The Rankine cycle is an idealized thermodynamic cycle of a heat engine that converts heat into mechanical work while undergoing phase change. The thermal efficiency equals 1 minus the ratio of the low-to-high pressures to the power of 1 minus the reciprocal of the heat capacity ratio.

The efficiency of current high temperature Organic Rankine Cycles does not exceed 24%. Typical steam Rankine cycles show a thermal efficiency higher than 30%, but with a more complex cycle design (in terms of number of components or size).

The water vapor with condensed droplets often seen billowing from power stations is created by the cooling systems (not directly from the closed-loop Rankine power cycle). This "exhaust" heat is represented by the "Q_out" flowing out of the lower side of the cycle shown in the T–s diagram below.

To calculate the Net Power Output, we can take the difference of the work output of the turbines and the work input of the pump: W n e t = W t u r b i n e − W p u m p Thermal efficiency can be calculated using: η = W n e t Q i n Where: Q i n is the total heat input, which is the sum of the heat supplied in the boiler ...