17.1 Context: When a Facility Can Use Both Electricity and Useful Thermal Energy
Combined heat and power, often called CHP or cogeneration, is an on-site energy system that produces electricity and captures useful heat from the generation process. A conventional generator converts fuel into electricity and rejects much of the remaining energy as exhaust heat, jacket-water heat, or other waste heat. A CHP system captures that heat and uses it for hot water, steam, process heat, space heating, domestic water, dehumidification, or chilled water through an absorption chiller.
In a power access acceleration project, CHP can be more attractive than simple gas generation when the facility has a meaningful and consistent thermal need. The same fuel can support both electric load and thermal load, improving total fuel utilization and project economics. A food plant may use heat for washing, cooking, drying, or sanitation. A pharmaceutical facility may need steam, hot water, humidity control, and clean-room support. A cold-storage or distribution site may use recovered heat for defrost, domestic water, or absorption cooling. A data center may have limited heat use on-site, but a campus or neighboring user may be able to absorb thermal output.
CHP is not automatically appropriate. The facility needs a thermal host: a real use for the captured heat at the time it is produced. If the heat cannot be used, the system behaves more like an ordinary generation and loses much of its advantage. The best projects have a steady overlap between electric demand and useful thermal demand. Projects become harder when thermal demand is seasonal, intermittent, low-value, too far from the generator, or at a temperature the system cannot supply efficiently.
For executives, CHP should be viewed as a bridge-power option, an energy cost strategy, and a resilience asset. It may help the facility operate before full grid service arrives while also reducing utility bills after permanent service is available. However, it brings complexity: gas supply, emissions permits, heat recovery equipment, piping, integration with boilers or chillers, maintenance, controls, utility standby charges, and long-term operating ownership.
CHP can also change the conversation around bridge duration. If the utility delay is short, a rental generator may be simpler. If the delay is long and the site has durable heat demand, CHP may justify deeper engineering because the asset can keep working after grid service arrives. That long-term usefulness is often what separates CHP from a temporary workaround.
The key question is not simply whether the site needs electricity. The question is whether the site can use both electricity and recovered heat in a way that improves cost, resilience, schedule, and long-term value.
17.2 Methodology: Matching Electric and Thermal Loads, Sizing CHP, Modeling Economics, and Integrating Heat Recovery
The methodology begins by testing whether CHP fits the facility’s load profile. A CHP system is strongest when electric demand and thermal demand occur together for enough hours to justify the equipment, fuel, maintenance, and permitting effort.
Step 1: Define the use case and operating mode. The team should determine whether CHP is intended to support bridge power, peak shaving, continuous baseload operation, backup power, process heat, steam production, absorption cooling, resilience, or long-term energy savings. The intended use affects equipment sizing, control logic, fuel contract, emissions permit, and commercial structure.
Step 2: Build hourly electric and thermal load profiles. The team should compare the facility’s 8760 electric load model with hourly or seasonal thermal demand. Thermal demand may include steam, hot water, process heat, space heating, reheat, drying, washing, defrost, or chilled water. The model should show normal days, peak days, seasonal conditions, ramp-up phases, and minimum viable operation.
Step 3: Identify the thermal host. A thermal host is the process, system, building, or neighboring user that consumes recovered heat. The host must be available when the CHP unit runs. The analysis should confirm temperature, pressure, flow, distance, redundancy, operating schedule, and quality requirements. Heat that is theoretically available but not operationally useful should not be counted in the business case.
Step 4: Determine heat quality and recovery method. Different technologies produce heat at different temperatures. Reciprocating engines may provide jacket-water heat and exhaust heat. Turbines may provide high-temperature exhaust suitable for steam generation. The engineer should determine whether the facility needs low-temperature hot water, high-temperature hot water, low-pressure steam, process steam, or chilled water through absorption cooling.
Step 5: Size the CHP system. CHP may be sized to follow the electric load, follow the thermal load, or optimize total economics. Electric-following systems prioritize power output and may reject unused heat. Thermal-following systems prioritize useful heat and may import more electricity when thermal demand is low. The team should test multiple sizes and phases rather than assume one full-build unit is best.
Step 6: Select the prime mover and heat recovery equipment. The prime mover may be a reciprocating engine, combustion turbine, microturbine, or other generation technology. The heat recovery equipment may include heat exchangers, heat recovery steam generators, hot-water loops, absorption chillers, pumps, controls, and piping. Selection should reflect load profile, available gas pressure, emissions limits, footprint, lead time, maintenance capability, and future expansion.
Step 7: Integrate with existing boilers, chillers, and process systems. CHP should not be designed as a standalone island unless the full plant can operate that way. It must work with boilers, chillers, cooling towers, air handlers, process equipment, water treatment, and controls. The design should define when CHP heat is used first, when boilers supplement it, when chillers operate, and what happens if the CHP unit is offline.
Step 8: Evaluate electrical interconnection and utility rules. The system may operate behind the meter, in parallel with the utility, or as part of a microgrid. The team must address protection, metering, export limits, standby charges, synchronization, islanding, and utility approval. A CHP project can be delayed if the utility interface is treated as an afterthought.
