Historic Corn Mill becomes home to an Archimedean Screw hydropower turbine

It’s been a few years now since the Archimedean screw hydropower turbine was installed and commissioned at Frensham Mill. However, I feel it gives a good insight into what can be achieved at old mill sites. You will see how the owners embraced hydropower and then made improvements to the landscape to increase the existing wildlife and natural habitat of the site.

Mill History:

Frensham Mill is an ancient mill site dating back to at least 1217 when the mill at ‘Feresham’ is mentioned in the Bishop of Winchester’s Rent Rolls. The mill had two mill ponds to ensure that the corn mill had a constant supply of water even if the main river supply ran low; one of which was built on a small Wey tributary carrying runoff from Frensham Great Pond. This large pond feeds into the Wey about half a mile above where the mill was located. The house was re-modelled in 1928 following the demolition of the old mill. At his time a Francis turbine was used to generate electricity. When the Mill was rebuilt in 1876 it was possibly the largest in SW Surrey. The oldest building, the Granary, was renovated in 2012 along with the gardens and the hydro/ heat pump project.

Frensham Mill during the Victorian era  Photo Credit: Frensham Mill
Frensham Mill during the Victorian era Photo Credit: Frensham Mill

The owners wanted to make the most of the renewable energy potential of the old mill race.  The solution was to combine an 11kW Archimedes screw hydropower turbine with a 30kW water source heat pump. Today the mill produces 70kWh of electricity per year and 90kWh of heat, saving over 50 tonnes of CO2 emissions per annum.

Installing the Archimedean Screw hydropower turbine  Photo credit: Mannpower Consulting Ltd
Installing the Archimedean Screw hydropower turbine      Photo credit: Mannpower Consulting Ltd

The Mill had been a barrier to migratory fish for hundreds of years. In order to improve migratory fish passage the Environment Agency specified a fish pass and upgraded stream to link upstream and downstream for the first time in hundreds of years to encourage trout, eels etc. The river banks were restored and the water meadow was reinstated with wild flowers. Around 10% of the river’s flow is directed down the fish pass and into an old ditch to provide a link between upstream and downstream. A series of 10 gravel pools were installed to step down the levels to the mill pond, providing areas of gravel as potential spawning areas.

Archimedean Screw commissioned and generating electricity   Photo Credit: Mannpower Consulting Ltd
Archimedean Screw commissioned and generating electricity Photo Credit: Mannpower Consulting Ltd

The green sand river banks had become severely eroded and were restored with an environmentally friendly planted coir roll system. With the environment utmost in their minds the owners decided to restore the river banks with this system designed to provide an enhanced aquatic habitat both above and below the waterline. Posts were driven into the river bed and pre-planted coir rolls were then placed on top of willow screening and back filled. Today the new banks have become very established.

River bank restoration at Frensham Mill  Photo Credit: Frensham Mill
River bank restoration at Frensham Mill         Photo Credit: Frensham Mill

A survey of the site also found evidence of Serotine & Brown Long Eared bats.  A light proofed area and improved access tiles were installed in the main roof as part of requirements to enhance their habitat. A survey found an established badger trail along the eastern boundary of the site ( that was left undisturbed by the works). Water voles and kingfishers have also been spotted on site.

Photo Credit: Mannpower Consulting Ltd
Completed hydropower project                   Photo Credit: Mannpower Consulting Ltd

And the Archimedean  screw is now set in a garden intended to reflect the spiralling curves of the screw. The water meadow is in the process of restoration with a plan to plant over one acre of wild flowers.

Archimedes set in a garden designed to reflect the spirals of the turbine
Archimedes set in the garden designed to reflect the screw spirals   Photo Credit: Frensham Mill

Once again we see the Ancient power of Archimedes being used for hydropower generation because if it’s fish-friendly credentials. The Archimedean Screw turbine provides a fish-friendly alternative to conventional turbines, ideally suited to low-head (1m-10m) sites, and sites with fish protection issues. Extensive fish passage tests have conclusively demonstrated that the large water chambers and slow rotation of the Archimedean Screw allow fish of all sizes, and debris, safe passage through the turbine. As a result, the Environment Agency has agreed that no screening is required.

