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Cadair Idris:
A Flexible Approach to
Penstock Specification
The rocky mountainsides of Snowdonia have been
a Mecca for walkers and the quarrying industry
for generations and, amidst the tourists, farming has
provided the bedrock of the Snowdonia National
Park’s rural communities. Some areas of the terrain are
too rugged even for hardy Welsh sheep, however, but
the landscape continues to deliver new opportunities
for jobs, commerce and essential commodities… this
time in the shape of hydroelectric power.
The Snowdownia National Park has been the location
for two new hydroelectric power stations over the
past year, both of which have involved the installation
of a PE penstock in the mountainside supplied by
GPS PE Pipe Systems, to carry the water to the
turbine at the base of the mountain.
Hafod y Llan hydro
The 640kW Hafod y Llan scheme will permanently add to
the uses that Snowdon has been put to over the years and
careful planning, design and project management meant
that the installation was effectively disguised within the
rugged landscape before it was even completed. But this
well-camouflaged scheme hides an extraordinary feat of
engineering: once fully operational, the hydro-electric plant
will play a key role in delivering the National Trust’s ‘Fit for
the Future’ initiative to invest in renewable energy, with a
generating capacity equivalent to the power requirements of
all the Trust’s properties in Wales.
Constructing such a significant scheme within such a
challenging landscape has been no simple undertaking, and
doing so while delivering the National Trust’s remit to conserve
and protect the environment has added to the project’s
complexities. However, that environmental responsibility was
central to Hydropower Services’ design for the scheme,
and local contractor GHJ Civil Engineering & Construction
leveraged its local and hydro scheme knowledge to manage
the project’s logistical and environmental challenges.
Specifying the penstock
The Hafod y Llan scheme will extract water from the Afon Cwm
Llan river at the head of the valley, which will be fed through
a 1km black PE100 penstock, supplied by PE pipe specialist
GPS PE Pipe Systems. At the foot of the penstock, GHJ has
constructed a power house designed to look like a typical
Snowdonia out house. Here the rapid flow of water will enter
the turbine, generating electricity before being returned to the
river downstream without any effect on the water quality.
PE pipe was chosen for the penstock installation thanks to
its flexibility, which has allowed the contractor to bend and
shape the pipe to the contours of the landscape, routing
the penstock as close as possible to the river. The use of
PE has also enabled the design team to match the wall
thickness (SDR) of the pipe to the required water pressure
at differing points along the route, providing cost and raw
material savings. The only exception to this is the final section
of penstock where the water enters the turbine at very high
pressure, and the wall thickness that would have been needed
for PE pipe made ductile iron a cheaper alternative.
Explains Alan Jones from GHJ, “Using PE pipe made the
installation less invasive on the landscape because the
pipe’s flexibility enables the penstock route to stay true to the
contours of the hillside. Using PE also made the installation
more cost effective because it required less excavation and
gave us some leeway for small diversions around clumps
of heavy rock. Indeed, the ductile iron’s maximum bend
tolerance of two degrees meant that we had to painstakingly
cut through rock to lay the final section of pipe at the base
of the penstock and the increased excavation time and costs
involved in this demonstrate the balancing act between
material costs and installation requirements on projects like
this.”
www.read-tpi.com March 2014 Tube ProducTs InTernaTIonal 117