This section describes how energy would be used in the clean energy pathways. In all cases, population increases by 29% and GDP is 2.2 times higher in 2050 than in 2015, as shown in Table A-1-2 above: both of which would drive up demand if all other things were equal. But all other things are not equal in the clean energy pathways: Each of the pathways includes: (1) increased electrification (including creating intermediate fuels from electricity); (2) higher efficiencies of energy use; and (3) some minor changes from mode shifting in transportation, such as moving cargo from trucks to trains. The rate of change in final energy per unit of constant dollar GDP from 2015 to 2050 is about -2%per year in the High Carbon Reference Case and about -3% per year in the Mixed Resources pathway.
Electrification also often results in higher efficiency, because electricity is more efficient at performing many tasks than combustion. The result is that final or end-use energy demand goes down in all the clean energy pathways compared to both 2015 and the 2050 High-Carbon Reference Case, but primary energy demand goes up compared to 2015 in the High CCS pathway, due to less efficient electricity generation with carbon capture and conversion losses inherent in converting fossil fuels into electricity. Electricity use increases substantially in the clean energy pathways (increasing by anywhere from 50% to 120% in the clean energy pathways compared to 2015, and increasing by 20% to 80% in the clean energy pathways compared to the 2050 High-Carbon Reference Case value). Electricity and electric fuels move from being about one-fourth of final demand in 2015 to more than half of final demand in 2050 for the Mixed Resources pathway, so the shift is substantial. This result is one of the most significant ones from the modeling: The clean energy pathways all rely on electrification of many end uses, especially in the transportation sector, compared to the High-Carbon Reference Case.
The next sections summarize how end-use demand would change in each of the major sectors in the clean energy pathways compared to today’s demand.
Buildings used three-fourths of U.S. electricity in 2015, so efficiency improvements in this sector (combined with electrification as long as there is also an increase in zero- and low-carbon electricity generation), significantly reduce greenhouse gas emissions (see case studies).
The most important uses of natural gas in buildings, space heating and water heating, are almost entirely switched to electricity in all pathways by 2050. This shift means more extensive use of electric heat pumps, which are very efficient at heating and cooling.
Energy efficiency in buildings also increases substantially, with big improvements in lighting, building insulation, heating, cooling, water heating, and other applications. The most important lighting improvement is adopting light emitting diode (LED) technologies, which will become universal well before 2050. Heat pumps bring greater efficiency to space heating, cooling, and water heating, while innovations in clothes washers, dishwashers, and other appliances also bring reductions in energy use.
The industrial sector is less affected in the clean energy pathways than are buildings and transportation. The lower rate of electrification of industry than in buildings (along with smaller efficiency improvements) results in only modest changes in industrial final energy demand compared to reference case levels in 2050.
There is process fuel switching to electricity in some sectors. In iron and steel production, for instance, electric arc furnaces with different iron feed stocks substitute for the coking coal and refinery gas intensive processes common for basic oxygen furnaces. Some heating and steam production is also electrified, but the effects of switching to electricity are much smaller than those for buildings.
End-use efficiency improvements are less important in the industrial sector compared to buildings. That’s because industry has already captured many of the savings from greater efficiency. This sector’s high energy costs—and relative infrequency of the “agency problem” that hinders efficiency investments in buildings—have already led to substantial efficiency improvements. Decision makers in industry are also generally better informed about efficiency options than in the buildings sector.
The clean energy pathways see some direct switching away from diesel fuel in agricultural pumping and construction vehicles, but these effects are relatively small.
The analysis shows that creating a clean energy economy requires major changes in how we use energy in transportation. Those changes include powering vehicles and planes with electricity or cleaner liquid fuels (such as biofuels and hydrogen), adopting new technologies to boost the efficiencies of every type of transportation, and switching from some modes of transportation to others. The magnitude and extent of these changes mean that the transportation sector is the most complicated one in the analysis.
Electrification in particular allows for substantial improvements in efficiency, so that final energy demand for light duty vehicles (LDVs) falls two-thirds in 2050 compared to the High-Carbon Reference Cases. LDVs use most of transportation energy, and more than 95% of them are battery electric vehicles (BEVs), plug-in hybrid electric vehicles (PHEVs), or fuel cell vehicles (FCVs) in all four of the clean energy pathways by the end of the analysis period.
Electrification is also important in transport by rail, but efficiency improvements (rather than electrification or fuel switching) result in reductions in final demand in other parts of the transportation sector (heavy trucks, aviation, rail, medium duty trucking, buses, and military applications, and other uses) of about one-fourth compared to the High-Carbon Reference Case in 2050.
Overall, the electrification of LDVs and efficiency improvements in other parts of the transportation sector dramatically reduce total petroleum use, which falls by 80 to 90% relative to today in the pathways. A large share of the remaining petroleum is consumed as a feedstock for manufactured products, rather than being used as a transportation fuel.
Efficiency improvements in light-duty vehicles come from reducing mass by using stronger, lighter, and more energy-absorbing materials like carbon fiber (see case studies), improving aerodynamics, and switching to electric or fuel cell power trains. Fuel economy in traditional internal combustion engine vehicles also improves substantially. Hybrid power trains bring greater efficiency to medium-duty trucks and buses. Other efficiency improvements are important for aviation and rail.
Heavy-duty trucking and aviation could rely more on biomass-derived fuels, though the challenges of making such biofuels cost-effectively remain daunting (see case study, Sec. A-4). Alternatively, trucks and buses could switch to electric power from batteries or hydrogen-based fuel cells15.
The analysis did not explicitly model changes to the urban landscape, land use patterns, the pace of smart growth development, or travel demand management that would shift the modes of transportation or reduce vehicle miles traveled (VMT). The High-Carbon Reference Case assumes a 14% increase in light-duty vehicle VMT per capita, which corresponds to the trends embodied in the AEO 2015 forecast. If VMT per capita does decline due to land use changes or mode shifts, however, achieving a clean energy economy would be easier than shown in the analysis.