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Power Science

Open Project to Develop Renewable Energy System 154

Posted by Zonk
from the sounds-very-sciency dept.
rohar writes "We have been working on a system that combines some existing indirect solar technologies to build a location independent, renewable, reliable and economically feasible indirect solar electrical power generation system. The idea is to 'roll-your-own' geothermal source by capturing heat from the ambient air with a solar powered absorption heat pump, store it underground and generate electricity from the air cooling convection. When the air is cooler the stored heat is then used in a reverse process to generate electricity by transferring the heat back to the air when it is cooler (at night or seasonal). There are many additional benefits including clean water capture from the "dehumidifier" effect of the air cooling, construction from common materials and thermal storage that may be incorporated into dwelling heat systems." After reading over their description, how likely do you think it is to work?
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Open Project to Develop Renewable Energy System

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  • How Likely? (Score:5, Funny)

    by Umbral Blot (737704) on Monday January 08, 2007 @03:35AM (#17505356) Homepage
    37.62% according to my calculations. But I haven't taken quantum effects into account yet, so I may be slightly off.
  • This sounds too good to be true. And you know what they say about things like that....
    • Re: (Score:2, Insightful)

      by kfg (145172)
      This sounds too good to be true.

      The problem is that I don't see any reason why it shouldn't work; and there are plenty of people who don't understand that just because something works doesn't mean it's not too good to be true as well.

      KFG
      • Re: (Score:3, Insightful)

        by shmlco (594907)
        "The problem is that I don't see any reason why it shouldn't work..."

        Think harder. The logic seems to be that we pump ambient heat from the air into the ground... which is where things seem to fall apart. For example, just how MUCH heat can we gather and store in the ground? What's the differential? How much can we get back?

        More to the point, how do we keep the heat we pump into a point in the ground from radiating away and disapating?
        • by IMustBeNewHere (899319) on Monday January 08, 2007 @06:26AM (#17506138) Journal
          I don't know about the part of his design that is above ground.

          The underground bit however, works well in practice, at least in the Swedish climate.

          Extracting heat from a temperature differential with a heat pump and storing it in the ground, is in wide commercial use here, and you can save money on it.

          In a quick search in the Swedish yellow pages, I found hundreds of contractors to choose from.

          There has also been plenty of research conducted in this field in various Swedish universities. The article author would probably save himself a lot of time if he looked some of it up. Here are a couple of abstracts (in English and Swedish):
          http://www.lib.kth.se/main/stems_projektrapporter. asp?subj=vp [lib.kth.se]
          • I actually see a problem that nobody has mentioned yet.

            Anhydrous Ammonia is used to make methanphedamines, hence you're going to have a couple of problems.

            Firstly, any chemical company that's going to sell you the required quantities (I think) has to report these sales to the athorities (which won't be an issue when they show up and you show them that you're working on a renewable energy system (and you've got all the proper permits, etc))

            Secondly, I suspect that you'll be a target for meth dealers who will
            • by daeg (828071)
              Lace your ammonia with rat poison and you won't have a problem.

              What? It works for garbage cans to get rid of raccoons!
              • Actually, rat poison is sometimes one of the ingredients in the mix to create crystal meth. You may be making their job easier for them if you lace it that way.

                With rat poison, starter fluid, and anhydrous ammonia being ingredients and mixing being done in wooden shacks and moldy basements, is it any wonder this stuff kills people?

                Please, if you're going to do illegal drugs, people, at least get something grown in the ground or made in a lab by people with training as chemists. Don't let "Three-tooth Junior
            • by mspohr (589790)
              Farmers and industry already use large amounts of anhydrous ammonia (farmers for fertilizer, industry for refrigeration and as a chemical component). The sale, storage, and use of this chemical is common and your home use of this chemical should present no regulatory problems.
        • Re:hmmm (Score:4, Informative)

          by tacocat (527354) <tallison1.twmi@rr@com> on Monday January 08, 2007 @06:57AM (#17506304)

          Effectively speaking, you can't store heat in the ground. If you could, then heat pumps today wouldn't work. And plumbing in the north would fail every year. The ground temperature much below 3-6 feet stays a relatively constant temparature all year round. I think between February and August it might vary 10F if that.

