(138c) Using and Measuring the Combined Heat and Power Advantage

Combined Heat and Power (CHP), also known as cogeneration, refers to the integration of thermal energy with power generation. CHP plants can be 70% to 80% efficient, and are a major energy conservation technique even when compared to a modern natural gas combined cycle power plant that operates at about 50% efficiency. The typical power plants built by electric utilities are steam plants that are 25 to 35% efficient (new coal plants are also in this range), meaning only about 30% of heat content of fuel is converted to power. Shortage and higher costs of energy resources and the need to mitigate environmental impact make CHP a viable resource even though the plants are usually smaller and more complex. It is the cheapest option for baseload generation as will be demonstrated with examples comparing CHP to coal, natural gas combined cycle, and wind. CHP can be used any place that heat is needed. The systems can be very large to serve the thermal load at a petroleum refinery or petrochemical complex, or small to match the heat load of a building, hospital, university campus, or school. CHP can use any fuel type; natural gas, biofuels, byproducts of agriculture and manufacturing, waste heat from manufacturing processes, and methane gas produced from landfills and anaerobic digesters. A variety of proven, reliable technologies are available to match any application including internal combustion engines, gas turbines, steam turbines, and heat recovery systems. It complements other energy conservation measures to reduce global energy consumption and thus reduce combustion related emissions. CHP currently provides about 8% of the power generated in the US, but there is potential for much more. Increased implementation of effective CHP will benefit not only the host site, but all energy consumers and the public with dramatic energy efficiency and air quality benefits in addition to improving the reliability of energy supply, reducing load on the transmission and distribution system, reducing water consumption, spurring economic development, and meeting potential carbon reduction requirements. CHP has been identified as an important greenhouse gas reduction measure with net economic benefits. The benefits of CHP will only be realized if there is a clear understanding and measurement of those benefits for comparison to other energy options. Unfortunately there is sometimes confusing information about the benefits of CHP. There is no universal standard for reporting the efficiency of CHP systems. This results in both overstatement and understatement of the benefits of CHP compared to other power generation systems. Efficiency is an important metric for use in assessing public policy and as a screening tool for economic analysis. The basis for determining power plant efficiency, and a method for calculating a comparison for CHP called Fuel Charged to Power (FCP), is reviewed. FCP is the energy, net of credit for thermal output, required to produce a kilowatt-hour of electricity. Thermally activated cooling receives credit for the power displaced for producing an equivalent amount of refrigeration. FCP for different types of CHP systems is compared to other types of generation. This provides insight into development of CHP projects that maximize economic and environmental benefits. CHP enhances the benefits of renewable resources because it extends the environmental benefit from the resource and adds more value. Renewable fuel projects are typically less efficient, so CHP provides more economic benefit because there is a higher percentage of useful thermal energy to recover. Renewable generation is generally less efficient than fossil fuel generation due to size and combustion characteristics, which means that there is more benefit from CHP because there is more waste heat available. Examples are presented demonstrating that CHP significantly improves the economics and environmental benefits for biomass to power.