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Technology Science

Efficient Solar Power Using Stirling Engines 146

Posted by timothy from the they-call-me-bruce dept.
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."
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Efficient Solar Power Using Stirling Engines More

Efficient Solar Power Using Stirling Engines

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  • pictures (Score:5, Informative)

    by pg133 ( 307365 ) on Tuesday November 23, 2004 @01:50AM (#10895957)
    Some pictures [stirlingenergy.com]
  • "large farms of Stirling solar dishes - say, 20,000-dish farms" Now, how about the space issue? I know that at least us poor folks in europe don't have room for this...

    • Re:Farms? (Score:5, Funny)

      by Andy_R ( 114137 ) on Tuesday November 23, 2004 @03:47AM (#10896340) Homepage Journal
      Here in England we are working on rain-driven turbines instead

    • Re:Farms? (Score:4, Informative)

      by Anonymous Coward on Tuesday November 23, 2004 @04:07AM (#10896399)
      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.
      • Or you could contract out to some relatively stable country in the Middle East to house them.

        And we'll contract elves to run them and fairies to clean the mirrors!

        -

    • the poor folks in Europe don't have the room

      but the rich certainly have plenty of land sitting idly by

      5 individuals in the UK receive £BILLIONs of farming subsidy per year between them for leaving their vast lands fallow.

    • 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 r
      • Systems based on imaging optics (including parabolic reflectors) can't make use of diffuse sunlight;

        Although you are correct, it should be noted that an overcast sky provides around 10% of the light intensity in watts per square meter compared to direct sunlight. So if you have a system that works equally well for diffuse as for direct sunlight, and direct sunlight is available 50% of the (day) time, then 90% of the produced electricity will be from the hours with direct sunlight anyway.

        Hence, in this e

        • The 11% produced during the time when everything else is working poorly and supplies are tight is worth more per unit than the 89% produced when everything is cranking and you've got a bumper crop; the more uneven your supply, the greater the investment you need in storage and backups.

  • Why so big scale? (Score:3, Interesting)

    by BigZaphod ( 12942 ) on Tuesday November 23, 2004 @02:34AM (#10896070) Homepage
    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.

    • Re:Why so big scale? (Score:5, Funny)

      by Rhinobird ( 151521 ) on Tuesday November 23, 2004 @02:41AM (#10896098) Homepage
      or a sundish shared in small community groups? Like shared water wells and such. That'd eliminate the middle man.

      You mean,like if, say, 6 dishes could power about 40 homes?

    • Re:Why so big scale? (Score:3, Insightful)

      by Delgul ( 515042 )
      > Why so big scale?

      Why not make it easy for everyone to have in his home?
      Simple: It would be more difficult to tax.
    • Because the middle man doesn't like to be eliminated.

    • Re:Why so big scale? (Score:4, Informative)

      by Smidge204 ( 605297 ) on Tuesday November 23, 2004 @06:51AM (#10896869) Journal
      Because as with internal combustion engines and turbines, building smaller makes them much less efficient. The technology does NOT scale well at all.

      =Smidge=
      • Strange you should say that. One of the profs at my old university (University of Wisconsin-River Falls) created what I have gathered is about the most efficient Sterling engine possible. It would work off the heat of sitting in your hand. It put out almost no real power, but then considering the energy source, that's not surprising.

        • Re:Why so big scale? (Score:3, Informative)

          by Smidge204 ( 605297 )
          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=

  • Close, but not there yet (Score:3, Informative)

    by Shihar ( 153932 ) on Tuesday November 23, 2004 @02:55AM (#10896152)
    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.

    • Re:Close, but not there yet (Score:5, Informative)

      by Urkki ( 668283 ) on Tuesday November 23, 2004 @04:03AM (#10896389)
      • I imagine a few feet of snow and -30 F temperatures render these things pretty useless.

