Energy yield of passive stall regulated fixed speed wind turbine with optimal rotor speed

This paper presents a lucid mathematical deduction of optimal rotor speed to maximize the energy yield of wind machines with passively stall regulated Fixed Speed Scheme (FSS). The power captured at a particular wind speed is dictated by the turbine characteristics in conjunction with the type of drive (variable speed or fixed speed). However, the energy yield estimation requires knowledge of wind speed frequency distribution. Studies have revealed that the probability density function could be fairly represented by Weibull distribution with wind velocity being suitably scaled. Considering these facts, the concept of Maxima Energy Indicator (MEI) for FSS has been developed from first principles to obtain optimal rotor speed (woptwopt) numerically. Alternatively, MEI is further simplified using Incomplete Gamma Function which forms the mathematical solution for woptwopt. It turns out that woptwopt of FSS varies with location owing to changes in Weibull parameters. Therefore, it is deceptive to compare the energy yields of FSS with its counterpart Variable Speed Scheme (VSS) without taking into consideration the optimum rotor speed of FSS. With this motivation, computations have been performed which compare the annual yields of both the alternatives, the rotor speed of the low cost stall regulated FSS being optimized.