Wind turbines and energy production

The efficiency of wind turbines depends on several factors, including their location, size, blade radius and capacity factor.

The amount of energy a wind turbine produces depends on its location and whether it is placed onshore or offshore. Offshore turbines are more efficient than onshore turbines because wind speeds are higher and more consistent at sea.

Turbine efficiency is also highly dependent on air density. Heavier air, that is, air with a higher density, exerts more lift on the turbine rotor blades, generating more energy. Air density is influenced by altitude, temperature and air pressure. Turbines located at higher altitudes are less productive because the air is lighter and less dense. The air at sea level is denser, making offshore turbines more effective. Offshore wind farms therefore require fewer turbines to create the same amount of energy as an onshore wind farm.

The blade radius of a wind turbine is also known as the “swept area”. This is the circular area covered by the rotating blades. The amount of energy produced by a wind turbine is proportionate to the swept area of its blades. A large swept area therefore captures more wind than a smaller area. Since the space at sea is unhindered, offshore wind turbines can be much taller and have larger blades than onshore turbines.

The wind turbine capacity factor measures how efficiently a wind turbine generates electricity compared to maximum potential output. This is calculated by comparing the actual amount of energy the turbine generates over a given time with the theoretical maximum amount of energy it could have generated in that time.

The capacity factor indicates how well the turbine is delivering compared to its potential. Wind turbines normally generate electricity at wind speeds of 4–25 metres per second (mps).Turbines will generally shut down at speeds above 25 mpsfor safety reasons and to prevent accidents during storms. Extremely cold weather can also cause the sensors to shut down the turbines.

Wind turbine capacity is ever evolving, but today, most onshore wind turbines have a capacity of 2–3 megawatts (MW), producing around 6 million kilowatts hours (kWh) of electricity every year, or enough to supply around 1 500 homes.

Offshore wind turbines are generally more efficient than onshore turbines as a result of their larger scale, the strong and consistent winds at sea and fewer external disturbances such as trees and birds, all of which provide offshore wind turbines with a steadier wind flow.

Offshore turbines have a capacity in the range of 4–15 MW, with most typically producing 8–10 MW of electricity, or enough to supply to around 3 000 to 4 000 homes. Offshore wind turbines generally run at 35–50 per cent capacity, whereas onshore turbines have a lower capacity of 25–35 per cent. A higher capacity factor means more consistent and reliable energy production, which will be essential to the future of renewable power in Europe and beyond.