Pumped-hydro power: why do we need it?

At present by far the greatest part of the world's energy storage is in pumped hydro

USA Department of Energy graph
This shows clearly that the vast majority of the world's energy storage is in the form of pumped hydro. Much of it was built to allow power grids dominated by inflexible nuclear and coal power to respond to variations in demand.

Tumut 3 power and pumped hydro station, Snowy Mountains, New South Wales, Australia The power station generates electricity when water flows from the upper storage, Talbingo Dam, into the lower storage, Jounama Pondage. When power is plentiful and cheap water is pumped from Jounama up to Talbingo. More information on this installation is on another page on this site; I've listed other pumped hydro sites in Australia on a page about the forms of electricity generation that are right for Australia.   Energy or power? Energy is defined in physics as the capacity for doing work; power is a flow of energy. Example: a 10 Watt LED light bulb uses 10 Watts of power; in one hour it will use 10 Watt-hours of energy. There is a lot of confusion between energy and power, even in people who should be well aware of the distinction.   Pumped hydro is peaking power, not base load In August and September 2017 there had been a lot of confusion between base load and peaking power in statements from politicians supporting the coal lobby, such as PM Turnbull. Coal and nuclear power stations inflexibly generate base load power; peaking power such as from pumped hydro, generated as required, is far more valuable. Why we should use pumped hydro to store large amounts of energy? It is the cheapest way of storing large amounts of energy; greater than a few hundred megawatt-hours (MWh). (An Australian National University group under Andrew Blakers identified 5000 sites in mid 2017 each seven to 1000 times larger than the Tesla Big Battery at Hornsdale, SA; that is, bigger than 1 GWh.); Once built, a pumped hydro system has a long life, at least decades rather than the years of batteries. How does pumped hydro differ from conventional hydro power? Conventional hydro only allows for water to flow out of a high level storage through turbines to generate power. It cannot pump in the other direction when electricity is cheap. It relies on rain to fill the storage. Building a pumped hydro system results in much less environmental damage than building conventional hydro because the storages can be much smaller and pumped hydro can be recharged as often as needed. Energy efficiency According to Wikipedia pumped hydro has a round-trip energy efficiency of between 70%-80%. That is, for each pumping-generating cycle, between 70% and 80% of the energy used in pumping is recovered in generation. What are the alternatives to pumped hydro? Batteries (electro-chemical) Batteries are the obvious alternative. The Tesla Big Battery (more formally called the Hornsdale Power Reserve) at Hornsdale in Mid-North South Australia had a lot of publicity as the biggest battery in the world in late 2017: it stores 129 MWh of energy (it can release this at a maximum power of 100 MW). By far the greatest part of the materials required to build a pumped hydro system have a simple chemistry and are easily disposed of, or recycled, at the end of their useful lives: steel, concrete, earth, rock. Lithium-based batteries, on the other hand, have complex chemistries and are difficult to recycle fully. The life of a battery varies depending on the type, but is likely to be a few years. On the other hand the main components of a pumped hydro facility will last many years (turbines), decades (tunnels, pipelines), even centuries (storages). Flywheels (electro mechanical) These can be used for storing very limited amounts of energy with a very rapid response time. Home Top Hydrogen storage Seems to have great potential for medium- to long-term storage of large amounts of energy, but at the present it is of questionable economic viability. I have written more on hydrogen and energy and power to (hydrogen) gas in Australia elsewhere in these pages. Thermal storage Molten salt is often used as the working fluid in a solar thermal power station; it can be stored efficiently for a period of several hours up to a few days. Well and good for a solar thermal power station, however, using electricity to heat something like salt and then using the hot salt to produce steam and generate electricity is very inefficient. Water supply matters   Pilot floating solar power installation On common effluent ponds at Jamestown in Mid-North South Austalia The quantities of water required for pumped hydro storages of the type being considered in Australia are of the order of a gigalitre and the hydraulic heads needed are typically 100 m or more. In