Not always true, see below:
It requires electricity to pump the water into the reservoir. Some of which is recouped when the water is subsequently released through the generators. The rain actually fell several hundred miles away from the reservoir which has no natural inflow (c.f. pumped storage).
Feel free to look up San Luis Reservoir on wikipedia for additional context.
Talk about unfair comparisons. A large generation station may produce 1,000,000,000 watts (1000 MW).
The generator will automatically compensate for changes in real power demand (generally by varying frequency, augmented by AGC).
For larger changes (e.g. everyone turning on their HVAC plant at the same time):
Smith Mountain Lake in Virginia works something like that. This is an explaination for its website
"Hydroelectric production: Smith Mountain Dam houses five hydroelectric generators with a combined installed capacity of 560MW. Smith Mountain Lake Dam utilizes pumped-storage hydroelectricity by which water that is released downstream can be pumped back into Smith Mountain Lake for re-use. The Leesville Dam regulates the Smith Mountain Lake's outflows and stores water to be pumped back into the Smith Mountain Lake for this purpose. Hydro-electricity is usually produced during high-demand times (day) and pumped back into the lake during low demand times (night). The Leesville Dam also produces hydro-electricity as well."
So while there is a cost of upkeep the water is pump back upstream is free. only loss is due to "friction"
The water flowing from Smith Mountain Lake generates X Kwh. The water pumped to Smith Mountain Lake overnight requires Y KWh.
Physics says that "Y" must be always more than "X". The fact that 1Kwh is a bit cheaper during the nighttime hours, is a bit of a chimera, just a blip on the supply-demand curve; there is still a cost to pump the water back into the lake that isn't present in standard hydro plants.
While true, the cost is mostly the incremental cost in wear and tear of running the turbines under high load instead of low. It may turn out that in terms of cost it's actually a net gain--sometimes running systems under reduced load increases wear over running at their design load.
"J. Clarke" wrote in news: snipped-for-privacy@news.eternal-september.org:
Didn't we go over this a year ago? In any event, the reason for pumped storage has nothing to do with the wear and tear of running turbines under high or low load. It's entirely due to the fact that _steam_ turbines decrease in efficiency drastically when they aren't run at their designed capacity.
Overall it's cheaper for the power company to keep their steam plant (coal/oil/gas/nuclear) running at it's design capacity, and absorb the excess power by pumping water uphill. By the same token, when there's a need for more power it's cheaper to generate power by letting the water run downhill, than it is to try and run the steam plant over it's design capacity. But it's all about keeping the steam plant at it's optimal state.
John
Nobody said anything about a reason involving wear and tear.
If the power to pump the water uphill is coming from steam turbines. Is it in this case?
It will be coming from the baseload generation, so probably yes. Everything except solar, wind and hydro requires steam. There may be exceptions in Washington and Niagra which have abundant hydro.
Even Niagara does off-peak recharge pumping.at the American lewiston/robert moses station, and the Sir Adam Beck on the Canadian side. (see
Also see:
This is an inovative private sector plan to use surplus night power to "create" a waterfall to produce power in peak demand periods - effectivey a "hydraulic battery". One way to rehabilitate an iron mine abandoned by Bethlehem Steel
"J. Clarke" wrote in news: snipped-for-privacy@news.eternal-september.org:
Are you having memory issues? _You_ said wear and tear was the reason.
John
snipped-for-privacy@slp53.sl.home (Scott Lurndal) wrote in news:U2bJy.99149$ snipped-for-privacy@fx14.iad:
As a general rule, hydro can be throttled, so there's no reason to use hydro generated electricity for pumped storage. Almost all pumped storage uses either excess power from steam plants, or from variable sources like wind power.
As Mr. Clare pointed out, one exception is when hydro is not from a dammed storage, as is the case in Niagara. Since that water is going to flow regardless, it may as well be routed thru the turbines all the time.
(specific to the example of Smith Lake, a little Googling shows that utility to generate 97% of it's power with steam plants, so I think it's safe to say that's where the pumping power for the pumped storage comes from).
John
There are also gas turbines but they're just used for peaking.
Are you having reading comprehension problems? I said no such thing.
Sorry, sounded like it to me, too.
"sometimes running systems under reduced load increases wear over running at their design load."
krw wrote in news: snipped-for-privacy@4ax.com:
Yeah, I meant to mention that yesterday and hit "send" too soon.
The hot concept in powerplants right now is what's called "combined cycle". The typical setup there uses two large gas turbines in parallel as the first stage, with the exhaust heat from them used to generate steam for a two stage steam turbine.
As you suggest, stand-alone gas turbines are just used for peaking.
John
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