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Clean Power pumped hydro

Published on May 7th, 2014 | by Tina Casey


Sacramento Eyes Giant Water Battery

May 7th, 2014 by  

The City of Sacramento, California is forging ahead with plans to construct a 400 megawatt battery made entirely out of water. That almost sounds like some kind of high tech miracle but it’s not. Water batteries, aka pumped hydroelectric facilities, use established technology and old fashioned gravity.

Pumped hydro is currently the only utility-scale energy storage technology in common use globally, including in California and the US. Another new pumped hydro project is already in the works for California, so you’re going to hear a lot more about pumped hydro in the future.

owa Hill pumped hydro project planned for Sacramento

Water (cropped) by Mohd Althani.

Why Pumped Hydro?

Given the drought in California the timing might seem a bit odd for water-intensive energy projects. However, the idea behind pumped hydro is to circulate the same water, rather than letting it run through as in a conventional hydroelectric dam.

In a pumped hydro system, water is shunted from a lower reservoir to a higher reservoir at night, during off-peak hours when electricity rates are lower, so the basic idea is to save money.

You also get bonus points for using renewable energy to do the pumping. Given their potential for enormous capacity, pumped hydro systems are ideal for storing energy from intermittent sources, namely wind and solar (check out this pumped hydro system in Wales for the wind angle).

Even without renewable energy, the carbon footprint reduction and financial savings both kick in because pumped hydro can reduce or eliminate the need to build new fossil fuel power plants to handle peak use periods.

Another sustainability aspect of pumped hydro is the potential for using existing reservoirs, as illustrated by a proposed pumped hydro system in New York.

Our sister site PlanetSave also notes that a company called Gravity Power, LLC has been developing a modular pumped hydro system that could help reduce the need for new reservoir construction.

The Iowa Hill Pumped Hydro Project

Sacramento’s planned pumped hydro system is called the Iowa Hill project. It is going to use Sacramento’s existing Slab Creek reservoir on the American River for the lower reservoir. The upper reservoir, which will not dam the river, will be new construction with a capacity of 6,400 acre-feet.

The project will also piggyback on transmission lines from Sacramento’s existing hydroelectric facility.

In the latest developments, recently the Sacramento Municipal Utility District engaged Jacobs Associates for preliminary design and yesterday the global engineering firm GEI Consultants, Inc. announced that it is leading the design team for the upper reservoir.

As for renewable energy, the Iowa Hill project already gets bonus points for reclaiming and re-using Sacramento’s existing hydro resources. Wind and solar also come into play, as explained in the Utility District’s FAQ:

It would play a crucial role in allowing us to add larger supplies of intermittent wind and solar power, because power generated at Iowa Hill could fill in supply “gaps” when the sun doesn’t shine or the wind doesn’t blow. In addition, it would allow us to use excess wind or solar power to pump the water uphill when demand for electricity is low.

The project is still undergoing feasibility studies, primarily to determine if the geology of Iowa Hill can support the new reservoir and related underground tunnels.

A final decision on moving forward is expected in 2017.

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About the Author

Tina Casey specializes in military and corporate sustainability, advanced technology, emerging materials, biofuels, and water and wastewater issues. Tina’s articles are reposted frequently on Reuters, Scientific American, and many other sites. Views expressed are her own. Follow her on Twitter @TinaMCasey and Google+.

  • Wayne Williamson

    yeah, the reference to acre feet is meaningless….

  • Rick Kargaard

    Another idea would be simply to use off peak generation for useful projects, such as desalination of water

    • Bob_Wallace

      The problem with ideas like that (and hydrogen production, for example) is that unless the equipment is cheap then it doesn’t work to have plants sitting idle many hours of the day.

      There was a company that was going to make synthetic fuel out of curtailed wind energy. Then they realized that wind hardly ever is curtailed. Their plants would have been sitting, staffed, for 90+% of the time.

      • TCFlood

        I think that’s why people often talk about designed renewable generation overcapacity. Budischak’s paper that you referred me to, for example, talks about a least-cost solution for 99.9% renewable electricity using three-fold overcapacity.

        • Bob_Wallace

          Absolutely. It’s got to be cheaper to overbuild than to store to some extent. The more power that can be used directly without storage the better.

          The curve is wider the further one drops below the peak. (Does that make sense? I may need a drawing.)

      • Rick Kargaard

        Battery solutions are also costly and free or cheap energy reduces the cost of capital

        • Bob_Wallace

          Battery solutions seem to be ready to lower costs. Vanadium flow batteries should be around 8c/kWh and liquid metal batteries should be cheaper.

          Free/cheap energy does offset the cost of capital. But one has to have “enough” free/cheap to make it worthwhile.

          I don’t know much about desalination but it seems like people are struggling to get the cost of output water down to affordable with the plant running as many hours a possible. That suggests somewhat high capital costs.

