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Co-generation and Tri-generation

Co-generation, or Combined Heat and Power (CHP), is the process of simultaneous production of electricity and useful heat. Co-generation has a potential global efficiency of over 80%, compared to typical efficiencies below 40% for traditional coal-fired power plants and approximately 50% for gas power plants.

Source: Association for Decentralized Energy (

There are many co-generation technologies available on the market, for a wide range of resources. The different CHP technologies take departure from various thermodynamic cycles, such as; combustion cycle, steam cycle, gas cycle or combined cycle (gas- and steam cycle).

Source: Association for Decentralized Energy (

Tri-generation, or combined cooling, heating and power (CCHP), use the same co-generation technologies and add electrical- and/or absorption chillers to the process for cooling production. The principle of tri-generation often is integrated into smart grids and district energy systems.

Tri-generation based on a gas engine is illustrated in the following diagram:


Source: HAC Australia (

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Waste-to-energy (WtE) generally refers to the process of producing electricity and/or useful heat from a variety of waste materials. Some waste-to-energy technologies also produce other fuels to be used for various purposes.

The most common and well-developed WtE process is the CHP incineration process, which involves burning waste to recover its energy content, often transferring the resulting chemical energy to water or steam in a boiler to produce power or heat. The most commonly used fuel for this process is municipal wolid waste (MSW); other types of combustible wastes include industrial, clinical, and hazardous waste.

Waste-to-energy processes include the following three types:

  • Thermo-chemical conversion, including incineration, co-combustion, residual derived fuel (RDF) plant, and thermal gasification.
  • Bio-chemical conversion, including bio-ethanol production, biogas production from anaerobic digestion, biogas production from landfills, dark fermentation and photo-fermentation producing bio-hydrogen, and microbial fuel cells.
  • Chemical conversion

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Renewable energy

Renewable energy refers to different forms of energy (i.e., electricity and thermal energy) that are derived from renewable resources, which replenish within a human time scale, and will not run out within a short time horizon. 

There are five main types of renewable energy:

  • Bio-energy, including biomass, biogas and biofuel.
  • Geothermal energy, including high temperature and low temperature.
  • Solar energy, including solar thermal, photovoltaics (PV), concentrated solar power (CSP) and concentrated photovoltaics (CPV).
  • Hydroelectric power
  • Wind power

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