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Solar Power Minus the Light 439

Posted by ScuttleMonkey
from the green-energy-saving-green dept.
An anonymous reader writes "Popular Science is running a story about a small company trying to take advantage of all the global warming hype. Matteran Energy uses 'thermal-collection technology to heat a synthetic fluid with a very low boiling point (around 58F), creating enough steam to drive a specially designed turbine. And although a fluid-circuit system converting heat into electricity is nothing new, Matterans innovative solution increases the systems efficiency to a point where small-scale applications make economic sense.' Notably, this comes during a record breaking heat wave here in the US. So has the day finally arrived where I can run my AC off of all that heat outdoors?"
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Solar Power Minus the Light

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  • by chriss (26574) * <chriss@memomo.net> on Tuesday July 25, 2006 @04:29AM (#15774753) Homepage

    Hm, looks simply like a small sterling engine or mini gas turbine used to drive an AC. They managed to make it cheap so it will be applicable in small installations, but both the sterling engine and the gas turbine (using a fluid in a closed circuit) require a temperature difference, so the machine would not be driven by heat alone. You'd have to cool down the steam after it had passed the generator to make it condensate to a fluid again and pump it back into the thermal collectors. The article does not mention how this should be done or where the energy for this should come from.

    Power stations using closed fluid circuits (e.g. nuclear plants) use a secondary circuit to cool the first one after the steam passed the turbine. They are usually located near rivers for this. Larger installations for sterling engines can store heat during the day in a water tank and use the difference in temperature between the water and the surrounding cooler air during the night to drive a sterling engine. This obviously works best in areas where the difference in temperature between day and night is significant, i.e. deserts. I don't think it to be realistic to turn 1/4 of your apartment into a heat/cold storage just to drive the AC.

    So in the end they made it cheaper, but inefficient (5%) even compared to solar panels (20%) without offering something that could replace a conventional AC. To achieve this you'd still have to build houses in a smarter way, e.g. isolate the walls from the inside and outside and use them as thermal storage. More energy efficient construction has been done for cold regions (where houses require almost no heating during winter when isolated well, the inhabitants' body heat is sufficient) and warmer regions (traditional buildings build with clay and wind-traps and smaller windows to the sunny side). So it is possible, but do not expect too much from our current architecture.

    • Presumably however, you'd at least be able to use the existing temperature difference to at least offset the cost of running the airconditioner? Obviously it's not a perpetual energy machine, so you'd lose out in the end, but it seems to me that at least it could use some of the cooled air that is otherwise just going to be wasted.
      • yeah it could use some of the energy from the air, key point. The machine doesn't have to be near 100% efficient, but the big question will be if it is efficient enough to be worth the added cost of purchase installation. That must always be factored in when piggybacking machines that take advantage of ambient energy onto fuel-driven machines.
        • Solar pannels might just work better. Besides with solar if you have an excess you can pump it back into the grid which is just the perfect cure during the high power demand scorching heat weather.
          • The trouble with solar is it's ruinously expensive. The surface area required generally isn't a problem for a house (use the roof), but when a solar panel costs £450 (about US $700) for a 120 watt panel, to actually get enough solar panel to do something like run your home becomes fantastically expensive. You'd need at least twice (preferably three times) the solar capacity that you actually use in many places, so you can store enough during the day for the night, and not be without power on a cloudy
            • by uioreanu (554486) *

              Solar energy is yet expensive, but it's easy just to look at the effects of the crisis in middle east over the fuel price to understand that we need to start thinking differently when we're talking about energy consumption. Most of the house devices we have could work just slower and consume half of what they do now; but this is a lesson we were not yet trained to learn.

              Our story resembles more and more with some Age of Empires game where we start on an island, burn out everything there is to burn over

              • The middle east will own the solar age like they do the oil age now, they have the sand and the sun, and huge deserts to coat with panels. They're just waiting for the oil to go before they get started.
                • The middle east will own the solar age like they do the oil age now...
                  Last time I checked, there was sunshine and open spaces in a lot of places other than the Middle East.

