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Tube Products International March 2014
GPS PE Pipe Systems
– UK
land itself is not viable as farmland as it is too steep, boggy
and covered in bracken and gorse for grazing livestock. The
landowners were able to see the benefits of the scheme both
in terms of generating clean energy and generating an income
from the feed-in tariff, but we also had to gain planning
permission and Environment Agency approval and secure
funding from a venture capital investor.”
Dragon Hydro secured investment for the project from Albion
Ventures LLP, and construction of the £1.3 million scheme
began in April 2013. The Cadair Idris hydroelectric power
station was scheduled to be completed in early September
and fully operational by mid-September following testing and
commissioning. It will deliver a maximum electrical output of
315kWe to the grid, enough to power up to 300 households.
A flexible solution
One of the key challenges for the design and installation of the
Cadair Idris hydroelectric power station was the specification
of the penstock. Not only do the location, gradient and rough
terrain make the site a testing environment for specialist
contractor Jim Dorricott Construction, they also mean that
the chosen pipe system must be durable enough to provide
a long-lasting and maintenance-free solution and flexible
enough to bend and twist with the landscape.
David continues, “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.”
Having decided upon PE pipe as the best material for
the hydro penstock, Dragon Hydro considered several PE
pipe suppliers before opting for PE pipe specialist GPS PE
Pipe Systems. The company has supplied several other
hydroelectric projects, including the National Trust’s scheme
at Mount Snowdon, and has in-house expertise that helps to
deliver technical support for hydro customers.
David continues, “Obviously price was a factor but technical
expertise in helping to ensure the penstock was as technically
appropriate and cost effective as possible was also key. So
too was GPS’s ability to respond to the specific needs of the
project: the nature of the site means that there’s restricted
space for manoeuvring materials and GPS agreed to supply
pipe in 10m lengths to help address this. They were also
able to supply us from stock with fortnightly deliveries which
helped to overcome the project’s issues with limited storage
facilities at the site.”
Tailored for pressure
The Cadair Idris hydroelectric scheme has two intakes from
two tributaries of the Afon Cadair river, and the Jim Dorricott
team constructed a weir to direct the flow and ensure that 50
per cent 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.
Explains Ken Wilson from GPS, “Where the water enters the
penstock at the intake the water pressure is low, so 315mm
diameter pipe was used in SDR 33, which gives a wall
thickness of just 5mm. 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 powerhouse at 15 bar pressure, and a
wall thickness of around 50mm is required for the 560mm
diameter pipe.”
The penstock will deliver the water to the power house, which
is of brick-faced construction with a slate roof to help it blend
into the landscape as a barn-like outbuilding. It will enter the
turbine at 15 bar, which will spin the generator to produce
electricity that is delivered directly into the grid. The water will
then be released back into the Afon Cadair, just as clean as
when it entered the penstock at the intakes.
Environmental legacy
Installation of the penstock began in April and, despite the
challenges of the terrain, has been progressing quickly, with
the first 400m stretch completed by the beginning of July. The
Jim Dorricott team began by making a track for the route and
stripping the soil back before digging a trench for installation.
Lengths of pipe were welded together on site using butt fusion
change pieces each time the SDR of the pipeline changes
along the route. Once the pipe is installed, it is simply buried
with specially treated topsoil over the top to encourage fast
re-growth of vegetation.
David adds, “With a project like this there is huge environmental
responsibility and we have worked closely with the National
Park and the Environment Agency and employed an ecologist
on site to observe the installation team throughout the
programme. Schemes like this one will help us further the
use of renewable energy to protect the environment for future
generations while blending into the landscape more-or-less
from day one, and the use of PE pipe for the penstock will
help ensure reliable, maintenance-free operation for the next
century.”
