Combined heat and power (CHP), also known as cogeneration, produces both electricity and thermal energy on-site, replacing or supplementing electricity provided from a local utility and fuel burned in an on-site boiler or furnace. CHP systems can be designed to operate independently from the electric grid providing reliable power and thermal energy to keep critical facilities running during grid outages. CHP systems increase energy security by producing energy at the point of use, and are generally 40% to 60% more efficient than non-CHP energy. The deployment of CHP is driven by several factors, including:
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Combined heat and power (CHP) systems are a highly efficient form of distributed generation, typically designed to power a single large building, campus, or group of facilities. These systems comprise on-site electrical generators (primarily fueled with natural gas, but biomass-fed systems may be feasible in some locations) that achieve high efficiency by capturing heat, a byproduct of electricity production that would otherwise be wasted. The captured heat can be used to provide steam or hot water to the facility. Capturing and using the waste heat allows CHP systems to reach fuel efficiencies of 75% or higher, compared to about 50% for the combination of utility-delivered power and an on-site boiler (see Figure 1). This efficient operation is both environmentally and economically advantageous. CHP systems can use the existing, centralized electricity grid as a backup source to meet peak electricity needs and provide power when the CHP system is down for maintenance or in an emergency outage. If the electricity grid is impaired, a properly configured CHP system will continue to operate, ensuring an uninterrupted supply of electricity and thermal services to the host facility. More information on CHP can be found through the DOE's Onsite Energy Program and the EPA's CHP Resource Center.
Figure 1: CHP Efficiency Compared to Separate Heat and Utility Power
CHP technology can be deployed quickly, cost-effectively, and with few geographic limitations. It has been employed for many years, mostly in industrial, large commercial, and institutional applications. There are currently about 4,000 CHP systems installed throughout the country generating nearly 80 GW of electricity. The DOE CHP Installation Database provides information on the location, size, technology, and fuel type of these systems. Figure 2 shows the locations of U.S. CHP installations.
Figure 2. Locations of U.S. CHP Systems
In addition to current CHP installations, a DOE CHP Technical Potential Report identifies the estimated market size for CHP in the United States, constrained by only technological limits. The report outlines market drivers for future CHP growth and identifies CHP technical potential for 20 industrial and 24 commercial/institutional application types by state and estimated CHP system size range.
- Reciprocating engine with heat recovery unit
- Microturbine with heat recovery unit
- Combustion turbine with heat recovery steam generator
- Boiler with steam turbine
Figure 3. Combustion Turbine or Reciprocating Engine with Heat Recovery
In the configuration shown in Figure 3, the engine or turbine combusts fuel (typically natural gas, oil, or biogas) to generate electricity while heat is recovered and converted into useful thermal energy, usually in the form of steam or hot water.
Figure 4. Boiler with Steam Turbine
In a boiler/steam turbine CHP configuration, fuel is burned in a boiler to produce steam, which is then used to generate electricity and useful thermal energy for the host facility. Boilers can use a variety of solid, liquid, and gaseous fuels.
The DOE CHP Technology Fact Sheet Series can provide more information on individual CHP technologies and a comparison of CHP characteristics for typical systems.
For more information on CHP technologies, project development guides, policy documents, and a variety other resources, please visit the Distributed Generation for Resilience Planning Guide Resource Library page.