Nationwide Assessment of Potential Output from Wind-Powered Generators

Abstract

A method of computing power output from wind-powered generators has been developed and applied to estimate potential power output at various sites across the continental United States. The method assumes a wind-powered generator system which can be characterized by a cut-in speed V₀, a rated speed V₁ and a cut-out speed V₂. The generator output power is assumed to be constant at the rated power P_r between V₁ and V₂ and to vary parabolically from zero at V₀ to P_r at V₁. The wind distributions at various sites have been found to vary according to a Weibull distribution between realistic values of V₀ and V₁. Values of the Weibull distribution parameters at approximately 135 sites across the United States have been evaluated. These results have been projected to a constant height of 30.5 m (100 ft) and 61 m (200 ft) using data determined from observed Weibull parameter height variations at several meteorological tower sites across the country. A contour map is presented for generator capacity factor values (fraction of rated power output actually realizable). The capacity factor values were computed, using the above method, for wind-powered generator systems having cut-in speed V₀ = 3.6 m s⁻¹(8 mph), and rated speed V₁ = 8.0 m s⁻¹ (18 mph), the characteristics of NASA's 100 kW Plumbrook unit, and V₀ = 6.7 m s⁻¹ (15 mph), V₁ = 13.4 m s⁻¹ (30 mph), hypothetical values for a 1 MW class unit. Results of the evaluation indicate that at a height of 61 m in the central United States and in certain portions of the New England coast over 60% of rated output power can be achieved on an annual average basis, i.e., an average of ≥60 kW from the Plumbrook 100 kW generator. In these same areas the 1 MW system would have over 20% capacity factors, i.e., an average of ≥200 kW from the 1 MW system.