Small hydro |
Right: The powerhouse and mountainside pipeline at Cwm Dyli hydropower station
Below: The Cwm Dyli pipeline carries water 342m down the mountainside to the powerhouse below
project also reflected a broader safety improvement programme across RWE’s UK hydro operations. “We used to average about three first aid cases per year, but in the last two years we have achieved zero harm in our UK hydro fleet,” Moorcroft says. According to Moorcroft, that improvement has been driven by a stronger emphasis on planning, risk assessment and contractor engagement. “Assessing risks at the planning stage and at the last
minute, before work begins, have been powerful levers in improving safety performance,” he says. The company also focused heavily on contractor
integration during the project, combining formal onboarding procedures with regular site engagement to reinforce expectations around safety and operational standards.
A continuing role in grid flexibility Although relatively small by modern standards, Cwm
Dyli continues to play an important role within RWE’s wider flexible generation portfolio. Unlike intermittent renewable generation sources, the station can store water and dispatch power when required, allowing it to support morning and evening demand peaks. The asset operates alongside RWE’s gas and biomass fleet and is coordinated through a central commercial optimisation team.
“It’s part of our firm, flexible generation fleet, alongside
our flexible gas and biomass power stations,” Moorcroft says.
That flexibility is becoming increasingly valuable as the UK grid incorporates larger volumes of wind and solar generation. Hydropower’s contribution extends beyond dispatchable renewable generation alone. Large hydro generators also provide system inertia, helping stabilise the grid during short-term supply and demand imbalances. “These heavy, rugged generators also make an important contribution of inertia to the energy network, helping the system to ride out momentary imbalances between supply and demand,” Moorcroft explains. For operators managing legacy hydro assets, Cwm Dyli also demonstrates the long-term economics of hydropower. While periodic refurbishment of major civil infrastructure can be expensive and technically demanding, the station’s ongoing operating and maintenance costs remain comparatively low. “Hydro is a very cost-effective generation technology with low ongoing O&M costs,” Moorcroft says. “Work on large civil infrastructure is very different though. You need to keep a good look-out for problems and carefully plan how to tackle them.” The station’s longevity also reflects the advantages of straightforward engineering concepts. The combination of a natural reservoir, high head and relatively compact layout has allowed the scheme to remain operationally relevant despite major changes in the wider electricity system over the past century. As electricity systems move toward higher levels
● Commissioned in 1906, making it one of the oldest operational hydropower stations in the UK.
Cwm Dyli: key facts
● Uses water from the natural lake Llyn Llydaw on the slopes of Snowdon. ● Operates with a 342m head and a generating capacity of 10MW. ● The powerhouse and water intake structures are both original. ● Became the first power station in the UK to generate alternating current. ● The station’s pipeline featured as the exterior of the oil pipeline in the James Bond film The World Is Not Enough.
● In 1989, four Pelton wheel units were replaced with a single Francis turbine and Bruce Peebles generator.
● The site receives around 3,700mm of annual rainfall, compared with a UK average of about 1,100mm.
of renewable penetration, older hydropower stations such as Cwm Dyli are increasingly valued not simply for energy production, but for their ability to provide responsive balancing services. Flexible hydro assets can ramp generation rapidly in response to changes in grid demand, helping compensate for fluctuations in wind and solar output. This operational flexibility is becoming a more significant consideration for network operators as thermal generation capacity continues to decline. Moorcroft believes that simplicity and durability remain important lessons for modern hydro development. “The original designers made the most of the local geography,” he says. That approach continues to pay dividends 120 years later.
https://uk.rwe.com/ 32 | June 2026 |
www.waterpowermagazine.com
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