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 batteries.

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 pipe
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 models.

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.