          The point being that if it takes 6 months of weather on the surface to effect a 10F change in the ground, you won't be able to create a heat pump powerful enough to make this project work. The earth has the property of being a massive heat sink with a reasonable thermal conductivity. This allows heat pumps to pull heat out of the ground in winter and push it into your house. They become inefficient at very low temperatures because the heat transfer freons don't work very well, not because the ground runs out of heat.

          It might be more possible to do this if you had an insulated/isolated storage of water and used that as the heat source for storage and retrieval. You could also do it with air and stone. But in every case, you have to provide a means of thermal isolation between the earth and the storage facility. Also, it would be far more efficient to store the heat by means of thermal exchange pipes (solar heated pools) than trying to pump the heat into place.

          The convection tower concept isn't new. I think someone came up with that in Australia about five years back. But the storage of heat for later retrieval is.

          • Re: (Score:3, Informative)

            by rohar (253766)
            Drake Landing Solar Community [www.dlsc.ca] is an example of seasonal thermal storage.
            • by tacocat (527354)

              That looks pretty neat! It would be great except I think Americans would be to quick to start bitching about the fat neighbor who runs around in skivvies all winter in his house of 90F because he's sucking up someone elses heat.

              It appears as if they are sinking most of the heat into a large volume and not worrying about the thermal loss to the earth. I would consider some kind of isolation to better insulate the storage but it might not be worth it.

              • by m0rph3us0 (549631)
                I think you mean Californians, not Americans, most American's wouldn't care because they know that person would be paying his share of the heat he used.
          • by salec (791463)
            So, if I understood you well, in a way, we have this "thermal ground" similar to "electric ground" by its constancy (of temperature instead of potential). The way to use it then would be to find the depth where the temperature is constantly in the middle of daily temperature extremes above ground, so that there is no need to "store" and "retrieve" heat, provided such "middle temperature point" exists in the ground, that is.
            • by nmos (25822)
              The way to use it then would be to find the depth where the temperature is constantly in the middle of daily temperature extremes above ground, so that there is no need to "store" and "retrieve" heat, provided such "middle temperature point" exists in the ground, that is.

              It's possible but I'd think it would be pretty expensive to drill down that far and lay collection pipes etc. In practice what people do is only go down a few feet and use a heat pump. How well that works depends a lot on what the ground
      • Re: (Score:2, Interesting)

        Wel simply why it doenst work good...
        why should warm ground air prefer to go trough a tube to cold areas?
        If it simply can bypass it and go from everywhere outside the tube up or down, with less friction. The same goes for the oposite direction.


        But no wories there is realy enough energy on this planet....
        you only have to dig a hole in the earth, as Lava is quite hot you know, and even without such deep holes, below earth there is enough heat energy stored which make oil and uranium look like a jok
  • So you're going to generate electricity and clean water out of think air. Next you'll be turning lead bars into gold :)

    • Re:Thin Air (Score:4, Insightful)

      by Anonymous Coward on Monday January 08, 2007 @03:57AM (#17505480)
      And i suppose you think that generating electricity from wind turbines or solar panels is impossible too?

      Generating electricity from a heat difference is entirely possible, its just a matter of how efficient the whole process is as to whether its worth it. Actually if your after more information on that (it works both ways too!), then have a read here: http://en.wikipedia.org/wiki/Peltier-Seebeck_effec t [wikipedia.org]

      And the water thing is just a by-product http://en.wikipedia.org/wiki/Condensation [wikipedia.org] :)

      Jacko
      • Re: (Score:2, Funny)

        by kfg (145172)
        And i suppose you think that generating electricity from wind turbines or solar panels is impossible too?

        I suppose you think it's impossible to turn lead bars into gold?

