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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
In the article they mention that with 6 dishes they could power about 40 homes. Why so big scale? Couldn't the size and stuff be scaled down a bit, mass produced, and then homes could have their own sundish or a sundish shared in small community groups? Like shared water wells and such. That'd eliminate the middle man.
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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.
From the article:
"Since each dish draws about 10 amps from the power grid for a few milliseconds when it starts up in the morning, startup must be staggered if a large dish farm is to avoid causing a blackout."
Question:
Why not add a fuel cell or battery to each dish that would be charged as needed during operation for use as a starter?
This would enable each dish to start up under it's own power without affecting the grid at all... and for a very small price in terms of daily output.
Any reason why not?
A fool throws a stone into a well and a thousand sages can not remove it.
Here's a great little intro to Sterling Engines, for those who have never heard of one.
Here in England we are working on rain-driven turbines instead
A pizza of radius z and thickness a has a volume of pi z z a
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.
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.
I read somewhere ( sorry, best I can do citation wise ) that hydrogen is more valuable for other uses, like upgrading existing petroleum stocks for it to be economical to waste hydrogen by burning it as fuel. Also, it seems hydrogen, being the smallest atom, leaks like a bastard, and requires super high pressure tankage to store. Gasoline requires only a thin walled tank, and does not need to be stored under pressure, making it a better, safer fuel. Why carry 500 lbs of hydrogen tanks in your trunk when a 20 lb tank can hold 10 gallons of gasoline? Why mess with high pressure fittings when a liquid fuel allows for a relatively forgiving station pump? Mythbusters even busted the myth that cell phones can cause gasoline fumes to ignite. Wouldn't we be better off using the hydrogen to make gasoline out of say tar, than trying to burn it directly?
The problem with solar power conversion has always been the high Total Cost of Ownership. You have to figure the cost of the real estate these items sit on, versus what other purposes the land could be used for.
In the case of other power technologies, the land use is relatively concentrated. Mines, transport routes, powerplants, refineries, etc. don't take up nearly as much space. In a number of cases the land surface can be used for dual purposes, as in ranging cattle on scrub land sitting on top of an oil patch, or growing crops on reclaim land.
There is cheap land available for this, but it's often located some distance from the use points, and energy doesn't store well and transport is expensive. Figure in the TCO of building that intertie to your solar farm in the middle of nowhere, and the pickings start looking a lot smaller.
*whup* "Get along, little electrons. Heeyah!"
Even if you managed the system such that one dish started off the grid and further dishes started off the ones already running (exponential progression), you'd still have an issue with the grid balance. Typical grid demand fluctuates by a few megawatts on the time-scale of seconds; if you fired up a 100 MW dish farm over 5 seconds you'd have generation increasing by 20 MW/second for some time. Unless you also had demand, reactive power, transformer taps etc. scheduled in synchrony with this, it would make a lot more sense to leave dishes pointed off-sun until you could guarantee demand and had down-regulation capacity ready to handle any excess. It might make more sense to fire up big farms over 15 minutes or more (unless you can start generating with the weak morning sunlight and eliminate transient issues by following the curve of incoming sunlight).
Sustainability and energy independence essay
[blockquote][i]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.[/i][/blockquote]
So, they're arguing around the limitations of the system by promising another completely different undeveloped system? I call bullshit.
If you wanted to store energy, the best way that's actually developed and in use would be to pump water up into a reservior, then run hydroelectic generators during peak usage. Especially since the motion of a Stirling engine is well suited to running a piston pump.
Jon Acheson
All opinions expressed herein are my own, and not those of my employers, who are appalled.
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.
First, coal is not cheap. The price is low because the mining and electricity corporations export every cost they can get away with onto the public at large. Mountaintop removal/valley fill mining practices illegally destroy thousands of acres of Appalachian hardwood forests and hundreds of miles of streams. Electricity generation plants dump millions of tons of CO2 into the atmosphere altering its composition with unpredictable consequences, create acid fog and rain that destroy forests, lakes, and streams, and dump hundreds of pounds of mercury into the environment where it ends up damaging our brains. If mining and generating corporations were forced to be good citizens and not force us to surreptitiously pay for their products' hidden costs then other energy sources would be economically competitive. Instead, they prefer to stuff pennies into the fuse boxes of capitalism and bitchslap any more responsible initiatives with their ill-gotten capital.