      Snow might do it, but -30F certainly should not, quite the opposite. The engine operates on temperature difference. Thermally isolating the "hot side" is relatively easy, so colder it is at the "cool side" the better. Of course extreme cold could make lubrication etc more difficult, but any temperature current automobile engines handle should be just fine for stirling engine too in that respect.
      • There was an article about an atronomical observatory in Anartica. Powered by a Stirling engine. Get it here. [slashdot.org]
      • Snow never really bothered my satelite tv dish, any snow just fell off it. Basicaly the dish points at a point the sun will cross, even got "sunfade" twice a year as the sun passed into the dish-satelite axis. As far as lubricating the engine, there are synthetic oils that will do it pretty easily especialy the dibasic class of ester based oils
        • A good stirling is totally self-contained and the pressure of the working fluid creates a fluid bearing within the engine housing. In other words, you don't need fancy synthetic oils, just a well-designed engine with a grand total of ~10 moving parts.

    • perhaps you didn't see this article [slashdot.org] on electric cars

      • No, I saw the article about the 100,000+ dollar car with the inability to stop at a gas station and quickly recharge, all while having the comfort (and safety) of a coffin. Like I said before, fuel cells are the only thing to make this solar power really do anything to quench oil consumption.
    • Lithium-ion, zinc-air... anything that has a lot of WH/kg and can take the automotive environment will do. (Electrolytic hydrogen has an end-to-end efficiency of about 50%, and is so bulky that current vehicles have ranges on the order of 50 miles. Even lead-acid batteries can do better than that; hydrogen is a boondoggle.)

      I addressed pretty much the same issue in this essay on my blog [blogspot.com].

    • Misleading - Coal isn't "cheap" (Score:5, Interesting)

      by Red Rocket ( 473003 ) on Tuesday November 23, 2004 @11:19AM (#10898962)

      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")

      • Woah, not only is coal cheap, it's a bargin! Can you imagine how much it would cost to illegally destroy thousands of acres of Appalachian hardwood forests and hundreds of miles of streams?

        And they do it free of charge!

        • Woah, not only is coal cheap, it's a bargin! Can you imagine how much it would cost to illegally destroy thousands of acres of Appalachian hardwood forests and hundreds of miles of streams?

          Uhh, I don't have to imagine how much it would cost. It's done every day and that cost is rolled into the product. It's actually much cheaper to mine this way than to use underground or traditional strip mining because large machinery can replace a hoard of miners. Even when you include the cost of purchasing state
  • to service 20000 reciprocating engines. Even without combustion, that's a lot of moving parts. TFA made no mention of actual maintenance costs, but I can't believe the seal is the only thing that can go bad.

    • Re:How many mechanics needed (Score:4, Informative)

      by Urkki ( 668283 ) on Tuesday November 23, 2004 @04:00AM (#10896381)
      • to service 20000 reciprocating engines. Even without combustion, that's a lot of moving parts. TFA made no mention of actual maintenance costs, but I can't believe the seal is the only thing that can go bad.

      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.
      • Well nothing lasts forever. They might last 20 years, say, but the calculation of cost per kWh will depend fairly critically on lifetime/maintenance of the dish.

        If they decided they would last 50 years with no maintenance in arriving at 6.5c/kWh then they might well be in for a shock!

      • Stirling engines may be simple, but there's more to these units. Since the entire unit swings around following the sun, you can bet that keeping everything properly lubricated will be important. The motors that control the positioning of the unit are going to require servicing as well. Not to mention the occasional washing/polishing of the mirrors to keep them up to spec.

        But it's not like conventional power plants don't employ hordes of mechanics as well. I'm sure it's all been factored in already.

      • Auto engines rarely use ball bearings.
    • There is only one engine for 20,000 mirrors. The light energy is focused in one place and that generates the heat to run the sterling engines.

  • One of the issues they have is startup energy (Score:4, Interesting)

    by foniksonik ( 573572 ) on Tuesday November 23, 2004 @03:22AM (#10896261) Homepage Journal
    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?


    • Any reason why not?

      Assuming that the guys designing this stuff aren't total idiots, rest assured that they looked into something like your proposal. Apparently they came to the solution that using grid power and software to control the staggered startup is cheaper than adding a battery to each dish.
      • hmmm sometimes it is the most obvious things that escape our attentions... you're probably right about them considering it but it seems to me that relying on software and timing is never a good solution to something that could cause catastrophic results..

