Combined heat and power for industry
How CHP captures the heat that power generation usually wastes, why it must be sized to heat demand, and where it fits as grids decarbonise.
What CHP is and why it can be efficient
Combined heat and power, or cogeneration, generates electricity on site and captures the heat that generation would otherwise waste. A conventional power station throws away most of the fuel energy as low-grade heat; a CHP plant sits next to a heat demand and uses that heat instead of rejecting it. By making both products from one lot of fuel, a well-applied CHP can use a much higher share of the fuel energy than separate generation and a separate boiler.
That high fuel utilisation is the entire point of CHP. It is only achieved if the heat is genuinely used — which is why CHP is fundamentally a heat-led decision, not a power-led one.
Why CHP must be sized to heat demand
The efficiency advantage of CHP depends on the recovered heat being used. If a CHP unit is sized for electrical demand but the site cannot use all its heat, the surplus heat is dumped and the fuel utilisation collapses towards that of ordinary generation — at which point the case largely disappears.
So the cardinal rule is to size CHP to the heat the site can reliably and continuously use, not to its electrical load. The best applications have a steady, year-round heat demand — process heat, hot water, steam or space heating that runs many hours a year. A site with only intermittent or seasonal heat demand is a poor candidate, because the engine would spend much of its time wasting heat.
Heat-to-power ratio and matching
Different CHP technologies produce different proportions of heat and power — their heat-to-power ratio. A good installation matches that ratio to the site's own ratio of heat to electricity demand, so both outputs are used.
If a site needs much more heat than power, a technology that produces relatively more heat fits well. If it needs more power, a different prime mover suits. Profiling the site's heat and electricity demands together — by quantity and by how they vary through the day and year — is the analysis that determines whether CHP fits and which type. Getting this match right is what separates a CHP that pays from one that disappoints.
Prime movers
Several technologies serve as the prime mover that generates the power and the recoverable heat:
- Reciprocating gas engines — common at small to medium scale, with heat recovered from exhaust and engine cooling; relatively more power, lower-grade heat.
- Gas turbines — suited to larger, steadier loads, with high-grade exhaust heat well suited to steam raising.
- Steam turbines — where high-pressure steam is generated and power is taken from it on the way to a lower-pressure process use.
- Fuel cells — an emerging option offering high electrical efficiency and clean operation.
The choice follows the scale, the heat grade required and the heat-to-power match, not a single best technology.
CHP on a decarbonising grid
The case for fossil-fuelled CHP has historically rested on displacing both boiler fuel and grid electricity that was itself largely fossil-generated. As grids add low-carbon generation, the carbon benefit of generating power on site from natural gas weakens, because the grid electricity it displaces is getting cleaner.
This does not make CHP obsolete, but it changes the analysis. Routes that keep it relevant include running CHP on low-carbon fuels such as biomethane or hydrogen, using it where on-site heat demand is genuinely high and continuous, and valuing its role in resilience and in supporting the grid. The decarbonisation question — what fuel, and how clean is the grid it competes with — now belongs at the centre of any CHP assessment.
How to assess CHP for a site
A disciplined assessment follows the heat:
- Reduce demand first — recover waste heat, fix combustion and insulate hot surfaces — so CHP is sized to a real, lean heat load.
- Profile heat and electricity demand together, by quantity and by how steady they are.
- Size to the continuous, usable heat demand, never to the electrical load alone.
- Match the prime mover's heat-to-power ratio and heat grade to the site.
- Test the carbon case against the current and future grid, and consider low-carbon fuels.
Where a site has a large, steady heat demand, CHP remains one of the most efficient uses of fuel available; where it does not, the heat is wasted and the case falls away.
Frequently asked questions
Why can CHP use fuel so efficiently?
Because it captures the heat that power generation normally wastes and uses it on site. By producing both electricity and useful heat from one lot of fuel, a well-applied CHP uses a much higher share of the fuel energy than separate generation and a separate boiler would.
Should CHP be sized to electrical or heat demand?
To heat demand. The efficiency advantage depends on the recovered heat being used, so a unit sized for power that cannot use all its heat dumps the surplus and loses the benefit. The best applications have a steady, year-round heat demand.
What is the heat-to-power ratio and why does it matter?
It is the proportion of heat to electricity a CHP technology produces. Matching it to the site's own ratio of heat to power demand ensures both outputs are used. A mismatch means either heat or power is wasted, undermining the economics.
Does CHP still make sense as the grid decarbonises?
It depends. As grids add low-carbon generation, the carbon benefit of generating power on site from natural gas weakens. CHP stays relevant where heat demand is high and continuous, on low-carbon fuels such as biomethane or hydrogen, and for resilience, so the fuel and grid context must be central to the assessment.
Related guides
Waste heat recovery in industry
Where industrial waste heat hides, the technologies that capture it, and how to judge whether recovery pays at your site.
Factory decarbonization: a practical roadmap
A sequenced, no-regrets roadmap for cutting industrial emissions — efficiency first, then electrification and fuel switching, then the hard residual.
How to improve boiler efficiency
The practical levers that move boiler efficiency — combustion, blowdown, feedwater, flue-gas heat and standing losses — and how to find them.
How to electrify industrial process heat
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Software that helps
Schneider EcoStruxure
IoT platform for energy and plant resource management.
AVEVA Predictive Analytics
Early-warning analytics for critical process and power assets.
AspenTech (aspenONE)
Process modelling and optimization for heavy process industry.