The efficiency principle

The principle is conceivably simple and has been known for a long time: Decentralized and flexibly controllable power plant units that make efficient use of the energy source used, not only by generating electricity, but also by making sensible use of the waste heat generated during engine operation. In the design of the energy transition, combined heat and power - CHP for short - is moving into focus as an efficiency technology.

For many, it still sounds like dreams of the future. But for Norbert Zösch, the managing director of the municipal utility in the Lower Franconian town of Haßfurt , it has long been a reality: Since 2017, Städtische Betriebe Haßfurt GmbH has been operating a combined heat and power plant (CHP) that can utilize regeneratively produced hydrogen in its pure form and convert it back into electricity in a highly efficient manner. The fuel comes from the company's own power-to-gas plant, which stores surplus wind power as hydrogen via electrolysis. The project, developed by 2G Energy AG and accompanied scientifically and technically by the Institute for Energy Technology at OTH Amberg-Weiden, is the first to implement a hydrogen-based and CO2-free storage chain for renewable electricity in municipal practice.

The example shows that cogeneration is used in large power plants - as well as in decentralized plants in the medium and small power range. Smaller CHP plants in particular can be excellently adapted to the needs of the respective operator - also because the principle is independent of the energy source. Currently, most plants are still operated primarily with natural gas or biogas. In the future, sewage gas, mine gas, hydrogen and possibly synthetic fuels will enable largely climate-neutral operation to close generation gaps.

CHP in application

In terms of numbers, combustion engine CHP plants are the most widespread. They are available with electrical outputs of a few kilowatts (mini CHP) to several megawatts in many different variants on the market. In the low power range, industrial engines derived from large-scale production are generally used. In the medium power range above 250 kW, on the other hand, engines optimized for CHP applications or developed from scratch are increasingly being used.

At the same time, storage technologies are increasingly making it possible to decouple power and heat generation and thus to operate the plants flexibly. Thus, in addition to heat generation by using waste heat to provide cooling - so-called combined heat, power and cooling (CHP-C) - it is also possible to air-condition buildings and even provide deep-freeze cooling for cold stores. CHP is also becoming increasingly widespread in the provision of compressed air - a field with very high efficiency potential.

The plant of the The company "Ponnath DIE MEISTERMETZGER GmbH" in Kemnath in the Upper Palatinate, which was awarded the Bavarian Energy Prize 2018, impressively demonstrates how combined heat, power and refrigeration can be used to provide a highly efficient supply of electricity, heat, steam and freezer cooling in food production. With the solution implemented jointly with AGO AG from Kulmbach and the Institut für Energietechnik GmbH of OTH Amberg-Weiden, Germany's second-largest sausage manufacturer achieves primary energy savings of around 30 percent and CO2 reductions of around 1,800 metric tons per year at its main site.

Changes in the energy industry

CHP units can be controlled to run on electricity or heat, depending on demand. The longer a CHP can run without interruption, the more efficiently and economically it will run. Since the model of the central generator of electricity or heat is no longer valid here, the regulatory framework must also be adapted.

A review of the past two CHP dates in 2020, including statements by Minister of State Hubert Aiwanger and speakers from 2019, as well as further information, can be found here: