Select Energy-Efficient Motors

Ever stop to think how many electric motors of various sizes are used on modern farms today?

 

The purchase price for an electric motor is often miniscule compared to the costs for electricity to operate the motor over its lifetime, especially when the motor operates more than one-third of the time. When the time comes to replace an electric motor, always consider making the extra investment in a high-efficiency motor (as compared to standard efficiency). Consider the following example.

 

You need to replace a 5-hp, 3-phase, 1740-rpm, totally enclosed, fan-cooled electric motor with a new 5-hp motor. A premium motor with an efficiency of 90 percent is available for a list price of $994. A standard motor with an efficiency of 82 percent is available for a list price of $722. (Please note that motors are almost always sold at prices below their list prices.) Assuming that the total cost of electricity is $0.10 per kWh and that the motor will be operating half the time throughout the year, can you justify paying the extra $272 for the premium-efficiency replacement motor?

 

The table below provides the annual costs for electricity to continuously operate a one-horsepower electric motor at full load for a range of electricity prices from $0.08 to $0.20 per kWh and for motor efficiencies ranging from 76 to 94 percent. Be sure to note that the electricity cost per kWh in the table refers to the total cost for electricity, including the costs for generation, transmission, distribution, service charges, demand charges, fuel adjustment charges, and taxes. For this example, the annual electricity costs for the premium motor with an efficiency of 90 percent and an electricity cost of $0.10 is $1,815 ($726 x 5 hp x 0.5 operating time). The cost of operation for the standard motor with 82 percent efficiency is $1,992 ($797 x 5 hp x 0.5 operating time). The amount saved each year associated with purchasing the premium motor is $177, resulting in a simple payback of 1.54 years ($272/$177), or just over 18 months. If the price of electricity increases over the next 18 months, then the payback period would be even shorter.

 

An electric motor converts electrical energy to mechanical energy in an efficient manner. It takes the work of about eight people to equal the work of just a one-horsepower electric motor. An electric motor has numerous advantages over a gasoline or diesel engine, including relatively low cost, low noise, no exhaust emissions, generally low maintenance, and easy to start and stop. The electricity to run the motor is a dominant factor for those motors that are run at least one-third of the time. Therefore, it's important to select energy-efficient motors for such applications, even though the initial investment is higher compared to a standard-efficiency motor. Investments that you make today to improve your efficiency will yield returns throughout the life of the motor. Furthermore, investments made today to improve the energy efficiency of your farming enterprise will shield you to a certain extent from escalating prices for energy.