Step 9: Assess gas supply, emissions, and permitting. CHP usually depends on natural gas or another fuel. The team should confirm firm or interruptible gas service, pressure, meter upgrades, pipeline capacity, emissions controls, air permits, noise limits, water requirements, and reporting obligations. The emissions permit may set runtime limits, fuel requirements, or control technology needs.
Step 10: Model economics and risk. The business case should include capital cost, fuel cost, maintenance, avoided electricity purchases, avoided boiler fuel, demand charge reduction, standby charges, emissions compliance, incentives, tax treatment, avoided delay, and residual value. The model should test gas price, electricity price, operating hours, thermal utilization, utility service timing, and equipment availability.
Step 11: Compare ownership and contracting structures. The company may own the CHP system, lease it, buy energy under a service agreement, or contract with a third-party developer. Ownership affects capital approval, maintenance responsibility, tax benefits, performance risk, and flexibility when the permanent utility solution arrives.
Step 12: Plan operations, maintenance, and commissioning. CHP requires active operating ownership. The plan should define who monitors performance, schedules maintenance, coordinates with production, manages gas supply, records emissions data, and responds when the unit trips. Commissioning should test electric output, heat recovery, controls, safety trips, utility interface, boiler integration, and operating modes.
The core deliverable is a CHP feasibility and design basis. It should state use cases, electric load served, thermal host, MW rating, useful thermal output, operating mode, fuel plan, permit path, heat recovery design, electrical integration, cost, schedule, economics, and risks. It should also identify whether CHP is a temporary bridge, permanent asset, or phased investment that supports both power access and long-term operating strategy.
17.3 Skills Required: CHP Engineering, Mechanical Engineering, Process Heat Analysis, Gas Procurement, Environmental Permitting
CHP engineering is the core capability. The engineer must understand prime movers, heat recovery, electric output, thermal output, dispatch, efficiency, maintenance, and integration with utility service. This role determines whether the system should follow electric load, thermal load, or an optimized operating strategy.
Mechanical engineering is essential because the value of CHP depends on moving useful heat to the right place at the right temperature. Mechanical engineers design hot-water loops, steam systems, heat exchangers, pumps, piping, valves, insulation, water treatment, and integration with boilers, chillers, and process equipment.
Process heat analysis is required when the facility uses heat for production, sanitation, drying, cooking, cleaning, sterilization, humidity control, or other operating needs. A process specialist confirms whether recovered heat can meet quality, pressure, temperature, reliability, and timing requirements. This prevents the team from counting heat savings that cannot actually be used.
Gas procurement and infrastructure expertise are needed to confirm fuel availability, pressure, service class, upgrade timing, tariff terms, firm capacity, interruptible risk, backup fuel, and price exposure. A CHP project cannot be banked if the fuel supply is uncertain or unavailable during the operating hours the business case assumes.
Environmental permitting expertise is required because CHP equipment emits regulated pollutants and may also create noise, water, and reporting obligations. The permitting advisor should engage before equipment selection, since technology, size, runtime, and controls affect the permit path.
The team may also need electrical engineering, utility interconnection, controls engineering, EPC management, commissioning, finance, tax, legal, and operations support. Electrical engineers manage paralleling, protection, metering, and standby service issues. Control engineers coordinate CHP output with boilers, chillers, batteries, and facility demand limits.
Finance models spark spread, avoiding costs, incentives, and downside cases. Operations confirms staffing and maintenance capability. Legal reviews utility agreements, gas contracts, performance guarantees, environmental obligations, and vendor responsibilities. The strongest teams can explain CHP in operating terms: when it runs, what it serves, what heat it provides, and what happens when it is unavailable.
17.4 Terminology: CHP, Cogeneration, Waste Heat Recovery, Thermal Host, Absorption Chiller, Spark Spread, and Overall Efficiency
CHP: Combined heat and power. An energy system that produces electricity and captures useful thermal energy from the same fuel input.
Cogeneration: Another term for CHP. It emphasizes the simultaneous production of electricity and useful heat.
Waste heat recovery: Capturing heat that would otherwise be rejected from a generator, turbine, engine, or industrial process and using it for a productive purpose.
Thermal host: The facility, process, building system, or neighboring user that consumes recovered heat. A reliable thermal host is essential to CHP economics.
Absorption chiller: A chiller that uses heat rather than mechanical compression as its primary energy input. It can convert recovered heat into chilled water for cooling.
Spark spread: The economic difference between the cost of electricity and the cost of fuel used to generate electricity. A favorable spark spread improves CHP economics.
Overall efficiency: The combined useful electric and thermal output divided by total fuel input. CHP can have high overall efficiency when recovered heat is fully used.
Prime mover: The main equipment that converts fuel into mechanical or electrical power, such as an engine or turbine.
Heat recovery steam generator: Equipment that uses hot exhaust to produce steam. It is often abbreviated as HRSG.
Thermal following: Operating a CHP system based primarily on the facility’s heat demand.
Electric following: Operating a CHP system based primarily on the facility’s power demand.
Useful thermal output: The portion of recovered heat that can actually be used by the facility or host, after losses and operating constraints.