        Essentially the big upside to using stored energy for startup rather than pulling from the grid is that if one of the 20,000 or 100,000 or even ten of these dishes doesn't start up on any given day, big whoop... send a crew out to swap a component or two,

    • Re: (Score:3, Insightful)

      by account_deleted ( 4530225 )
      Comment removed based on user account deletion

      • Grid transients in general are an issue (Score:4, Interesting)

        by Engineer-Poet ( 795260 ) on Tuesday November 23, 2004 @11:03AM (#10898761) Homepage Journal
        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).
        • Or, simply task fuel burning generators off the grid as the solar comes online, but that does require coordination between different types of generators.
          • The fuel-burning generators often have limited rates of change, unless you want to perform an emergency shutdown (not recommended). The grid operators already have command and control systems to regulate generators, but cutting the power output of a boiler putting out a GW-thermal is not something that happens in a few seconds.

            According to what I've read about grid regulation, it's not uncommon to have the slower-reacting plants ramping in one direction to follow the general trend while the fast-reacting p

            • Transients are typically handled with "peaker" natural gas turbine driven generators.

              Large scale hydroelectric installations with dams are easy to throttle as well... the reservoir = a big battery. My company is a major hydro investor (one of the biggest in N. America) and most of our dams have 30 days of full power behind them and turbines can be brought on-line or taken off-line very quickly. That is plenty to smooth out daily and weekly cycles.

              These heliostat type stirling engines use a at least one

              • Large scale hydroelectric installations with dams are easy to throttle as well...

                How do you manage this outside of the west, where there are few hydro installations? Even there, how do you manage this while also allowing the river to have its normal seasonal cycles instead of weekday surges as our demand produces?

                These heliostat type stirling engines use a at least one stage of heat exchange fluid.

                Two things to make you doubt that conclusion:

                1. The engine in these systems is mounted directly to the rec
        • 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 fo

          • 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.

            Nope. As implied by the article, the engines are tied to synchronous alternators. These will generate at a few hundred volts (such small units do not have the physical size for the insulation needed for high voltages). Conversion to high-tension is done with transformers; there is no storage.

            Eve

            • Actually, _you_ should read the article. The small units will have the sync-alts, but when the farm gets to their target size they hope to get on the long distance grid at the very-high voltages.

              "From 2007 to 2010, the program proposes mass-producing dishes to create a 20,000-dish farm supplying 230,000 V of long-haul power from its own substation directly connected to the grid."

              This was the point at which the whole rising power thing becomes an issue in terms of a sustained, steadily increasing supply.

              • Actually, _you_ should read the article.

                Talk about irony. I read it, and I know what it says. I also know what it does not say that I would demand to know before making technical decisions about this scheme, and it's a lot.

                See that "Engineer" in my moniker? It's not just for show.

                Plus the "electronics" arn't going to effectively be able to put power onto the grid until the station has got a little head.

                Don't be silly. You can put power on the grid with a couple of solar panels and a synchronous inv

                • I *DEFY* you to (meaningfully) "put power on" the 230,000 volt long-haul grid "with a couple of solar panels and a synchronous inverter"
                • A reference as to the issues of placing a multiple generation farm onto the grid.

                  http://library.abb.com/GLOBAL/SCOT/SCOT289.nsf/ V er ityDisplay/29D24AC36EEACC6A85256D2E003F2E6E/$File/ WindPanelPaperPart2.pdf

                  Granted, with wind, the rate-of-change and frequency-of-change is more substantial compared to the sterling engine system (just because of persistence of heat compared to wind etc).

                  This was found with a quick google, so it may be less than perfect as a reference.

                  But section III-B sounds very like th
                  • On the issue of your degree. Arguing to authority. (and almost certianly outside of your field of expertise, since I didn't hear you calaiming to have built (been involved in building) a 20,000-independent-unit sync-alt generation station.)
                    Does that mean you're taking the bet? Either you really think I'm wrong and you're ready to profit from it, or you're just jawboning without having any confidence in what you're saying. As the saying goes, the latter walks.

    • 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 [maxwell.com]


    • Why not add a fuel cell or battery to each dish that would be charged as needed during operation for use as a starter?

