Before you choose your windmill, you must know the water level in your well. It doesn’t matter how deep the well is—it’s the static level of the water and the vertical distance the windmill needs to lift the water that is important. You also need to know if the water level changes seasonally, or if the water level “draws down” or falls below the static level when water is pumped.
Unless you know how to make the wind blow on demand, you also will need storage for the water that is pumped. For water storage, I’ve used everything from plastic barrels to ponds. The best method, if you have enough height to create sufficient pressure (about 70 feet of vertical drop will give 30 psi, which is suitable household pressure), is to locate a storage tank above the point of use, and gravity-feed the water from there.
Once you’ve determined the vertical distance your ’mill needs to lift water within the well and the additional vertical lift to the storage tank, you can investigate your windmill options based on the amount of water you need and your budget. Here’s an example: If the lowest water level in the well is 60 feet below ground and you need to lift water to a tank that is 20 feet above the well, the total lift is 80 feet. Using the Pumping Capacities table, you can find what size windmill to use, as well as correctly determine the cylinder diameter to use.
The amount of water your windmill can pump is regulated by the size of the pump cylinder, the elevation to which the water needs to be raised, the size of the wind wheel, and how much wind you have at your site.
A typical windmill with an 8-foot-diameter wheel can lift water 185 feet and pump about 150 gallons an hour in 15 to 20 mph winds when using a 1 3/4-inch pump cylinder. The size of the wind wheel and pump cylinder impact the maximum lift that’s possible and the volume of water that can be pumped, respectively. A bigger wind wheel can lift water higher than a smaller one, and a larger cylinder pump can deliver a greater volume of water. If we increase the size of the pump cylinder to 3 inches while still using the same 8-foot-diameter wheel, the volume delivered increases to 470 gallons per hour, but the maximum lift decreases to 68 feet. If we stay with that 3-inch cylinder, but increase the windmill to a 16-foot diameter wheel, we will be able to deliver the same 470 gallons a total of 360 feet.
The above examples use a windmill configured in the standard (long-stroke) mode at wind speeds between 15 and 20 mph. Most windmills have the ability to change the length of the stroke of the pitman arms. At the same wind speeds, but in the short-stroke mode, the windmill will pump at lower wind speeds, but will pump less water.
Windmills are made with wheel diameters ranging from 6 to 20 feet, although the most common size wheel is 8 feet in diameter. Add a 33-foot steel tower to it and the cost is about $4,000 (windmill: $2,100; tower: $1,900). A 20-foot-diameter wheel windmill with a 50-foot-tower will cost close to $25,000. If you’re still unsure how to choose the right windmill for your site, don’t worry—most windmill suppliers will be happy to help size the windmill and pump cylinder correctly.
With sharp edges on 18 sheet-metal blades and a sizable heft (a complete 8-foot windmill weighs about 350 pounds), installing a windmill can be very awkward at best, and outright deadly without proper training and equipment.
Professional installers can be found in almost every region of the United States, or a windmill and tower can be assembled and erected by most do-it-yourselfers who take a one-day class (see Access). Some people choose to erect the windmill and tower without the benefit of a boom truck or lift, though this is not recommended.
For well installations, it is important to center the windmill directly over the well. Any bending or flexing of the pump rod will lead to excess friction and early failure of the moving parts. Also make sure that the top of the tower is level when the installation is complete. All windmills are designed to rotate on the tower axis to face into the wind. If your tower is not level, your windmill will turn downhill when the wind is calm and will not return to face the wind as easily.