ing, and constructing these plants adds additional uncertainty, which can be reflected in the risk premiums for investments in first plants. The successful construction of a suite of evolutionary plants on budget and on schedule in the United States would demonstrate the commercial viability of this technology and enable its wider deployment after about 2020. This is an important option for meeting the projected national need for non-CO2-emitting electricity generation technologies.

The failure to successfully demonstrate the viability of these technologies during the next decade will greatly restrict options to reduce CO2emissions from the electricity sector. In particular, such a failure would remove the options of retrofitting and repowering existing coal and natural gas power plants with CCS, of replacing existing plants with new coal or natural gas plants with CCS units, and of deploying new nuclear plants. The failure to demonstrate the viability of these technologies could also prompt a major shift to natural gas for electricity generation; that is because gas plants can be built relatively quickly and inexpensively and their electricity prices could be more attractive than those of other low-carbon supply technologies such as renewables with energy storage. Unless optimistic forecasts of natural gas availability and price prove correct, however, such a shift could create the same kind of dependence on imports of LNG from outside North America that now exists for petroleum. Moreover, an electric power generation system dominated by natural gas plants without CCS would still emit significant quantities of CO2 compared to renewable and nuclear technologies (Figure 2.15).

It will take decades to achieve deep reductions in CO2 emissions from the electricity sector. Building large quantities of new generation of any technology requires learning, licensing, permitting, and public acceptance. The urgency of getting started on these demonstrations to clarify future deployment options cannot be overstated.

Reducing greenhouse gas emissions from the liquid-fuels-based transportation sector will also require a portfolio approach because these emissions occur in millions of mostly nonstationary sources. As shown in Figure 2.16, the deployments of some alternative liquid fuels—cellulosic ethanol, biomass-to-liquids with or without CCS, and biomass-and-coal-to-liquids with CCS—are estimated to have zero or negative CO2-eq emissions: that is, their production and use do not contribute to atmospheric CO2 and might even result in net removal of CO2 from the atmosphere. The other liquid-fuel options shown in Figure 2.16 have CO2-eq emissions that are roughly equal to, or exceed, CO2-eq emissions from gasoline



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