Why are current turbines not cost-competitive in a low wind speed site?
• Most turbines are designed for high wind speeds – therefore they include higher design margins. • But the real issue is tip speed ratio design. Tip Speed Ratio = actual velocity of tip of blades / wind speed • High wind designs must be designed one way. For example, gearboxes are configured a certain way for higher velocities. • In a low wind speed, if have the generator and gearbox of a high speed wind turbine, then would need a bigger rotor diameter to capture the same power • Distribution of wind is an important difference between high and low wind sites – how often is the wind blowing @ any given velocity – the peak velocity is its class rated average – wind blows at that speed almost all the time • Rayleigh Distribution: wind velocities vs. time – how fast it blows and how often • Class 4 and 6 can have similar distribution shapes, but different peaks – the class 6 site gets more power at its peak. • The rated speed for turbine is where it reaches its peak power. • Capacity fact
