Advances In Wind Turbine Development

Carl-Erik Olsen

The modern and automatically operated wind turbine is now more than 20 years old, but mankind has made exploitation of wind energy for centuries. Successful experiments with wind powered electricity was actually carried out in Denmark as early as 1891, and the first stall regulated and grid connected wind turbine began operation 44 years ago.

Through the years Research & Development focus has changed. It was relatively easy to get the wind turbine to produce power using an asynchronous motor and operate it as generator. At first the major concern was to control the power output and avoid overproduction in high wind as well as having sufficient safety and brake systems. There were problems in getting the early blades to last and to learn the aerodynamic behaviour of the blade profiles 3-D operation. The rotor blade profiles used were based on thorough measurements and tests of aircraft wing sections, which all operate in a twodimension world only. The extra dimension was and still is a big challenge! Later, high efficiency as well as the right level and time of power control became a dominant priority. In the beginning the majority of Danish manufactures used stall control. Later power control by pitching the blades was introduced and the gain was other problems to solve. What ever you do, you have a gain/loss situation. Apart from the blades the wind turbine manufacturers at first purchased off-the-shelf components from sub-suppliers and designed the wind turbines on basis of available experience. Grid quality was becoming an issue as well, and more sophisticated technologies were introduced like variable rotor speed and high complex power electronics. Actually variable speed is a must for pitch controlled wind turbines to reduce stress from wind peak loads. Still most of the designs looks the same, and no technology has proven to outperform any competitors, except that all survivors of today have 3-bladed, up-wind placed rotors, active yaw system and grid connected wind turbines.

Regardless the kind of power controlling technology used the different wind turbines are remarkably equal in price per produced kWh annually. And stall controlled machines with dual rotor speed are just as efficient pr. square meter rotor disc as pitch regulated variable speed counterpart. Surveys show this fact very clearly. More important, wind power has now become competitive with conventional power production, which use fossil, hydro or nuclear energy.

Above all there were always economical considerations. Cost efficiency and profitability to all players, wind turbine maker, developer, owner and operator. Going hand-in-hand with energy prices, interest rates, demands in power capacity, industrial growth, creation of new jobs, environmental concerns, all fuelled by political initiatives.