Hydro turbine generates nearly a third of Devon Wildlife Trust's power
Posted by Cathy Debenham on 2 March 2012 at 9:14 am
When Devon Wildlife Trust moved into historic Cricklepit Mill in Exeter, it decided to use the Anglo Saxon mill leat to generate electricity. In 2010 it installed a an Ecowave cross flow micro-hydro turbine, manufactured in nearby Crewkerne.
There have been watermills on the spot since 1220, although they would have been used for grinding flour, rather than generating electricity. The Wildlife Trust still runs the old mill wheel once a month for demonstrations of traditional milling. Although it reduces the flow to the hydro-turbine a bit, it is possible to run them both at the same time. In fact, the conditions for milling have improved as there is a better head of water now. A third mill wheel, which free-wheels in summer does not affect the performance of the hydro system at all.
The leat that feeds the turbine is fed from the river Exe. To ensure there is a constant 'head' of water, the trust has installed an automatic gate just upstream of the mill. This closes to build the water up to the required level, and regulates the flow to the turbine.
The water is fed from this holding tank to the turbine through a large steel pipe, called the penstock tube. This narrows as it reaches the turbine, which forces the water through at high pressure. The turbine itself is a lateral water wheel.
Installation of the turbine has given staff and visitors a closer relationship with the weather. "If it's raining you come in wondering how much electricity the turbine will generate," says communications officer David Ireland. "It's surprising how quick the effect is. If there's rain 30 miles away on Exmoor, we see the result downstream at the turbine about 10 hours later."
The system isn't fit and forget. Staff at the Trust have to monitor the Environment Agency website each day to check the water level in the Exe and make sure that there's enough for them to be able to 'abstract' it and use it to run the turbine.
In dry periods, when water levels are low, the turbine sometimes temporarily shuts down to allow a head of water to build back up. Once there's enough water in the intake tank the gate opens again and the turbine restarts.
Installing the turbine cost £100,000. Devon Wildlife Trust received grants from BRE, EDF and Devon Association for Renewable Energy, so no members money was used to buy it. It currently takes about 48kWh per day to power the building. Depending on the amount of rainfall, the system generates between 5 and 100kWh per day. It produces a total of 8,960 kWh of electricity a year, which is a bit less than a third of the charity's annual electricity consumption.
“The Hydro turbine has been a success for us on many levels, says DWT operations co-ordinator, Stuart Hodgkiss. "Firstly, it is a daily source of interest for the staff and volunteers based at Cricklepit Mill. Indeed it is very rare to see one of the team walk past the turbine without checking to see how much it is generating and I am asked most mornings how much 'we did' over the previous day!
"Seeing renewable energy in action is so important and the idea that the building can be powered a natural resource that flows past the building every second of every day really captivates everyone.
"But its not just the people that benefit - the wildlife seem to like it too! The otters that live around the mill are regularly seen investigating (and even swimming in) the artificial pool created below the turbine, and we now have daily visits from the dippers who are attracted by the shallow fast flowing water that it expels. It really has been a hit all around”By Cathy Debenham
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