Suggestions for improving wind turbines power curves

The question is usually not whether a wind turbine can be designed to optimise the power production at the site, but rather whether an existing wind turbines with a certain rotor can be modified in order to improve the power production. In this paper the various methods for improving the wind turbines power output were investigated experimentally and theoretically. The effect of changing the rotational rotor speed on the power performance of Nordtank 300 kW stall-regulated, horizontal axis wind turbine was investigated experimentally. This was performed by changing the setting program for operating the wind turbine. The variation in the aerodynamic performance of the wind turbine rotor due to changing the pitch angle was investigated experimentally in Hurghada wind farm. The manufacture setting tip angle for Nordtank 300 kW wind turbine is (–1.8°). In this study, the angle was changed to two values (–2.8°) and (–0.8°). Also, to improve the blade performance of a wind turbine operating in low wind speed ranges; the vortex generators may be used. These vortex generators were placed over low-pressure surface of blade or tip blade part. In this study, two types of vortex generators, rectangle and triangle shapes were investigated.

(1) To design a wind turbine for a specific wind condition, that should involve not only the location of the maximum efficiency, but also the detailed shape of the efficiency curve (efficiency as a function of the wind speed). The question is usually not whether a wind turbine can be designed to optimise the power production at the site, but rather whether an existing wind turbines types with a certain rotor can be modified in order to improve the power production. (2) If the rotor RPM increases, the rotor aerodynamic power increases also and vice versa. Also, the cut-in speed may not be affected by the changing of the rotational speed of the wind turbine rotor. The aerodynamic efficiency (Cp), is improved by increasing the rotational rotor speed of the wind turbine (RPM). This modification can be used to improve the performance of the wind turbines operating in sites, which have low wind speed conditions and high variability. (3) Putting vortex generators on the rotor blades surface leads to delaying stall and increasing the lift coefficient of the moderately-thick airfoils, also it improves the power output from the stall-regulated horizontal axis wind turbines, which operates in low annual average wind speed sites. (4) The improvement in power output of wind turbine with installing rectangle VGs fins is better than triangle VGs on the blade surface due to the increasing of vortex flow with rectangle type which accelerates the air motion on the surface blade higher than other type. So, in low annual average wind speed sites, vortex generators may be added to the tip sections to improve the wind turbine power output. The VGs on tip parts lead to increase the maximum power (peak) produced by wind turbine in low wind speed sites, but the power output is reduced in high wind sites due to the effect of additional drag due to installing the vortex generators. Nomenclature P(u) E(u) AR u uci uco ur S A, k P W c CL L D Ut Up r a h w Vo RPM CP power output from turbine at wind speed, u total available power (energy) passing through swept area swept area wind peed cut-in wind speed. cut-out wind speed rated wind speed slope of the power curve Weibull distribution parameters (scale & shape factors) mean power produced from the wind Turbine relative (effective) velocity element local chord element lift coefficient lift force drag force velocity tangential to blade element due to rotor rotation velocity perpendicular to the rotor plane blade element radius interference factor height of vortex generator width of vortex generator free stream wind velocity revolution per minute turbine power coefficient Greek symbols r air density a element attack angle Φ (flow relative velocity) angle q element pitch angle Ω rotor rotational speed