Second, BWAH HAH HAH HAH. That would be hilarious about the "pretty solid job at cleaning up the health risks" if it weren't so tragic what is happening. Granted, they are better than they used to be, but those gains come from laws passed in the '70s and '80s which are being rolled back now. (See the "Clear Skies Initiative")
- Hail to our fearless misleader! Fool speed ahead!
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.
One such design, which some of you here are familiar with, is known as an "OTEC" - or "Ocean Thermal Energy Conversion". Pushed greatly by the book "The Millenium Project" - OTECs are devices, sitting on ocean-based platforms, which use the thermal gradients in the ocean at different depths to drive a Stirling-type engine which runs a generator to generate electricity (for a variety of uses in the book). These are actual devices, which have been built and tested (I am not sure if they are in real production or not). This is a very interesting use of stored (in the ocean) solar energy - the amount of energy taken out by OTECs would be miniscule, and would very likely not cause harm to flora and fauna (the ocean is HUGE).
On a similar note, I have, in the past, proposed here on Slashdot the idea of a "reverse OTEC" - which I proposed for be called a DTEC/GTEC/TTEC, for "Desert Thermal Energy Conversion" (or, alternatively, "Ground"/"Terra"). The idea being that we use the energy differential that exists between a few inches under the soil (hot side), and several feet down (cold side). Alternatively, we could bury the "hot" side of the collector in the concrete/asphault that makes up our roadways and parking lots (as well as place them on roofs). We could then gain heat from the sun, increasing the temperature differential (in the winter, when the ground is frozen in some areas - or at night, when surface temperatures drop, these engines would still work - the temperature gradient is still there, just smaller (or inverted in the winter) and not as large).
Using Sterling engine technology in this way helps to offset the "land use" argument - your land actually becomes more valuable, because not only does it provide parking or roads, but energy as well! The tradeoff being that road/parking lot construction and repair would become waaay more complicated, and probably more expensive. These issues would need to be studied. It could very well be that the economics don't work out for this and other reasons. Perhaps the issue then is to design better roadways and parking lots that don't fall apart in a few years, and instead last for a very long time (so you don't have to repair them as often).
I think such a design for Stirling engine use, coupled with more traditional solar heat panels (to drive the Stirlings as well), where they can be used (perhaps putting the panels on the rooftops would be better?) could easily help supplement the energy usage needs of many large urban sites, like malls and office complexes, as well as possibly neighborhoods.
Reason is the Path to God - Anon
Oh, and where do you suggest we get this "tar" to make gasoline from? Do you even know how we make tar?
If all this should have a reason, we would be the last to know.
(I see your bullshit and raise you unnecessary use of attitude.)
They discus the economies of scale (somewhat) by talking first about the "daytime only" nature of the power, and by _coincidence_ the fact that daytime is peak power demand time, where near-term provision will do a lot of good.
The blockquoted text is part of an "not addressed at this time" conjecture. Just liek the part where they talk about a "100 square mile generation system" not as if they are proposing one be built, but as if they were trying to convey the issues of scale and return.
At least it was clear to me when I read the article, and appreciated the "dumbed down explinations" presented, that they were trying to get effecient solar power working instead of wrapping themselves around the *POINTLESS* axle of "what about at night?".
As for the pumping water up a hill (e.g. the "gravity battery" of potential energy) I think you over-estimate the effecency of hydro-power rather a bit as well. Granted the elements are well understood, but I don't think you get the whole "pump head" issue of volume vs lift vs return potential very clearly, otherwise you would not imagine for a moment that the driect mechanical output of the systems in question were "well suted" to running the kinds of pumps you'd need, just because the striling enginges turn and so do pumps.
