COMMUNITY ENERGY IN GARGRAVE & MALHAMDALE
Hydro power – traditional renewable energy in the dales.
The generation of electricity from the power in a flow of water via a water turbine is called hydroelectricity.
The late 18th century saw the setting up of a number of water powered cotton mills in the Dales. Most were superseded by steam power in the first half of the 19th century, however two mills in Malhamdale that survived were Scalegill and Airton mills. While the mill buildings are now converted into accommodation these schemes offer potential locally for developing hydro-electricity at a community scale. The Yorkshire Dales National Park Authority recognises the opportunity to preserve and bring back into use the original water control structures and in 2008 commissioned a study of all the mills in the park to assess their viability for electricity generation. Both Airton and Scalegill sites were considered worthy of further consideration.
As part of a mix of renewable energy resources hydro can make a valuable contribution to the electricity demand of a community and complements other renewable sources such as wind and solar to provide a reliable year-round source of clean energy.
The majority of mill sites in the Dales relied on “run-of-river” flows with only enough storage capacity to suit the daily mill operations so output fluctuates according to the rate of natural run-off, and is dependent on local weather conditions. The actual mill buildings, if they still exist, may be used for accommodation so cannot house a water turbine. An Archimedean screw type turbine which is a new application of an ancient technique for drawing irrigation water from rivers such as the Nile, is one way of harnessing the potential of the existing water supply system and an archimedean screw turbine is shown here being installed at Bridge End Mill, Settle by Settle Hydro Ltd.
The amount of electricity a hydro plant is capable of producing from a flow of water is dependent on the quantity of flow through the turbine and the fall of the water between inlet and outlet which is known as “head”. To make a reliable estimate of the potential annual energy yield daily flow monitoring over a long period of time is required unless records exist. Rainfall and run-off can vary widely from year to year and comparison with rainfall records in the catchment area will be required.
This dependence on the two variables of flow and head gives two possibilities. Either a small stream with a high head, for example a fall of 50 feet or a large stream with a low head of only 5 feet but 10 times the flow rate will give a similar output of energy. Because the low head turbine, inlet, sluice gates, etc all have to be designed for a large quantity of flowing water the low head installation is more expensive and difficult to construct than the high head scheme. Victorian water mills driven by water wheels were traditionally built on the banks of large rivers, powering slow turning but highly geared water wheels to turn the machinery of the mill, so these sites are typically low head. In very hilly areas such as upper Malhamdale there is potential for small high head installations such as the one shown here on Malham Moor which has been providing electric power to Tennant Gill Farm for many years. It is likely that many more such sites have yet to be exploited in this way.
The National Park generally prefers small scale hydro schemes as they are less visually intrusive than either wind turbines or solar panels. However abstracting water from a river, even if you are putting the water back again, needs a water abstraction licence from the Environment Agency and the conditions attached to such licences can be quite rigorous in order to protect fish, wildlife and the interests of other river users.