0

How does the volume of water going through a hydroelectric dam affect electricity production? Could the flux of the generators not be modulated to different amounts of electricity with the same flow of water? If so, what would the minimum flow be?

Derek Seabrooke
  • 101
  • 2
  • 2
    "*Could the flux of the generators not be modulated to different amounts of electricity with the same flow of water.*" You could, but that's a waste of water. Better to just control flow rate as much as possible. Minimum flow required is determined by turbine design (minimum head pressure). – DKNguyen Jan 30 '23 at 21:55
  • 1
    How about zero water , that would not waste any. – blacksmith37 Jan 31 '23 at 00:38
  • 1
    Some hydro installations have a minimum flow set to keep the generators spinning but not producing power. That way they can go from basically zero to full output (in megawatts) in about 10 seconds. – Solar Mike Jan 31 '23 at 10:25
  • @DKNguyen my point of the question is to know if the dam could be used for two separate purposes, controlling flooding of land on either side of the dam and to generate electricity without the need for electricity being the reason for the decision of how much water to let through. – Derek Seabrooke Jan 31 '23 at 22:07
  • 1
    @DerekSeabrooke It would affect efficiency and RPM. If you had an excess of water you might not care about efficiency but you also don't want the turbines to over speed. And of course, there are just bypass gates. – DKNguyen Jan 31 '23 at 22:12
  • 1
    water going over a dam doesn't do anything to power generation, it's the water going through a dam that matters. – Tiger Guy Feb 01 '23 at 09:41
  • So if I understand the crux of the answers are there is a maximum amount of electricity that can be generated from a certain flow but no minimum. No surprise really. Therefore there is no cost to letting more through to prevent flooding but a definite cost in the event of a drought. – Derek Seabrooke Feb 03 '23 at 02:26
  • 1
    @DerekSeabrooke if there's too much water, you have literally free energy and why wouldn't you run the generators as much as possible, because you are getting paid for that energy that costs you nothing to produce? – user253751 Feb 07 '23 at 09:36
  • @user253751 this is true except that the water could cause wear and tear on the dam that could have a cost to maintain. Also there isn't unlimited demand for electricity. Eventually the grid will be saturated as there will be more generated than is being consumed. – Derek Seabrooke Feb 09 '23 at 02:14
  • 1
    @DerekSeabrooke I think it's quite rare that hydro dams have to be throttled as the more expensive energy producers are usually throttled first. Maybe on a national holiday with good weather in New Zealand or Norway. – user253751 Feb 09 '23 at 08:52
  • @user253751 nevertheless possible. – Derek Seabrooke Feb 10 '23 at 23:19

2 Answers2

1

The Efficiency of a turbine is expressed in a Hill Chart -enter image description here

The efficiency can be improved at off-design points by using variable geometry guide vanes in the induction section, as described in the paper below. This is the best we can do at the moment in terms of variable flow and variable head and variable demand.

https://iopscience.iop.org/article/10.1088/1755-1315/1079/1/012083/pdf

Phil Sweet
  • 4,130
  • 7
  • 15
1

Hydraulic power is the product of a flow variable (mass per second) times the effort variable (pressure head). To increase the output power of a hydro plant, the flow is increased by opening up the inlet valve to the turbine so the flow rate goes up.

Knowing the characteristic curves (the Hill Chart) for the turbine, the operating point of the hydro plant can be chosen so as to coincide with the maximum efficiency point of the turbine(s).

To cover as broad a range of power outputs as possible, while still maximizing efficiency, it is common to build a hydro plant with a number of separate turbogenerator units in place. Then in times of peak demand the power output of the plant is increased by bringing additional turbo units on-line, where all of them are operating at their peak efficiency point.

niels nielsen
  • 13,033
  • 1
  • 11
  • 30