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Efficient Solar Power Using Stirling Engines
tscola writes "The EE Times is reporting that the U.S. Energy department believes it can make solar collectors that generate electricity at efficiency levels that rival other methods. Instead of using photovoltaics, they want to use Stirling engines to convert the heat of the sun into electricity."
RTA much?
By storing the energy in hydrogen fuel cells during the day, Stirling solar-dish farms could supply U.S. electrical-energy needs at night too, as well as enough juice for future fuel-cell-powered automobiles, the DOE believes.
Some pictures
If this is true, this is a pretty interesting advancement. I can't help but be a little skeptical about the price tag they are assigning it, but I am a sour old bastard at heart. Are the prices they are spitting out for one of these things sitting in the Arizona desert or northern Maine? The article threw in some stuff that I found questionable. Namely, it talked about moving away from reliance on foreign oil - utterly ignoring that the US (and most nations for that matter) gets most of its power (in the power grid) from coal. While it would be nice to get away from coal, there are two things stopping this. First, coal is cheap. Second, in recent years they have done a pretty solid job at cleaning up the health risks associated with coal.
I am not saying that this isn't a worthwhile discovery, just that I don't see much in the market that is going to push to adopt this technology other then governments wanting to use something that is cleaner then coal. Oil is good stuff because you can throw it into a car and have it run. The real technology that is going to make solar cells like these worthwhile and get the market onboard would be cheap hydrogen fuel cells you can stuff into a car. Charge up a cheap fuel cell with one of these solar cells, ratchet up the price of gas some more, and now you are talking about cleaner cars and the ability to care about the Middle East about as much as the US cares about Africa (which is to say almost not at all).
The only other two real problems I see is that first; in the north I imagine that the cost per kilowatt hour is much more expensive. I imagine a few feet of snow and -30 F temperatures render these things pretty useless. Second, to power a place like LA I imagine you would need a massive bank of these things. I wonder if a massive bank of these would have an effect upon the environment or the weather patterns in a noticeable way. That said, I suppose if you just throw them all in a desert no one is going to care.
So, neat technology, but I don't expect an energy revolution over night.
Here's a great little intro to Sterling Engines, for those who have never heard of one.
Stirling engines are mechanically extremely simple, low-RPM and low-vibration. I'd expect the mechanical parts to last "forever", considerng how long ball bearings, cam shafts etc of even cheap automobile engines last (excluding manufacturing defects etc) in much more hostile environment. There's really surprisingly little wear under low loads, and stirling engines only have low loads.
The space issue probably wouldn't, however, exist for the United States. For example, the state of Oregon has a population of 3.5 million. It covers an area a bit under 100,000 square miles (about 259,000 square kilometers), which is about the size of the UK. Much of this land is desert and open rangeland. A 20,000 dish farm would fit quite inconspicuously in SE Oregon, perhaps in Harney County which covers about 10,000 square miles with a population of only about 7200 people. The area gets lot of sunlight (but can get pretty cold in the winter).
But realistically, these probably don't need to be built in a huge farm someplace. You could conceivably stick two or five of them on top of buildings, float a dozen of them on barges anchored in a reservoir, etc., and built the network piecemeal.
If they really are valuable enough, it probably wouldn't be hard to find space for them in open space in Europe: someplace in Spain might be found, even if some amount of agriculture might need to be displaced for the installation. Or you could contract out to some relatively stable country in the Middle East to house them.
If they're chiefly used to generate hydrogen they might be very useful to install in Northern Africa; hydrogen tankers could carry the energy to Europe.
Because as with internal combustion engines and turbines, building smaller makes them much less efficient. The technology does NOT scale well at all.
=Smidge=
Systems based on imaging optics (including parabolic reflectors) can't make use of diffuse sunlight; anything coming from off-axis gets bounced to one side of your target and goes off uselessly. While the Sahara would be solar-concentrator paradise, areas where large amounts of the total insolation is diffused by clouds are going to collect more useful energy (and a LOT more during periods of lower supply, when it's more valuable) with flat-plate and non-imaging collectors than with the dishes required to run a Stirling engine.