(_Directly_ using the mechanical energy of the small Stirling Engines to move "enough" water high "enough" to be useful in filling a resivour big "enough" to turn meaningfully sized turbans or water wheels to generate "enough" nightime electricity is a laughable debacle _before_ you consider laminar flow resistance (rising and falling), evaporation loss, pump maintenance (clogging), seeapage loss, providing source water in the first place, simple acreage or water-tower shadows, and so forth.)
The fact remains that cutting N% off our fossil fuel and polution problems is pretty much a win of N%. If we could replace 50% of the runtime on the nations fill-in generators, that would be *huge*. _TEN_ percent would be huge too.
The article and the investigators are trying to solve *their* part, what are you trying to solve by bitching about their off-hand mention of hydrogen?
The fact remains that the "energy storage" problem remians no matter what the generation system. "Batteries" for electric cars, holding solar, wind, or tidal power for return when those are not at peak. That sort of thing will remain no matter what.
The "don't bother with solar until you solve the nightime issues" frame of mind is defeatest as hell and so not terribly useful.
I suspect, were I to have to prognosticate, that we will need to revive nuclear power. Invent better batteries/fuel cells, look into _sonic_ (as opposed to electical) separation of water into hydrogen and oxygen [very promising but not often mentioned], and biomass-fuels, and all sorts of things to "solve" the current problems.
Meanwhile, if we could learn to turn off the freaking lights when we leave the room (guilty here more often than I'd like 8-) and learn to wear a sweater instead of heating the house to 75F (which I *am* good about 8-), and all sorts of simple stuff things will be "Better."
And better is... better.
Innocent people shouldn't be forced to pay for inferior software development.
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The "steadly increasing" 20MW/second isn't that problematical if you don't put it on the grid right then but instead wait till it was needed, or use it to charge a (whatever) storage battery to span lulls and, I don't know make the hydrogen for the on-site matenence vehicles or something.
There is a complete non-issue about how to cut in this power source (compared to any other kind of generator).
How not to "waste" the power generated when you aren't cut in is a "what to do with the gravy" kind of issue for the most part.
Since they have to get up to the (230,000-volt was it?) levels to get menaingfully onto the grid in the first place I suspect that a giant bank of capacitors and a fast switching doodad are pretty much mandatory. The plant's start-up cascade should be private anyway as they could go "on-sun" exponentially before they cut in.
Of course, the larger problems of the power grid are larger problems. Especially with deregulation and "known bad places" as per the recent blackout. So wer are borrowing problems here anyway.
Innocent people shouldn't be forced to pay for inferior software development.
--"Code Complete" Microsoft Press
Remembering that the actual heat isn't going very far, the cooling isn't *that* interesting.
.5 to 2 times the size of the farm. The thermal might cast a rain shadow but not for more than twice (?) the length of the chord distance that the prevailing wind passes over the farm.
We arn't reflecting the heat off into space (a la snow-cover), we are reflecting it to a heat sink about 20 feet off the ground.
The heat passes through that heat-sink and into the air. The air temprature will probably *rise* during the day because the ground isn't soaking it up _directly_. Any given square-inch of ground will be in shdow for about two extra hours a day per dish (wild-ass geuss from just looking at the thing) and will be subject to the shadows of three dishes max. So any given square inch will be "shaded" for half the day.
A good bit of that heat will get back into the ground anyway.
The net environmental impact would be about the same as for sparse tree cover (But without the water use and with a dissimilar habatat provision).
Soil water retention would go up just a tiny bit.
The most liekly impact woudl be changes in midle-size air masses within a range of about
So worst case, (total wog again here) about the same climatological impact as if say one-third the same area were covered with "water that couldn't evaporate" or concrete sculptures of trees.
A similar area covered with buildings would probably be worse in general. It would be the classic "downtown effect" (where it is hotter downtown during the day and colder downtown at night).
Innocent people shouldn't be forced to pay for inferior software development.
--"Code Complete" Microsoft Press