Correct Answer - Option 2 : Both a and b are true
Efficiency in extracting wind power:
The efficiency in wind power extraction is quantified by the Power Coefficient (CP) which is the ratio of power extracted by the turbine to the total power of the wind resource
CP = PT/Pwind
Turbine power capture therefore is given by, \({P_T} = \frac{1}{2}\rho A{U^3}{C_P}\)
which is always smaller than Pwind.
There exists a theoretical upper limit on the maximum extractable power fraction - known as the Betz limit.
According to Betz theory, the maximum possible power coefficient CP = 16/27, that is, 59% efficiency is the best a conventional wind turbine can do in extracting power from the wind. The reasons for this are:
- 100% efficiency is not possible is due to the fluid mechanical nature of wind power, dependent on the continuous flow of air in motion.
- If, hypothetically speaking, 100% of kinetic energy was extracted, then the flow of air would be reduced to a complete stop and no velocity would remain available to sustain the flow through the energy extraction device, irrespective of the specific wind turbine technology used.
The maximum extraction efficiency is achieved at the optimum balance of the largest wind slowdown that still maintains sufficiently fast flow past the turbine.