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Regarding pumped storage hydropower,

In the case of some high altitude upper reservoir that feeds several turbines located at the bottom of a valley, where there's a lower reservoir too.

Assuming in this case turbines are not reversible by design, and cannot act like pumps, and therefore separate dedicated pumps are required to pump up water to the upper reservoir.

Should those pumps be fed electrically? Or should those pumps be directly linked to turbines using some clutch? How does efficiency of "converting hydraulic to electrical and back to hydraulic" compare to only "convert hydraulic to hydraulic" ?

user721108
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  • why would the pumps be connected to the turbines? ... what would be the purpose of the turbines then? – jsotola Feb 23 '23 at 20:22
  • Why don’t you check out Dinorwig aka the water mountain before posting.? – Solar Mike Feb 23 '23 at 20:28
  • @SolarMike I don't know about Dinorwig and very little about hydropower in general, hence the question. thanks btw I'm reading about it and will remove this post if it answers my question – user721108 Feb 23 '23 at 20:50
  • @jsotola pumps would be connected to turbines' shaft to pump water back up in upper reservoir. Purpose of the turbine is to power an electric generator, and in this case to allow to switch from powering a generator to powering a pump, when required. – user721108 Feb 23 '23 at 21:01
  • that makes no sense ... just shut off the water flow ... why waste water to pump some of it back – jsotola Feb 23 '23 at 21:49

2 Answers2

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Yes, electrically.

The normal purpose of these systems is to provide peak power generation capacity. Peak power often has to be generated via expensive fossil fuel systems. Peak power demand is often the late afternoon due to heat loads and people returning home at the end of the work day, plus additional line losses (I-squared-R losses) due to high power draw. These systems can provide peak generating capacity by drawing down the water level in the upper reservoir.

The water is pumped back up when electrical demand is low (like at 3 am) and lower cost power can be used (such as a base-loaded nuclear plant).

Tiger Guy
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This is the simplest pump-storage-power generation scheme:

During the high electricity utilization period, the upper reservoir releases water that turns the turbine to generate power, and excess power is stored in the battery. The pump will then uses the stored power to pump the water from the lower reservoir back to the upper reservoir during the low electricity utilization period.

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https://www.energy.gov/eere/water/pumped-storage-hydropower

https://www.bing.com/videos/search?&q=pump+storage+power+plant&view=detail&mid=B8C0B73DCF4B751B6DE3B8C0B73DCF4B751B6DE3&FORM=VDQVAP&rvsmid=D9C856B2F4B7ED93963ED9C856B2F4B7ED93963E&ajaxhist=0

r13
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  • "some of the generated power is stored in the battery which is connected to the pump" I don't get this part – user721108 Feb 23 '23 at 21:58
  • you can't pump water back up using power you generated from that same water. – Tiger Guy Feb 23 '23 at 22:23
  • @TigerGuy On top of its original stored water, the upper reservoir usually gets water from a small creek, so there is no need to pump the entire water used in generating, but to make up the water lost through evaporation. Otherwise this concept won't work as pumping always need greater power. – r13 Feb 23 '23 at 23:13
  • you are missing the point of the hydraulic battery - to provide peak power. Putting power into a battery would conflict with this. – Tiger Guy Feb 24 '23 at 01:50
  • @TigerGuy Please read yourself. https://www.energy.gov/eere/water/pumped-storage-hydropower – r13 Feb 24 '23 at 04:29
  • @r13 the upper reservoir is "the battery." – Tiger Guy Feb 24 '23 at 15:18
  • @TigerGuy During pumping the turbine reverses and needs power to overcome the negative head. The power is furnished by the generator, similar to start-up cars, which require electricity to start, the start-up electricity is usually from a storage device, which is termed to be "the battery". – r13 Feb 24 '23 at 21:06
  • @r13 the water is pumped using power from the grid. – Tiger Guy Feb 25 '23 at 08:15
  • @TigerGuy "Hydropower is an extremely flexible resource. It can supply electricity or store it to meet real-time energy needs." It is self-sufficient and does not require an outside source to kick start. The pumping stage is similar to starting a car, with a healthy battery, do you need a jump start! – r13 Feb 25 '23 at 13:48
  • @r13, "Storage" is the upper reservoir. You might be able to find an installation today that has on-site battery power storage, but 100 years ago when this idea began you would not. It is not a core part of the technology. – Tiger Guy Feb 26 '23 at 01:13
  • @TigerGuy I bet your car does not need a battery because your oil tank stores the energy. – r13 Feb 26 '23 at 01:37
  • @r13, I've seen a lot of industrial electric motors, and exactly none needed a battery. I really don't know where you're going here. Pumps are not internal combustion motors. – Tiger Guy Feb 26 '23 at 04:45
  • @TigerGuy The fuel in the combustion chamber is pumped up from the gas tank beneath the car, which is similar to the lower reservoir in the PSP, and the combustion chamber and pistons act similarly to the combination of the upper reservoir and turbine generator. I don't think I need to repeat where the power required to start the pump and ignition comes from, which is where our difference lies. – r13 Feb 26 '23 at 21:11