FIGURE 2.15 Estimated greenhouse gas emissions from electricity generation. Estimates are in units of grams of CO2-equivalent (CO2-eq) emissions per kilowatt-hour of electricity produced. Estimates for all technologies (with the exception of coal, coal-CCS, NGCC, and NGCC-CCS) are life-cycle estimates, which include CO2-eq emissions due to plant construction, operation, and decommissioning, levelized across the expected output of electricity over the plant’s lifetime. For coal, coal-CCS, NGCC, and NGCC-CCS, only emissions from the burning of the fossil fuels are accounted for. A 90 percent capture fraction is assumed for CCS technologies. Negative CO2-eq emissions mean that on a net life-cycle basis, CO2is removed from the atmosphere. For example, the negative CO2emissions for biopower result from an estimate that the sequestration of biomass carbon in power-plant char and the buildup of carbon in soil and roots will exceed the emissions of carbon from biofuel production. The life-cycle CO2emission from biofuels includes a CO2credit from photosynthetic uptake by plants, but indirect greenhouse gas emissions, if any, as a result of land-use changes are not included.
Note: CCS = carbon capture and storage; CSP = concentrating solar power; NGCC = natural gas combined cycle; PV = photovoltaics.
Sources: Data from Part 2 of this report and from NAS-NAE-NRC (2009a).
sector will be possible only if existing coal plants and natural gas plants are retrofitted or repowered with CCS technologies or are retired.18 However, retrofitting these plants will require diversion of some of their energy input to capturing and