Applications and Wind Industry - Wind Energy: Renewable Energy and the Environment - page 209

r Productive loads should have been established at the beginning.

r A skillful technical operator should also provide some services to users and encourage

wise use of electricity.

The large initial investment for renewable energy village power is beyond the financial resources
of the local residents and local government.
Four villages in Barkol County have been powered by renewable energy since 1999. Each one is pow-
ered by a wind turbine system, and another two large villages are powered with a 30 kW wind system.

10.6 WATER PUMPING
The pumping of water and sailboats are the oldest and longest-term uses of wind power. The two
common examples of mechanical water pumping are the historical Dutch windmill for pumping
large volumes of water from a low lift and the farm windmill for pumping small volumes of water
from a high lift [35-37].
For mechanical windmills or wind turbines the important considerations are the power in the wind
and how that power can be transferred by the system. This means that the characteristics of the wind
turbine (primarily the rotor) and the characteristics of the pump are combined in an operating system.
The type of pump in many cases dictates the mode of operation of the rotor and how the rotational shaft
power is transferred to pump power. Of course, the size of the system depends on the dynamic pumping
head and the quantity of water to be pumped. For the farm windmill, the efficiency depends on the load
matching of the rotor to a positive displacement type, in general a reciprocating pump (piston).
The American farm windmill ( Figure 1.3 ) is still in widespread use around the world for pump-
ing low volumes of water from wells or boreholes. It is estimated that there are around 80,000 oper-
ating in the Southern High Plains of the United States. World production is estimated at 3,000 per
year. The American farm windmill is well designed for pumping small volumes of water for live-
stock and residences, and the design has not changed since the 1920s and 1930s. The only change
has been in materials used for bearings and the use of plastic pumps and drop pipes.
The American farm windmill is characterized by a high-solidity rotor (also called a wheel)
consisting of fifteen to eighteen blades (also called vanes), which are normally made in a slight
curve ( Figure 10.6 ). The large number of blades provides a high starting torque that is needed for
operating the piston pump. Most units have back gearing (reduction in speed) that transfers the
rotating motion of the rotor to a reciprocating motion for pumping water. All wind turbines have a
way to reduce efficiency and not capture all the energy possible at high winds. On the farm windmill
the rotor axis and yaw axis are offset to rotate (yaw) the rotor out of the wind. This is called furling.
At low wind speeds, the tail and the spring bring the rotor perpendicular to the wind.
The rotor has a peak power coefficient (C P ) of about 30% at a tip speed ratio of around 0.8. The
efficiency for a reciprocating displacement pump is essentially constant at 80% over the operating
range of wind speeds. The overall annual efficiency (wind to water pumped) is around 5 to 6% (see
Section 8.5 ).
In the 1970s and 1980s, different research groups and manufacturers attempted to improve
the performance of the farm windmill [35, chap. 5] and reduce the cost. Many of these projects
were designed to pump water in developing countries. Designers believed that the performance
could be increased by the following changes:

1. Reduce the solidity (reduce the number of blades or area of blades), which means higher
rotor rpm.
2. Change the characteristics of the pump by using variable stroke or variable volume to
match the characteristics of the rotor.
3. Develop a windmill for the low wind regions of the tropics.
4. Counterbalance the weight of the rods, pump, and water column.