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Background
The solar power tower concept works on the theory that air underneath a collector near the ground heats up and tries to rise and can only exit via a large tower at the centre of the collector.
to ve cost-effective soalr towers need to be very large. this makes them expensive and technically
difficult.
Proposal
Built a large pool or lake, paint the bottom black with a transparent plastic membrane a couple of feet above it.
The water between the bottom and the membrane will heat up and seek to rise but the membrane will prevent it from doing so.
In the middle of the pool, a vertical structure rises from the bottom to slightly above the surface. Warm water is forced up through the central structure and allowed to run through a generator before going back into the pool.
Alternately if there's a river nearby you could pump the warm water back into the river and replace it with cool water.
The water would support the central tower (you could put the generators on rafts so the tower doesn't need to support their weight) which could be much lighter as a result.)
The generators would be at the surface of the water and therefore much easier to service than generators on top of an atmospheric solar tower.
The generators could also be smaller since you need a much smaller amount of water than air to generate the same amount of power.
(?) Thermal pollution
http://outreach.eco...ershed/thermal.html
[Iangould, Oct 26 2006]
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Sorry Ian, Loooooots of very bad science here :) |
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Rather than me explain all of it please consider some things and report back to the group. |
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1a. Entropy in closed systems, or |
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1b. Ecological ramifications of //pump the warm water back into the river// |
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2. Equations for attenuation rate of light/radiant energy in water. (hint - how deep is your lake?) |
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3. Consider the statement //you need a much smaller amount of water than air to generate the same amount of power// and tell the group what on earth is meant by this. |
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4. Consider the statement //generators on top of an atmospheric solar tower// and report your sources for a solar tower design that places the generating turbines at the top of the tower rather than around the perimiter of the collector structure. |
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25 marks per question - essay response due 01 November. |
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1a. Explain the relevance of the question. |
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1b. why not ask the operators of all the thermal power plants, both fossil and nuclear, which do exactly that? |
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2. How deep does it need to be? Ever hear of solar ponds? Want a link? |
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3. Compare the size of a wind turbien with the size of water-powered turbien with the same power rating, i'm sure the answer will come to you. |
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4. Actually the turbines in the enviromission desien are at the base of the tower so while my comment was incorrect so was your's about placing them at the "perimeter" of the collector. |
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<picks up shredded exam paper, wipes spittle off desk, enters D- on Ian's report card> |
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1a. If its a closed system then it will tend to equilibrium and stop. Of course, you don't have a closed system in energy terms because you have some degree of insolation on those areas of the pond not shaded by your turbine rafts. |
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1b. No thermal power plants dump hot water into ecosystems. Aside from the fact that they wouldn't be allowed to, why would they? There's an awful lot of expense in heating up that thar water and they certainly wouldn't be dumping that precious heat. |
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2. Solar ponds are a different concept entirely - relying on temperature gradient thermocouple generation. Solar ponds are still. I know them backwards. Your concept relies on capturing energy from heat induced vertical water movement - ergo, you need large masses moving large distances vertically... but wait!! the energy input in your design must be at some depth in the body of water (onto your black membrane). The question was meant to make you think about how much of the radiant energy is lost as the water column depth increases, but obviously it was a pearl cast before a swine. |
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3. What's a turbien?. If you mean turbine, then a turbine of the same power rating is identical whether it be driven by wind, water or gas from fermenting apples. In this house, we obey the laws of thermodynamics and the question was meant to see if you woke up to the need to define //amount// when perhaps you meant 'volume' - with volume having little to do with energy calculations - you should be talking about mass and speed. |
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4. The enviromission design has had more revisions than a White House speech. |
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//2. How deep does it need to be?// Wow. |
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Sorry Consul, I agree with all your points but 1b. By definition, any thermal power plant will HAVE to eject heat into the environment. Some get away with using radiators, thereby not dumping heat into a lake or ocean, but the rule still applies; they are dumping heat to the atmosphere instead. Most coastal powerstations use closed loop seawater cooling. I'm sitting inside a powerstation right now (25MW MAN diesel plant for a remote mining community) that uses a manmade 55 Megalitre pond for cooling, coupled with a radiator system to limit heat load. The old plant used seawater cooling through heat exchangers to the freshwater coolant loop. your car engine uses a coolant loop with a radiator, coupled with a certain ammount of radiative, conductive, and convective cooling (especially if it's a VW)... oh, and the hot exhaust gasses too... |