        KFG
        • Not impossible, but highly impractical. Lead bars are far too thick. Lead ribbon, now you're talking. Just need *free* energy and we're all set to ruin the metals markets :-)
          -nB
          • Re: (Score:3, Funny)

            by yada21 (1042762)
            Natural gold has intrinsic value. Artificial gold is by definition a fiat currency, and henceforth is worth no more than the paper it's printed on.
            • Assuming I have limitless energy I can make the metal atomically correct. After bombardment I can seperate the gold atoms by density, and re-bombard the light ones with neutrons, the heavy ones with protons to the point they fission (or should I manage to capture enough positrons I can smack those around to lighten it), and the random other bits can be used to operate my antimatter reaction vessle :-)

              Point I was making is that once it costs less than gold to make gold, then the market for gold (as currency
              • Re:Thin Air (Score:4, Insightful)

                by Anonymous Coward on Monday January 08, 2007 @06:35AM (#17506178)
                Point I was making is that once it costs less than gold to make gold, then the market for gold (as currency) will be broken.

                And I think the point KFG was making was a parallel one, that alternative sources of energy, right now, net so little gain in comparison to the fossils fuels that there's little point. And when the fossil foils become horribly expensive unfortunately so will all the the alternatives, since producing and maintaining them depends on a rather nontrivial amount of fossil fuels. It's easy for people to shrug off fossils fuels as just another energy source but really, think about what they are... millions of years of condensed, stored, solar energy, with a dash of geothermal thrown in too. And we're burning through that million years of energy in decades. When the oil is gone, I think our descendants (assuming any survive the bloody resources wars) are going to be absolutely furious with us that we just burned the stuff.

                • Foo. Our descendants will reap the benefits of the technology that was developed utilizing ff. Bloody resource wars will only occur if we fail to become a space-faring race. We will graduate beyond them (fossil fuels) and our progeny will be grateful we did. Unless you think they'd rather be living in caves.
                  • Sounds great! Current estimates say that it will take 20-50 years for FFs to become more energy expensive to extract from the environment than there will be energy gained from using them.

                    Should I appoint you as the person in charge of making us a fully space-faring race that doesn't depend on FF anymore? Can you get it completed within the next 50 years?

                    Personally, I think FFs will last longer than 50 years, but I DO think that we probably only have around that amount of time before sending large obje

    • Re: (Score:2, Funny)

      by Soko (17987)
      So you're going to generate electricity and clean water out of think air.

      Hmmm... think air...think air... *SNAP* Hey, Al gore invented the Internet and is all about green energy, maybe I should think like him. Here goes:

      With Global Warming, we've got a lot of extra heat in the air - meaning that the atmosphere is both warmer and wetter than would be before we stared using energy stored in hydrocarbons to power our economy and release all the trapped CO2 back into the air. On first glance the method in the a
    • by cheekyboy (598084)
      http://cat.inist.fr/?aModele=afficheN&cpsidt=3407 6 62 [inist.fr]

      Sewage sludges from German municipal wastewater treatment plants possess high gold concentrations (280 to 56,000 g/kg in dry matter) similar to some ore deposits which are being mined for gold. In addition, the sludges exhibit elevated platinum (10 to 1,070 g/kg) and palladium values (38 to 4,700 g/kg), and low osmium (3 to 51 g/kg), iridium (0.6 to 26.5 g/kg), ruthenium (2 to 390 g/kg), and rhodium contents (2 to 352 g/kg Major amounts of these metal
      • (280 to 56,000 g/kg in dry matter)


        So, in units people feel comfortable with, there's at least half a pound of gold in two pounds of shit? And under favorable circumstances, shit is 5600% gold? Something smells around here, and it's not fishy.

