What is pumped storage hydro?
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.
Hydropower can also be very effective at a smaller, more local level, using relatively small rivers. These smaller hydro facilities can bring renewable electricity to remote areas and serve local needs. All they need is an abundance of flowing water to spin their turbines.
Bought by Drax in December 2018, Cruachan Power Station is one of only four pumped storage hydro stations in the UK and has a capacity of 440 MW – enough to power more than 90,000 homes.
How does pumped storage hydro work?
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.
How do river-powered hydro schemes work?
River-powered hydro schemes, also known as run-of-river hydro schemes, work by using the natural flow of a river to generate electricity without the need for large reservoirs. They can operate in different ways, such as:
- Diverting water: A portion of the river’s flow is diverted through a channel or penstock, directing the water towards the hydroelectric power station.
- Turbines: The diverted water flows through turbines, which are large machines with blades. The force of the water causes the turbines to spin.
- Electricity generation: As the turbines spin, they are connected to generators. The mechanical energy from the spinning turbines is converted into electrical energy through electromagnetic induction.
- Transmission: The generated electricity is then transmitted through power lines to homes, businesses, and industries for use.
One of the key advantages of run-of-river hydro schemes is that they have a lower environmental impact compared to conventional hydro schemes with large reservoirs. However, their power output may vary depending on the river’s flow, which can be affected by seasonal changes and weather conditions.
Drax Group acquired the Lanark and Galloway run-of-river hydro schemes, located in south-west Scotland in 2018. The schemes have a combined capacity of 126 MW – enough to provide electricity to more than 100,000 homes.
Why is pumped storage hydro important for decarbonisation?
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.
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.
The future of pumped storage hydro in the UK
With the UK increasingly reliant on intermittent sources of electricity such as wind power, pumped storage hydro is becoming even more important to national energy security.
At Drax, we are progressing an £80 million refurbishment of Cruachan Power Station which will increase the plant’s generating capacity to 480 MWs. This will allow Cruachan to play an even bigger role in the future, strengthening our energy security and enabling more renewables to come online.
