An Economic Analysis of Rewind, Premium, and Standard Efficiency Vertical Hollow Shaft Motors for Irrigation

Vertical hollow shaft motors are commonly used for vertical turbine pumps for irrigation. They are a specialty motor which has been exempt from the Department of Energy (DOE) requirement for improved energy efficiency. We evaluated the payback and net present value (NPV) of standard efficiency, energy efficient, and premium efficiency motors for motor sizes used in irrigation. For motor sizes between 22 and 56 kW (30 and 75 hp), the NPV and payback analysis indicated that premium efficient motors are more advantageous than standard efficiency. In motor sizes greater than 75 kW (100 hp) standard efficient motors are more cost effective than replacing a motor with a premium efficiency motor. When considering a repair or rewind of a motor, the result is highly dependent on the quality, and the resulting efficiency expected after the repair. If a repaired motor nameplate efficiency could be attained after rewinding and repair, then rewinding is most cost effective. However, if original nameplate efficiency is not attained, then it may be more cost effective to purchase a premium efficiency motor over rewinding. New DOE requirements may be advantageous for irrigators even though capital costs will be higher for new motors.