How can I improve the efficiency of electric motors in my irrigation system?
Answer: Especially in times of high energy costs, efficient irrigation equipment is essential to the viability of farms and ranches. Following are some effective hardware improvements for electric motors:
• Rebuild older motors and gain several percentage points in motor efficiency. This procedure typically involves replacing the bearings, rewinding, and “dipping and baking,” and is done by qualified motor repair shops.
• Consider a premium-efficiency motor instead of a standard-efficiency motor when installing a new system, when replacing over- or undersized motors, and when the cost of rewinding exceeds 65 percent of the price of a new motor. Premium-efficiency motors are two to four percent more efficient than standard-efficiency motors. Besides saving energy, premium-efficiency motors usually have higher service factors, longer insulation and bearing life, and less vibration than standard-efficiency motors.
Caution: Some premium-efficiency motors draw a higher startup current. Make sure your system can handle it.
• If you put in a new system, be aware that an 1,800-rpm motor is more efficient than a 3,600-rpm motor. For example, an open, drip-proof, 3,600 rpm, 40-horsepower motor is 91.7 percent efficient, whereas an 1,800-rpm, 40-horsepower motor is 93 percent efficient. Since 1,800 rpm motors make half the revolutions of 3,600 rpm motors, maintenance needs are lower and motor life is longer.
• Consider a variable speed drive (also sometimes called a variable frequency drive) if you need to produce a wide range of flows and pressures to meet varying system needs. For example, a pump serving three pivots and equipped with a variable speed drive could run at slow speed with one pivot turned on, at a higher speed with two pivots turned on, and at full speed with all three pivots turned on. Steep terrain and the use of corner “swing arms” on pivots also cause changing flow and pressure requirements and sometimes justify the cost of a variable speed drive. Whether this investment is cost-effective for your situation depends on operating hours, pump size, and crop value, among other factors.
• Constant-pressure valves or flow-control nozzles may be a lower-cost alternative to a variable speed drive, although they are less energy-efficient. Contact your equipment supplier for more information.
You can also make improvements to engines, pumps, mainlines, sprinkler systems, and more to further increase your efficiency. Learn more about a host of strategies in the ATTRA publication Energy Saving Tips for Irrigators. This publication describes recommended irrigation system installations, explains how utilities charge their irrigation customers for electricity, and describes common causes of wasted energy, as well as common energy-saving hardware improvements. It also includes a do-it-yourself method to estimate the efficiency of electrically powered irrigation systems.