In a cogeneration system, electricity and useful thermal energy is obtained based on a single fuel.

When generating electricity with a generator or a turbine engine, the efficiency of primary energy fuel is 25% to 35%. The rest is lost. Cogeneration can increase that efficiency up to of 70% to 85%. The key is the re-utilization of waste heat from cooling systems of internal combustion engines to generate electricity.

In a Combined cycle, two thermodynamic cycles co-exist in the same system. The principle upon which is based is to use the exhaust gases at high temperature of the gas turbine for supplying heat to the boiler or steam generator of recovery, which in turn feeds steam to the steam turbine. The main advantage of using the combined cycle is its high efficiency.

In this area there are legal disputes about alleged damages in turbines, boilers, etc.. In the case of cogeneration, there is a strong regulatory component, since the electricity is sold at a feed-in tariff.