U.S. Department of Energy - Energy Efficiency and Renewable Energy

Federal Energy Management Program

Combined Heat and Power Basics

Combined heat and power (CHP), also known as cogeneration, provides thermal energy for buildings or processes while simultaneously generating part of the electricity needed at the site. It is the sequential production of two forms of useful energy from a single fuel source. Numerous applications for CHP exist.

Benefits

In combined cooling, heat, and power systems, fuel consumed in the prime mover (typically a turbine, microturbine, engine, or fuel cell) produces mechanical power and waste heat. The mechanical power turns a generator, creating electricity; and the waste heat is used in some type of thermal process.

Process flow for a typical CHP system leverages heat created during electricity generation to decrease facility electricity demand.

A CHP system recovers heat from electricity generation for productive uses such as heating, cooling, dehumidification, and other processes. This heat is usually wasted at conventional power plants. Because the electricity is generated near the point of use, it is subject to fewer transmission losses than electricity supplied by distant central power plants. For these reasons, properly designed CHP systems can be more than twice as efficient as the average U.S. fossil fuel power plant. Growing numbers of Federal facilities are turning to CHP technologies to gain greater control, reliability, supply quality, and flexibility in their power systems, as well as to cut costs and to meet Federal energy efficiency and emissions reductions goals.

The conversion of fuels to electricity produces large quantities of waste heat as a by-product, which conventional power plants simply reject to the environment. There has been an upsurge in interest in fuel-efficient distributed energy resources such as CHP among project developers, Federal facility managers, and policy makers because these systems help mitigate some key power sector constraints. For example, CHP systems decentralize power generation to locations near facilities having thermal requirements that can be met with waste heat. Also, CHP systems are potentially 70% to 85% efficient in utilizing fuels. They can also meet increased energy needs, reduce transmission congestion, increase power quality and reliability, and increase the energy security of a facility.

In a traditional central station power plant, approximately 32%-56% of the energy going into the plant is turned into electricity; the remaining 44%-68% is lost in thermodynamic and equipment inefficiencies. Subsequently, transmission and distribution of the electricity results in 8% losses, so the total efficiency of the central station power plant is about 30%-51%. Conversely, a CHP system results in 15%-35% generation losses with 40%-50% of the waste heat recovered and used in a thermal process on-site. This results in much higher total efficiencies, around 70%-85%.

CHP systems recover usable heat and avoid transmission and distribution losses to potentially deliver total efficiencies of 70% to 85%.

CHP is commercially available today. It offers extraordinary benefits in terms of energy efficiencies and emission reductions. CHP can also facilitate a transition to cleaner fuels of the future (e.g., hydrogen) that would use the same infrastructure as combined heat and power.

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Technologies

CHP systems combine on-site power generation with the recovery and use of waste heat for making steam, heating or chilling water, or compressing air. Systems can use a number of technologies to generate power and use recovered heat to drive heating and cooling equipment, such as absorption chillers and desiccant dehumidifiers.

The following DER technologies are described across the Department of Energy (DOE) Industrial Distributed Energy Web site:

  • Turbines
  • Microturbines
  • Fuel Cells
  • Reciprocating Engines
The quality (or temperature) of the recoverable energy from a CHP system dictates the types of technologies appropriate for that application. For example, at 180 degrees F, internal combustion engines and residential PEM fuel cells are the most appropriate DG technologies, while single-effect absorption chillers and desiccant technologies are the appropriate thermally-activated HVAC technologies. Around 360 degrees F, microturbines, fuel cells, and double-effect absorption water-cooled chillers might be used. Gas turbines, solid oxide fuel cells, and triple-effect absorption chillers are appropriate technologies at much higher temperatures—around 600 degrees F to 800 degrees F.

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Challenges

Several challenges to implementing CHP projects in Federal facilities exist, including:

  • CHP technology is not new, but has been applied chiefly in very large industrial systems. The technology for mid-size to large CHP systems (more than 500 kilowatts (kW) in capacity) is well advanced. But each project still requires custom, site-specific applications engineering to design a system from commercial components to assemble in the field. With little experience and even less performance documentation as a guide, Federal facility and energy managers could be hard-pressed to bring a CHP project to life.

  • Interest in distributed energy resources such as CHP has run far ahead of policies and regulations to accommodate them. Technical issues are often elementary compared to obstructing policies and regulations.

  • Lack of capital is a nearly universal obstacle.

FEMP and other partners are addressing these challenges. Read more about CHP challenges and solutions in FEMP: Making CHP Accessible to Federal Agencies (PDF 1.3 MB).

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Resources

The FEMP Accelerated Development and Deployment (ADD) CHP program makes information and technical assistance on CHP technologies available to Federal agencies interested in reducing primary energy use while increasing security and flexibility through on-site power generation.

Through the ADD CHP program, FEMP teams offer a full range of support, technical assistance, and financial guidance for CHP projects. FEMP, other groups in DOE, and the Environmental Protection Agency (EPA) are addressing many of the obstacles to CHP. State public utility commissions, such as those in Texas and California, are leading the way to clarify local regulations for permitting and interconnection.

FEMP can provide expert, unbiased technical assistance specialized in CHP systems to any Federal agency interested in developing a CHP project. FEMP assistance includes:

  • CHP quick screenings for interested Federal sites
  • Site survey and feasibility verification
  • Baseline data collection
  • Fostering of partnerships between Federal sites and private-sector project developers and financiers
  • Design and technical assistance to selected projects
  • Support for addressing policy and regulatory constraints such as siting and permitting, grid interconnection requirements, exit fees, and backup charges
  • Conceptual design verification
  • Component matching verification
  • Sizing verification-thermal/power profiles
  • Technical/price proposal evaluation

If agencies need private financing, FEMP can help identify appropriate partners (e.g., energy services companies or utilities).

The U.S. Combined Heat and Power Association (USCHPA) may also be of assistance in evaluating CHP systems for Federal facilities.

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