Electricity is the highest-value energy carrier because it is clean at the point of use and has so many end-use applications to enhance personal and economic productivity. It is effective as a source of motive power (motors), lighting, heating and cooling and as the prerequisite for electronics and computer systems. Electricity is growing faster as a share of energy end-uses (Figure 4.18) than other direct-combustion uses of fuels with the result that electricity intensity (Electricity/GDP) has remained relatively constant even though the overall global-energy intensity (Energy/GDP) continues to decrease. If electricity intensity continues to decrease due to efficiency increases, future electricity demand could be lower than otherwise forecast (Sections 4.4.4 and 11.3.1).
Figure 4.18: Ratio of electricity to total primary energy in the US since 1900.
Life-cycle GHG-emission analyses of power-generation plants (WEC 2004a; Vattenfall, 2005; Dones et al., 2005; van de Vate, 2002; Spadaro, 2000; Uchiyama and Yamamoto, 1995; Hondo, 2005) show the relatively high CO2 emissions from fossil-fuel combustion are 10–20 times higher than the indirect emissions associated with the total energy requirements for plant construction and operation during the plant’s life (Figure 4.19). Substitution by nuclear or renewable energy decreases carbon emissions per kWh by the difference between the full-energy-chain emission coefficients and allowing for varying plant-capacity factors (WEC 2004a; Sims et al., 2003a). The average thermal efficiency for electricity-generation plants has improved from 30% in 1990 to 36% in 2002, thereby reducing GHG emissions.
Figure 4.19: GHG emissions for alternative electricity-generation systems.
Electricity generated from traditional coal-fired, steam-power plants is expected to be displaced over time with more advanced technologies such as CCGT or advanced coal to reduce the production of GHG and increase the overall efficiency of energy use. Previous IPCC (2001) and WEC (2001) scenarios suggested that nuclear, CCGT and CCS could become dominant electricity-sector technologies early this century (Section 4.4). Although CCS can play a role, its potential may be limited and hence some consider it as a transitional bridging technology.