Water supplies such as wells and dugouts can often be developed on the
open range. However, the availability of power supplies on the open range
is often limited, so some alternate form of energy is required to convey
water from the source to a point of consumption. Wind energy is an abundant
source of renewable energy that can be exploited for pumping water in
remote locations, and windmills are one of the oldest methods of harnessing
the energy of the wind to pump water.
How much water can a wind-powered pump deliver?
The amount of water a wind-powered water pumping system can deliver depends
on the speed and duration of the wind, the size and efficiency of the
rotor, the efficiency of the pump being used, and how far the water has
to be lifted. The power delivered by a windmill can be determined from
the following equation:
P = 0.0109(D**2)(V**3)n
where P is power in watts, D is the rotor diameter in metres, V is the
wind speed in kilometres per hour, and h is the efficiency of the wind
turbine. As can be seen from this expression, relatively large increases
in power result from comparatively small increases in the size of the
rotor and the available wind speed; doubling the size of the rotor will
result in a four-fold increase in power, while doubling the wind speed
will result in an eight-fold increase in power. However, the efficiency
of wind turbines decreases significantly in both low and high winds, so
the result is that most commercially-available windmills operate best
in a range of wind-speeds between about 15 km/hr and 50 km/hr. The following
chart shows one way in which manufacturers present information relating
to performance of their products.
What kinds of pumps are available for use with windmills?
If the windmill is used to generate electricity to power an electrically-powered
pump, it will probably be necessary to store the electricity in batteries
due to the variability in generation. Therefore, a pump powered by an
electrical motor for use in conjunction with a windmill that generates
electricity should have a Direct Current (DC) motor. For such systems,
it is important to use good-quality deep-cycle batteries and to incorporate
electrical controls such as blocking diodes and charge regulators to protect
The most common type of pump used with windmills is the positive-displacement
cylinder pump driven by a reciprocating rod connected to a gear box at
the windmill rotor. The performance of these pumps can be enhanced through
the addition of springs, cams and counterweights that alter the stroke
cycle and off-set the weight of the drive rod, thereby reducing the starting
torque and allowing the system to perform better in light winds.
An alternative to the traditional cylinder pump is the air-lift pump.
The air-lift pump is a type of deep-well pump, sometimes used to remove
water from mines. It can also be used to pump a slurry of sand and water
or other "gritty" solutions. In its most basic form this pump
has no moving parts, other than an air compressor driven by the windmill,
and the efficiency of the air compressor is a prime factor in determining
the overall efficiency of the pump. Compressed air is piped down the well
to a foot piece attached to the discharge pipe. As air is discharged into
the water column in the discharge pipe, a two-phase mixture of air and
water is formed that is less dense than the surrounding water in the well.
This apparent density difference is what causes water to rise in the discharge
How much does a wind-powered pumping system cost?
The cost of a wind-powered pumping system will vary according to its capabilities,
but the cost of most systems for stockwatering applications ranges between
$1,000 for small compressed air systems to $6,000 for the larger well
What is required to maintain a wind-powered pumping system?
One of the attractions to wind-powered pumping systems is their simplicity
and robustness. It is prudent to check all rubber diaphragms annually,
and, on compressed-air models, to check all valves. The anchoring system
for the windmill tower should also be checked to ensure that the windmill
is not toppled during high winds. As with any pumping system, a wind-powered
pumping system should be checked regularly to ensure that cattle have
an adequate supply of water.