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In terms of thermodynamics, this is where efficiency comes in. A 50% efficient power plant (go on.. try for better than 50%) will extract 50% of the heat generated in combustion (or from whatever your heat source is, say like the sun), the rest being vented to the environment one way or another. In terms of concepts, you've got a heat source and a cool body. the heat source say being the hot combustion gasses, and the cool body being the coolant. An engine, or steam plant, etc is simply an inneficient heat pump that transfers heat energy from the hot body to the cool (entropy, anyone?), doing a bad job and incidentally wasting some of the heat by spinning a rotor, crankshaft, etc. This is how thermodynamics allows us to convert heat energy to more useful rotational, etc. Some things like PE cells and Peltier systems seem to violate these laws, but if you talk to those quantumn guys, they'll talk all sorts of mumbo jumbo about excited electrons, qunatum states, etc, and try to pretend they're not breaking any thermo laws. bully to them, I say, but if it works, cool. |
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So I would argue that ALL thermal power plants dump heat to ecosystems, one way or another. If I'm not mistaken, even hydro powerstations result in a miniscule increase in water temperature... |
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Worrying about dumping heat is a pointless, in terms of solar power. In the case of solar power, the amount of total energy that the sun rains down is fairly constant. The net heat stored/loss in that environment would be the same weather a pool is there or not. |
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I think this would work best in areas that have huge tempurate difference between day and night, to improve the circulation. |
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Consul:"1b. No thermal power plants dump hot water into ecosystems.' |
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Discharge of warm water to water courses is a standard practice at virtually all thermal power plants. |
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Consul: "In this house, we obey the laws of thermodynamics' |
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I'm sure you do, but I'm not sure you comprehend them. |
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You also seem to be somewhat vague on concepts like mass and energy. |
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Water is denser than air. I'm sorry if this surprises you. |
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Moving one litre of water through a turbine requires more energy than moving one litre of air - and a turbine can extract more energy fro a litre of water than a litre of air. |
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Given the same size collector and the same insolation, you will be moving a smaller volume of water throuh the tower but the energy content (assuming similar efficiency in converting insolation into heat) will be the same. |
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Check it out - for a given energy output, you need a significantly smaller and cheaper turbine if your workign fliud is water rather than air. |
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Now I'm not sure I can simplify this any more but if you're still confused ; let me know and i can try (let me know how I'm doing on being snide and patronising while you're at it). |
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easy tiger, you don't seem all that famiar with mass & energy either. |
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"and a turbine can extract more energy fro a litre of water than a litre of air." |
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Hmm. A bit confused are we? Generally, water (in liquid form) has constant volume, and is inefficient to transfer at high speeds due to viscous losses. Water in a turbine exhibits negligible expansion in the flow direction and effectively the turbine extracts the kinetic energy. |
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Turbines for use with gasses allow the gas to expand in the flow direction, and a large part of the energy extracted is as a result of realising the potential energy of the expanding gas. Read: the volume of the gas is not constant, whereas with the water it is. |
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So whentalking about energy density, are you referring to a litre of air at atmospheric pressure, or what? |
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do you really know what you were referring to? |
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stones, pots, glass houses and black kettles. |
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heated discussion. could we get some energy from it? |
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/ Built a large pool or lake, paint the bottom black with a transparent plastic membrane a couple of feet above it. / |
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No membrane required, if pond is still. |
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In Israel they built a solar pond that used salt water with fresh water on top. The heat was trapped in the salty section, but no membrane was required.
Maybe it was a gradual transition. Piping in the mud allowed them to pull very high temp heat exchange fluid from the collector pond. Must have been old news twenty years ago when I read it in a journal. |
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