Cogeneration, often referred to as Combined Heat and Power, represents the simultaneous production of electricity and heat from a single energy source, in an integrated system, in order to either maximize energy efficiency (which can reach 90% or more) and tap as much energy as possible from the primary fuel. Cogeneration therefore offers energy savings ranging between 15-40% when compared to the separate supply of electricity and heat from conventional power stations and boilers; all this translates into:
increased efficiency of energy conversion and use: cogeneration is the most effective and efficient form of power generation;
lower environmental emissions, in particular CO2, one of the most harmful greenhouse gas: cogeneration is the single biggest solution to the Kyoto targets;
large cost savings, providing additional competitiveness for industrial and commercial users, and offering affordable heat for domestic users;
an opportunity to move towards more decentralized forms of electricity generation, where plants are designed to meet the needs of local consumers, providing high efficiency, avoiding transmission losses and increasing flexibility of system use;
improved local and general security of supply – local generation, through cogeneration, can reduce the risk of consumers being left without supplies of electricity and/or heating. In addition, the reduced need for fuel resulting from cogeneration reduces import dependency.
(source: Cogen Europe – http://www.cogeneurope.eu/what-is-cogeneration_19.html)

Cogeneration is quite popular in certain countries, where large plants (>1 MW) have been serving industries and communities, providing decentralized heat and power. The vast majority of CHP plants use combustion of traditional fossil fuel such as coal, oil or LNG, being such conversion technology a proven and reliable one; nevertheless, higher CO2 savings and less fuel cost can be reached using alternative technologies (like gasification) and non-fossil fuels such as biomasses, vegetable oil, biodiesel, ethanol, or through the exploitation of fuels originating from biological degradation processes such as biogas (from anaerobic digestion), landfill gas and so forth. These technologies, including biomass gasification, have been improving also at smaller power ranges, till reaching a proper reliability degree.
Energy production from renewable, non-fossil fuels, has been boosted over the last years by a number of support scheme policies, feed-in tariffs, green certificates and tax rebate for investment in this direction, with the goal of reducing GHG emissions and help combating climate change, beside promoting distributed power generation and reduce electric power distribution costs.
Cogeneration can evolve into Trigeneration and Quadrigeneration whenever other outputs are tapped, such as cooling, biochar and CO2. An example of this is represented by CO2 demanding industries like breweries, food and beverage (for example Coca Cola) or cement industries; among the most interesting and profitable applications, greenhouses, horticulture and plant nurseries can benefit from using simultaneously the 4 output of a cogeneration system: power, heat, biochar (for soil fertilization) and CO2 for carbonic fertilization, where an increase of the CO2 concentration in the atmosphere boosts photosynthesis, resulting into higher crop yields.