Long-duration energy storage: why pumped storage is a ubiquitous technology

Worldwide there are 820,000 off-river pumped storage sites with 86,000,000 GWh of storage. Image courtesy of ANU

New solar and wind generation capacity is being installed around the world five times faster than all other new electricity sources combined, which is compelling market-based evidence that solar and wind generate the cheapest electricity.

As revealed by the Australian National University’s recent comprehensive high-resolution global survey of potential pumped hydro energy storage (PHES) sites, the world has 820,000 PHES sites with a combined storage of 86M GWh – equivalent to the usable storage in two trillion electric vehicle batteries.

Providing a vastly available, highly mature, lowest-cost, lowest-impact, long-duration energy storage solution to support solar and wind energy, PHES constitutes 95% of global energy storage, with most of the rest being provided by batteries.

Premium quality PHES provides long-duration energy storage in the size range of 5-5000GWh at a capital cost that is five times lower than batteries (US$8-40 per kilowatt-hour) and with a lifetime that is ten times longer (150 years). A 5000 GWh PHES system can provide all the storage needs for a fully decarbonised and electrified economy relying exclusively on solar and wind energy and servicing 100 million people.

Premium PHES sites usually have large head (400-1600m height difference between the reservoirs); large water-rock ratio (a large amount of water is dammed by a small rock wall, in a volume ratio above ten) and short pressure tunnels of a few kilometres.

Long-duration energy storage with low impact

No new dams on rivers are needed for PHES. Minimal mining is required compared with mining for battery metals. Reservoir walls are built by scooping rock from the bed of the reservoirs. Increasing the energy storage volume costs little: scoop more rock to make the walls a bit higher.

Water requirements for PHES are very small compared with equivalent batteries (including mining and refining). Land requirements for PHES are also very small. Premium-quality PHES stores 5 to 100 GWh per km², compared with utility batteries at around 15 GWh/km².

Indeed, the land and water requirements to provide all the storage needed for an affluent and fully electrified and decarbonised economy relying on solar and wind energy are in the range of 2m² per person and 2 litres per person per day, respectively.

Local economic content for PHES is high and includes construction of reservoirs, tunnels, powerhouses and transmission. In contrast, most countries import batteries.

PHES in Australia

In Australia, 99% of new power over the past decade has been provided by rooftop solar, solar farms and wind farms. Australia generates more solar energy per person than any other country and is tracking towards obtaining 82% of its electricity from solar, wind and hydro in 2030. Coal and gas generation is rapidly declining.

On sunny and windy days, wholesale electricity prices often become negative because supply of electricity exceeds demand: energy storage companies are paid to store excess electricity. Batteries and pumped hydro are replacing gas and coal generators in providing ancillary services to stabilise the grid. It is storage that keeps Australians powered when there is sudden failure of one of Australia’s ageing coal-fired power stations or when a transmission line is damaged.

Class AA 500 GWh pumped storage site near Araluen, Australia

Enter large scale long-duration energy storage

Australia has 23,000 potential pumped hydro sites, which is far more than needed. Of these, 315 are of premium quality (Class AA in the pumped hydro atlas). They range in size from 2GWh up to 5000GWh. There are interesting sites in Queensland, NSW, Victoria, South Australia, Western Australia and Tasmania but the country would only ever need about a dozen of these.

With three existing PHES systems, Australia also has two more under construction, including Snowy 2.0. A premium-quality system with energy storage of 350GWh, Snowy 2.0 is equivalent to the usable storage in seven million electric vehicle batteries or 350 large utility batteries.

Snowy 2.0 is fundamentally new to the Australian electricity system. It has five times more storage than all existing pumped hydro and batteries combined; its capital cost is five times lower than batteries per unit of energy storage; and its lifetime is ten times longer than batteries. The cost of Snowy 2.0 amounts to about one cent per day per Australian over its 150-year lifetime.

Large-scale pumped hydro energy storage like Snowy 2.0 comes into its own particularly in winter, when there are frequent wet and windless periods of multiple days when neither wind nor solar contribute much electricity. Wholesale prices become continuously high and fossil fuel generators make a lot of money. Short duration batteries have little opportunity to be recharged with low-priced electricity. Batteries are expensive for storing energy overnight.

During normal periods, Snowy 2.0 and other pumped hydro storage will contribute to meeting the regular morning and evening peak demand and will also provide some of the electricity required overnight. Indeed, Snowy 2.0 is large enough to generate flat out for a whole week. It can directly contribute to the load and can also trickle-recharge batteries day after day outside peak periods, which allows both the batteries and the pumped hydro to help meet the peak load during high-price periods.

Pumped hydro can also act as a form of insurance against high prices. One third of Snowy 2.0’s revenue is expected to come from contracts to firm up solar and wind generators and to take on the risk of high electricity prices from energy retailers. Snowy 2.0 has an opportunity to snatch a large portion of revenue and market share that currently goes to coal and gas.

Pumped storage is ubiquitous

Nearly every country has PHES or can find it nearby. For example, Europe has unlimited PHES potential in Norway, the Alps and southern Europe, and in old coal mines in Czechia.

Dry US states such as Texas and New Mexico have great sites to store their excellent solar and wind energy overnight in a 15GWh site, or for a season in a 5000 GWh site. California, like all the western states, has an embarrassment of excellent sites, vastly more than it would ever need. The Appalachian states in Alabama up into Canada are also well endowed.

Southeast and East Asia, Central and South America, Africa and the Middle East have vast numbers of excellent sites right where most people live. India has thousands of excellent sites, not just in the Himalayas, but also in the south. PHES construction in India is taking off in concert with rapidly increasing deployment of solar and wind.

And then there is China, perhaps the best-endowed country in the world, to match its vast scale of solar and wind deployment. China has a PHES completion-pipeline of 16GW per year, coupled with hundreds of GWh of energy storage.

Long-duration energy storage coupled with solar

Solar coupled with PHES is ideal for providing 24/7 power to data centres. For example, a 1GW data centre in New Mexico can be powered by 5GW of SE and SW facing solar panels with high tilt (for winter). Hybrid storage is provided by 2GW of 25-hour PHES (50GWh) plus 1GW of 4-hour batteries (4GWh, to harvest peak power around noon). The PHES storage can be trickle-recharged from the grid outside peak periods, and both PHES and batteries are remunerated for helping to stabilise the grid during stress periods.

Together, PHES and batteries are gas-killers. Batteries eat the high-value revenue streams for ancillary services and morning and evening peaks. Pumped hydro soaks up excess solar and wind at low or negative cost and delivers power when prices are high during wet and windless nights, weeks and seasons.

Some people have the misperception that PHES requires new dams on rivers, lots of land, lots of water, and high cost – all of which is wrong.

Global PHES Atlas

The Australian National University’s Global PHES Atlas uncovered hundreds of thousands of superb off-river sites. Users can pan and zoom to any reservoir. Clicking on a reservoir or a tunnel route produces different information pop-ups containing 26 items of detailed information. Different sizes can be selected in the lefthand pane. Click on “Explore Map Data” to add and combine data layers. Select Map Settings/3D Terrain for a 3D view. The best sites are marked with stars (cost Class AAA), triangles (Class AA), or dark red dots (Class A). Lower classes comprise B, C, D and E.