Welsh marvel How hydroelectric plant plays vital role in keeping the lights on

Seconds after a catastrophic series of power cuts struck across the UK in the summer of 2019, a phone rang in the control room of the Dinorwig hydropower plant in north Wales.

- Jillian Ambrose

It was Britain's energy system operator requesting an immediate influx of electricity to help prevent a wide-scale blackout from crippling power grids.

The response was swift, and in the end just under 1 million people were left without power for less than 45 minutes. While trains were stuck for hours and hospitals had to move to backup generators, that phone call prevented Britain's worst blackout in a decade from being far more severe.

Almost six years later, the owners of Dinorwig, and its sister plant at Ffestiniog on the boundary of Snowdonia (Eryri) national park, are preparing to pump up to £1bn into a 10-year refurbishment of the hydropower plants, which have quietly helped to keep the lights on for decades.

Ffestiniog was one of the first pumped hydroelectric systems in the UK when it opened in 1963, while nearby Dinorwig - the largest and fastest-acting pumped storage station in Europe - followed in 1984. The refurbishment could mean the plants continue to provide reliable clean energy on demand for decades to come - and serve as giant grid batteries to store renewable electricity for when it is needed most.

Miya Paolucci, the UK boss of the French energy firm Engie, one of Dinorwig's owners, said that refurbishing the plant would cost a third of the investment that would be needed to build a new hydropower plant on a similar scale, making the overhaul an "intuitive" decision to secure another 25 years of life from the "much-loved" power station.