GE Energy provided full turnkey construction, and operates and maintains the wind farm. Originally scheduled for completion in October 2004, the Cefn Croes Wind Project’s power is sold to the Non-Fossil Fuel Purchasing Agency and distributed to the national grid through SP ManWeb. The wind plant’s estimated annual generation serves about 40,000 households. It contributes to the UK’s aim to produce 15% of its electricity from renewable sources by 2015.
The project gave on-site employment to more than 100 people over the construction period, with four ongoing service jobs on completion. It is located on 7.5kmยฒ of land leased from the Forestry Commission. A ยฃ250,000 land management project is restoring the site’s ecological value lost through commercial forestry and intensive agriculture. A community fund is expected to generate about ยฃ60,000 per year for local community projects like energy efficiency, environmental education, conservation and environmental management, tourism and community development.
1.5MW wind turbines
GE’s 1.5MW wind turbines were the first of their size to become commercially available. They are active yaw and pitch regulated with power/torque control capability and an asynchronous generator. A bedplate drive train design joins all nacelle components on a common structure for durability. The generator and gearbox are supported by elastomeric elements to minimise noise emissions.
GE’s control system continually adjusts the wind turbine’s blade pitch angle for best rotational speed and maximum lift-to-drag at each wind speed. This “variable speed” operation retains highest level efficiencies, unlike fixed speed wind turbines which only attain peak efficiency at one wind speed. The result is greater annual energy production yield than constant speed machines.
Unlike constant speed rotors, too, GE’s variable speed operation converts the loads from gusts of wind to electric power. Generator torque is controlled through the frequency converter. This control strategy allows the turbine rotor to overspeed operation in strong, gusty winds, thereby reducing torque loads in the drive train. The operating speed range is notably wider than the “slip” range used by other technologies, which produce heat rather than electric power when regulating power in strong, gusty winds.
GE’s variable speed system also provides active damping of the entire wind turbine system, resulting in considerably less tower oscillation when compared to constant speed turbines. Active damping of the machine also limits peak torque, providing greater drive train reliability, reduced maintenance cost and longer turbine life.
Optional WindVAR control improves transmission efficiencies and supplies the utility grid with reactive power (VARs), increasing grid stability. This automatically maintains defined grid voltage levels and power quality within fractions of a second. It reduces the risk of voltage collapse, and minimises the impact of grid disruptions, particularly valuable for weaker grids or larger turbine installations.
Low voltage ride-thru technology
GE’s turbines remain online, and feed reactive power to the electric grid despite major system disturbances. Low Voltage Ride-Thru (LVRT) enables wind turbines to meet transmission reliability standards similar to those demanded of thermal generators. Transmission “system events” – lightning strikes, equipment failures and downed power lines – are a fact of life on utility grids. GE’s turbines do not simply trip offline during instantaneous voltage drops, maintaining high availability.
Packages for the 1.5MW turbine are currently available that deliver ride-thru down to 30% voltage at the point of common coupling for 100msec. In addition, beyond coping with the initial disturbance, LVRT remains engaged until after the fault is cleared, helping to bring the system back to normal operating conditions
Wind power project objections
There were objections to the development, complaining about the effect on the site’s scenery and ecology. Campaigners claimed that planning conditions were flouted.
A concrete-making factory, for example, was constructed in the middle of the site, with water being extracted from the River Wye. A new quarry face was excavated from the main forestry track up to Cefn Croes, and 11 “borrow pits” were allegedly excavated before gaining planning permission.
Key players
RDC and Falck Renewables Limited have developed and built a number of wind energy projects in England, Scotland and Wales, focusing primarily in Scotland. RDC also obtained planning approval for the UK’s largest offshore wind project (150MW at Rhyl Flats). Falck Renewables Limited is a wind energy subsidiary of the Falck Group, an Italian company with headquarters in Milan.
GE Energy produces wind turbines with rated outputs ranging from 1.5MW to 3.6MW.
