h a l f b a k e r yQuis custodiet the custard?
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to cut costs of wind generation, gather the energy gathered with multiple windmills into a shared generator. Instead of using complicated shafts and gears, each winmill compresses air and pipes the result into a shared generator. Masts can be lighter, cheaper, and generators can be bigger, more efficient.
Also, compressed air can be stored during peak winds/gusts. Machinery can even be quieter too. Chaper to maintain. Win, Win, Win!
- Water instead?
you'd have to excavate plenty of space and store lots of liquid. Air is better as it compresses well and stores space-efficiently, and is also doesn't need such large pipes as water. Water would have to be hauled 'uphill' from somewhere, which would be a non-starter in dry regions.
- why not just store the energy?
well of course you can. Choices are having a big grid to feed it into, or chemically (lead/acid, etc..), or as hydrogen (cf. catalytic seperation membranes), or, if not storing it, just waste it at no extra cost.
But generator machinery typically runs at maximun efficiency within a specific power-band (the same reason you change gears on a car), so thus managing the input to the genny could be more efficient.
- windmill size?
I've personally stood under 100-meter-high (at hub) mills in galicia, a pretty impressive sight.
But the each one needs individual complex gearing and an individual generator for it all to work.
That means extra cost in maintenance and spares.
I think using simple compressors on-hub would greatly reduce and simplify the machinery, given a suitable compressed-air generator capable of high-efficiency in narrow-power-band operation.
Think about it.
Americas Wind Energy
http://awe-wind.com/
not pneumatic, but gearless wind turbines. [willard_b_trophy, Oct 04 2004, last modified Oct 21 2004]
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Another way to do this same idea would be to have each windmill pump water up to a resevoir which is then drained through a single hydraulic generator. Same idea, just hydraulics rather than compressed air (if it is any cheaper). I assume that the reality is it is much cheaper to just build the generator into each windmill. |
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Bigger windmills for stronger generation, As the size doubles a rough rule of thumb says energy triples. So if one mill puts out one watt. Three mills put out three watts, but take up three times the space. One mill doubled in size will put out three watts. Or, if you have four mill spaces you can have four watts with one watt mills, or six watts with two three watt mills.
But don’t store the energy, sell it back. |
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spartanica wrote:
> I assume that the reality is it is much cheaper to just build the generator into each windmill
I'm really not convinced of the economics.
I read in the Financial Times that wind power was 'almost as cheap as gas'.
I though 'Great' and then 'wait, why the hell does it cost anything?'
Apart from the capital expenditure of building the things etc, the cost-per-MW will be a function of the maintenance cost divided by however many average MW you expect from the thing, depending on size and average windspeed, basically..
I gather that these things are usually in the 0.25 to 0.75 MW maximum capacity range, generally running on average at 25% capacity.
So lowering the maintenance costs are critical in making it cheaper than fossil fuels. Ergo, reduce complexity and take advantage of economies of scale (in plant) wherever possible. |
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Aside from what's been said, if your one generator goes down you get no juice. Having multiple generators equals more maintenance, but also provides fault tolerance. |
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Good point phoenix. Large pneumatic geared mills are a good idea, but may go down. This could be fixed with a second back up generator. The advantage of a shared generator means that the mills would be less top heavy, assuming the extra pipe and fluid had equal distribution over the full length, you could have taller mills, and taller mills would mean more wind.
The real problem may actually be the amount of energy required to push the massive amounts of hydraulic fluid. Probably washes the advantage of height or energy storage. |
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Or with giant cones, you could funnel the wind into pipes that distribute the pressurized air directly to homes for ventilation, hairdryers, etc. |
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Sorry this doesn't stand up technically or economically. For low flow losses you need to go for high pressures, which gives you high leakages in your pump and motor. High pressures gives you high temperatures, if this is conducted away on the way to the central motor you have an irreversibility hence entropy increase hence inefficiency. If you are pumping into a common manifold you need a 1MW high- pressure variable-displacement air compressor to match the variable speed capability of an electric generator + power electronics (current state of the art), plus a 30MW-ish motor for the farm. Due to compressibility and low viscosity of air these are very difficult machines to make with decent efficiency. High pressure oil is much better than air for large scale mechanical power transmission, you can use an accumulator if you need storage. Captital expenditure and servicing the debt is by far the dominant cost for wind plant. Of this the majority is civil/structural so it makes sense to spend a bit more on your power transmission to get high effiency to maximise return from your investment. |
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I agree with respect to compressor storage, but I have seen economical wind driven pumped storage mechanisms that are used for irrigation pumping. |
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Can you say "wasted energy"? |
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Well I don't think compressors are cheaper than electircal generators and they tend to be break down a lot. However, the problem with wind energy is indeed storage so you may have something with using commpresed air for use during non windy times. but efficiency is really bad. Ever notice how compressors get really hot when the air is compressed. That's all wasted energy. Having said that it still might be worthwhile. ineficient storage is still better than NO storage which is the case today on all commercial wind generators. |
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Losses would be high, and you couldn't store a useful amount of energy. That's what we [effectively] have power grids for. |
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The most efficient way to compress air (or any other gas) is in multiple stages, with intercooling. |
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Logically, the best way to use pneumatic storage of wind power would be to have a wind farm where each wind turbine powers an air compressor, but only one of these compressors takes air directly from the atmosphere -- each of the others takes compressed air from the prior compressor and compresses that air further. |
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All of the piping in between compressors acts to cool the compressed air between one stage and the next, reducing the amount of energy needed to reach the maximum pressure. |
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To make up for heat loss, we could reheat the air after the last stage of compression and before the compressed air generator. This reheat stage could be done using either fossil fuels or concentrated solar power. An added benefit of reheating is that it obviates ice formation in the generator's exhaust. |
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