        Micrograms, perhaps?
      • by drsquare (530038)
        Sewage sludges from German municipal wastewater treatment plants possess high gold concentrations (280 to 56,000 g/kg in dry matter)

        So 1kg of dry shit contains 56kg of gold? Fetch a fishing net and a pair of rubber gloves, I'm going to make myself a millionaire.
      • by njh (24312)
        You don't think it's just a few random wedding rings that fell down the toilet? (Where's your muse when you need them?)
  • by mwilliamson (672411) on Monday January 08, 2007 @03:48AM (#17505428) Homepage Journal
    here's a project using solar heat to drive a ammonia absorption cycle freezer. [PDF] [homepower.com]
  • Wind turbine (Score:5, Informative)

    by Technician (215283) on Monday January 08, 2007 @03:53AM (#17505454)
    After looking at the diagram, it is evident the math is not done. A few things come to mind. The most glaring is the wind turbine. Anybody you know of put a turbine in the fireplace flue to get electricity from the heat draft? This is a draft with a large heat change. How much draft do you expect to get from the day/night differential. Don't expect enough juice to power the water pump in a water cooled PC.

    Getting the heat to provide the high pressure ammonia to feed the expansion valve is also a problem. Time to do the math.

    A good place to start is Modern Refrigeration and Air Conditioning.
    http://www.bizrate.com/technologybooks/modern-refr igeration-and-air-conditioning--pid4254146/ [bizrate.com]

    Instead of trying to get high pressure ammonia, look up continious cycle absorption cycle refrigeration. The key is using vapor pressure to your advantage. Day/night cycles are not going to provide the requried amount of pressurised liquid ammonia for the job.

    Study and learn continious cycle absorption cycle refrigeration then redesign and eliminate the expansion valve, & turbine. Add a light weight inhert gas to the entire system to make distilation of ammonia possible and stop uncontrolled reasorption into water.
    • Re: (Score:3, Interesting)

      by dbIII (701233)

      Getting the heat to provide the high pressure ammonia to feed the expansion valve is also a problem. Time to do the math.

      OK - I have not read the article but I will point out that a century old kerosene refrigerator uses a wick and not a great deal of fuel plus a bucked of water to handle expansion and condensation. Solar thermal has potential and scales up - things will be practical given a large enough size, and practical things become smaller given a larger heat differential.

      • Re:Wind turbine (Score:4, Informative)

        by Technician (215283) on Monday January 08, 2007 @08:31AM (#17506812)
        OK - I have not read the article but I will point out that a century old kerosene refrigerator uses a wick and not a great deal of fuel plus a bucked of water to handle expansion and condensation.

        Early kerosene refrigerators used a single cycle sytem where the ammonia boiled or evaporated as it was absorbed into water. To get the ammonia back and the water, the cold side was stuck in the bucket of water and the room temprature water chamber was heated by the kerosene flame to seperate the ammonia from the water. Do a Google search on "iceballs ammonia" for a version that still entertain people today who build their own.
        Before you build your own, remember this runs on high pressure during regeneration, and uses ammonia, a relatively hazardous material.

        http://www.ggw.org/~cac/IcyBall/crosley_icyball.ht ml [ggw.org]

        Simple day/night tempratures will not complete the regeneration cycle. The temprature is too low. Even though very little kerosene is burned in those refrigerators, the burning kerosene did provide the required tempratures to complete the regeneration cycle.
  • So... (Score:4, Insightful)

    by CookieOfFortune (955407) on Monday January 08, 2007 @03:54AM (#17505464)
    So this relies on a difference in ambient temperatures. You could also drill a hole deep into the ground and send in heat pipes, since it's pretty hot underneath the ground. The issue here is economics, how much power you get out compared to how expensive it is to build the system. Drilling a deep hole probably isn't cheap, and I don't think building a tower is either. At least you don't have to worry about temperature swings underground (sure it could happen, but I'd think air temperature would change more drastically). I think the issue is pretty much based on economics, there are cheaper ways to get energy, and the concept of using ambient temperature isn't new.
  • by advocate_one (662832) on Monday January 08, 2007 @03:54AM (#17505466)
    just as soon as I get back from the patent office...
  • by Scareduck (177470) on Monday January 08, 2007 @03:55AM (#17505468) Homepage Journal
    They cite a mistaken analogy to Linux as one of the reasons they feel their project could succeed, but in fact the problem is that such a system will require capital to run. This in fact makes it the opposite of the situation obtaining with Linux, when one of the key ingredients, low-cost commodity PCs, helped drive and unify development.
    • by dbIII (701233)
      They cite a mistaken analogy to Linux as one of the reasons they feel their project could succeed,

      Which is really bizzare becuase open source software is just a subset of the sharing of knowlege that got science to the point it is today.

