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Page 3

Newsletter 107, Winter 2014 © Hampshire Mills Group

 

HMG Visit to Town Mill, Alresford

 

Eleanor Yates, Ivor New , Peter Mobbs    photographs - Keith Andrews

 

On October 21 2014, eight members visited this site to see a newly installed Hydropower facility.

The river Arle comes from the Old Alresford pond, which was originally a fish pond for the Bishop's Palace at Bishop's Sutton.  Town Mill on the Arle was rebuilt in the 1890s on the site of earlier mills dating back to the 14C.  This building was a roller mill using two turbines in the river below the building but in the 1920s, it stopped grinding flour and only sold animal feeds until the rollers were removed in 1939.  The rest of the milling equipment was sold in 1969 and the building used for storage and later a laundry and a toy factory before being turned into two residences.   The turbines are thought to remain in situ in the old turbine room under the kitchen’s concrete floor.

In 2008, our host David Fitzgerald started the long drawn out planning procedure necessary to replace the Victorian turbines with a modern state of the art Hydropower unit. Some HMG members had looked at early plans for this installation in 2011.

David outlined some details of the process.  This involved meetings with the Design Consultant, Environment Agency, the Council and the Electricity Board.   It was essential to obtain reliable values for the water flow rate and available head so a flow meter was installed and monitored over a period of several months. This established that there is an average flow of about 0.7 cubic metres/sec. A fall of 3 metre is available. 

A decision was made to install a "cross flow turbine" drawing up to 0.6 cubic metres/sec, which can generate up to 10 kW electric power. It was estimated that 75% of this output would be exported to the National Grid.

The EA were worried that the penstock would act as a barrier to fish, so provision was made to install a fish ladder with 18" steps that incorporate a small pool behind each step.   This would allow the fish to recover before their next leap! The ladder has a minimum design flow rate of 80 litres/sec.

Winchester City Council and New Alresford Town Parish Council were very supportive of the proposed development although there were concerns about noise from the turbine and alterations to the weirs.  Local concerns included the impact on wildlife, water-flow, possible flooding and that little electricity would be generated.  All these worries were satisfied before planning permission was granted.

 

 

The planning procedure took 5 years and it was not possible to start construction until  autumn 2013.  Luckily the water level was low because a coffer dam had to be constructed for the eight weeks while the penstock and bypass were built, the mill wall reinforced, the new turbine installed and a sound-proof box put round it.  There was no way of using a crane so the turbine was installed using man power.

A 10mm leaf screen has been installed over the entrance to the penstock to stop debris, leaves and elvers being washed through the turbine.  This needs constant clearance in autumn and when weed cutting has taken place upstream.

At the time of our visit, the water was high and David is getting over 9kW.  The electric output is controlled, monitored and recorded by a large control cabinet inside the mill.   While we were enjoying a welcome cup of coffee the display on the control box recorded the decline in power generation from 9kW to near zero. This was due to a reduction in water flow caused by the screen becoming choked with leaves.  It is planned to source an automatic screen cleaner to eliminate this problem.

David is very pleased with the installation.  He told us that it should take about 5 years to pay off all cost incurred. Thereafter all income from the National Grid will be profit!

Members might like to look at WCC's: PDC0939-WCCItem07.pdf which outlines the whole planning procedure.

HMG would like to thank Mr & Mrs Fitzgerald for showing us the turbine and for their hospitality.

 

 
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