Commercial Wind Turbine Systems and Applications - Wind Turbine Technology: Fundamental Concepts of Wind Turbine Engineering - page 251

Stand-Alone Wind Turbine Applications
As the name implies, wind energy systems intended for stand-alone applications are
designed as the sole or principal source of mechanical or electrical energy, and are not con-
nected in any way to an electrical distribution grid. The major tasks of stand-alone turbines
are those that have been performed throughout the history of wind power: pumping water
and generating electricity for local consumption.
As shown in Figure 4-30, the electrical output from a stand-alone wind turbine can be
DC for charging batteries to power low-voltage DC appliances, or DC for inversion to 0
VAC, or variable-frequency AC for resistance heating , or utility-grade AC to operate lights
and motors directly. In practice, most of the commercial wind generators for remote applica-
tions are designed for charging batteries. No wind power system has been marketed success-
fully that is intended solely for producing heat.
Figure 4-30. Output configurations for stand-alone wind turbine generators.
Residential and Agricultural Heating By Wind-Generated Electricity
Resistance heating , because of its insensitivity to the quality or frequency of electricity,
allows the designer to tailor a relatively simple wind turbine for variable rotational speed,
which results in more efficient operation. Controls necessary for the generations of utility-
grade power are eliminated, along with most power-conditioning electronics. Researchers in
the United States and Ireland have experimented with the variable-voltage, variable-frequency
output from wind-driven AC alternators and DC generators for producing heat with re-
sistance elements. Another concept for heating with wind power was the wind furnace
[Cromack and Heronemus 977], which used water heated by a wind driven mechanical
churn. Several firms have tried to commercialize these concepts, but without success.