Constructing the direct fuel scenario

Fuels used for purposes other than electricity generation, called "direct fuel use" accounted for 65% of the primary commercial energy used in the world. Direct fuel use includes the coal, natural gas, and petroleum that are used for transportation, industrial process heat, space heat, and other purposes. The demand for fuel increases only 31% between 1990 and 2050, compared with a 265% increase in electricity demand, based on the IPCC accelerated policies scenario [50]. However, the share of primary energy accounted for by the direct use of fuel in 2050 is 61%, only slightly less than at present, owing to both the expected higher efficiency for generating electricity and the losses incurred in manufacturing synthetic liquid and gaseous fuels.

In constructing the renewable-intensive scenarios, particular attention is paid to liquid and gaseous fuels. The demand for liquid fuels used directly, which accounted for more than half of the fuel used, is projected to increase about 11%, driven largely by growth in the transportation sector, which accounted for 60% of all petroleum consumption. The demand for gaseous fuels used directly, which accounted for about a quarter of direct fuel used, is projected to double by 2050. The principal candidates for transportation fuels from renewable sources are ethanol, methanol, hydrogen manufactured from biomass, and hydrogen manufactured by electrolysis of water (fuel cells) using renewable sources of electricity.

Measured in energy terms (dollars per gigajoule) all these fuels will probably cost more to produce than petroleum-based transport fuels in the early years of the 21st century. However, as in the case of renewable electric technologies, the economic viability of each of these fuels will be determined in the context of the system in which it is used. When an alternative fuel is considered as part of a system designed and optimised for that fuel, the economic performance will often be much better than the case where the alternative fuel is simply substituted for, say, gasoline in an internal-combustion-engine vehicle optimised to run on gasoline.

New transportation systems are likely to emerge that involve both new fuels and new vehicle types. The economic and environmental merits of alternative systems will be judged on the basis of the costs and environmental impacts of providing transportation services with alternative combinations of fuels and vehicle types.