Work out combined cycle efficiency instantly with clear inputs, formula shown and shareable results.
A combined cycle recovers gas turbine exhaust heat in a steam cycle, so total output is the sum of both turbines against a single fuel input. Modern H and J class plants reach 62-64% gross. The steam turbine typically contributes a third of total output at no additional fuel cost.
Combined cycle efficiency
Gross efficiency = (GT output + ST output) / fuel input; net = gross x (1 - auxiliary load)
Heat rate
Net heat rate (kJ/kWh) = 360,000 / net efficiency %
A simple cycle gas turbine throws away exhaust heat at 550-650 C. Recovering it in a steam cycle lifts efficiency from around 40% to over 60% using the same fuel.
Turbine inlet temperature, which is set by blade materials and cooling technology, and the thermodynamic limit of the bottoming cycle. Each generation of hot-gas-path materials has added a point or two.