What is CHP?

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Answer by Dale Blundell (Atkins)

CHP (Combined Heat & Power) or Cogeneration, is a system that simultaneously generates electricity and heat from one fuel source on site, giving an overall improvement in efficiency. 

CHP is a principle that is fuel and technology independent i.e. there is no one single fuel or one single technology that defines CHP, for example, a gas fired engine or a biomass boiler with steam turbine can be regarded as combined heat & power plant.

Taking account of the typical efficiency of centralised electricity generation plant, and the additional losses in the transmission and distribution network, the net efficiency of grid supplied electricity will typically be 37-39%.  In addition, heat produced on site is typically provided by boilers with a conversion efficiency of 70-90%.  With a typical mix of electricity and heat, the overall provision of energy (power and heat) from conventional sources may therefore be around 50-60%.

In contrast, by generating electricity close to its point of use and capturing as much waste heat as technically possible, CHP can achieve efficiencies as high as 75%-90%, subject to scale, technology and energy demand.

In addition, on a fuel like basis, by generating on site at these high efficiencies, emissions of harmful greenhouse gas emissions such as carbon dioxide (CO₂) are also reduced. 

In the event that the supply of power from the grid is disrupted.  Properly designed CHP may  be used to provide standby power generation to support some or all of the site’s electrical demand until the mains supply is reinstated.

As the system capacity margin (difference between expected maximum demand and total generation capacity) is squeezed during peak demand periods, the distribution network can come under stress.  Decentralised CHP systems may be employed to help support the shortfall for short peak periods, provided triggers/rewards are in place for so doing for plant operators.