Time is Nature's way of keeping everything from happening at once... the bitch.
Actually a cheaper solution (than batteries) for a startup current is to use something called an "ultra capacitor". They charge up faster, last longer, and can provide very high currents for short durations.
Here is one manufacturer's ultra capacitor FAQ: Maxwell Technologies FAQ
O=='=++
First I'd like to say that there has been a record amount of interest in this post. (dont mod me down, I can't help being disapointed in a posibly world saving subject being ignored in favor of less important subjects)
Take it easy. You know, there have been prototypes of these stirling dish things since at least the early 1980:s. If they can be made economically viable in the 2010 timeframe as the article suggest, I'm sure they will be discussed a lot.
There was a project some years ago in Australia where the heat difference between (one of our) desert surface and pipes/heat exchange buried underground was going to power a whole lot of engines. I'm not positive but I think they were Stirling engines that had been changed in some way (possibly day and night running- desert cold at night). They got to the stage of cupple of dozen in a test area to show efficiency workability etc. then nothing. Googling it doesnt show much. Rumors of state govt being bought out by the local energy companies which rezoned and shut them down. The usual Nexus style hippies chanted conspiracy, maybe it just wasnt as efficient as it could have been at that time.
Anyway, plenty of room and plenty of heat and cold differentials in the desert(s).
The efficiency of a heat engine is proportional to the heat difference between the cold and hot sides. In the proposal above, the heat difference is pretty small, so you'd need lots of expensive engines and piping to produce little power. I assume that was what killed it, rather than some Big Oil conspiracy.
Just something bothers me. Wouldnt the loss associated with transporting the energy back to where it is needed (suberbia, industrial and city use) by leakage make it not sustainable?
No worries, mate. Modern high voltage DC transmission lines, often used for long range transmission, have losses of about 4 % per 1000 km.
What are the efficiency ratings of other energy storages such as spliting water into Hydrogen and Oxygen to be stored separately and recombined when needed to make combustion engine generate power?
Appalingly low. Electrolysis is about 70 %, liquefaction 66 %, burning the hydrogen in a combustion engine about 40 % for a medium sized stationary engine. In total, 18 % efficient, compared to 96 % efficient for 1000 km cabling.
Quite the contrary.
Flywheel batteries (for lack of a better term) are designed to be free-floating within their housings. Its much easier to let the thing precess then try to tie it down. This doesn't work for disk drives because you need the heads in contact with the drives. For a flywheel, you don't need anything to be in contact, so you can let the axis move around as it likes. (You do energy transfers using magnetic fields.)
Regarding the energy of the spinning earth. First, any change you made to the earth's spin by energizing the fly-wheels, you would get back when you took the energy back out (minus friction of course). So you're not really affecting the total energy much.
Second, you clearly are not understanding the magnitude of energy we're talking about in the earth's rotation. If you could siphon energy from the earth's rotation, you could power the whole U.S. for 1.4 million _years_ and only change the length of a day by 1 second.
Ooops.
Well, 10,000 square miles is 6.4 million acres.
There are 7.8 million acres of coal mines currently under permit. This 7.8 million excludes over 2 million acres of old mines which have been reclaimed. Note that reclaimed mine land is not the same as being in pristine condition.
The 7.8 million also excludes down-stream/down-river areas which may be impacted by run-off from mine waste rock and tailings.
So, its not as good a comparison as I originally thought, but the land needs are actually pretty close in size.
Keep in mind, though, that this solar use is potentially easier on the land (and nearby land) than strip-mining is.
You can buy those as kits. They're called "LTD" (Low Temperature Differential) engines. They even run backwards if you put them on ice!
Those things are anything BUT efficent. They are just very delicate and carefully constructed so they don't need much to run. Remember Carnot efficiency is 1-(Th/Tc)
=Smidge=