Knoydart is not connected to the National Grid. Electricity supply to the village of Inverie comes from its own hydro electric generator, running off a pen stock from Loch Bromisaig.

A supply was never run from Inverie to Sandaig bay and so electricity at Sandaig was previously generated totally by diesel generators, as in many remote places. Now however the need for generator power has been overcome.

The Concept:

The Sandaig burn runs through our land.It has a substantial catchment area and we obtained data on the estimated monthly flows in the burn.This showed we could generate up to 4 kW for most of the time and 0.8 kW for nearly all of the time.

So in 2007 we installed a micro hydro generator, running off the Sandaig Burn, to act as the primary source of electricity, with the diesel generator being kept as backup. The power from the hydro is between 0.8 and 3.6kW, according to season and rainfall and is used to charge batteries at the cottage and at our neighbors, John and Janet Sellars.The remainder heats radiators in the cottage. The installation of this system has been a 3 year project with the majority of the work being done during 2 weeks of each year.

Each line in the graph above illustrates the percentage of time over the year that flow in the burn is expected to exceed the respective flow rate. THus it is clear that we can always expect at least 20l/sec at least 95% of the time. (please click graph to enlarge)

Dam and pen stock

The system is a ‘run-of –the –river’ scheme requiring no impounding of water.There is a small dam or weir, with an intake box over the top.We built the dam in concrete, at a location where there is a small waterfall and good rock foundation for the dam.Water enters a box on the downstream face of the dam, via a grill (a Coanda screen) which eliminates debris.

Then once collected it is diverted into a 4” pipe leading to a settling tank. This is in a sheltered ledge away form the main flow in the burn, which can be a torrential flood at times.This tank establishes a relatively calm and stable inlet to the ‘pen stock’ (the pipe then running down to the turbine).This is 800 meters long and 8” in diameter.It is buried under the moor and consists of HDPE (High Density Polyethylene) which is the blue pipe commonly used for mains water supplies. We welded the individual 12m lengths together using an electro-fusion machine powered by a 6 kW generator, which we hauled across the moor on a boat trailer!

Turbine and its valves

The turbine is of the Turgo type in which jets are directed at an angle onto a wheel or ‘runner’ consisting of small plastic buckets mounted on a vertical axis.Above the wheel is a Crompton generator, which generates up to 3.6 kW at 50 Hz alternative current.

Flow form the pen stock passes into three 2” diameter pipes in the turbine house, each of which lead to a jet. There is a valve on each of the pipes. When all three valves are open, 3.6 kW is generated.One of them is permanently open, providing 0.8 kW.The other two valves have remotely operated actuators to enable them to be opened or closed automatically, in accordance with the amount of water passing into the settling tank.This is monitored by a pressure sensor which measures the depth of water in the settling tank. Signals from the sensor are relayed down a (800m long) signals cable, to a control box by the turbine, which then opens or closes the two valves accordingly.

The turbine, valves and control box are in a small hut which is in a dell 250m away from house, so that the turbine cannot be heard, although it is anyways very quiet.

Generated electricity

The generated electricity, at 50 Hz a.c., runs in buried cables to the battery (24 volt d.c.) banks at the cottage and at the Sellars’ house, where it is stored.When there is demand from the houses, the stored electricity is ‘inverted’ by two inverters, to 240 volt a.c. which is the normal domestic supply. The turbine and electrical system was designed and installed by Richard Drover, of Greenearth Energy in Wales.http://www.greenearthenergy.co.uk/

Advantages of the system

This system is in line with current thinking on conservation of resources, including the all current thinking about reduction of emissions and saving fossil fuels. It prevents

·Ongoing cost and effort in transporting diesel to Knoydart

·Noise pollution from the diesel generator

·Fumes from the generator

·Possibility of pollution due to diesel spillage in transport