Small hydro |
Enduring power at Cwm Dyli
Cwm Dyli hydropower station has generated electricity beneath the slopes of Snowdon in Wales, UK, for 120 years. As RWE reflects on the site’s long operational history and recent refurbishment works, the project continues to demonstrate the durability of early hydro engineering and the long-term value of flexible renewable generation
more than three times the UK average. Water is collected and stored naturally in Llyn Llydaw, avoiding the need for a major dam structure. That decision continues to provide operational and maintenance advantages today. “Making use of a natural lake also gave Cwm Dyli a great advantage because there is no dam requiring expensive maintenance,” says Moorcroft. The scheme operates with a gross head of 342m, among the highest in the UK, enabling the station to generate 10MW for up to five days when reservoir levels are full. Water travels down a single 1.2m diameter pipeline at a rate of 3.5m3
The original layout has remained largely unchanged.
Above: General view of the project pipeline
Right: Materials and welfare units were transported by helicopter to support refurbishment works along the mountainside pipeline
IN AUGUST CWM DYLI hydropower station in Snowdonia (Eryri) marks 120 years of continuous electricity generation, underlining the longevity of hydropower infrastructure and the continuing operational role of legacy hydro assets in the UK energy system. Owned and operated by RWE, the 10MW plant
remains one of the oldest operational hydropower stations in the UK. Located on the slopes of Snowdon and supplied by the natural lake Llyn Llydaw, the station has benefited from a remarkably simple original design that continues to shape its operation more than a century later. The station’s long operational life also follows the completion of a major refurbishment programme focused on the pipeline support structures. The large pipeline plinth refurbishment project was completed across 2022 and 2023 and highlighted both the resilience of the infrastructure and the engineering challenges involved in maintaining remote hydro assets in difficult terrain. Keith Moorcroft, RWE’s UK Hydro Cluster Manager, says the project demonstrates the long-term value of getting the fundamentals right in hydro development. “The civil engineering needs to be built to last – build it once and build it right,” he explains. “The mechanical and electrical plant is much easier to modify and optimise as technology evolves.”
Cwm Dyli’s original designers made extensive use of
the surrounding geography. The catchment area on the slopes of Snowdon is relatively small at just 4km2 site receives approximately 3,700mm of rainfall annually,
30 | June 2026 |
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The powerhouse and water intake structures are both original features dating back to 1906. Although the generating equipment has been modernised over time, the broader design philosophy remains intact. The station’s most significant modernisation came in 1989, when four Pelton wheel units were replaced with a single 10MW Francis turbine manufactured by Boving, coupled to a Bruce Peebles six-pole air-cooled generator operating at 1,000rpm. The Boving machine was replaced in 2003 with a unit of similar size manufactured by ALSTOM. Today, the plant is remotely monitored and controlled from RWE’s hydro operations base at Dolgarrog power station near Conwy, alongside the company’s wider UK hydro fleet. “All 24 of our UK hydropower stations are monitored
/sec before reaching the turbine.
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