Remember that the annual costs of operating a motor can be several times higher than the original cost of the motor! There are several methods of evaluating the savings resulting from the use of energy efficient motors. The following formulas represent a few simplified methods of calculating energy savings and payback. Although the formulas do not take into account such factors as the detailed electric utility rate schedule, the time value of money, or depreciation, they can be used as a basic screening tool for making comparisons between competitive motors.
For example, if you were comparing a 25 hp energy-efficient standard motor with an efficiency of 91% to another motor with an efficiency of only 88.5%, the energy dollars saved would be calculated as follows:
Assume:
Energy dollars saved = 0.578 kW x $0.06/kWh x 4,000 hrs./yr. = $138.95 per year
On the other hand, if a high efficiency motor was being considered, the annual savings as compared to a typical 25hp motor would amount to $300 per year. Assuming a price differential of $370 between a high efficiency motor and a less efficient model, the time in years to save the added cost of the more efficient motor would be calculated as follows:
(Note: Calculation does not take into account possible increase in power costs, which would result in an even faster payback. Calculation also assumes the motor is fully loaded. Partial loading would result in a longer payback.)
