posted
I think the Laws of Physics are really just suggestions.
I refuse to be held down. I refuse to relinquish my momentum merely because of some arbritrary limit discovered by some rich, dead, white guy.
Posts: 14554 | Registered: Dec 1999
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quote:Originally posted by aspectre: Go ahead, make my day
I saw that earlier today. I guess we've identified someone else who is lurking at hatrack and stealing our best ideas.
Posts: 12591 | Registered: Jan 2000
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posted
Morbo: While I would disagree that the standards of an academic journal are not something to aspire to especially on a academic topic like this, I fully recognize that kwea is hardly obligated to provide a link, which is part of why I asked nicely.
But on the other hand, you have to recognize that especially on the Internet, one always has to take hearsay from people you don't personally know with a grain of salt. It doesn't matter if its a newbie or a long-time poster, and its nothing personal either which is why I do hold myself to the same standard when presenting information, providing sources when possible.
The Rabbit: I think your explanation seems to more sense, especially in the Ontario context where we use coal to a much smaller extent than the US as a whole. Being able to shut down a section of the plant pending seasonal demand makes more sense than being forced to run the whole thing at 70% always.
I also agree that it is not possible to tell from the data which is more efficient. However, my guess is that between the energy conversion loss of two conversions (electricity->water potential NRG->electricity), the cost of the reservoir, and the increased emissions of generating full power from coal at any time, it might be cheaper and better for emissions to take the money for the dam (assuming that the dam is purely for storage and cannot generate power without pumping) and simply build more natural-gas fired plants and shutdown as much coal totally as possible, especially when we combine that with the potential of soaking-up off-peak electricity with PHEVs as they become available "anyways".
Posts: 7593 | Registered: Sep 2006
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posted
Our local hydro dam does something similar: pumps water back into the lack during the night, so there'll be more power during the day.
Posts: 544 | Registered: Mar 2007
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quote:However, my guess is that between the energy conversion loss of two conversions (electricity->water potential NRG->electricity)
Pumping and hydroelectricity generation are extremely efficient processes. It turns out that this is probably the most energy efficient way to store electricity. I'll go hunt my references to try to find and exact number.
quote:the cost of the reservoir, and the increased emissions of generating full power from coal at any time
This one has been worked out in detail. I'll talk about the cost of the reservoir later but the combination of the low efficiency of ramping power plants up and down, low efficiency when operating at less than full power and the electricity that's currently thrown away far out way the inefficiency of pumped water storage. This one definitely results in a net decrease in emissions.
quote:It might be cheaper and better for emissions to take the money for the dam (assuming that the dam is purely for storage and cannot generate power without pumping) and simply build more natural-gas fired plants and shutdown as much coal totally as possible, especially when we combine that with the potential of soaking-up off-peak electricity with PHEVs as they become available "anyways".
As I mentioned before the economics of this have been fully worked out and your assertion is wrong. At least its wrong if you don't consider the externalities. Combined capital and operating costs for new hydroelectric power are much lower than the combined capital and operating costs for new coal and gas. There are already operational systems like this out there. It works and its economical.
Unfortunately the picture changes when you look at the externalities. Large hydroelectric dams have possibly the highest adverse environmental impact of any technology including greenhouse impact. Studies of the large damns recently built in China show that destruction of vegetation and the release of methane gas from land flooded by the new reservoirs is extremely high.
When you consider the external costs, pumped water storage only makes sense if you can pump into an existing reservoir.
Posts: 12591 | Registered: Jan 2000
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Qaz: Big difference between using an existing reservoir attached to an existing hydro dam that normally generates power and pumping water (possibly using nuclear power) and building a new dedicated reservoir just to store water that is pumped using thermo plants. As I mentioned, we already do the former in Ontario. AKAIK, we do not do the latter.
quote:Originally posted by The Rabbit: ... the low efficiency of ramping power plants up and down, low efficiency when operating at less than full power ...
As I noted earlier, this is an assumption which is still under debate. If we accept it, I admit that the equation would be different. But for now, it is unresolved as far as I am concerned.
Also, I do appreciate the reference hunting re: efficiency
quote: Combined capital and operating costs for new hydroelectric power are much lower than the combined capital and operating costs for new coal and gas. There are already operational systems like this out there. It works and its economical.
