Pumped Hydro - The forgotten storage solution
Storage is in the energy news now, in more places than can be listed.
Everyone is looking to the day when battery technology can economically partner with the popular yet variable renewables: solar PV and wind.
But what if today there was a proven way to store vast amounts of energy at capital costs lower than what battery technologists hope they might achieve in 20 years time? A technology with high round-trip efficiency and one heck of a lifespan: 85 years and counting!
If you have read this article's title, then you know where we are going with this: pumped hydro.
You may know, in energy terms, pumped hydro can be enormous (the Bath County Virginia facility with 3 GW of generation capacity and 30 GWh of stored energy is said to be the "world's largest battery"), or niche (the 11 MW El Hierro pumped hydro facility, partnered with wind, now makes that Canary Island 100% renewable).
Possibly you already know that pumped hydro – with 140 GW of generation capacity installed globally – dwarfs all other forms of frequently and deeply cycled, on-purpose energy-storage technologies such as batteries, compressed air, flywheels, molten-salt-thermal storage, or synthetic chemicals created to store energy, combined!
Why? Because for so long pumped hydro has been the cheapest. At the University of Melbourne Energy Institute (MEI) we surveyed literature costs for pumped hydro projects globally and found capital costs as low as $100 to $200 capital per kWh of useable energy stored. Chemical battery makers are aiming for costs in the range of $200 to $500 capital per kwh (useable) to be on the market in 2025.
Due to this technology-cost gap and other factors such as the growing penetration of renewables, you may know pumped hydro is resurging globally: in China and Europe, and it is again being considered in Japan, Canada, and the US (California, Hawaii, North Carolina, and even in the desert state of Arizona.)
You may know Australia already has three large-scale pumped hydro facilities in Queensland and New South Wales, operating for more than 30 years: Shoalhaven (240 MW), Wivenhoe (500 MW), and Tumut 3 (600 MW).
However since we haven't built any large-scale pumped hydro in Australia for 30 years, you may think that's it. We live on a flat continent, a dry continent, and we won't be damming the Franklin River in Tasmania any time soon. No we won't. One reason being, we don't need to. Because here are three things you don't need for pumped hydro: a lot of land, a lot of water, or even a river valley.
Small footprint: Pumped hydro differs from conventional hydroelectricity in that it doesn't need to store a lot of water. Whereas Lake Eucumbene in the Snowy Mountains might meet the irrigation needs of downstream farmers by storing massive amounts of seasonal rain and snow-melt in a 15,000 hectare lake, useful pumped hydro reservoirs might be only 50 hectares, or even as small as five.
Small water top-up: With pumped hydro, water is recycled over and over again from the upper to the lower reservoir and back again. Other than the first fill, the only water top-up required is to balance evaporation and leakage versus rainfall. Nearly all of the world's pumped hydro facilities use freshwater, but if you prefer to use saline or seawater, the coastal cliff-top seawater pumped hydro facility on Okinawa has been helping to keep that Japanese island powered since 1999. In the case of Okinawa, the lower reservoir is quite large, because it is the Pacific Ocean.
Pumped hydro is no turkey: Rather than damming a river valley, many pumped hydro facilities around the world use water storages that would be known in Australia as "turkey-nest" dams: water reservoirs built on flat ground by excavating earth from the centre of the reservoir and moving it to the edge to help form the dam walls.
What you do need for low-cost large-scale pumped hydro are two ponds separated by an elevation of at least 100 meters in a near-the-grid location where the two ponds are not more than three kilometres apart. Be assured, there are thousands of such sites in Australia. It can be more challenging to work out ways to reject sites than to find them, as ROAM Consulting learned when they undertook their review of pumped hydro for the Australian Energy Market Operator's eastern states 100% renewable energy study.
With limited time and budget, ROAM had to devise a computational way to reduce the number of sites analysed from "over 100,000 sites" down to around 70. We had the same problem when we mapped coastal sites in South Australia and western Victoria. Beyond the eastern states, suitable pumped hydro sites have also been described in Western Australia and the Northern Territory.
But there is one more thing you need for economic pumped hydro: the right market incentives. Our pumped hydro energy-arbitrage analysis found times and places where, if there was more pumped hydro in the National Electricity Market (NEM), it would play a role in balancing electricity supply/demand and in moderating wholesale prices, for example, during summer heat waves when electricity prices spike to over $10,000 / MWh.
However given falling electricity demand and excess generation capacity now in the NEM, it isn't surprising that you don't hear many commercial firms openly talking about investing in new pumped hydro for Australia. Although there was the recent Leyshon Resources Ltd. media release about re-purposing two dis-used gold mines at the fringe of the Queensland grid.
And who can predict the future around renewables and other aspects of our Australian energy markets? Pumped hydro arbitrage value may be on the rise again as renewables penetration grows and El Nino approaches. For those Australian energy users and suppliers that would like to see the grid be stable, better-utilised and not “abandoned”, now is a good time to examine the future role to be played by pumped hydro.
Tim Forcey and Dylan McConnell
Solar; Energy storage; Geological resources; Energy systems