A tried-and-tested technology that’s key to keeping renewable energy systems stable.
Pumped storage hydro (PSH) is a large-scale method of storing energy that can be converted into hydroelectric power. The long-duration storage technology has been used for more than half a century to balance demand on Great Britain’s electricity grid and accounts for more than 99% of bulk energy storage capacity worldwide.
The principle is simple. Pumped storage facilities have two water reservoirs at different elevations on a steep slope. When there is excess power on the grid and demand for electricity is low, the power is used to pump water from the lower to the upper reservoir using reversible turbines. When demand is high, the water is released downhill into the lower reservoir, driving the turbines the other direction to generate electricity.
Pumped storage hydro plants can also provide ancillary services to help balance the power system, such as inertia from spinning turbines, which ensures the system runs at the right frequency and reduces the risk of power cuts.
Governments around the world are shifting from fossil fuels to renewable energy sources to meet their climate goals. But critically important power technologies such as wind and solar pose challenges for power grid operators.
Being weather-dependent, the supply from these renewables is intermittent. For example, wind farms accounted for almost a quarter of the UK’s total electricity generation in 2020, but on some days, less than 10% of the country’s electricity needs were met by wind. Changing weather patterns and extreme weather events with prolonged periods of little wind or reduced daylight are a further the threat to grid stability.
When output from renewables falls, grid operators mostly turn to gas-fired power stations to plug the gap. But relying on fossil fuels such as natural gas in the long term to balance the grid will compromise efforts to reach net zero emissions by 2050.
Pumped storage hydro facilities act as vast ‘water batteries’. They are a flexible way of storing excess energy generated by renewables, cost-effectively and at scale.
As old thermal power plants are decommissioned and renewables provide an increasing share of the electricity supply, storage capacity will need to grow if climate goals are to be met. Over the next two to three decades, Great Britain’s energy storage capacity alone will need to increase tenfold, from 3 gigawatts (GW) to around 30 GW.
Pumped storage hydro power stations require very specific sites, with substantial bodies of water between different elevations. There are hundreds, if not thousands, of potential sites around the UK, including disused mines, quarries and underground caverns, but the cost of developing entirely new facilities is huge. A more cost-effective way to increase storage capacity is by expanding existing plants, such as the Cruachan Power Station in Scotland.
“Britain’s pumped hydro storage stations have never been more important to the country’s decarbonisation. They play a vital role in keeping the grid stable and enabling more wind power to come online”
“Flexible and responsive power generation and storage capacity from pumped hydro projects like Cruachan are essential for delivering the UK Government’s net zero by 2050 target. With the right support framework from Government a new generation of pumped hydro storage power stations can be built, supporting new jobs and helping the country decarbonise faster.”
Will Gardiner, CEO, Drax, March 2021