          Run that plant <10% of the time and the output cost would increase by a large amount. 10x?

          • Rick Kargaard

            Energy use seems to be the major cost of desalination but it is apparently not onerous and does not increase the cost of water for household use by an unreasonable amount. Water for irrigation may be different. A cursory search of the internet has indicated to me that off peak power is already used to reduce costs at many desalination plants. The experience would be in Australia, Isreal, Texas and California.
            I believe the middle east usually uses cheap oil and gas for desalination.
            Perhaps power plants built specifically for desalination could be used to supply some peak power needs in some cases

          • Bob_Wallace

            I don’t have any cost breakdowns for capital vs. operating expenses.

            If it doesn’t harm desal plants to go offline for a while they might be able to earn some extra money by offering themselves up as dispatchable load. But while offline they would still have capex and finex expenses to cover. Along with fixed operating expenses such as staff.

            All very speculative at this point in time….

          • Rick Kargaard

            An engineering problem, but my thought is that we do not hesitate to install solar power systems that are off line for at least 50% of the time.

          • Eins Null

            What exactly is new about this system of power generating? There was a site in Northern Germany, not far from Hamburg, which was generating power this way in, latest, 1978. Any further information of the history of this means from 1978, to date, would be most welcome.

          • Bob_Wallace

            PuHS was first used in Europe in the 1890s.

            It’s not about a new technology. It’s about the US getting ready to build more. (We’ve already got 150 PuHS systems. Most/all built to time-shift nuclear.)

          • Eins Null

            Thanks Bob. That was really useful information. I’d love to know more

          • Bob_Wallace

            If you’re serious, here’s my Google Doc page where I dump the stuff I find on PuHS.


            Some of the stuff won’t be “fleshed out”. Just a link, maybe a couple of words to help me find something later when needed.

            I’ll leave it available for a while.

          • Eins Null

            Bob, thanks very much!! I’ve saved the document so that I can read it with more time available and also send it to a friend who has an interest in the subject. You have obviously spent a great deal of effort compiling that lot, for which we all should be grateful.

          • Bob_Wallace

            If you find more info (or mistakes) please let me know.

            I’ve set up a bunch of Google Doc “boxes” where I dump stuff as I find it. From time to time I organize a box as needed. Some of them are real messes.

          • Eins Null

            Will do. Do you have an email address, as I’ll probably forget this one after a few months?

          • Otis11

            Very good read – will have to go through more of the links as time allows.

            Thank you!

  • Thinktank

    What I don’t know is power factor for displacement for the return path hydro pumping ? … 2:1, 3:1 any idea what it is?

    • Bob_Wallace

      “power factor for displacement for the return path hydro pumping ”

      Are you asking what the round trip efficiency is for PuHS?

      Generally 70% to 80% with some sites claiming close to 90%. Put in 100 MWh of electricity and get 70 MWh to ~85 MWh back.

      When people talk about the storage cost ($0.05/kWh, whatever) that energy loss is figured in.

  • Kiwiiano

    Anyone figured out the energy efficiency? Wind turbine -> generator -> motor -> water pump -> pipe friction both up & down -> water turbine -> generator. I guess if the wind is free and blowing at an inconvenient time, it doesn’t matter what the losses might be.

    • Bob_Wallace

      Pump-up hydro efficiency runs 70% to 80% with some sites claiming about 85%. This, being a new facility might be 80% or a bit better. I’m not sure what role evaporation will play in lowering efficiency. This is a hot, dry area in the summer.

      There is a cost to electricity generation. A small amount of wind and solar will be ‘free’ because it will come from infrequent supply peaks, but that’s not enough to supply a process like this. Most of the energy going in will be purposely generated for storage and later use.

      We now know that wind was sold, on average for 2.1 cents/kWh in 2013. That tells us that the cost of production was between 2 and 3 cents (adding back in the subsidy). Let’s say 3 cents.

      Input some 3c electricity, lose 20%, and what comes out is 3.75c electricity. Plus 5c(?) for storage. 8.75 to 10 cent electricity for peak demand supply. That is a very good price.

  • Ross

    The largest “water battery” is the earth’s warming oceans.

    • Burnerjack

      I’ve been saying for quite some time that a national viaduct system the size of the Interstate Highway system should be built for drought/flood management. This could be incorporated to further enhance the benefits. Capital intensive, to be sure, but then, so was the Interstate system. Are projects on such a scale only possible by the Greatest Generation? I hope not.

  • Bob_Wallace

    I don’t think many people realize that the US already has 150 pump-up hydro storage sites in operation. Over 25 GW worth.


  • arne-nl

    6400 acre-feet. How much is that in SI?

    • dgaetano

      About 7.9 giga liters (is that a thing?). A cube about 200m on a side.

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