Commercial Wind Turbine Systems and Applications - Wind Turbine Technology: Fundamental Concepts of Wind Turbine Engineering - page 231

turbine must be located away from the water source, modern electrical water pumpers are
a better choice. These machines drive a piston-type pump in a well that normally ranges
from m to more than 50 m in depth. For remote, unattended locations, battery chargers
employing highly reliable rotor control methods are selected. If power is required to supple-
ment the needs of homes or small businesses, small AC units with outputs up to 25 kW are
the machines of choice.
The major components of water-pumping windmills are the rotor, the crank mechanism,
the tracking mechanism, the pump , and the tower . Attempts have been made to improve upon
these multi-blade turbines by using articulating paddles or blades in vertical-axis designs, but
with little success.
Windmill Rotors
The “mathematical” windmill, as the first American rotors were called, substituted
curved metal sheets for the wooden slats previously used for blades. This design, which
nearly doubled the system performance to about 5 percent efficiency, dominated the market
until the 980s. Most of the rotors have high solidity (ratio of total blade area to rotor swept
area) and contain 0 to 20 radial blades. These rotors operate at slower speeds and have
higher starting torques than two- or three-bladed, low-solidity wind turbine rotors. A high
starting torque is desirable for those wind machines that pump water from deep wells. The
deeper the well, the longer and heavier the pump rod and the higher the water has to be lifted,
so more starting force is required. Rotor diameters range from about 2 to 7 m. Wind tracking
is generally achieved by the use of a tail vane .
Crank Mechanism
The crank mechanism illustrated in Figure 4-7 converts rotational motion into vertical
reciprocating motion. A slight gear reduction (about :3) is often used between the turbine
shaft and the crank shaft. This reduction decreases crankshaft speed and increases available
torque.
Figure 4-7. Schematic view of the power train of an American water-pumping wind-
mill. Shown are the gear reduction between the rotor shaft and the crankshaft and the crack
mechanism for converting rotary motion to reciprocating motion.