Advanced Power Generation Systems

1.7 Efficiency Definitions

Efficiency is a major criterion for assessment of systems, applications, and processes of any kind. The term efficiency originates mainly from thermodynamics. The attempt of assessing heat conversion into work led to its initial formulation as the “net work generated per total heat energy input.” This efficiency criterion is based on the FLT, also called energy efficiency. Equation (1.27) expresses the energy efficiency for a heat engine.

The general efficiency expression of a system—as a measure of its performance and effectiveness—is represented by the ratio of useful output per required input

$\eta =\frac{\mathrm{Useful}\mathrm{output}}{\mathrm{Total}\mathrm{input}}$

  (1.66)

If the system is an energy system then its input and output must be forms of energy. Therefore, ...