In the last two decades, wind turbines have increased in size by a factor of more than 100 (from 25kW to 2500kW and beyond), the cost of energy has reduced by a factor of more than 5 and the wind turbine rotor diameter has increased by a factor of 8. The largest wind turbine currently in operation has a rotor diameter of 126m and a capacity of 7,58MW (Enercon E126).
The wind turbine design technology evolution is based on increased reliability and efficiency, noise reduction, compatibility with the grid network and effective aerodynamic blades. Over the years, many different designs have been prototyped and today the majority of commercial turbines use a three blade horizontal axis design. The blades are connected to a rotor which transfers the power towards the generator which in turn transmits the power towards a transformer and eventually to the grid. Wind turbine blades begin to spin when the wind reaches 7,5-9,5 miles/h and keep spinning up until 50-55 miles/h at which point the wind is considered too strong.
Offshore wind turbines allow for larger capacities to be explored. They are placed in the sea at depths up to 30m deep and are able to take advantage of the stronger and more constant winds. Currently, offshore wind power capacity is still around 50% more expensive than onshore wind power. Until today offshore wind farms are using wind turbines with capacity up to 5MW. Larger wind turbine designs are being explored and are expected to give a boost to offshore wind farms. Onshore wind turbines, usually take advantage of capacities in the range of 1 – 3MW.
New potentials and innovations in wind turbine designs are continuously being exploited and are mainly concentrated in the design of lower-weight blades with better aerodynamic features. This would allow for higher performance wind turbines (that also take advantage of the lower wind speeds) with increased reliability and better compatibility when connecting to the grid. The present advanced wind turbine concept is based on horizontal axis design with 3 blades, variable pitch and variable speed is most likely to prevail. Overall, the wind energy industry achieved great advancements over the past two decades and this will play an important role in the goal to increase the production of electricity from renewable energy sources.