Case Studies

Cadair Idris Hydro

  • Sector: Renewables
  • Product: Excel (PE100)
  • Client: Dragon Hydro
  • Contractor: Jim Dorricott Construction

One of Snowdonia’s most popular peaks, Cadair Idris is located in Gwynedd, at the Southern edge of the National Park. In 2008, hydro-electric power development company, Dragon Hydro, identified some farmland at the mountain as a potential site and after securing landowners agreements from the two farmers that own the land, planning permission, environment agency approval and funding from a venture capital investor, the project began construction in spring 2013.

Completed in September 2013, the Cadair Idris hydro-electric power station generates an average 1,300MWh of electricity per year, enough to power up to 300 households. 

A Flexible Solution

One of the key challenges for the design and installation of the Cadair Idris hydro-electric power station was the specification of the penstock.  The location, gradient and rough terrain at Cadair Idris made it a diffcult site for specialist contractor, Jim Dorricott Construction,  and also that the chosen pipe system for the hydro penstock must be durable enough to provide a long-lasting and maintenance-free solution while flexible enough to bend and twist with the landscape.

David Roberts, consultant to Dragon Hydro commented: “PE pipe was really the only viable solution – both technically and commercially.  It wasn’t going to be feasible to import any backfill material up the mountainside for the installation of concrete or ductile iron pipe and only PE could offer the flexibility required for the terrain. Commercially, the ability to tailor the wall thickness of the pipe to the pressure requirement of the penstock at different points along the route meant that we could minimise the amount of raw material used, helping us to manage the cost of the penstock, which is one of the main costs of any hydro-electric installation.”

Dragon Hydro  selected GPS PE Pipe systems as the PE pipe supplier for the hydro penstock thanks to the company’s technical support and responsive approach.

David continues: “Obviously price was a factor but technical support was also key. GPS agreed to supply pipe in 10m lengths to help address the restricted space for manoeuvring materials on site. They were also able to supply us from stock with fortnightly deliveries which helped to overcome the project’s issues with limited storage facilities.”

Tailored for Pressure

The Cadair Idris scheme has two intakes from two tributaries of the Afon Cadair river and a weir was constructed to direct the flow and ensure that 50% of the water from each source remains in the river.  From the intakes, the penstock follows a 400m route across open, boggy terrain before joining the route of an existing farm track for 1.2km and then passing through grazed fields for the final 800m stretch.  GPS has provided black PE 100 pipe for the installation with a steadily decreasing SDR (Standard Dimension Ratio) as the water pressure increases during its descent.

Where the water enters the penstock at low pressure 315mm diameter pipe was used in SDR 33. The pipe diameter then increases to 500mm at SDR 33, then the wall thickness increases to SDR 26, then SDR 21, SDR 17, SDR 13.5 and finally SDR 11 where the water enters the turbine at 15 bar pressure, spinning the generator to produce electricity.  

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