Small Solutions4 May 2002
A 350kW hydro plant forms part of a 202ha family estate on the shores of Loch Sween in Mid Argyll, Scotland. Carrieann Davies talked to the estate proprietor, Martin Foster, and discovered how the plant is operated and maintained
SITUATED on the picturesque shores of Loch Sween in Mid Argyll, Scotland, the 202ha Ashfield family estate boasts enterprises such as farming, forestry and holiday cottages. This impressive estate is also home to the 350kW Ashfield hydroelectric power station.
Developed and built in 1985, with the intention of using the river Lussa to produce power which could be sold to the then North of Scotland Hydro Electric Board (NSHEB), the plant has proved to be a popular tourist attraction in this national scenic area, renowned for its abundant variety of wildlife, including seals, otters and deer.
'When we started this project, we knew it was important that we didn't harm the landscape because we are in a popular tourist spot. We wanted to make sure our clean credentials were preserved,' says estate proprietor and operator of the plant, Martin Foster. 'Because of this, we built the powerhouse in a stone building with a slate roof, and we buried the accompanying pipeline. We wanted to demonstrate that we were serious about building an environmentally acceptable project.'
The plant - fitted with a twin jet vertical shafted turgo impulse turbine from Gilkes - is controlled by monitoring equipment within the powerhouse, and an ultrasonic level sensing device in the 1.5m high dam.
According to Foster, the power produced by the plant is totally reliable. 'The only thing we can't do,' he says, 'is forecast precisely what we're going to produce because we are obviously dependent on rainfall. When it's raining, we've got lots of water and the plant runs at full power. Within two or three days of the rain stopping, we're starting to wind down on output and we normally get about 65% of plant utilisation.'
Since he began building the hydro plant, Foster has had to overcome several challenges in its operation and maintenance. He explains: 'We had the plant up and running by September 1986, but we ran into difficulties straight away with the pipeline. The 1375m long pipe had to run across a mountain, which had ridges of solid rock and gullies of deep peat. When we laid the pipe, we dug the tops of the ridges away and filled the gullies.
'When we first filled the pipe, everything appeared to be satisfactory. Soon afterwards however, the weight of the water broke the back of the pipes, because the peat filled gullies allowed the pipe to sink down. This problem persisted intermittently for two years,' he adds.
Foster also explains that the water itself has caused problems. 'In this particular area we have very peaty water. The peat suspended in the water sticks to the inside of the pipeline, causing ripples on the pipe. This reduces the flow rate by 20%.'
To combat this problem, every six months Foster has to clean out the pipe.
'We drain the entire pipeline,' he says. 'We then put a bristled pig at the top and turn the valve on slightly at the top. The water pressure pushes the pig down, and when it comes out the bottom, usually after about five minutes, the pipe is clean.
'The dirty water from the pipe sits in a small pond near the bottom of the pipe, but it eventually settles out and goes back into the river,' he adds. 'There's nothing we can do about this problem really, we just have to keep cleaning it.'
Another aspect of the plant that Foster is keen to point out involves problems with the pricing structure for the electricity produced, which he now sells to Scottish and Southern Energy.
'Basically, in 1987 we got 3.35 US cents per unit (cpu) for 16 hours and 2.29cpu for eight hours, and we were charged US$409 per month' he says. 'Today we get pool purchase price. During October, November and December 2001 and January 2002, a time when most of our production is made, we averaged 2.87cpu for 16 hours. We were also charged administration fees of US$268, a settlement fee of US$17.5 and metering cost us US$65.6 a month. The income was better 15 years ago!'
Foster points out that this price drop was due to the local electricity board needing to purchase its power in the most economically feasible way. 'I think it was decided it was cheaper to buy gas then it was to buy from us. The price had to come down to compete.'
However, this situation may change with the Renewables Obligation (Scotland) (ROS), which will oblige all licensed electricity suppliers in Scotland to obtain renewables obligation certificates (ROCs) sufficient to cover a specified proportion of the electricity supplied to their customers in Scotland.
'Obviously, the ROS is totally going to transform our cashflow because it gives an added value to the product we produce,' says Foster. 'We now sell the power, the renewables obligation certificates, the levy exemption certificates, and any embedded benefits, whereas originally we were just selling the power at wholesale price. Things are really changing now.'
Despite these problems with operation and maintenance, Foster is planning to build a new hydro plant in the future.
'We're currently in the process of obtaining planning permission for a new hydro plant on the estate,' he says. 'This kind of clean power is going to be ever more important in the future, and with the introduction of the renewables obligation it's going to be more economically feasible.
'This area is ideal for developing new hydro schemes,' he adds. 'As long as we take into account landscaping, water quality and environmental issues, building new plants could really help benefit the area and offer a cleaner source of energy.'