Fluid Mechanics and Thermodynamics of Turbomachinery, 5e

Small HAWTs
Small wind turbines with a horizontal axis were developed in the nineteenth century
for mechanical pumping of water, e.g. the American farm pump. The rotors had 20 or
more blades, a low tip–speed ratio but a high starting torque. With increasing wind
speed pumping would then start automatically. According to Baker (1985), the outgrowth
of the utility grid caused the decline of the wind-driven pump in the 1930s.
However, there has been a worldwide revival of interest in small HAWTs of modern
design for providing electricity in remote homes and isolated communities that are “offgrid”.
The power output of such a wind-powered unit would range from about 1 to
50kW. Figure 10.4b shows the Bergey Excel-S, which is a three-blade upwind
turbine rated at 10kW at a wind speed of 13m/s. This is currently America’s most
popular residential and small business wind turbine.
Growth of wind power capacity and cost
Wind Turbines 329
FIG. 10.4. (b) The Bergey Excel-S, three-bladed, 7m diameter wind turbine, rated at
10kW at wind speed of 13m/s. (With permission of Bergey Windpower Company.)
The British Wind Energy Association (BWEA) stated that improvements in wind
energy technology mean that the trends which have led to the dramatic fall in the cost of