                  • Well, there's lots of oil in other places also, so why does the middle east still control the world energy market? Easy, for the same reasons they will control the solar market.

                    1) Cheap labor
                    2) All their open land doesn't have any NIMBY neighbors to complain
                    3) No environmental restrictions/regulations
                    4) The open land cannot be used for anything else, especially crops.

                    The big downside they face is how do you transfer all the energy collected to the markets that need it? The great thing about oil is
                • America's largest supplier of oil is ...

                  wait for it ...

                  Canada.
        • It is just cheaper to add a new gas or coal plant and update the grid. As long as this is true (and it will not be forever) people are going to choose the dirty way. PV costs several times what dinofuel does. This isn't what you want to hear but it is the truth.
          • Nuclear Please.

            I want to breathe.
      • If your air-con is over-efficient, you will save twenty times as much energy by turning the thermostat up than you could ever reclaim with this process - it's only ~5% efficient, remember?
    • You want cool? bury it! The temperature underground tends to stay nice and cool, even during the heat of the summer... If you've ever lived in a house with a full basement... you'll know that during the summer, that basement is the coolest part of the house... Similarly, in the winter time, that basement doesn't get as cold as the rest of the house can... (obviously heat rises so if you heat the house the upper levels will get warmer quicker, but if you didn't heat the house the basement would be the war
      • Radiant COLD? No such thing.
        • I beg to differ; If you make an object cooler that the surroundings, there will be a net radiative heat transfer from the surroundings to that object. It's been done.

          The catch is, if you're going to use an existing radiant heat floor/wall/ceiling system, you have to keep the temperature of the surface above the dew point or things will get wet.
          =Smidge=
          • But that's still not radiant cold. You can't have a radiant cooler. If radiant heating is being done then it's the surroundings heating the cooler parts - the warmer surroundings are doing the radiating, not the thing that's cold.
            • Yes, and when transfering heat away from the object we're concerned with we typically call that cooling. Sure the heat goes somewhere but we don't care if it isn't our house.

              For instance, if you park your car in a car port (no walls - ambient temperature,) and your neighbor parks his car outside on a cold clear night there is a fair chance that your car won't have ice on the windshield, but his will. Why? because the net radiation your car sees (Tcar^4 - Troof^4) is near zero - no heat transfer, while the
            • For fight pedantic with pedantic: unless the object's temperature is 0 Kelvin, it's radiating heat.

              Similarly, a hot object is also receiving radiated heat from other, cooler objects that surround it.

              "Radiant Cooling" simply means you are removing heat energy from a space via radiation absorption by means of a surface of object that you are actively keeping at a lower temperature than the surroundings. In other words, the space is being cooled by radiating the heat, not by some magical device that emits "ant
        • Radiant cool: think like the floor and the walls of a fully underground basement
      • by Jedi Alec (258881) on Tuesday July 25, 2006 @05:16AM (#15774864)
        this very principle is currently being put to use in a part of the Netherlands that used to be mined for coal. The water in the now abandonded mine-shafts will be used to provide heating in the winter and cooling in the summer.
      • What's the thermal conductivity of the ground? Even though the overall temperature of the ground might be cooler than the air, the area around the buried pipes will just heat up and reduce your temperature differential. The poorer the thermal conductivity of the ground, the larger the apparatus needed to exploit the temperature differential.
      • Actually as you go deeper underground the temperature of the soil gets closer and closer to the average yearly temperature in that area as shown here [nrc-cnrc.gc.ca]

        How fast the temperature approaches the yearly average as depth increases depends on the type (and moisture content) of the soil, but as a rough guide, at 8m depth the temperature is very close to the yearly average.

        Note that this is not valid for extreme depth (or vulcanic areas) for the obvious reason ;)

        BTW, the graphic was taken from here [nrc-cnrc.gc.ca] - if you want to kn
    • by MichaelSmith (789609) on Tuesday July 25, 2006 @04:40AM (#15774794) Homepage Journal
      Hm, looks simply like a small sterling engine or mini gas turbine used to drive an AC

      Summer power consumption by aircon units determines max peak load on the power grid here in Melbourne, Australia. I think aircons should run primarily on photovoltaics because that way you get the highest power when it is needed the most.