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A return visit to Penllergare Valley Woods hydropower scheme

On our recent trip to the London we decided to bring the car and take the ferry to Fishguard to visit some of the hydropower sites we have worked on over the last year. Our first port of call was a visit to Penllergare Valley Woods, a picturesque landscape hidden away in a steep valley just a stone’s throw, yet a world away, from the M4 in north Swansea.

The Archimedean Screw along side the man made waterfall
The Archimedean Screw along side the man made waterfall

As part of the upgrade and restoration of Penllergare Valley Woods a 30kW Archimedean Screw Hydro Turbine was installed to ensure a sustainable future for Penllergare Valley. A little over a year ago the hydropower scheme was commissioned and is now generating clean green electricity to power the new visitor centre with excess being sold back to the national grid. The Archimedean Screw with a length of 11m and a capacity of 2880 m3/h is situated next to the waterfall. The enclosed compact design was the preferred design of screw for this particular site as the design minimised the installation cost and doesn’t intrude on the existing landscape.

30kW Archimedean Screw
30kW Archimedean Screw

With its lakes and waterfalls, terraces, panoramic views, exotic trees and shrubs, this forgotten Victorian paradise is being slowly restored and brought back to life by the Penllergare Trust. Penllergare Valley Woods was once a famous gentry estate and home to John Dillwyn Llewelyn, the notable 19-century horticulturalist, philanthropist and pioneering photographer. It is Llewelyn’s design, vision and influence behind the picturesque and romantic landscapes of the park.

A return visit to Penllergare Valley Woods Hydropower schemePenllergare Valley Woods is a place where you can enjoy the sound of birds, delight in the profusion of wild flowers, discover evidence of exotic plantings and uncover for yourself the hidden features of a grand design. Wildlife research carried out by Swansea Council has found the estate is very significant for amphibians and acts as a “corridor” for animals to thrive and move about.

One of the many ancient Rhododendrons in full bloom
One of the many ancient Rhododendrons in full bloom
Through hard work, persistence and community spirit by local volunteers and with the financial support of sponsors and the Friends of Penllergare membership scheme, they have been working hard over the last decade or so to maintain and to restore the Penllergare landscape to the romantic style shown in the photographs of John Dillwyn Llewelyn who created it. The rhododendrons, the legacy of the ‘plant hunting’ Dillwyn Llewlyn family in the 19th centurywere a popular sight along every walk way.
Beautiful woodland walk
Beautiful woodland walk
It was obvious throughout our visit that volunteers had been working hard replanting specimen trees and ornamental shrubberies which had been lost from the existing landscape. They have also been thinning and managing areas of dense trees and shrub to reopen historic views.
A return visit to Penllergare Valley Woods hydropower scheme
Visitors can enjoy over 12km of walks including along the Carriage Drive to the now demolished former home of the Dillwyn Llewelyn family, and also down into the gorge where the family created the upper lake with a stunning man made waterfall. Paths and tracks lead on down alongside the afon Llan as it meanders its way to Fforest fach.
A return visit to Penllergare Valley Woods Hydropower scheme
A return visit to Penllergare Valley Woods Hydropower schemeThroughout the last few years the upper lake has been de-silted, and steps, terraces, the stone-arched Llewelyn bridge, waterfalls and cascades have been repaired and restored to reinstate the picturesque and romantic design.
Some of the many ancient trees
Some of the many ancient trees

A return visit to Penllergare Valley Woods hydropower schemeUsing photographic evidence from the 19th century, the old stone bridge was recreated in the traditional style by local stonemasons.

The original stone bridge
The recreated stone bridge

After walking for hours and checking out the Archimedean Screw we spent some time browsing through the information books and leaflets in the visitor centre and then enjoyed a cup of coffee at the small cafe which has stunning views from the cafe terrace to the upper lake. If you’re ever in the area it is well worth a visit. Dogs are also welcome 🙂 🙂