US-based power firm Duke Energy plans to increase the energy storage capacity of its Bad Creek pumped storage hydroelectric station by 200MW. The expansion is scheduled to start in 2021, and complete in 2024.

The 1,065MW South Carolina facility, the firm’s largest hydroelectric station, was constructed in 1991 to power 850,000 households. Duke Energy said the upgrade will see it power a million homes.

The facility runs as a normal hydroelectric power station using the flow of water between an upper and a lower reservoir at the site to spin turbine generators.

Located just 1,200 feet from Lake Jocassee near Salem, the Bad Creek facility can also use excess energy from other power plants to pump water from Lake Jocassee to the upper reservoir, which can be stored and released as electricity is required.

Duke Energy said the Bad Creek facility can be particularly effective at capturing excess power from intermittent renewable sources such as wind and solar. The company has out considerable focus on solar PV development of late, having added 300MW of PV energy in North Carolina last year.

There are 40 pumped-storage hydropower plants in the US accounting for 97% of the country’s energy storage at present, according to the National Hydropower Association.

The technology has spread worldwide. For example, in August, the organisers of luxury sporting estate Eishken announced plans to install 300MW of pumped hydro storage on the Scottish Isle of Lewis to store energy primarily from wind farms on the island – the first such system to be installed in the UK for 30 years.

Last year’s electricity storage Roadmap released by IRENA estimated that to meet international renewable energy targets, some 150GW of battery storage and 325GW of pumped hydro storage will be needed.