A wind turbine that draws on the technology of sailing boats to maximise efficiency has been designed by a firm from Exeter.
Tradewind Renewable Energy this week officially launched their Square Rigger vertical-axis wind turbine (VAWTs) which has furling sails instead of the traditional blades found on more common propeller-type horizontal axis wind turbines (HAWTs).
The firm claim that the novel design overcomes the performance and structural limitations of conventional VAWTs as the surface area of the sails can be varied according to wind speed and to reduce the surface area of the sail on the upwind stretch of the rotational cycle.
The design also overcomes a design flaw of conventional HAWTs, which have to limit the size of their wind capturing blades to avoid overpowering in high wind conditions.
“It’s a completely different approach to capturing wind energy,” said business development director, Simon Moorman.
“What our turbine does is orientate the sail in the downwind cycle like a spinnaker, flat to the wind, and when it starts to come back upwind the sail orientates itself to be an aerofoil in the upwind cycle, just like beating into the wind. That means we have got positive rotational force on the upwind cycle as well as the downwind cycle.
“What that means is we generate huge amounts of energy not least because we can have a massive area presented to the wind when the wind is low, but also we can orientate our sails so on the downwind cycle we are generating huge amounts of energy but also generating power in the upwind cycle. That means we can generate huge amounts of torque.”
Standing just 10 metres high the turbine is considerably shorter than the average HAWT, but its ability to start generating power at just 3m/s means it does not need to be tall or positioned on hills to take advantage of the higher wind speeds found at greater elevations.
A lower profile and the fact that it is relatively slow turning means it makes very little noise and the visual and environmental impact of the turbine is greatly reduced.
The fact that is slow moving also reduces the amount of stress on the mechanics of the device that is composed of components, 80 per cent of which are off the shelf.
“Much of the design is 19th Century chain drives and power gears so really simple. There are patent protected elements of the design but we have gathered together established technologies and combined them to do what we want to and that is what’s patented,” said Moorman.
“It’s really very simple. It has easily available components and the manufacturing technology to create the turbines is not complex and readily available around the world.”
The device is not currently suitable for on-grid generation as the firm has yet to get approval from the Microgeneration Certification Scheme due to the cost and time involved, but they plan to in the future.
Instead they are marketing the turbine, which can also be used to power a pump rather than generating electricity, to off-grid customers, and with the cost of installation likely to be repaid in a matter of years and very low maintenance costs Moorman claims the technology compares “very favourably” with the diesel generators it is competing with.
The turbine’s peak electrical output, the industry standard for measuring wind turbine power, is 7kW but Moorman says this scale is misleading as many designs will not operate in low winds and the turbines 7,000 kilowatt hours per year at mean wind speed of 5m/s gives a more useful indication of its capabilities.
“It’s a very erroneous thing to present as a headline,” he said. “It’s rather like buying a car because it can do 155mph.”
The firm is currently in discussion with a with a large engineering firm works with the Ministry of Defence, the name of which they are currently unable to disclose, to begin large-scale manufacture of the devices.
But they are also seeking licensees abroad as the applications and low-cost of the turbine lend themselves to use in the developing world.
A test model is currently being demonstrated at a site in Devon, but the firm has also received their first order from Kenya to provide power for a remote medical clinic in a game reserve in the north of the country.