  • Geothermal.. (Score:2, Insightful)

    by Anonymous Coward
    This design seems to be a complicated form of utilizing geothermal energy. I don't see any reason why the geothermal energy shouldn't instead simply be used for space heating instead of electricity generation, especially in areas with low levels of geothermal energy availability.

    In areas such as Iceland or Hawaii, this technique would be more feasible, but simply using the more abundant geothermal energy sources to drive steam turbines without the use of refrigerants or air turbines would probably be more e
    • by dbIII (701233)
      I don't see any reason why the geothermal energy shouldn't instead simply be used for space heating

      I do - however it is over 30C here in a house built for the climate and it is after 10pm at night. Hot water is a different story.

  • There's too much energy transfer/transformation to make this very feasible. Just stick with solar energy/cooling for fuck's sake.
  • hmm, just wait with that one till I get my perpetual motion generator set to work...
  • This might work in some places where there is a large difference in temperature from day to night. Where I am living on the edge of the Saharah desert we have hot temperatures all year around but the temperature does drop considerably at night. However, the places like this that have such differences generally need the electricity during the day for cooling rather than at night for heating. So the system would need a good way of storing the energy for day time use and I am not sure of the best way of doing

    • While living in Nigeria in the 1970's I proposed a system similar to this, and tried to patent it when I returned ot the UK. However, the company I was using to licence my ideas "Cambridge Intellectual Properties Ltd" (Cambridge, England) appeared to have stolen my idea and sold it to an organisation in Spain, who actually built it as I described it to CIP (as opposed to my actual proposal, which I did not disclose).

      The spanish organisation built one, and it worked for at least 7 year to my certain knowled

      • --- or more air volume. I was discussing this type of idea with an architect who wanted to build large multifamily housing of good quality in Houston, TX. His idea of having hollow walls between units (for fire protection, utility access, component upgrading and modularity and thermal cooling, plus a "wind farm" of vertical windmills at the corners, plus a large vegetation plot on the roof (similar to the Ford plant in Michigan), plus heating and cooling control by having chambers of eutectic salts around a
      • by nasch (598556)

        C) There are people in Australia working on a huge energy tower, several miles high

        These people [enviromission.com.au]? "The tower will be over there," Davey says, pointing to a spot a mile distant where a 1,600-foot structure will rise from the ocher-colored earth. "Several miles high", even if "several" means three, would be over 15,500 feet. According to Wikipedia, "Currently, the tallest standing structure is the KVLY-TV mast near Fargo, North Dakota, at 629 m (2,063 ft)." I don't think anyone is planning anything seven o

    • by Znork (31774)
      "This might work in some places where there is a large difference in temperature"

      You dont really need that much of a temperature difference to generate electricity; there are model stirling engines that work off the difference between the heat of the air and the heat of your hand.

      Of course, you still do need enough of a total stored energy diffrential to actually generate the electricity needed, so at low diffrentials you may need larger initial storage generators or storage volume.
  • by Knutsi (959723) on Monday January 08, 2007 @04:40AM (#17505704)

    It may be that this particular case will not work, but the idea is great. Roll it yourself systems developed, improved, forked and tested online through an open source ideology... great stuff (: One has to admire the potential social consequences of the open source ideas, both in technology, law and governance.

    Sadly for some, this also applies to warfare [typepad.com].