Energy Units I have noted that the energy involved in 1 GL falling 100 m is 270 MWh. A gigalitre is one billion litres or a million kilolitres. In What is the real cost of water?, written 2007/09/14 I noted that the cost of water in Australia varied from $0.0013/kL ($1.30/ML) in the Murrumbidgee Irrigation Area to around $1/kL for a domestic consumer in South Australia (the cost to domestic consumers in SA had increased to around $3/kL by 2017). Most of the variation is due to the costs involved in getting the water to where it is required. In Reducing evaporation losses from farm dams I discused the large evaporation losses from open water storages and some of the methods used to reduce them. The Australian Bureau of Meteorology records an annual evaporation rate at Port Augusta, South Australia, of around two metres. In his study of pumped hydro sites Andrew Blakers states that the typical area of a pumped hydro dam will be between 10 and 100 hectares, so at two metres evaporation per annum that amounts to between 200 ML and 2 GL lost to evaporation each year. Blakers has estimated that if South Australia was to build enough pumped hydro energy storage to allow 100% renewable energy less than 1% of the state's water extraction from the Murray would be required for topping-up. One way of reducing evaporation losses would be by floating rafts of solar PV (photovoltaic) panels on the dams, giving the advantage of generating power at the same time. This has been done on a very small scale (photo on the right), and proposed on a much larger scale, at Jamestown in South Australia. There would be challenges relating to the frequent filling and emptying of the dams beneath the floating panels. Solar panels have been installed on a bigger scale, a megawatt, over irrigation channels in Gujarat, India in a project expected to reduce evaporation by 34 ML per year. Forty megawatts of floating solar panels have also been installed in an area flooded due to coal mining subsidence in China. Home Top Link ABC 4 Corners program on the illegal extraction of water from the Murray-Darling system, 2017/07/24.   Methods of energy storage Energy storage capacity plotted against discharge time No single method of storing energy is suitable for all needs. Some methods are good for storing and recovering energy over very short times, others over much longer times. Generally those methods used for short-term energy storage have low capacity, while those used over the long-term have much higher capacity. CAES: Compressed air energy storage PHS: Pumped hydro storage SNG: Substitute natural gas At the time of writing more than 99% of the world's energy storage was in pumped hydro (not considering water in hydropower dams as energy storage). Hydrogen and SNG were not proven on a commercial scale. By mid 2018 the upper limit to the size of batteries had gone from the 30-40 MWh shown on the graph to more than 120 MWh. Image credit: Hydrogen Energy Storage: A New Solution ot the Renewable Energy Intermittency Problem, Renewable Energy World; written by Mark Schiller; July 2014 Pumped hydro using seawater Using seawater for pumped hydro in the drier parts of Australia has obvious advantages over installations using fresh water. Seawater is plentiful and cheap, there is no need to build a lower storage, it is available in lots of places where there are nearby high hills suitable for building the upper storage – coastal cliffs. It is more challenging in that corrosion and fouling problems would have to be guarded against. It concerns me from an environmental ground. Anti-fouling chemicals would have to be used to stop organisms from attaching themselves to the turbines and pipes. Since the water would be periodically taken from the sea and put back into the sea it seems that the chemicals would be released into the open sea with possible toxic impacts. Confining the chemicals in a lower storage so that they did not impact sea life removes the financial advantage of not having the lower storage. So far as I know seawater pumped hydro has only been done once with a high head, as would be used in Australia; a trial project at a Okinawa, Japan. Links: seawater pumped hydro Science Direct; Seawater pumped-storage power plant in Okinawa island, Japan; Akitaka Hiratsuka, Takashi Arai, Tsukasa Yoshimura Wikipedia; Okinawa Yanbaru Seawater Pumped Storage Power Station Links: seawater pumped hydro in South Australia Energy Australia: Consortium assessing pumped hydro storage plant in Spencer Gulf, South Australia Article on the Spencer Gulf project by Simon Holmes a Court, 2017/09/29, in RenewEconomy. Simon goes into detail in the figures, including financial figures as well as storage volumes and power output and storage.

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