      • It would be nice, except for the cost. I bet a 120 watt solar panel costs around AU$1000 in volume. Even in a sunny place you're going to want at the bare minimum 10 of those panels per kilowatt you need, so by the time you're done you're going to be spending $200,000 on solar panels to run your house.

        • by the time you're done you're going to be spending $200,000 on solar panels to run your house.

          I am thinking more about office buildings with unused roof space. If you write the building regs to require solar cells to run the aircon systems you will increase the economies of scale in solar cell manufacture and drive costs down overall.

          • It will never happen and for one very good reason. There just isn't enough energy hitting the roof of even a moderate office block to power the aircon irrespective of the price of solar cells. Energy from the sun totals about 1kW per sq m. Look at amount of unused space on the roof mostoffice blocks. The amount of power you can generate simply isn't enough to power the aircon even if solar cells were 100% efficient. Even the best solar cell is 20% efficient and that drops with time (not counting the fact th


            • There just isn't enough energy hitting the roof of even a moderate office block to power the aircon irrespective of the price of solar cells. Energy from the sun totals about 1kW per sq m. Look at amount of unused space on the roof most office blocks. The amount of power you can generate simply isn't enough to power the aircon even if solar cells were 100% efficient. Even the best solar cell is 20% efficient and that drops with time (not counting the fact that huge amounts of power go into making a solar c

        • by B2382F29 (742174) on Tuesday July 25, 2006 @05:58AM (#15774971)

          Wow, that would be expensive. Here (germany) you get 2kW (10x200W) for 9000 EUR [energetik.de]

          Next time please don't pull prices out of your ass.

          • Why so hostile? The prices were "not pulled out my ass" but sample prices from a supplier of panels. You could have said something a little bit less rude such as "I think you're incorrect, we can get panels in Germany for this price here" instead of making a mindless flame that makes you look like an asshat.
          • Additionally, before you flame also check your maths. EUR9000 per 2kW is still EUR 90,000 per 20kW - converted to AU$, that's still over $150,000 for 20kW - which I maintain is ruinously expensive for that much power.
        • It would be nice, except for the cost. I bet a 120 watt solar panel costs around AU$1000 in volume. Even in a sunny place you're going to want at the bare minimum 10 of those panels per kilowatt you need, so by the time you're done you're going to be spending $200,000 on solar panels to run your house.

          Nice to know you pulled a nice round number out of your ass. I know a small CNC machine shop (think several large computerized cutting machines constantly running), complete with air con at 74 degrees and sev

      • by dbIII (701233) on Tuesday July 25, 2006 @06:34AM (#15775063)
        I think aircons should run primarily on photovoltaics
        Run them on heat instead - instead of having water in a rooftop solar hot water system you could have your airconditioning working fluid (eg. ammonia) getting hot then expand it through a nozzle to give you cooling. This gives you cooling with no moving parts and would use a lot less roof space than the photovolatics required to run an electric airconditioner. Electricity is not the answer to everything - it's a way to get energy from one place to another.
    • It's stirling engine [wikipedia.org] after Rev. Robert Stirling, not sterling engine.
    • by IBitOBear (410965) on Tuesday July 25, 2006 @05:22AM (#15774881) Homepage Journal
      On the average, the underground temprature at ten feet below ground level is something like 52 degrees. (I am looking into geothermal [q.v. ground-sourced] heat pumps.) If the fluid boils at 58 degrees and you put a reasonably large ground loop you would have your temprature differential.

      Toss a solar collection array on the hot side, and if the latent heat of vaporation of the mistery fluid isn't too high you should be able to get a pretty flow.

      You might need to pull-start it (8-) to get the initial pressure differential, but once the system was running the cost of using some of the energy to replenish the boiler from the condensate coils should be low enough.

      It mostly comes down to a matter of surface area.

      In a steam/turban plant the energy to move the turban doesn't _really_ come from boiling the water, it comes from super-heating the steam. You have to move the steam through the turban energetically enough to move the machinery (which cools the steam as the pressure is relieved (etc). So it isn't so much the boiling temprature, its how much energy the media can carry _after_ boiling. A lot of volatiles do an incredibly poor job as a (relatively, in this case) super-heated fluid because of crosiveness or viscosity.

      ASIDE: If I were trying to build a solar-powered air conditioner I'd use basically the same material and design as a propane-fired refridgerator and a Clever Arrangement(tm) of concentrating mirrors. The whole system is low pressure and has no moving parts. The mirros would have to track, but those moving parts wouldn't ever have interract with the volatiles.
      • in a steam/turban plant the energy to move the turban doesn't _really_ come from boiling the water, it comes from super-heating the steam. You have to move the steam through the turban energetically enough to move the machinery...

        Steam-powered turban?? There's a few pakistani taxi drivers who might be interested ^^

    • by bhima (46039) <Bhima.PandavaNO@SPAMgmail.com> on Tuesday July 25, 2006 @05:40AM (#15774933) Journal
      "I don't think it to be realistic to turn 1/4 of your apartment into a heat/cold storage just to drive the AC."

      I see you haven't met my ex-wife.
    • by Smidge204 (605297) on Tuesday July 25, 2006 @05:56AM (#15774966) Journal
      Photovoltaic panels get hot because they absorb all that sunlight with only ~20% efficiency. Install the heat exchanger in close proximity to the back of the solar cells to make use of this high temperature and take advantage of the shade it provides (prevent the heat sink from being heated by the sun as well. Now your microturbine may be only 5%, but that's effectively ~25% overall for the PV-turbine system combined.

      Make that a concentrating PV and your efficiency increases for both systems.

      Every little bit helps.
      =Smidge=
    • by _Shorty-dammit (555739) on Tuesday July 25, 2006 @06:43AM (#15775083)
      it very clearly states in the animation at the company's website that ambient air temp is sufficient to cool it back down. You seem to be forgetting that those big black panels on rooftops that heat water using the sun's solar energy heat the water up to a much higher temperature than the ambient air is. What exactly would be the point of a solar water heater if it only gave you water that was the temperature of the ambient air? Anyway, so, you use that heat source to boil the liquid in the closed circuit. Don't forget, it ain't water. It's some liquid that boils at a pretty low temp. And then you use the ambient air for the heat exchanger to cool the 'steam' in the closed circuit back down, condense, and start all over again. So, from what I gather the only requirement for this to work is that the boiling point of the liquid in the closed circuit needs to be higher than the ambient air temp, and lower than the temp you can achieve from a device similar to / same as those rooftop solar water heaters. Then you should have no problem boiling or condensing that liquid, since you have the capability of getting the substance up to the boiling temp, and back down below that temp so it condenses again.
    • Well,

      There is a lot of options:

      * you can build a simple radiator and expose it to wind, on a area protected from sunlight

      * you can put it near your house's water pipes, so the running water would absorb the heat.

      * or increase the temperature differential, put the engine on your rooftop, directly exposed to the sunlight, paint it black, etc... And the ambient temperature will be cool enought to make this engine work.

      * combine all the options above :-)
    • There's a link in the article to the company's website. They've developed a motorless feedpump system, and there's a rather elaborate flash animation that describes specifically how it works, and several possible sources of energy... solar water heaters, sub-boiling geothermal sources, or even wood stove waste heat. The point is that they think it can work efficiently with a 50 degree temperature differential above ambient temperatures, which is pretty easily achievable without a lot of elaborate heat/col
    • I don't get how this works without bleeding the efficiency of the systems it draws from.

      I don't see what's wrong with having a parabolic mirror concentrate sunlight on the hot side, and running the cool side through a finned radiator, and blowing ambient air through it (mounted under the mirror to take advantage of its shade would be most efficient, I think). You could go stirling (more efficient, lower speed) or turbine (less efficient, higher speed) that way.

      I wouldn't be worried about night-time or clou
    • They managed to make it cheap so it will be applicable in small installations, but both the sterling engine and the gas turbine (using a fluid in a closed circuit) require a temperature difference, so the machine would not be driven by heat alone.

      Well, this new development solves the difficult part of the equation--it provides a low-cost way to capture that heat. The cold-side of the operation is the easy part. You are onto the solution already:

      Power stations using closed fluid circuits (e.g. nuclear plan
  • Thermo (Score:3, Interesting)

    by LesPaul75 (571752) on Tuesday July 25, 2006 @04:31AM (#15774761) Journal
    So has the day finally arrived where I can run my AC off of all that heat outdoors?
    Ok... I'll be the first to admit I wasn't paying close attention when this was discussed in my college physics class, but something having to do with the laws of thermodynamics feels wrong here. :)
    • Re:Thermo (Score:4, Interesting)

      by Umbral Blot (737704) on Tuesday July 25, 2006 @04:37AM (#15774783) Homepage
      What's specifically wrong is this: to condense the steam back into a liquid you need something colder than its boiling point. Thus on a hot day you couldn't get it to condense, and thus it wouldn't work. What you really need is a a large heat sink, like the ocean or a big peice of ice, and then you could turn the tempertature differential into energy using this device (at the cost of heating up whatever cold thing you were dumping heat into).
      • Well, you could put the condensing coil in your fridge. Problem solved !

        (I know, just being silly)
      • Re:Thermo (Score:4, Informative)

        by warewolfe (877477) on Tuesday July 25, 2006 @05:08AM (#15774849) Homepage

        Energy is being extracted from the fluid circuit system and being converted into electricity. Steam re-condenses into fluid because it has lost it's energy to the turbine.

        No perpetual motion or violation of the laws of thermodynamics involved, just energy transfer.

        • cooling water needed (Score:2, Informative)

          by Anonymous Coward
          "Steam re-condenses into fluid because it has lost it's energy to the turbine....
          No perpetual motion or violation of the laws of thermodynamics involved,"

          Yes, perpetual motion or violation of the laws of thermodynamics involved. Plus, if you look at their website, that's not what they are claiming.

          If you put the steam through the turbine, you now have lots of low-pressure steam that you can't get any more useful work out of. They are condensing the steam back into liquid using copious amounts of cooling w
      • In many places in the world the deep soil temperature never reaches summer air temperature maximum. In such cases it is theoretically possible to use the Sterling cycle to obtain energy by, effectively, transferring heat from air into the soil. However, eventually this is going to stop working as the soil around the heat exchanger warms up. There is also the problem that the efficiency of a heat engine cycle is limited to 1- the ratio of output to input temperature. Since the ratio is rarely lower than abou
      • How about using the ground, which stays cool even during hot summers. Geothermal heating/cooling systems draw heat from or sink heat in the ground or a body of water depending on whether they're being used for heating or cooling. In this case, you'd run the system underground and deposit your heat there. Obligatory Wiki [wikipedia.org]
      • to condense the steam back into a liquid

        Hm. PV=nRT, right?

        Why not have a compressor somewhere removed from the thing you're trying to refrigerate?

        With the right engineering/business model, that work could come from people on exercise bikes.

        Attack power generation, fat, and unemployment problems in parallel.

        This idea is too good to work in practice.
      • What you really need is a a large heat sink, like the ocean or a big peice of ice

        I'm sure Al Gore will love you for suggesting that.
  • Carnot efficiency. (Score:5, Informative)

    by Anonymous Coward on Tuesday July 25, 2006 @04:42AM (#15774797)
    58f = 14.4C or 287.6K

    Now lets be generous and let our panel "superheat" the stuff up to 80C or so, and put the cold reservoir in a bucket of ice.

    That gives us a heat source at 353.15K and a sink at 273.15.

    Efficiency = 1.0 - cold/hot = 1.0 - (273.15/353.15) = 0.226, or about 23% efficient.

    Not great.
    • Why do you make any assumption that the liquid needs to be heated anywhere near 80 degrees? I see nothing saying that at all on the company website.

      If the boiling point of the liquid is 58f then you only need to heat it to a range of 65f and condense it at around 52f. Thats 284.26 to 291.48. Quite a difference.
  • it aint that great (Score:5, Interesting)

    by hamburger lady (218108) on Tuesday July 25, 2006 @04:43AM (#15774799)
    ~5% efficiency.

    what's wrong with a reflective dish and a stirling engine [stirlingenergy.com], anyways? much higher efficiency, materials aren't as expensive as solar panels and not nearly as bad for the environment.
    • by chriss (26574) *
      The main problem with stirling engines and reflective dishes is that they consume a lot of space, most of which is the empty area between dish and engine. While they may be more efficient and their production be less hazardous to the environment, they cannot compete with solar panels which can be put on roof tops or basically any flat surface. Newer PV technology even promises "paint on" solar cells. They are simply less invasive and therefore can be put into more places, leveling their lower efficiency. Fo
      • i'd say you'd have the same problem with the system in the story, with a turbine and all.

        as for a stirling dish-solar system, they would work alright in the city; one would easily fit on the roof of my rowhouse (since a satellite dish would fit just fine). it actually has a smaller footprint, per kwh, than solar cells. however, if you're talking about the suburbs, you're right; solar roof shingles etc are a much more usable option.
      • they cannot compete with solar panels which can be put on roof tops or basically any flat surface

        There is the issue of scaling. If you double the area of photovoltaics you only get double the power output. If you double the size of a thermal power generation method you usually get more than double the output - which is why the idea is to build really big solar thermal power installations on bits of land no-one wants. This happens because you can use bigger turbines and more of them to get more out of the

  • by Hal_Porter (817932) on Tuesday July 25, 2006 @04:48AM (#15774807)

    Notably, this comes during a record breaking heat wave here in the US. So has the day finally arrived where I can run my AC off of all that heat outdoors


    I guess you're making a perpetual motion joke, but the strange thing is it's not a daft as it sounds.

    You could have an electrically powered heat pump to pump heat into the ground in summer, and back out again in winter.

    http://www.igshpa.okstate.edu/geothermal/geotherma l.htm [okstate.edu]

    Very popular here in Sweden.

    If you insulate your house enough, the energy required to heat or cool it is pretty minimal, so you could generate it from solar panels, at least in the summer. And heat pumps are 3 to 4 times more than resistive electric heaters.

    As wikipedia puts it

    http://en.wikipedia.org/wiki/Heat_pump [wikipedia.org]

    When used for heating on a mild day, a typical heat pump has a COP of three to four, whereas a typical resistive electric heater has a COP of one. That is, one joule of electrical energy will cause a conventional heater to give off one joule of warmth, while under ideal conditions, one joule of electrical energy can cause a heat pump to move more than one joule of heat from a cooler place to a warmer place. Sometimes this is expressed as an efficiency value greater than 100%, as in the statement, "XYZ brand heat pumps operate at up to 400% efficiency!" This is not quite accurate, since the work does not make heat, but moves existing heat "upstream". This does not violate the second law of thermodynamics, because it takes less work to move the heat than to make the heat.

  • Very inefficient (Score:5, Interesting)

    by Cyberax (705495) on Tuesday July 25, 2006 @04:56AM (#15774828)
    This turbine can't be very efficient. Efficiency of any heat engine is limited by the Carnot cycle (http://en.wikipedia.org/wiki/Carnot_cycle).

    Basically, you can estimate it with this formula: e=(T2-T1)/T1 where T2 is the highest temperature of the working body and T1 is the lowest temperature. For such a small temperature drop as in this engine we'll get a very minuscule efficiency.
    • by KiloByte (825081)
      Yet, you're forgetting that heat is exactly what we have too much of. It's for all practical purposes free, so efficiency energy-wise doesn't matter.

      What matters, is the efficiency time-wise, space-wise or monetary cost-wise. Having twice as much power from the same heat would be nice, but it isn't the point.
      • The only problem: you'll need a lot of these devices to generate usable amount of energy.
        • The only problem: you'll need a lot of these devices to generate usable amount of energy.
          Exactly, that's what I meant with "space-effective" and "cost-effective". If these devices can be cheap and compact, efficiency isn't really a concern.
    • Re:Very inefficient (Score:2, Interesting)

      by IcePop456 (575711)
      I thought we only worry about efficiency when the energy supply is low? Granted I wouldn't want a huge piece of equipment, but considering how much thermal energy is in the air during the summer, cost is what I'm worried about more than efficiency.
      • You need a temperature differential, not just a high temperature. I see that one can use water from a river/lake/sea in which case this device might very handy.

        But in most places such device will be less effective then solar panels (which are not limited by the Carnot cycle, BTW).
  • by Anonymous Coward on Tuesday July 25, 2006 @05:00AM (#15774837)
    ... all the global warming hype? I guess in the US of A the hype warms you.
  • by zimsters (978940) on Tuesday July 25, 2006 @05:34AM (#15774913) Homepage
    best solution: pop more holes into the ozone so we can get the absolute zero temperatures of outer space cooling the earth ;) come on everybody, act now to save the planet! Buy the biggest SUV money can buy!
  • by JumpingBull (551722) on Tuesday July 25, 2006 @05:36AM (#15774920)

    First, the refrigerant used in their independent calculation is R-22, a cloroflorocarbon that kills the ozone layer, implicated in crop failure due to high uv exposure.

    Second, the cooling cycle uses water. Considering that potable water is in short supply, this is a problem...

    Third, the thermodynamic Carnot cycle is a cap on the efficiency. Higher working temperatures do give a better efficiency, but you still have to cool them!

    A different working fluid can be used. unfortunately, organic fluids tend to be flammable. Methanol might be a candidate. It is less toxic then ammonia.

    Before the advent of mechanical refrigeration, some AC was done with evaporative air coolers. (for cinemas at the start of the 20th century). This might mitigate the second point.

    Perhaps we are missing an important use. The humidity usually makes an environment uncomfortable. This system might find even more effectiveness driving a dehumidifier.

    Finally, it might be equally effective to use a two stage boiler. A flat plate to get the fluid up to working temperature, and a solar concentrator to superheat the fluid to drive the system to a higher efficency

    • It is a pity about the chlorofluorcarbons. There is a good alternative process that uses ammonia and water that has been around for some time. It is more efficient than the straight water cycle, and the system is closed so the water isn't going anywhere. See for example http://www.geothermie.de/gte/gte46/geothermal_powe r_plant.htm [geothermie.de]
    • "It uses water" ... "Potable water is in short supply"
      If all water was Potable, it wouldnt be in short supply ;)
    • Potable means drinking.

          You don't need drinking water to use for cooling something.

          There are plenty of places with water that isn't potable, thus such a system would have no problem being used in places with undrinkable, yet available, water sources.
    • First, the refrigerant used in their independent calculation is R-22, a cloroflorocarbon that kills the ozone layer, implicated in crop failure due to high uv exposure.

      This one is not a big deal because R-22 can almost always be replaced one of the common modern refrigerants (I'm not sure which offhand, might be R-409c), which has extremely similar properties and is often used to replace R-22 in old air conditioning units. It's a little bit less efficient though (and most equipment can be redesigned to use

  • by Ancient_Hacker (751168) on Tuesday July 25, 2006 @05:46AM (#15774944)
    Ahem, this thing won't work.

    The diagram shows 10 PSI gas being condensed. Then somehow, without a pump, the 10PSI liquid "flows" into a 65 PSI boiler. No way, Jose. And no, you can't use the height of the condenser to supply "gravity" pressure. There is no free lunch.

    Then there's this dang thing called the Carnot Cycle, which is impossible to violate, and dooms all these low-temp difference heat engines to extremely low efficiencies. So low, in most cases, you can't even keep up with paying the interest on the investment.

    I didnt see a single numeric calculation for the loop efficiency, a really bad sign. These calculations have been basic, simple, and mandatory for upwards of a century and a third.

    • by _Shorty-dammit (555739) on Tuesday July 25, 2006 @07:08AM (#15775167)
      Link to animation [matteranenergy.us] Page 7 explains how it works. The liquid is heated by an external source, such as solar water heaters on a rooftop, to a temperature much higher than ambient air temp. This heat is transferred to the liquid, which boils and gets pressurized, and goes through the turbine. After which it is condensed in the condensor, which is cooled via ambient-temperature water. Then the second heat exchanger comes into play. This second one is isolated by valves at both ends. Before the condensed liquid is released into the second heat exchanger, the empty HE is cooled by the same ambient-temperature water as the condensor was. Once the HE is roughly the same temp as the condensed liquid, the top valve opens and the condensed liquid enters the HE, and then the valve closes. Now it is isolated by both valves inside the HE. And the HE is then heated by the same solar heater, bringing the liquid up to the same temp and pressure as it is in the boiler. Then the bottom valve is opened, and the liquid moves into the boiler. The valve is then closed. Then the HE is cooled again, so it can receive more condensed liquid. And on and on. The animation, and their more clear explanation, shows the entire operation rather well. Click it, I say! Click it!
  • AC?? (Score:3, Funny)

    by AcidLacedPenguiN (835552) on Tuesday July 25, 2006 @06:01AM (#15774980)
    So has the day finally arrived where I can run my AC off of all that heat outdoors?

    I thought you just had to log out to run AC.
  • by dbIII (701233) on Tuesday July 25, 2006 @06:12AM (#15775002)
    So has the day finally arrived where I can run my AC off of all that heat outdoors?
    Early refrigeration used heat sources such as kerosene to expand the working fluid - so there are such things as the kerosene fridges with no moving parts used in remote areas. A big curved mirror reflecting the sun could have been used as the heat souce a century ago, but is a bit inconvenient. It would make far more sense to use solar heating to drive your airconditioning than have a not paticularly efficient way of converting solar energy to electricity first and then a not paticularly efficient way of using electricity to move heat about. Doing other stuff that can only be done with electricity is a different story and solar thermal scales up - but doing stuff with heat when you already have a heat source is not the best way to do it.
  • Thermodynamics allows you to convert a temperature differential into mechanical energy. Heat in itself is basically worthless as enegry source. So if it gets warmer everywhere, this does not generate the possibility to produce energy.

    One thing that usually can be done is to have heat/cold storage and to radiate the heat into space at night. Ironically deserts are best suited for that.

    • and it is dumping the heat into the ambient air. Solar water heater = much higher than ambient air temperature. Much higher than ambient air temperature = ambient air will cool it. Nobody is trying to say this is defying thermodynamics. And it doesn't. It's not even terribly effecient. But it would work, provided you had a suitable liquid in that closed circuit that powers the turbine. Suitable meaning, the solar heat source's temperature is sufficient to boil it, and ambient air temperature is low e
  • by digitaldc (879047) * on Tuesday July 25, 2006 @06:54AM (#15775117)
    How about recycling the gathered water back to the steam engine with energy collected by solar roof shingles [oksolar.com], then you have both heat and light-powered A/C.

    This house [oksolar.com] would be the best of both worlds.
  • If you have something cold to work as a heatsink, eg, cold water, why not just take a bath in it? A one-minute cold bath beats hours of AC any day!
  • by giafly (926567) on Tuesday July 25, 2006 @08:04AM (#15775416)
    ... by planting Trees nearby. Their shade keeps your house cool [lgc.org], all trees produce fuel for the winter, and if you choose the right varieties they deliver free organic fruit. You'll save power by not having to run your air conditioner so much [wcisa.net]. Why must some engineers make things difficult for themselves?

Time to take stock. Go home with some office supplies.

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