Pumped Hydro Storage (PHS)

Preface. This is the only commercial way to store energy now (CAES hardly counts with just one plant and salt domes to put more in existing in only 5 states). Though of course hydropower is only in a few states as well, 10 states have 80% of hydropower, and PHS needs to go far above existing reservoirs. There are very few places this could be done.

Alice Friedemann   www.energyskeptic.com  author of “When Trucks Stop Running: Energy and the Future of Transportation”, 2015, Springer and “Crunch! Whole Grain Artisan Chips and Crackers”. Podcasts: Practical Prepping, KunstlerCast 253, KunstlerCast278, Peak Prosperity , XX2 report


Pumped hydro storage generates power by using electrically powered turbines to move water from a lower level at night uphill to a reservoir above.

During daylight hours when electricity demand is higher, the water is released to flow back downhill to spin electrical turbines. Locations must have both high elevation and space for a reservoir above an existing body of water.

Pumped hydro uses roughly 20–30 % more energy than it produces, with more electricity required to pump the water uphill than is generated when it goes downhill. Nonetheless, pumped hydro enables load shifting, and is important to balance wind and solar power.

Appearances can be deceiving: Pumped hydro is not a Rube Goldberg scheme. Many of you have used a kilowatt or two of pumped hydro yourself. PHS accounts for over 98 % of what little current energy storage exists in the United States, and is the only kind of commercial storage that can provide sustained power over 12 hours (typically, the other 12 hours are spent pumping the water up).

Existing PHS facilities store terawatts of power annually, but account for less than 2 % of annual U.S. power generation. In 2018, the United States had 22.9 gigawatts (GW) of pumped storage hydroelectric generating capacity, compared with 79.9 GW of conventional hydroelectric capacity. This isn’t likely to increase much, since like hydroelectric dams, there are few places to put PHS. Only two have been built since 1995, for a grand total of 43 in the U.S., with most of the technically attractive sites already used (Hassenzahl 1981).

Most were built between 1960 and 1990; nearly half of the pumped storage capacity still in operation was built in the 1970s (EIA 2019).

Existing PHS in the U.S. can store 22 GW, with the potential for another 34 GW more across 22 states, though high cost and environmental issues will prevent many from being built. Additionally, saltwater PHS could be built above the ocean along the West coast, but so far the high cost of doing so, shorter lifespan due to saltwater corrosion, distance from the grid, and concerns of salt seepage into the soil have prevented their development. Underground caverns and floating sea walls are other possibilities, but also aren’t commercial yet.

PHS has a very low energy density. To store the energy contained in just one gallon of gasoline requires over 55,000 gallons to be pumped up the height of Hoover Dam, which is 726 feet high (CCST 2012).

In 2011, pumped hydro storage produced 23 TWh of electricity across the U.S. However, those plants consumed 29 TWh moving water uphill, a net loss of 6 TWh.

So, how many PHS units would it take to give the U.S. that one day of electricity storage, 11.12 TWh? Over 365 days, our 43 existing pumped hydro plants produced two days of energy storage (23 TWh). Thus, the U.S. would need more than 7800 additional plants (365/2 * 43). Rube Goldberg, I can imagine what you would make of this.


CCST. 2012. California’s energy future: electricity from renewable energy and fossil fuels with carbon capture and sequestration. California: California Council on Science and Technology.

Hassenzahl, W.V. ed. 1981. Mechanical, thermal, and chemical storage of energy. London: Hutchinson Ross.

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15 Responses to Pumped Hydro Storage (PHS)

  1. Hamish McGregor says:

    Your first paragraph could be a lot clearer.

    “Pumped hydro storage –generates– (should be “stores”) power (energy), by using electrically powered turbines to move water from a lower level at night uphill to a reservoir above. ”

    Pumped Hydro, stores energy by using electrically powered pumps (or reversible turbines), to move water from a low elevation to a higher elevation, during off-peak-hours. The storage is very short term, usually a few hours.

    In addition, the electricity used to pump the water, often comes from conventional power stations and allows them to spend a greater amount of time running near full power (nameplate capacity).


    I’m not familiar with your intended audience. Are you assuming they understand; Kilo, Mega, Giga and Terra (Watt Hours)?

    • energyskeptic says:

      Thanks. I’m assuming people know how to do an internet search on anything they don’t know. I don’t know who my audience is, but I imagine it is people who are aware of peak oil, limits to growth, are energy literate, ecology oriented sorts of folks.

  2. Bernard Beveridge says:

    I taught high school science (mostly physics) for some 38 years and took students on exactly ONE field trip. It was a trip to the Northfield Mountain pumped hydro facility along the Connecticut River in western Massachusetts. Part of the tour consists of a bus ride “up” to see the man-made reservoir where the water gets pumped to at night. The other (and more exciting part) is the trip by bus “down” underground to view the pumps/generators. I hope that the students have some very fond memories of seeing “physics in action.” My wife and I home school our granddaughter and hope to take her there in a few years as well – assuming, of course, that there will be energy available to get us there!

  3. Weogo Reed says:

    Hi Alice,



    I’m a big fan of micro-hydro, and rather than damming waterways, only diverting a portion for harvesting energy.
    What is the proper amount of flow, 10%? 50%? that can be diverted with minimal environmental disruption? I don’t know.

    Pumped hydro is kinda crazy. When the alarms sound and water starts draining you really don’t want to be a service worker doing a water survey out on the upper reservoir!
    And when it starts to fill, you don’t want to be eating your lunch on the shore.
    I wonder if any wildlife has adapted to thrive around pumped hydro.

