h a l f b a k e r y"Look on my works, ye Mighty, and despair!"
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Weather power plant
Uses heat differential between outside air and insulated mass to create electricity. | |
This device would use the difference between a heatsink in the open air, and an insulated mass(eg large solid metal rod encased in a vacum flask with sealed hole for device), using a thermocuple or similar (eg. peltier). When the weather changes the heatsink will either heat up or cool down (relative
to large insulated mass). either way the thermocuple creates electricity which can then be used for all needs.
if you have a problem with this idea *Please* tell me, rather then just boneing!
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Why not just connect the thermal mass to a stirling engine? Or dig a hole in the earth and attach a sterling engine to the top and tap the differential between the earths average temp and the surface air temp. |
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[i have just changed my changed username] |
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wj - your idea would work (and is basically my idea if you change thermocouple to stirling engine). |
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One question though- has this ever been implemented? |
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I thought it was an idea to make a "power plant" that "creates weather". (i.e. heats up or cools the citÿ)... I'de give a nice bun to that one. :-( |
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I'm boning it because your insulated mass would have to be er.. massive. Using such an engine would make it approach the environmental temperature to the degree power is being generated. The amount of thermal mass would far outweigh interaction between the mass and its local environment. How about the granite core of a large mountain? Can you effect a sufficient degree of heat transfer? |
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Heat engines work by allowing heat transfer form the hot to the cold body, and by parasitically <sp> doing some useful work. In other words, no matter how large your insulated mass, entropy dictates that you only have a finite ammount of energy you can extract until the insulated mass reaches ambient temperature. This is of course per cycle. |
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If you had a place somewhere with extremely predictable and extremely bipolar weather conditions, you could probably design a thermal mass to be suitable. You'd need to tune it because if the thermal mass were to ...massive, your system's ability to react to the weather cycles would be insufficeint. |
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You'd have to model this with differential equations - essentially you're tracking two curves, one of inside, and one of outside temperature, and the inside temperature will be governed by the outside temperature, and your rate of heat transfer over time. You'd have to tune the thermal mass and heat exchange rates to ensure deltaT is maximised. |
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Interesting, Interesting. If you can find an area of suitable termperature flux we might be in business. theoretical maximm efficiency is governed by the temperature difference between hot&cold side, so your generating capacity will depend heavily on how well you manage the temperature of the thermal mass. |
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oh, bun by the way. I started off rather skeptical, but as I thought through, I actually really like the idea. You just need somewhere with extremes of temperature over a short timescale, preferrably daily, rather than seasonal. |
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The outside temperature variation curves are going to be following something fairly close to a sine wave. Which is to say that the extremes are short duration, while the nearly-averages are common. Look up "root mean square" for a way to calculate available energy. |
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I thought about this once, and decided that it would be better to have a cold mass and a warm mass, rather than trying to play the averages off just one. Put an outside heat exchanger on each, and run them any time they'll do any good. The two masses can be used all the time, then, to run the power generator off their difference temperatures. |
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Aha, but therein lies the crux of the issue. The act of generating power from the temperature difference will act to reduce that difference. All you are doing is hijacking some of the hat energy on it's way from the hot mass to the cold mass, and using it to do stuff. The entropy monster gently molests you while you're trying to make a cheap buck. He makes sure that, generally speaking, at least 50% of the energy is still flowing fromt he hot mass to the cold in the form of heat. This means the hot mass gets a bit colder and the cold mass gets a bit hotter. For a given two masses, and given temperature difference, you have a finite ammount of energy available. |
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The zen of this idea is that you're using the change in temperature of a weather system, and cleverly using an isolated thermal mass to cheat the system. It's not free energy, or anything like that, you're just playing the numbers and keeping the thermal mass's temperature curve out of phase with the outside temperature, and using this difference to create a flow of heat from one to the other, suimultaneously leeching some of this heat flow as useable energy. The trick will be to carefully controll the ammount of heat allowed to flow between the masses to maximise system stability. |
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This will not be a constant, or even 100% duty cycle generator. I think you will find that the system will only be stable when the thermal mass is ~90 degrees out of phase <trailing, of course> the outside temperature. It follows that your generating potential will be a 50% duty cycle truncated sine pattern, where the "on" parts of the cycle will be somewhat parabolic in terms of generating capacity. |
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I wish I had MATLAB with me, I'd do some quick calcs and show you the graph. As I said, I'm really quite taken with this idea. |
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I'd like to know if it's actually feasible to get something like this to work somewhere - ie using a black surface/cosmic radiator somewhere in the desert as your fluctuating outside thermal mass, and probably an insulated saline bath or whatever as your isolated "load". |
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This essentially describes a heat pump used for home heating, where the insulated mass is a deep part of the ground (insulated by many feet of dirt). I'm not convinced using man-made insulation is any better than a deep hole. Man-made is scalable, but expensive. Can you convince me that a man-made heatsink is better? |
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Using a fluid as the insulated mass could allow faster heatflow. |
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There is a toy from Edmund Scientific that does this. So on a small scale, it's dandy. |
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I wouldn't think about this in terms of weather, I'd think about this in terms of day/night. (This is called the "diurnal temperature variation".) Desert temperatures can vary 50 degrees C between day and night. |
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[jutta]'s anno tips the balance to [+] for me. |
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Sink a wide, shallow concrete tank into an insulated hole in the desert, and fill it with dense brine. The thermocouple (or peltier stack) is the lid of the tank, and is painted black (powdercoated, etc) |
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Above this, a venetian blind-like array of mirrors pivot in unison about their longer axes. In the daytime, they tilt up at an angle to track the sun's elevation and reflect it down onto the lid/thermopile. At night, they sit bolt upright to allow the heat to radiate away into the cold night sky. When necessary (inclement weather, dawn/dusk) they can sit flat and form an insulating layer to keep heat in/out. |
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Conventional construction industry insulating materials should be near as efficient as a vacuum flask at a minuscule fraction of the cost, especially as we are only seeking to retain/reject the heat over a 24 hour cycle, and not a 12 month cycle. |
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Now, anyone care to run the numbers, using [jutta]'s 50C differential and an ISO standard Olympic swimming pool? |
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