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A thermoelectric system that generates electricity using high temperature heat as a primary source of (such as that generated by combustion) also necessarily produces heat at a lower temperature, which is typically released into the environment. When this heat, in whole or in part, is recovered when used by a thermal unit, there is a cogeneration system, which improves the thermodynamic efficiency of the process.

A CHP or cogeneration system, through the combined production of electricity and heat for a given electric and thermal unit, therefore, makes it possible to obtain a primary energy savings of fuel, compared to the separate production of the same quantity of electrical energy and heat. However, this advantage is obtained in relation to an increase in system complexity, which results in an increase of investment costs and the issues dealing with it. For this it is necessary that the energy saving achieved by the CHP system with respect to separate production is significant. There are Italian and European directives that provide the tools to measure the energy performance of a CHP system, through indices of energy saving: IRE index (Energy Saving) defined by Italian resolution 42/02 by the AEEG (Authority for Electrical Energy and Gas); PES index (Primary Energy Saving) defined by Directive 2004/8/EC European Community.

The cogeneration systems have sizes ranging from a few electric kW to a few hundreds of MW and are in the form of different technologies, some are prototypes or demonstration plants (ex. fuel cells, Stirling engines), others available commercially (ex. internal combustion engines, gas and micro-turbines, steam turbines and combined cycles). In addition, cogeneration systems can be powered by fossil fuels (in Italy the most used fuel is natural gas) or renewable energy source (ex. biomass, thermodynamic solar, geothermal).

The objective of RSE activities concerning CHP is the definition of technology, economic and environmental perspectives and the diffusion of small and medium size cogeneration and tri-generation, supported by targeted experimentation. RSE also provides support to public administrations and institutions to define the legal requirements to diffuse these technologies, which are of strategic importance to our country.

Cogeneration and tri-generation plants have been developed and tested in RSE laboratories: a 100 kW electric gas micro-turbine, capable of providing thermal energy to the district corporate heating network or an absorption refrigerator, is electrically connected to the low voltage network of the RSE "test facility for distributed generation", along with organic Rankine Cycle micro-turbine cogeneration fueled by 10 kW electric biomass.

The experiments performed on these systems has allowed us to develop new tools for ad hoc control for better management of these systems and to verify the reliability of the mathematical models that represent these technologies that are developed within the System research.

For other activities the results of experiments on the test facility were used:

 - Models for economic and environmental analysis of tertiary and residential cogeneration applications have been devised and developed
 - Software has been developed that can optimize the energy process of an industrial district, from the definition of the territorial and energy parameters that define the use

RSE has proposed the application of these tools to support initiatives for the development of cogeneration in Italy.