of SSP, using big concentrators and Brayton-cycle engines. When you optimize the radiator (which really turns out to be big) the system efficiency comes out at 25-30%. Several reasons I didn't pursue this much further: we were already assuming magic photovoltaics with 50%+ conversion efficiency and no degradation in radiation, and I knew I couldn't beat that with solar dynamic. Also, the pointing problem is much more acute, but in fairness, none of the photovoltaic versions of SSP ever had a non-laughable approach to solar pointing and stabilization. Just one of those things the physicists tended to dismiss as "just engineering..."


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PostPosted: May 02, 2007 12:30 pm 
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Here's more rebuttal for the space solar power argument, along the same lines I was mentioning (about power transmission) but with the equations and much more detail. They also go into the problems with laser transmission.

Entropy Production: Solar Power Satellite


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PostPosted: May 02, 2007 6:38 pm 
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However I do suspect we will make use of space solar power someday... mostly because the radiative capacity of earth is limited.

This is rather many centuries in the future before its an issue however.


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PostPosted: May 03, 2007 10:36 am 
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dezakin:

"radiative capacity of earth is limited."

That implies a vast increase in population or per capita energy use or both. If either happens it would be best to put the people & industry in space to use the solar energy rather than beaming it to earth.

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PostPosted: May 03, 2007 2:33 pm 
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Thats sort of implied... With limited radiative capacity and you beam power to earth, the only alternative is to build giant radiators or something impossible.


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PostPosted: May 22, 2007 6:39 pm 
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How good can we get it SSP?
Not necessarily to replace all energy on earth but for space based applications, although I would like to see more numbers on calculations with assumptions that I list below.
Such as powering a magbeam or for space based power needs.
Assumption scenario 1-
Just launching a solar power system in the 20MW-500MW range using chemical rockets to power a magbeam. Using 3000-10,000ISP plasma to help boost sub-orbital vehicles to orbital and then to higher orbits.

A study of the magnetically inflated system had a model of
http://www.niac.usra.edu/files/library/meetings/fellows/mar06/1133Powell.pdf

Of a 200MW solar concentration system that weighed 92 tons. 913 meter diameter mirror.

====
a second scenario is if we have low launch costs and very light concentrators or solar cells

http://www.physorg.com/news5890.html
Carbon nanotube sheets can be made thin enough that a square kilometer of solar sail would weigh only 30 kilograms.

http://www.technologyreview.com/Nanotech/18259/
Carbon nanotubes are being looked at for solar cells

Assumptions - scenario 2 - non-chemical launch systems such laser arrays can reduce launch costs to that of electricity.
http://advancednano.blogspot.com/2007/05/internet-lessons-for-space-nasas-should.html

Magnetically inflating systems and gigantic space bubbles or large numbers of formation flying systems could achieve a large area without construction infrastructure.

It seems that with molecular nanotechnology that the lower weight and construction capabilities and launch capability would radically alter the situation.
It seems that if one wanted to get to future power capabilities of a Kardashev 2 society (I know well beyond the current energy debates, K2 needs a trillion times the power or basically a dyson shell around the sun with solar collection. At that point fission would not be enough.

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PostPosted: May 22, 2007 6:43 pm 
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http://ieeexplore.ieee.org/Xplore/login.jsp?url=/iel5/6668/25789/01145675.pdf?arnumber=1145675

Considerable progress has been made in the critical area of microwave power transmission. At 5.8 GHz, DC-RF converters with efficiencies over 80% are achievable today. Rectennas developed at 5.8 GHz have also been measured with efficiencies greater than 80%. With optimized components in both the transmitter and rectenna, an SPS system has the potential of a DC-to-DC efficiency of 45%.

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Coal kills 300+/day and fossil fuel pollution 1000+/day and is a major contributor to climate change. Nuclear power is needed until coal and oil are eliminated.


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