      It would be better to just wind up a clockwork spring and use that to restart the engine. That way you don't lose as much energy to conversion.
      • Actualy that's a great idea, the problem isn't starting the sterling engine, it's the clock-motor pointing the dish, is parking the dish face-down, and pointing North at night. I suppose this is to alow any acumilated debris to fall off the mirror. This motor will pull the most current when its stalled, and the dishes inertia is the highest. Using a spring to make sure the dish is just moving and the clock motor is turning, before it's energized would reduce the start-up surge.

    • 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?

      Two reasons:

      1. Adding a battery doesn't eliminate the need for software to control array startup to prevent swamping the various control and distribution systems within the array, as well as to prevent causing p
      • I was under the impression that the problem was the dishes would draw too much power all at once, within milliseconds which would overload the ability to provide power anywhere else, causing a blackout... the proposed solution being to stagger the startup times. It's not a bad solution but it seems overly complicated for the problem.

        #1 reason... maybe I misread the article. I thought the problem was the draw on the system, not the load it would create by generating more power... that's a problem for any hi
        • all you have to do is send a startup command to the dish, and wait until it replies its started, then tell the next one. Maybe your system can handle starting 10 dishes at once so just run that many insances of the sartup command program. Only one ethernet card can talk at a time, yet the internet still works, they just detect the collission and re-send at a randomized time. The system is robust because its build with a lot of slop in it, not beacuse it is perfect.
          • ""If you have to start up 20,000 dishes, you can't do it all at once or you'll bring down the grid," said Andraka. "But you can't stagger them 5 seconds apart either, or your last one won't even come on by the end of the day. We estimate that staggered startups will need to be limited to 5 or 10 milliseconds if we want all the dishes to go online in a reasonably short period."

            These are the requirements.... if you use a battery store for the startup energy needed you can do it the way you describe. Pulling
            • We estimate that staggered startups will need to be limited to 5 or 10 milliseconds
              These things are going to feed the existing 60 Hz power grid, that means 60 Hz is available to the system. 60Hz Ac changes polarity every 0.0166 seconds; so turn on one drive every half cycle. You are just not seeing this as something relatively simple, turning on electric motors at a particular time isn't rocket science, doesn't need real time OSes or anything like that.

              Syncing electric alternators is not hard, in fact it
    • I'd imagine it's just cheaper to stagger the start-up times than to add the added equipment. Sometimes you just have to comprmise between perfect and good enough.
      • But they haven't demonstrated the viability of the staggered startup approach and the software is yet to be written... it's an obstacle in the way of a fully functioning system. The added cost would be small and possibly only a marginal difference over the cost of software development plus quality assurance testing and compliance qualification for use in a power station.

        Real time software isn't cheap and this would have to control hardware to within milliseconds to avoid causing an escalation problem that

  • How Stirling Engines Work (Score:5, Informative)

    by spin2cool ( 651536 ) on Tuesday November 23, 2004 @03:24AM (#10896269)

    Here's a great little intro to Sterling Engines [howstuffworks.com], for those who have never heard of one.

    • Slightly off topic, but does anyone know why someone hasn't developed a hybrid car that uses a Stirling engine to capture waste heat and turn it to electricity? Granted, some heat is required to keep the engine at optimal operating temperature, but most of the energy from combustion is blown right out the radiator.
      • I'd suspect that big enough electric motors and battery packs are just too expensive. Mostly hybrid cars (well, Prius at least) have quite a small electric engine and a smallish combustion engine, and when a lot of power is needed, both provide power for the wheels directly.

        With stirling engines this would not be practical. And this has at least two drawbacks:
        1. less efficient since energy *always* has to be converted to electricity first
        2. more power (==cost, weight etc) is needed from electric motors a
  • Wasn't Dean Kamen working on this?

    Why yes, he was [stirlingengine.com].

    I hope he is working on this solar project (or one like it). He could certainly sort out the remaining issues.

  • ...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...

    I would think that flywheels [wikipedia.org] would be a more appropriate way to store power for the night-time use. Hydrogen fuel cell has become a a buzzword, and I wonder if that was thrown in there because no alternative power sounds cool unless it deals with hydrogen and cars. (Although the EE times is v

    • I'm not sure, but it could be that fly wheels are harder to maintain and/or are not as eficient. If you've got a link to information on flywheels to the contary I'd like to see it.

