Electrical efficiency

The efficiency of a system in electronics and electrical engineering is defined as useful power output divided by the total electrical power consumed (a fractional expression), typically denoted by the Greek small letter eta (η – ήτα).

If energy output and input are expressed in the same units, efficiency is a dimensionless number.

For example, the heat rate of a fossil fuel power plant may be expressed in BTU per kilowatt-hour.

The term "efficiency" makes sense only in reference to the wanted effect.

Inefficiency probably produces extra heat within the system, which must be removed if it is to remain within its operating temperature range.