For thousands of years people have used dams for flood control and to store water for human consumption, agriculture and industry. Today dams and natural reservoirs have a further use as pumped hydropower storage plants, a method of electricity storage that harnesses the power of huge volumes of water and the force of gravity.
Pumped hydro plants work by using excess electricity that is not needed at times of low demand — often in the middle of the night — to pump water stored in a reservoir lower down a hill or mountain to one higher up. This creates a huge reserve of potential energy. All the water in the reservoir above is simply waiting to be released, and when a power boost is needed, hydroelectric turbines use the liquid and gravitational force to generate huge amounts of electricity.
If the higher reservoir is full enough this power can be produced almost instantaneously at the push of a button. Later, when the need for power has fallen again, the water can be pumped back up to the higher reservoir, ready to be used whenever it is needed.
The UK’s largest pumped hydro plant is housed within a gigantic complex of tunnels and man-made caves carved inside a mountain called Elidir Fawr at Dinorwig in Snowdonia — also known as ‘Electric Mountain’.
Dinorwig was brought online in 1984, and now provides Short-Term Operating Reserve (STOR) power at times when a rapid response is needed. This can be because of short-term changes in power demand such as a TV pickup, when supply from other power stations fail due to an unplanned outage or as is increasingly common on Great Britain’s electricity system, when the weather changes and intermittent forms of power such as wind and solar need support. It can generate up to 1,728 megawatts (MW) of power very quickly, making it one powerful ‘battery’.
However Dinorwig is dwarfed by the mighty Bath County Pumped Storage Facility in Virginia, USA. With a capacity of 3 gigawatts (GW), this giant is known as ‘the world’s largest battery’ and can almost match the output of Drax Power Station or the proposed new nuclear plant, Hinckley Point C. And even Bath County won’t be number one for long, with the proposed Fengning plant in Hebei, China set to have a capacity of 3.6GW once completed in 2021.
Giant batteries — the shape of things to come?
Storage has a key role to play in the coming years as renewable but intermittent sources of electricity continue to increase their share of supply on the National Grid. Just as biomass is a renewable fuel that can provide flexibility, pumped hydro is one way to capture the power of the wind and the sun and save it for a rainy day.
One challenge with pumped hydro is hinted at by Dinorwig’s other name — ‘Electric Mountain’. It takes a mountain, or at least a very big hill, for pumped hydro storage to work efficiently. Potential for further pumped hydro projects in the UK may be limited by Mother Nature.
What’s more, suitable mountains are mainly to be found within beautiful — and protected — landscapes. The plants at Dinorwig and Glyn Rhonwy in north Wales were allowed partly because they reclaim land that had already been blighted by the slate mining industry.
And even when they are permitted, pumped hydro facilities in the mountains of the UK are still likely to be a long way away from the cities where their electricity is needed. That means investment in expensive transmission infrastructure — at Dinorwig for example, the transmission cables that take the power generated to the National Grid had to be buried underground for a distance of approximately six miles.
All of which means we can’t depend on pumped hydro plants alone to back up intermittent renewables. We will still need to develop a mix of technologies to keep the lights on.
At Drax Power Station in North Yorkshire, another giant storage facility with a capacity of up to 200MW is going through a planning and consultation process. Batteries don’t yet exist at the scale and affordability needed to be relied upon to back up a 100% renewable and low carbon power grid, however, which is why Drax is also planning to build four, rapid response power stations — two of which will be located in Wales.
Read the full story on every storage technology you need to know about on Drax.com here.