    (this blog speaks of, amongst other things, how "open source warfare" (OSW) is the key behind the insurgency success in Iraq. The methods applied by what is essentially guerilla groups testing wildly different approaches across the nation, then learning from their success, contrary to a carefully planned and centralized military system)
    • by zCyl (14362)
      It may be that this particular case will not work,

      That seems like the likely outcome.

      but the idea is great. Roll it yourself systems developed, improved, forked and tested online through an open source ideology... great stuff (:

      Hmm. Perhaps they should consider putting the design under a wiki which specifically encourages original research, and see what happens to it.
      • by Knutsi (959723)
        Such things could possibly also stimulate more interest in engineering and science, and work as great comunity-competence building worldwide. If enough components are available at low price, it may be very usefull things for developing nations as well.
  • by DerekLyons (302214) <(moc.liamg) (ta) (retawriaf)> on Monday January 08, 2007 @05:17AM (#17505840) Homepage
    After reading over their description, how likely do you think it is to work?

    Not very likely at all - because the creator doesn't really have any idea how steam engines, or refrigerators work. Also, like most armchair engineers he's really, really light on the math.
     
    I find this part particularly amusing;
     
    2. The principles and project management of Linus Torvolds with Linux and the many other contributors to Open Source and Free Software has shown such success with large projects.
    3. There are many people with good ideas and a willingness to help, but Mechanical and Electrical Engineering and Physics are not their field. The project is based on bringing people together to work on something that has benefit for everyone.

    I think the creator quite misundertands how F/OSS works - he somehow thinks that people who aren't programmers get together and somehow create the programs, and that the same magic wand will work for making this kludge a reality.
     
    Then he makes laughable statements like this:
     
    In the capital investment for energy sources that are renewable, the capital investment is not important. Once the system is built and producing electrical power, it doesn't run out.

    I guess in his world structures and machinery aren't subject to wear and tear - but here in the real world they are.
    • Re: (Score:2, Insightful)

      by TubeSteak (669689)

      I guess in his world structures and machinery aren't subject to wear and tear - but here in the real world they are.

      The miracle of modern technology is that consumer grade stuff just works, with very little extra input required. I'd submit that is why someone can seriously suggest such a project without factoring in maintenance.

      Other than a car, I can't really think of many consumer grade pieces of 'equipment' (which people regularly interact with) that require regular maintenance.

      Even newer cars don't requ

      • look down, what are you typing on.... is it maintenance free?
      • by drinkypoo (153816)

        Radiators don't really need to be flushed anymore.

        WRONG. Please do not dispense your automotive advice, you will be directly responsible for the destruction of other people's cars.

        I will now tell the assembled populace the truth, so that they do not believe you. I have received ASE certification in automotive heating and cooling systems - the only certification I bothered to get. I could have easily passed the automotive electrical exam, as I aced the class, which was a six unit class. These are my c

        • by treeves (963993)
          Some corrections to your correction:

          Engine coolant has three main ingredients, not two: you forgot corrosion inhibitors. They passivate the metals in the cooling system and prevent the galvanic corrosion you mention without naming.

          And it's ethylene glycol (or propylene glycol), not POLYethylene glycol as the other ingredient besides water.

          The radiator cap allows the pressure the in the cooling system to increase so far before it relieves pressure. It is the increased pressure which raises the boiling po

          • by drinkypoo (153816)

            Engine coolant has three main ingredients, not two: you forgot corrosion inhibitors. They passivate the metals in the cooling system and prevent the galvanic corrosion you mention without naming.

            Actually I wasn't trying to go through the laundry list of ingredients in antifreeze; the product that you put in your radiator up to 50/50 in normal places or 70/30 in seriously fucking cold ones is still called "antifreeze".

            And it's ethylene glycol (or propylene glycol), not POLYethylene glycol as the other

      • by syukton (256348)
        "Consume grade" machinery doesn't require maintenance because it has a tendancy to just up and break rather often, requiring repair. Toaster ovens, microwaves, blenders, all manner of home appliances will inevitably fail, possibly just outside of their warranty period. Washing machines are another great example of a "consumer grade" piece of equipment that will just mysteriously stop working, usually due to a motor shorting out or a similar electrical problem. Anything with an engine or motor is generally u
      • I guess in his world structures and machinery aren't subject to wear and tear - but here in the real world they are.

