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In September 2020, the European Commission proposed raising the target for reducing greenhouse gas emissions by 2030 compared to 1990 levels from 40% to 55%, in line with the objectives of the Paris Agreement to combat global warming. One of the measures that the commission considers necessary to achieve this is the increase in energy efficiency, through systems such as cogeneration.

What does cogeneration consist of?

Cogeneration is the set of processes in which electrical-mechanical energy and thermal energy are produced jointly from a primary energy source.

In this way, following the principles of the circular economy, almost all the thermal energy produced by the combustion processes is not dissipated into the environment, as occurs with traditional plants, but the heat in the exhaust gases is used to heat water in a recovery boiler.  This boiler produces steam or thermal energy, which in turn can be used in production processes and/or to produce electricity.


Cogeneration plants usually consist mainly of reciprocating engines, gas or steam turbines, which transform the energy contained in the fuel into mechanical energy and waste or exhaust heat. Mechanical energy is usually transformed into electricity with an alternator, and the waste heat can be recovered in the form of water vapor, hot water, thermal oils, and hot gases, as heat transfer fluids and disposed for their thermal applications.

Although cogeneration has always been linked to industrial processes that require a lot of heat in their transformations or “heat-intensive”— food, chemical, or ceramics industries —its installation on a smaller scale has allowed its use in urban centers with a high demand for thermal energy such as residential buildings, housing blocks, sports centers, heated swimming pools, and hospitals.

Cogeneration systems


Depending on the technology used, there are several types of cogeneration: 

  • Gas turbine cogeneration: On this case, gas, usually natural gas, is used as fuel. The gases produced in the combustion of the raw material are fed into a turbine that transforms the mechanical energy into electricity. The residual energy obtained in the form of hot gases can be reused for the industrial process itself or for other uses.
  • Steam turbine cogeneration: The steam turbine is a turbomachine that transforms the energy of a steam flow into mechanical energy. The main advantage of the steam turbine is that it accepts any type of fuel such as biomass, coal, natural gas, or municipal solid waste.
  • Cogeneration with an internal combustion engine: Internal combustion reciprocating engines convert the chemical energy contained in a fuel product into electrical and thermal energy. The principle of operation of a reciprocating engine is based on achieving the rotation of a shaft by means of linear and reciprocating movements of the pistons. The electrical energy is obtained through an alternator coupled directly to the engine shaft, while the thermal energy is released in the form of exhaust gases and hot water from the cooling circuits. 

Repsol and energy cogeneration

Repsol is one of the largest cogenerators in Spain with an installed power of 660 MW, distributed among its industrial complexes. This highly efficient technology generates part of the heat required for the production processes.

Investment studies are currently underway to adapt them to use synthetic fuels and renewable hydrogen, therefore contributing to the energy transition.