How to Calculate Power Efficiency

Power efficiency is calculated as the expected power output times the actual power output (expressed as a decimal percentage), minus any incidental losses such as priming losses. This calculation can be expressed easily through the linear equation "y = mx - b", where efficiency is "y", "m" is actual output, "x" is expected output and "b" is subtraction of incidental losses. This also can be expressed as the function "f(x) = mx - b". Calculating the overall power efficiency of a system is as easy as substituting some numbers into this formula and calculating the result using simple math.

Instructions

1. Multiply the actual power output percentage, which can be a unit of measurement (such as watts, BTUs or volts) multiplied by the rated or expected power output. For example, if you were testing a computer power supply rated for 1,000 watts with an actual power output of 750 watts you would multiply 1,000 by 0.75.

2. Take the result from the previous calculation and subtract any incidental losses from it. For example, when wiring a generator over a long distance of wire, the amount of power loss due to voltage drop is constant and unchanging. Subtracting this value from the previously calculated value accounts for this loss.

3. Take this final value and compare it to your power efficiency requirements. If it falls below your requirements, a change in the power system may be required. Matters as simple as the power system's environmental temperatures can effect efficiencies and lower a system's performance.

Tips & Warnings

• You can graph this linear equation to get a rough estimate of what variables are needed to set up a power system that is required to meet your power efficiency needs.

References

• Purchon: Example of Efficiency Equations
• Purchon: Alternate Power Efficiency Calculations