        The miracle of modern technology is that consumer grade stuff just works, with very little extra input required.

        The reality of modern consumer grade technology is that, yes, it just works - until the day it doesn't. (Kinda like my washing machine which recently required repairs.)

        Other than a car, I can't really think of many consumer grade pieces of 'equipment' (which peopl

    • by dbIII (701233)

      I think the creator quite misundertands how F/OSS works - he somehow thinks that people who aren't programmers get together and somehow create the programs, and that the same magic wand will work for making this kludge a reality.

      It really isn't all that hard - it only took me four years of intensive education to get a grasp on engineering and a bit of experience to get more of a grip. A lot of the education is available on line now and there are ways to get experience even in remote areas. If they out in

    • by drsquare (530038)
      3. There are many people with good ideas and a willingness to help, but Mechanical and Electrical Engineering and Physics are not their field.
      If they don't know anything about mechanics, eletrical engineering or physics, how helpful can they really be? Anyone can come up with ideas.
  • I think the idea is flawed but on the right track. Direct solar energy to electricity conversion is currently about 10-15% efficient, so you need very large areas to get a decent output. On the other hand, absorbing solar energy as heat in a medium such as water is vastly more efficient, but the problem is to get useful energy out of the heat. Using a Stirling engine and an ordinary alternator could be one practical way, and you'd still end up with overall system efficiencies (maybe up to 50%) that direct s
    • Re: (Score:2, Interesting)

      by Calinous (985536)
      You might get some "energy capture" efficiency of 100% from solar energy into water - however, keep in mind that any thermal engine is restricted by the Carnot efficiency (1-Tcool/Thot, with temperatures in Kelvin). For a not-so-dangerous temperature differences (using a frozen pond in winter) of freezing-point - to boiling-point (273Kelvin to 373Kelvin), efficiency (max, theoretical, when using a gas) would be about 25%. This is where you start

      Photovoltaics have extraordinary efficien
  • Rough efficiency (Score:3, Informative)

    by clare-ents (153285) on Monday January 08, 2007 @05:53AM (#17505990) Homepage
    Assuming a hot temperature of 70C (black plate in strong sunshine) and a cold temperature of 20C, the theoretical efficiency limit is (343-293) / 343 or 14.6% - assuming a perfectly efficient generator and a very large capacity foe the 85% waste heat capacity.

    At night, it's going to be more like 30C -> 0C which is down at 9.9% efficiency.

    Even cheap solar cells do better than that, you'd be better off just buying solar cells.
    • As the efficeincey of PV cells is generally less than 5%, I think not. Also, the cost per watt of capacity for PV cells is way higher, so your post supports the concept quite strongly, rather than opposing it.
      • I can't see any costs on the site so I don't understand how you can possible make an assertion about this being cheaper.

        An amorphous silicon cell is typically 6-8% efficient, lots of commercially available cells are 14-16% efficient - more efficient than this scheme can possibly be.

        I respectfully refer you to Homer Simpson, 'In this house we obey the laws of thermodynamics'.
    • by rohar (253766)
      I don't quite understand what the efficiency of Solar PV at night is supposed to conclude.

      15% efficiency of Solar PV with no input source for 1/2 of the 24 hour cycle (NM cloudy days) and the silicon shortages mean that for Solar PV to become feasible for anything more than supplementary power generation, they have to become way more efficient at capturing solar energy when the sun is shining. A feasible power storage system needs to be implemented for it to be reliable. These two factors make Solar PV a

  • From the article:

    Renewable and portable energy products like Ethanol and BioDiesel now take more fossil fuels to produce the input crops than if the fuel was burned directly.

    This has nothing to do with their method, but I think that claim is a bit misleading. From the wikipedia article on ethanol:

    For ethanol to contribute significantly to transportation fuel needs, it would need to have a positive net energy balance and the U.S. Department of Energy has concluded that it does, stating in a recent re

    • With ethanol being produced in such large quantities, such as in Brazil, I don't understand how this is subject to debate.

