Energy Glossary

Combined heat and power generation

Combined heat and power (cooling) generation (CHP) is the simultaneous generation of mechanical energy, which is usually converted directly into electricity, and usable heat for heating purposes (district heating or local heating) or for production processes (process heat or cooling absorption plant) in a cogeneration plant. It is therefore the extraction of useful heat, particularly when generating electricity from fuels. In most cases, CHP power plants provide heat for heating public and private buildings or, as industrial power plants, they supply companies with process heat and extract district heating. The release of unused waste heat into the environment is avoided as far as possible. Smaller CHP plants are becoming increasingly important for supplying individual residential areas or individual apartment buildings and even single-family homes, so-called block-type combined heat and power plants (CHP). These can be operated with both fossil and renewable energy sources.

The advantage of CHP is the reduced fuel requirement for the provision of electricity and heat, which greatly reduces pollutant emissions. Funding through the Combined Heat and Power Act (KWKG) and the Renewable Energy Sources Act (EEG) is intended to accelerate expansion.

The spectrum of electrical and thermal output of CHP plants ranges from a few kilowatts to several hundred megawatts. This means that CHP solutions are now available for the entire spectrum of heating requirements.

The typical thermal power plants, which still cover a large part of the electricity demand in Germany, only generate electricity with the heat released from a fuel. If the waste heat is also used, e.g. for process heat or fed into a district heating network, these are called CHP plants; they have a higher degree of utilization. While purely electricity-generating plants achieve efficiencies of between 33% (older plants) and 58.4% (gas and steam combined cycle power plants), CHP plants achieve efficiencies of more than 80% and, in conjunction with low temperature or condensing boiler utilization, even significantly higher. With CHP, thermal energy [kWhth] can therefore be used in addition to electrical energy [kWhel]. However, in the case of cogeneration plants operated with steam as a working fluid - these are usually extraction-condensation plants - this increase in the degree of utilization is accompanied by a reduction in electricity production (lower electrical efficiency). The steam must be extracted before the final turbine stages so that its temperature is sufficiently high for heating. In contrast, in power plants without combined heat and power generation, all the heat is released into the environment via the condenser and the cooling tower. With the Kombi Power System in the GuORC or GuD version, it is also possible to extract high-temperature process heat after the 1st power generation stage.

The high overall savings potential that has not yet been realized in Germany through CHP has prompted legislators to promote CHP in order to overcome market barriers that exist due to the central supply structures that have developed over 100 years.

Sources :

Wikipedia http://de.wikipedia.org/wiki/Kraft-W%C3%A4rme-Kopplung

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