Turbines with Power Ratings above 30 kW to 300 kW

Wind turbines in this size range are typically too large for residential applications and are most commonly used to provide energy to businesses, farms and remote communities. Only 15 years ago, most utility-scale wind turbines would have fit into this size category. The typical size of turbines in the first large windfarms in California in the 1980s was about 150 kW. With most large wind turbine manufacturers now following the larger and more lucrative utility market (using machines of 1 MW and more), few are still producing machines under 300 kW. So while some of the 30-300 kW turbines have a long track record and can claim a certain degree of technological maturity, they have not benefited from the same recent improvements as their larger counterparts.

As with the other size categories of small wind turbines, the most common turbines in the 30-300 kW range are 3-bladed horizontal axis machines. Because turbines of this size are generally designed for on-grid operation or as part of wind/diesel hybrid systems, they typically use induction generators. A gearbox is used to step up the rotational speed of the rotor to match it to the operational speed of the generator. Such generators are typically connected directly to the grid and self-synchronize to the frequency of the grid’s alternating current (AC). These machines operate at near constant speed; as the rotor attempts to speed up in response to stronger winds, it is counteracted by increased torque from the generator.

The use of these turbines in remote and northern locations is a somewhat unique and potentially important application that has its own special technical challenges, including:

• Integration of wind turbines with diesel generators (particularly the issue of controller technology and control strategies);
• Icing, ice mitigation and cold weather performance;
• Special cold-weather lubricants;
• Cold weather alloys;
• Nacelle insulation;
• Specialized installation techniques (e.g. tilt-up vs. crane, foundations in permafrost);
• Maintenance in extreme and remote conditions.

A number of turbine manufacturers who market their machines for northern applications offer optional cold weather features that address some of these issues (e.g. black blades for ice mitigation, insulated and heated nacelles, etc.). Others incorporate some of these features into their standard design. A number of different SWTs installed in locations ranging from Alaska to the Canadian arctic have demonstrated that wind turbines can operate effectively in extreme cold climates.

Costs for medium-sized turbines start at about $2,200 per kW for the turbine itself and $3,300 per kW for an installed system. A more demanding installation, such as in a remote northern location, can result in the cost being two or three times higher. Fluctuating material costs, particularly the cost of steel, also have a significant effect on turbine prices.

The life expectancy of a well-built and well-maintained medium wind turbine is generally expected to be over 20 years. This may vary significantly depending on operating conditions (e.g. high turbulence winds, extreme dust or cold). The designs of the medium-sized machines generally allow for the replacement of virtually all major components, allowing the system’s life to be extended almost indefinitely.

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