      The debate being that working on a Sugar plantation producing ethanol, like where I am working, we can produce Ethanol with a positive ERORI.....BUT, there is so much of the infrastructure, resources, supply chain and distribution network that still relies on fossil fuels that the whole measurement of the EROEI is a bit misleading. Yes, we have a positive ERORI while we have fossil f

    • by rohar (253766)

      Renewable and portable energy products like Ethanol and BioDiesel now take more fossil fuels to produce the input crops than if the fuel was burned directly.

      The point I was trying to make is that if agriculture was moved towards using cleanly generated electricity and away from fossil fuels, it lowers the amount of fossil fuels required to produce and deliver consumer Bio-Diesel and Ethanol. I understand that everything from equipment manufacture, fuel delivery and even the transportation of labour to the farm currently requires fossil fuels, but the point is to "fix" agriculture first and as more Bio-Diesel and Ethanol are produced, the required fossil fuels

  • It's more to do with cost per kiloWatt. While it may be more efficient to put in photovoltaic cells or a ground source heat pump for space heating, it may not be cheaper.
  • I just got a bill for $320 for using 1,300 kWatt hours, last month it was $280 for using 1,200 kWatt hours. I have been looking at how to reduce my dependence on the electric company. But I have yet to find a solar solution that is not priced at break even amounts of money. Where should I look? Also, in my community, this is a non-community-type-issue, I am alone in this quest.
    • by nmos (25822)
      But I have yet to find a solar solution that is not priced at break even amounts of money.

      Normally when people are looking into this what they want to know is "How long is it going to take for this investment to break even?". The underlying assumption is that after break even you'll continue to generate a positive return even after maintence costs etc.

      What just about everyone who seriously considers solar electricity finds out is that the initial cost to supply their current usage requirements is so high t
  • bought a corn stove (Score:3, Informative)

    by codepunk (167897) on Monday January 08, 2007 @10:07AM (#17507600)
    I got real pissed off last year and decided that I am no longer gonna be subjected to
    swings in the fuel market. I bought a corn stove and installed it, best thing I ever did, so far
    this year heat has cost me less than 1/3 of what it normally does. Much simpler system than what is described here, corn in and heat out. My stove is also multi fuel if corn goes high I can buy wood pellets, barley, cherry pits etc whatever is running the cheapest.
  • I have been studying a variation on this exact problem for some time and have reached a tentative conclusion: that the energy and cost of such a system is economically prohibitive, not scientifically prohibitive.

    By which I mean I did the math using the available solar insolation figures for the metro area closest to the middle of the US as a sample, the Carnot equation for thermodynamic efficiency [Max efficiency of a heat engine before losses = 1 - the ratio of the low temp/high temp in absolute degrees (

  • Check alt.energy.* for more practical, proven ideas that are cheaper and easier to do for your home.
  • by SnarfQuest (469614) on Monday January 08, 2007 @01:29PM (#17510366)
    I'm going to hook up my dog to one of those retractable leashes, and attach that to one of those generators used for the OLPC. Then, when a squarrel runs across the lawn, I'll generate enough electricity to run most of my appliances. Should work, as long as the supply of squarrels doesn't run out.
  • More importantly, if it works well and catches on, has anyone looked into what it'll do to the surrounding climate and weather? Or would even vast stretches of urban sprawl built with this system have negligible effects?
    • by rohar (253766)
      I think it's not really possible to build a system that is "large-scale" relative to the earth and sky. I think that if you could build a system that could actually influence weather, that would really be interesting.
  • First, thanks to the /. editors for accepting the submission, the increase in email inquiries and interest in the project since the story was posted have been phenomenal.

    The design methodology of the project has been to research the deficiencies in current energy sources and to attempt to design a system that overcomes these problems, but the project is still very much in the concept stage.

    The real question is, "This [energytower.org] is what they have so far, what enhancements to the design are needed to make this feasib

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