The message from The Natural Philosopher contains these words:
Hmm. Unless I have done something abysmally stupid in my calculation the alleged peak flow of 12 billion gallons a day translates into about 620 tons of water a second, and with a head of over 6 feet, that should generate slightly more than 1hp. Summer flow is allegedly about one ninth of peak flow.
The message from Tony Bryer contains these words:
Lock depth 2.1m.
Raw power is Head(m) * Flow(l/s) * 9.81 = Power(watts)
2.1 * (6*10^8/86400) * 9.81 = 143062.5WOr 143kW. Typical effciency is arpound 70% so in theory 100kW, but that is running *all* the water through the turbine(s). None over the weir or through the locks...
I could probably get a 10 to 20m head down our paddock but don't have a handy stream. B-(
No the dams don't affect the power available in the water they just facilitate the scheduling of the power.
AJH
I could get a 300ft head of water across my land. However there's no water at the top of it other than what is supplied by the water company, and I suspect using that water would work out a tad expensive.
There's a stream at the bottom of the land but the fall is minimal, more of a marsh with a slight downward inclination than a stream.
Yes this seems a better comparison, on the surface an overshot wheel looks pretty efficient I wonder how it compares with a turbine. It must have a higher capital cost.
AJH
Bzzt, wrong.
A 300 metre high dam makes a lot more power available then a 10 metre high dam.
It makes no difference, the water has to get to the top of the 300m dam or the 10m dam and as has been pointed out dam catchment areas are many times greater than the surface area of the lake behind the dam. IIRC the catchment for the blackwater dam above Kinlochleven is 62 square miles. In that case it's the fall through the penstock that is more significant than the height of the dam.
One of the interesting things about renewable power is how we make use of its variability, dams were the obvious first choice but there must be other ways and it's these that could mean we can better exploit these resources.
AJH
Did you fail Physics?
Now calculate not the head, but the pressure DROP across your wheel.
Nothing LIKE 6ft.
Its totally inefficient.
Its almost impossible to extract power from a large volume moving slowly.
The message from The Natural Philosopher contains these words:
That is what water wheels do. It might not be 100% efficent but it is no where near 0%.
Where Pelton wheels score is the reversal of flow of the water jet.
I'm off for a couple of days so don't expect any further response from me in the immediate future.
The message from The Natural Philosopher contains these words:
Eh? What has that got to do with it. Atmospheric pressure wwill be much the same only 6 feet up. The velocity of the water will have some effect but the major output is as a result of gravity.
620 tons per second falling 6 feet liberates a lot of energy.
As I said I thought the turbine would be more efficient but I still wonder how good a converter the overshot wheel would be. Plainly it converts the head to movement but at the same time it discharges the water with some kinetic energy so the energy it gets out is mgh minus
1/2mv2, what other losses are there that are not common to the turbine?As I said three messages up "As the head gets lower although the total energy might look similar from mass times head times gravity considerations it's harder to get any power" but it isn't impossible just debatable whether it's worthwhile. I think there are a couple of large submerged turbines, one off the SW coast. There's also an oscillating wing device being trialed.
AJH
Steve you snipped that selectively, so you probably don't understand the point.
Yes the head from the top to the bottom of a dam is higher in one case than the other but it's not relevant to my point and that was that the impoundment does not add to the energy of the water that has fallen behind the impoundment, the dam does not make the water climb to its top. The further implication was that a known, scheduled supply was more valuable than a steam running from spate to spurt.
I know usenet is a natural forum for the argumentative but why do you feel the need to provoke? If I make a wrong statement I am happy for it to be corrected. If you wish to misunderstand my point I'll try to back up my original statement. If proven wrong I am quite happy to take the education and retract. I won't enter into a long debate over my education.
AJH
Scheduling of the ramp up and ramp down of thermal generation to meet predicted demand curves is perfectly feasible and practical. Dinorwig along with a great many generating sites isn't completely essential to keep the lights on.
As for the "lot of waste heat" from spinning reserve that is completely untrue. The boiler is fired to meet the heat demand of the turbine (and thus the output of the generator) Fire at 95% of the demand on a 500MW unit and you generate 475MW. The thermal efficiency is I'll admit marginally lower than when operating on full load but with similar, if not identical steam/feedheat/vacuum conditions for the period of time the lower output is needed it's hardly a major problem. Operation at 80% load could quite easily result in almost identical efficiency to operation at close to 100%.
But as much as it might offend the environmentalists thermal efficiency within the context of UK electricity supply doesn't really matter anymore, 15 years ago it played a major role in generation scheduling. In the sad world of 2006 you could have a power station with the worst thermal efficiency generating 24/7 - providing you have a cheap fuel source, say from slave labour in China, and thus can bid into the system at the lowest cost. You of course need to make sure your rivals don't get the cheap coal, maybe by greasing specific palms with large dollops of cash.
It's Dinorwig by the way and not Dinorgig. It was Dinorwic for a short period of time before the Welsh nationalists got their way - can't see why they caved in, its a lot harder to burn water that a holiday cottage.
They changed it from Dinorwic to Dinorwig because the former is incorrect! some muppet manager prolly put it down wrong! it would be the same as me insisting London should be called Londom because some muppet spelt it wrong :-) Havent had a "holiday home fire" for 15 years. But the locals are getting restless as the house prices soar way and above what they can afford, and the only people that are buing houses are "not Welsh" and quite frequently for second homes. Anglesey is becoming the UK wind wally, jetski and Howards Way brigade's first home !!! at the W/E its hell getting accross the bridges blocked with millions worth of boats and jetskis (I hate those little buggers!!).
Untrue, I simply have little patience with people making pronouncements on the basis of ignorance. Your statements were incorrect, because you appear to believe that the potential energy in a hydroelectric scheme is proportional only to the flow of water from the catchment area. This is profoundly incorrect. The potential energy is proportional to both the height of the dam and to the flow of water.
So when you say "In that case it's the fall through the penstock that is more significant than the height of the dam."
You are completely and utterly wrong.
Here's a sensible summary of HEP.
Its alot closer than yiuy think.
Where pelton wheels score is that its a lot easier to use a small volume of water moving VERY FAST.
It won't be missed. Your concepts of thermodynamics are fairly flawed.
>
No it doesn't
Because it still has most of its energy when it leaves the turbine.
It KEEPS its energy.
No doubt its got LOTS of energy., So does a few grams of deuterium. Its getting it out usefully that is the problem...in both cases.
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