Define capacity factor for a wind turbine and how taller towers influence it.

• A. Wind capacity factor is the maximum theoretical output; taller towers have no effect.
• B. The wind capacity factor is actual energy output divided by the turbine's rated energy; taller towers access higher wind speeds, increasing capacity factor.
• C. Wind capacity factor is the ratio of rotor speed to wind speed; taller towers reduce wind speeds.
• D. Wind capacity factor is the turbine efficiency; taller towers reduce load.

Answer: (B)

Capacity factor measures how much energy a wind turbine actually produces over a period compared with the energy it would have produced if it ran at its rated power for the same period. In other words, it’s the actual energy output divided by (rated power × time). This ratio shows how effectively the turbine is delivering energy over time, not just its maximum capability at a single moment. It’s typically expressed as a percentage and depends on wind conditions and the turbine’s power curve.

Taller towers influence capacity factor by placing the rotor higher where winds are generally faster and more stable. As height increases, wind speeds rise due to the wind profile with height, and turbulence often decreases. Since a wind turbine generates power more readily at higher wind speeds (according to its power curve), the turbine can spend more time near or at its rated power, producing more energy over the same period. That rise in average output raises the capacity factor. Of course, the gains depend on the local wind resource and the turbine design, and taller towers involve trade-offs, but the main effect is clear: higher hub height often leads to a higher capacity factor by accessing stronger, steadier winds.