    Thanks and good health, Weogo

  4. NJF says:

    “To store the energy contained in just one gallon of gasoline requires over 55,000 gallons to be pumped up the height of Hoover Dam, which is 726 feet high.”

    Whoever performed this calculation is wrong. They are off by a power of about 3.75 by my calculations. And that’s assuming 100% thermal efficiency of gas which is impossible due to Carnot limitations.

    • energyskeptic says:

      I have a peer-reviewed citation, you have a calculation that needs to be backed up as well.

    • Hamish McGregor says:

      Energy in 1 U.S. Gallon of gasoline = 114,000 BTUs = 120 million joules.

      Gravitational Potential Energy (in Joules)
      = mass (in Kg)
      times constant g (acceleration due to gravity, 9.80665 m/s^2)
      times height (in meters)

      mass (Kg) = 3.79 x 55,000 U.S. gallons.
      g = 9.80665 m/s^2
      height (meters) = 726 feet / 3.281 = 221.285
      Energy (Joules) = 3.79 x 55,000 x 9.80665 x 221.285
      = 452.349 million joules.

      120 million joules (in 1 U.S. gallon of gasoline) is almost a quarter of 452 million joules (in 55,000 U.S. gallons of water stored at 726 feet).

      There is no need to consider Carnot cycles or efficiency of energy conversions. The appeal to peer-reviewed citations for authority (argumentum ab auctoritate) is also not constructive. This is not controversial.

      • Hamish McGregor says:

        This comparison would have been better made to simply state that there is an enormous amount of incredibly useful energy stored in a gallon of gasoline – how far does a gallon move your vehicle, and how long would it take you to manually push it the same distance (if that was even possible).

        To really drive home the absurd nature of the comparison, consider that (for a dam) the Gravitational Potential Energy of water is for a “column” of water, not a plane at 726 feet.

        The water half-way up the dam has considerably less stored energy than the water at the surface.

        Writing these types of articles is fraught with difficulty and probably why I write so little. Who wants to spend there spare time wading through an engineering dissertation?

      • NJF says:

        Exactly the numbers I got.

        Even recalculated assuming that they had rounded, or that they used imperial gallons for fuel. None of them closed. Don’t know what they did.

        I beg to differ about the Carnot comment. There IS a precedent for 80%+ efficiency in hydroelectric facilities. There isn’t even a theoretical precedent for a single engine that converts heat from gasoline to electricity. Not even close.

        Hydrogen fusion “theoretically” has TONS of energy. But the process isn’t doesn’t break even due to practical concerns. It’s not a very useful metric to talk about gasoline without the context of the efficiency of the machines that use it.

  5. Hamish McGregor says:

    I searched for “CCST 2012” and found:
    Searching through the PDF for “Hydro” found a lot of references to Hydrogen and other things, nothing on PHS or the energy stored in water at raised elevations.

    I guess it is possible that the article has a link that my browser is not showing.

    PS. Do you have anyone to help with proof-reading, etc?

    • NJF says:

      I found her claim in that paper, not sure if you’re looking at the right one.

      She did her homework and cited it. It’s the California government goofballs who messed up a first semester college physics calculation.

      It’s really not that far off in the grand scheme of things. The point was correctly illustrated: Electrical fields hold more energy than gravitational ones do for the same mass.

    • NJF says:

      You have the wrong paper. You’re looking at building guides.

      The title should be: Electricity from renewable energy and fossil fuels with carbon capture and sequestration. It has a green title page

  6. EnterpriseSpaceShip says:

    ….There is no need to consider Carnot cycles or efficiency of energy conversions“.

    After 250 years of extensive mass fossil fuels extraction, it is beyond the mental capacity of any human to accept now a Joule of energy in fossil fuels is a product of a colossal total solar energy Life has been exposed to, capturing and making the fuels in the distant past at just <=2% capacity of photosynthesis and other living processes.

    That is 50+ more solar than what we find today in fossil fuels.

    Plus, another 10000+ times more chemical and physical energy were also applied over the ages until that Joule has become energy-full, portable, ready for extraction, stored deep in the underground.

    Add to that the energy required to construct and run the industrial base that has extracted enough joules to then construct and run a daughter industrial base to extract our one single Joule – and you conclude that:

    Nothing built with fossil fuels can repay back the energy put into it.

    A joule in fossil fuels is not like any other joule – being not a product of fossil fuels.

    A joule from a Pumped Hydro Storage and others – is.

  7. Hamish McGregor says:

    Talking of Pumped Hydro Storage, the BBC today (2019.10.18) is reporting about a possible massive new PHS in New South Wales, Australia, that could represent as much as 10% of their entire production.

    From the article; on the one hand:

    “In the mid-2020s we are going to have to start significantly changing how our electricity system operates to cope with the variability of wind and PV. You need to spread the resources widely, so you are sampling different weather at different times. You need a certain amount of storage, and pumped hydro is by far the cheapest way to store energy.”

    On the other hand:

    “Snowy Hydro 2.0 was a political get-out-of-jail card, played at the public’s expense,” he [director of the Victorian Energy Policy Centre, Bruce Mountain] told the Australian Broadcasting Corporation. “This is a project that we can confidently forecast will be a drain on the public purse and whose service in the transition to a cleaner energy future can be met far more cheaply from other sources”.