    • You ever try to mount a flywheel? Some of the old mainframe disk drives needed a special foundation because if left loose they would move in relation to the earths rotation. Enough energy in flywheels to run the US overnight? I think you would push the earth off orbit if you tried it.

      I'm not sure if this is funny or insightful. Anyone care to do the physics?

      • Re:Flywheels instead of hydrogen cells? (Score:5, Informative)

        by Chuckstar ( 799005 ) on Tuesday November 23, 2004 @12:44PM (#10900082)
        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.
      • I just had a image of Marvin the Martian holding on to the north pole with one hand and an Acme gyroscope in the other hand, and explaining to Bugs Bunny how he was going to destroy the Earth.

  • Land prices always kill this... (Score:3, Interesting)

    by human bean ( 222811 ) on Tuesday November 23, 2004 @09:57AM (#10898009)
    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.

    • Re:Land prices always kill this... (Score:5, Insightful)

      by Red Rocket ( 473003 ) on Tuesday November 23, 2004 @11:49AM (#10899400)

      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.

      If the corporations profiting from fossil fuels were required to pay the real estate costs for the production of their products then solar would come out way ahead.
      Hundreds of miles of streams have been burried by mountaintop removal/valley fill coal mining (no charge) -- Thousands of acres of lakes and rivers mangled by acid rain (no charge) -- Millions of acres of forests damaged by acid rain (no charge) -- Thousands of miles of streams and millions of acres of ocean polluted with mercury (no charge) -- All the air on the planet altered in compostion by CO2 exaust with unpredictable consequences (no charge)
      They get away with it because we let them. We want "cheap" energy but we only get it by ignoring the real costs.

  • Something that I have mentioned before... (Score:4, Interesting)

    by cr0sh ( 43134 ) on Tuesday November 23, 2004 @12:56PM (#10900236) Homepage
    Stirling engines do not "run on heat", rather, they take their energy from "heat differentials" - as long as there is a difference in temperature, a Stirling engine will run (in theory, at least - I have never seen a Stirling engine run on say, liquid hydrogen on the "cold" plate, and liquid nitrogen on the "hot" plate - but in theory it would work). This leads to interesting design possibilities, much more so than other conventional heat engines.

    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.

    • Some cold-temperature researchers used a reverse Sterling engine to cool helium (or hydrogen? I think it was helium) to the point of liquefaction. Even better, they used the liquid helium to lubricate the Sterling engine! I read about this in a thermodynamics text in college physics about 21-22 years ago...
      • Ah, yes - didn't mention it because it wasn't relevant, but yes - when you operate a stirling engine in reverse (that is, supply motive power to the pistons to move them), the 'hot' side gets hot, and the 'cold' side gets cold (very hot and very cold) - they use such devices for cryogenic applications - as you noted to produce liquid gasses, as well as for cryo-freezers, etc. There is one company that makes such a device and sells an "experimenter's kit" - it runs on AC, causing the piston to move up and do
  • A few comments have already brought up the space issue (not outer space, but surface area). Where will these things go? In open areas like much of the western United States, this is not an issue. In Europe I would bet it is.

    This same concern is brought up everytime wind power is discussed. Why not combine the two? Place win farms and these new "solar farms" together? YOu could create a much higher power creating density using such a method.

  • This company just bought the tooling to a failed McDonnell/Douglas solar project from the 1980s. And now they're trying a Stirling engine from United Stirling in Sweden, which has been building marginally useful Stirling cycle engines since 1962. At one point there was a Stirling-powered Ford Pinto, and later a Stirling-powered Ford Taurus, but neither was very successful.

    Some background is here. [crest.org] "Ken Stone discussed how the United Stirling engine and parabolic dish system was taken out of moth balls an


  • According to the DOE report "Total net generation of electric power in August 2004 was 366.3 terawatthours"

    Just for August!

    So, Google says 11 square miles is 28,489,869.2 square meters.

    So it's 366,300,000,000 watt hours, divided by 28,489,869.2 sq meters = 12,857 watthours per square meter for the month of August.

    Checking the Naval obserivitory data, it there's about 13.5 average hours of sunlight in August.

    Dang, at this point I'm stumped. I figure we would put these in the best spot in the US, New Mex

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