Why are operating hours decisive when deciding to switch to a high-efficiency motor?

A motor with higher efficiency produces slightly fewer losses than the old motor in every hour it runs. This small difference turns into a meaningful amount of energy only when it is multiplied by a large number of hours; that is why annual operating hours are the main multiplier that determines how long the investment takes to pay for itself.

A simple chain of reasoning

The annual energy difference can be thought of roughly as: the difference in power the motor draws from the supply under load × annual operating hours × unit energy price. The power difference is a small number; the unit price is fixed for the plant. That leaves the multiplier with the greatest variability: the hours. Between a single-shift workshop and a plant running around the clock, this multiplier can differ many times over.

What affects the calculation besides hours

• Power: on a large motor, the same proportional difference corresponds to more kilowatts.
• Loading: if the motor is loaded well below its nameplate, the estimated gain must be corrected according to measurement.
• Application: on fans and pumps, system improvements such as speed control instead of throttling can make a bigger difference.
• Condition of the old motor: the real losses of a rewound motor may be higher than those on its nameplate.

What to do on machines that run few hours

On a machine that turns a few hundred hours a year, the energy gain may not cover the difference in purchase price even over many years. For these machines it is more appropriate to base the replacement decision on reliability, dimensional fit and the spare plan. Even so, if the motor has already failed, choosing an efficient model at the moment of replacement means taking on the extra cost at its lowest point.

You can make the comparison with your own hours and power values in the energy saving calculator and review the options on the high-efficiency motor page for applications that run many hours.