Re-inventing the waterwheel10 February 1999
Paul Bromley* recounts his experience of using a small waterwheel installation to bring electricity to a rural community in Sri Lanka
In 1991 a small, private conservation trust in the UK decided to build and install a modest 2.5m horizontal axle waterwheel on its stream in Cheshire. The original aim in using this Roman invention was to demonstrate to young people how, in this high-technology age, electricity can be generated from renewable energy.
A derelict Ferguson tractor gave us a solution to the problem of how to gear up the waterwheel from 10rpm to drive an alternator. Using the back axle and gearbox from the tractor successfully resulted in most of the available energy being used to run the gears and, with the little bit at the end lighting a bulb, we were hooked. There followed months of futile ‘improvements’ until a young electronics lecturer dropped by on his motor bike. He casually offered to control the wheel electronically and thus enable us to generate at 240V AC, using a standard induction motor as a generator. Weeks later and with a few turns of an electrician’s screwdriver, we were operating a small power station producing 1kW.
We were now co-operating with universities in the UK and learning of an initiative overseen by the UK Department of Overseas Development** to establish a cheap low head turbine for use in developing countries. Small high head turbines were already being introduced but these were only of use in mountainous areas, hence the need for a low head machine.
During testing procedures it became apparent that the humble waterwheel was quietly turning out efficiencies which exceeded the experimental turbines. It had other advantages too: no trash problems, simple technology, capable of local manufacture. The biggest hurdle of all had, we thought, been overcome when a major tractor manufacturer offered to help with the supply of used tractor gears overseas.
Upon our arrival at a village which required a waterwheel in Sri Lanka we found that our carefully defined location requirements — 4m head, 100 litres/sec flow, road access — had received a somewhat more colourful interpretation. Several hours of rugged and nerve-racking driving carried us to a small village high in the Southern Uplands, an area of stunning beauty with water gushing everywhere.
The villagers’ Electricity Consumers Society, optimistically formed for the occasion, greeted us and saw their first ever photos of a waterwheel before taking us to the site. Our hearts sank as we climbed in single file along a stream tumbling through rock pools and realised that we were at 500m. But suddenly circumstances of cunning simplicity were revealed: two old irrigation channels, one 5m below the other, were a perfect low-head site, high in the mountains.
We marked out the positions for the waterwheel and powerhouse, removed the leeches, had a cup of tea, and left. The villagers had agreed to build the civil works and we would return with the waterwheel/generator.
Back home again we spent a great amount of time replacing tractor gears with a duplex chain primary lift, driving through a small industrial gearbox ultimately belt-driving a 4kW induction motor/generator. We now knew a lot more about torque and understood why the 30,000 old English waterwheels had disappeared.
Three months later we returned to Sri Lanka with our engineer friends. First stop was the workshop in Colombo which was fabricating the wheel parts. On approaching we saw a 3.5m wheel erected in the yard — just for inspection, of course, and to be dismantled some 1200 bolts later for transportation. On arrival at the village the Electricity Consumers Society took us up the valley to their newly built powerhouse, which was awaiting its wheel.
Fourteen days later the British High Commission representative officiated at the lavish opening ceremony. He kindly acknowledged his initial dubious assessment of the project in his warm and encouraging speech, before opening the wheel and bringing 100W to each of the 24 houses in the village. As the speeches ended the heavens opened, terminating a long drought, and we drove away looking back through the rain at lights in a village which, thirteen short weeks before, had provided our first cup of tea and honoured a simple verbal commitment.
To some raising of eyebrows, the wheel has turned and generated more or less non-stop throughout the last twelve months. The only interruption has been a generator burn-out, which was simply and inexpensively replaced. The cause is uncertain, but we suspect an over-generation of power (of which the wheel is capable) caused by a peak demand on TV screens when the Sri Lankan cricket team was beating England.
We are not satisfied that the bucket design and wheel speed are correctly matched, but these can be improved. They are the result of our trying to increase the speed of the wheel in an effort to take advantage of spare head and thereby also to lower the torque and ease our gearing problems.
The experience for us has been vast. We are wiser, humbler, and keen to repeat the experience with an improved design benefiting from lessons learned. Our working prototype in that English stream now links the wheel directly into an off-the-peg 133:1 geared induction motor, making cost and installation savings and improving safety and maintenance requirements. Now the efficiency, as a ratio of electrical output to theoretical power available, is in the order of 60-65%.
As a small private charity aimed at increasing environmental awareness, Pedley Wood Conservation Trust is now focusing on encouraging similar waterwheel installations to help developing communities. This year’s project will probably be in the next valley in Sri Lanka.