That may be true, but its the wrong comparison. We're comparing the operating costs of operating coal plants at full off-peak + capital and operating cost of a new reservoir) vs. (combined capital and operating costs for new coal or gas).
That combined with the long build time of a reservoir and the short build time of gas, plus the fact that the province has already committed to build more nuclear power anyways leads me to believe that the equation would be very different for different jurisdictions.
quote: When you consider the external costs, pumped water storage only makes sense if you can pump into an existing reservoir.
quote:Originally posted by Mucus: As I noted earlier, this is an assumption which is still under debate. If we accept it, I admit that the equation would be different. But for now, it is unresolved as far as I am concerned.
Also, I do appreciate the reference hunting re: efficiency
As far as I'm concerned, its neither an assumption nor debatable. Its an established fact. I am engineering prof., I've taught courses in this. You aren't required to believe me on any of those points but its not worth my time or effort to keep argue.
You are speculating in an area where there is no need to speculate.
quote:That may be true, but its the wrong comparison. We're comparing the operating costs of operating coal plants at full off-peak + capital and operating cost of a new reservoir) vs. (combined capital and operating costs for new coal or gas).
That's not the correct comparison either. Whether you believe it or not, a significant amount of the electricity produced is wasted.
Posts: 12591 | Registered: Jan 2000
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quote:Originally posted by The Rabbit: As far as I'm concerned, its neither an assumption nor debatable. Its an established fact. I am engineering prof., I've taught courses in this. You aren't required to believe me on any of those points but its not worth my time or effort to keep argue.
Honestly, I think you're being unfair. Seriously, hearsay and "because I said so" are reasonable techniques for establishing the truth to you?
Consider if our positions were reversed, if I was presenting an unintuitive result from my field and in response to your questions I was only able to present A) not only an appeal to credentials, but my own credentials to boot B) hearsay from another poster who heard it from a friend, then I would fully expect you to be skeptical and it would be warranted too. This skepticism would only be enhanced if you do have access to several actual sources that seem to indicate otherwise.
Present me with evidence, math, actual numbers and then I'll fully consider them. I have no personal stake in this debate. Try to shut down the discussion with rhetorical tricks and I will remain skeptical. If our positions were reversed, I doubt you would do very differently.
As someone noted, this is the *Internet* after all.
Posts: 7593 | Registered: Sep 2006
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quote:Originally posted by King of Men: Some places in Norway use it to heat housing. Not a very scalable method, though.
The idea of combined heat and power generation does have a lot of possibilities. Though there aren't enough potential uses of hot water in rural Georgia to make this worthwhile at my plant, it works well for smaller distributed generation plants.
For example, a hotel or office building in a big city will have need for hot water for heating guest-room water, room heating, laundry water, etc. Plus they can have an absorption chiller which takes hot water in as a power source and uses it to chill cold water. The cold water can be used for air-conditioning and refrigeration. The electricity generated can be used to lower the hotel's power bill, particularly if it decreases the peak demand the hotel needs during the month, which lowers the price per kilowatt hour of all electricity used in the month. (Power companies charge their largest customers a rate according to their peak demand, to help cover the capital costs of providing Megawatts only needed during peak times.) That's a good use for the 60% of the energy of generation that would otherwise be lost as waste heat.
For nuclear plants, though, it's best to put them in places with low population density, so emergency planning is made easier. And there just aren't any uses of hot water there that I can think of that pay for themselves. Oh well, I guess the birds are glad of it.
During the recent outage one day I saw about 20 birds perched on the top of the unit 1 tower as though waiting for the elevator to start back up. =)
Posts: 6246 | Registered: Aug 2004
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posted
I wonder how the efficiency of capturing cheap off-peak electricity in the form of hydrogen via electrolysis might compare to the efficiency of pumping water uphill to run it through a turbine. It'd have to be quite a bit better to win on efficiency, I suppose, because converting the chemical energy of hydrogen back to electricity wouldn't be very efficient. However, hydrogen storage tanks might have a lot less impact on the environment. (Storing hydrogen couldn't be that much more dangerous than storing large quantities of oil or gasoline, could it?)
Posts: 4287 | Registered: Mar 2005
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posted
It doesn't have to be all that efficient to be useful. In some of the solar power plants being built, they're talking about storing energy (so that some electricity can continue to be produced when the sun isn't shining) in the form of heated water, which has got to be terribly inefficient.
Posts: 16551 | Registered: Feb 2003
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