Waterwheel-based turbine works at slow speeds

Kingston University is to test a hydroelectric turbine based on a traditional waterwheel that produces electricity even at very low water speeds.

The device, developed by Hales Marine Energy, is designed to provide a continuous source of renewable energy from rivers and tidal seas with minimal impact on the environment.

The wheel is mounted on a vertical axis on its side and sits on the sea or river bed in a submergible tank that can be floated up to the surface when required.

It rotates at relatively low speeds of up to 50rpm, which creates less stress on moving parts and minimises habitat disturbance.

‘The large blade area on the drive side produces very high amounts of torque (rotational force) at low speed, in the range of 10 -20rpm,’ said designer Paul Hales.

‘Coupled with modern permanent magnet generators that can start producing electricity rotations as low as 2rpm, my turbine can offer the possibility of tidal generation worldwide.’

The unit under test is 1m in diameter and produces about 1kW, but the design is scalable and the firm claims 5m turbines suitable for inshore deployment could generate around 20kW.

‘To overcome the high resistance on the wheel blades that on one side are trying to move against the water flow, they are shaped and hinged to present a minimum resistance,’ said Hales.

Kingston’s engineering department plans to measure the exact torque the turbine produces in order to gauge its power output.

‘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,’ said senior lecturer Rod Bromfield.

‘Also, for this technology to succeed in the emerging green power market, it must be capable of continuous and predictable energy production.’

The tests will involve Torquesense wireless sensors from Sensor Technology, which are suited to vertical mounting and slow speeds.

To measure the torque, two sensors are bonded to the turbine’s 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 remaining static.

The potential opportunities in small-scale hydro schemes are now being realised across the UK. Click here to read more.