The Only Wind-Powered Bookshop
in the World?
Our 6kW wind turbine was erected on the 18th Feb.'99 adjacent to our house and Bookshop.
It was made by Scottish wind power specialists - Proven Engineering of Stewarton, Ayrshire and has a rotor diameter of 5.6 metres (18ft 4in). It sits on top of a self-supporting 9m (29.5ft) galvanised steel pole.
The rotor has three wood laminate blades which drive a brushless permanent magnet generator. This generator produces its 6kW at 200rpm.
No gearbox is required resulting in a machine that is both quiet and reliable in operation.
Above the rated wind speed of 23 mph the blades, which operate downwind of the pole, automatically alter their pitch to limit maximum speed so that the turbine can withstand the strongest gales even without a load.
The generator produces a 48volt 3 phase output which is rectified and used to charge a large lead acid battery. Normal 240 volts a.c. mains is produced from this battery via a 4.5 kW solid state inverter which can synchronise with mains frequency.
The power is fed to household and bookshop mains circuits. If there is insufficient wind power to meet the needs of the house/bookshop, power is automatically taken from the grid. When there is too much power coming in from the turbine and the battery is in danger of being overcharged, a 3 phase heating load is automatically switched in.
The site is exposed to winds from the East round to the North West. Prevailing south-westerlies whistle across the fields unhindered.
The house and bookshop shelter the turbine a little from winds from other directions. This causes turbulence - bad news for turbines.
Winds, and therefore power, are more plentiful during the winter months.
The power in the wind is proportional to the cube of the windspeed. i.e a little more wind means a lot more power.
The turbine starts to produce power in about a 6 mph wind. At 15 mph 2 kW is generated rising to 6 kW at 23 mph.
Although generated power is not metered I estimate that 10,000 kW/hours are generated annually - approximately a third of the needs of the house/bookshop.
The bookshop lights, computers etc use 2kW of power when the shop is open but if the shop wasn’t there, the power requirements for the house, averaged over the year, could all be met by the turbine (space heating excluded).
In a power cut, the battery has enough capacity to keep the Book Centre running all day with no wind - including kettle! In a fresh breeze we need never close.
Cost (in 1999)
Full installation £15,000 (+VAT) including turbine @ £7000.
It will be 16 to 20 years before the installation pays for itself, depending on maintenance costs and future electricity price rises. The turbine has a life expectancy in excess of 25 years.
For me the reward of seeing power coming in from a natural renewable source far outweighs the shock of the initial cost - the turbine will take years to pay for itself but I've got years and years of feeling good!
Simon
If you go to the Proven website you will see that they make smaller and larger turbines than mine.
When calculating the size that you need remember that the power output quoted is the maximum power in a high wind. Multiply by approx. 0.22 to get the average power for a windy location with little turbulence. Always get the highest acceptable pole.
Links
British Wind Energy Association
Simon Brocklehurst simon@harvestgreen.co.uk
I set up a company R-Wind awhile ago with the intention of starting community projects using much larger turbines. This is going through the doldrums just now but may be resurrected in the near future.