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05/08/2010
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A small section of the Thames is to be illuminated using power generated by the flow of the river, as Kingston University tests a prototype of hydroelectric turbine.
 The turbine will sit on a pontoon in the river, accessible by small boat, and provide a floating test and measurement laboratory, with a range of sensors and monitoring equipment, for research and development.
Hales Marine Energy, near Eastbourne, developed the turbine, which it hopes eventually to deploy in tidal seas as well as rivers. In operation, the turbine will be lowered on a submersible tank that sits on the river- or sea-bed, ready for floating to the surface when required to operate.
Significantly, its developers reckon the design is almost infinitely scalable: the turbine under test is 1m diameter and produces about 1kW. Turbines of 5m diameter for inshore deployment would generate 20kW each.
"It's based on the traditional water wheel, but mounted on a vertical axis," explains design engineer Paul Hales. "Using modern engineering and materials it is possible to take this early turbine and, by turning the output shaft to the vertical, to immerse the whole turbine into the tidal flow," he adds.
Importantly, the large blade area on the drive side also produces very high amounts of torque at low speed, in the range of 10 -20rpm. Coupled with modern permanent magnet generators technology, Hales says it can start producing electricity at rotations as low as 2rpm.
However, for the test, with access to the test site limited, Rod Bromfield, senior lecturer in the Faculty of Engineering at Kingston University, says equipment had to be both simple and comprehensive. "To say that this is a harsh environment for laboratory equipment is a bit of an understatement," he comments, adding: We can only use robust kit with a proven industrial pedigree."
Since the critical measurement is torque – with its direct relationship to power output – Bromfield went for TorqSense wireless torque sensors, from Sensor Technology. "We had to be certain that we would get continuous measurements over an extended period of time, because we need to map power production against actual river flow," he explains.
"When I contacted Sensor Technology I was very concerned about vertical mounting and harsh environment performance. "Fortunately, TorqSense has been installed vertically – including on vertical axis wind turbines, where they have to withstand gales and lashing rain."
In operation, the TorqSense device fitted uses two saw sensors bonded to the shaft at 45deg to the axis of rotation. When the shaft is subjected to torque, a signal is produced that is transmitted to a stationary pick up via a capacitive couple comprising two discs, one of which rotates with the shaft, the other being static.
"When, over the test period, people stand on Richmond Bridge and watch a modest array of lights bobbing about on a buoy, they may not know it but they will be seeing the future," comments Hales.
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Author
Brian Tinham
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