Primary and Final Energy
Primary energy by source across scenarios is shown in Figure 15. Where CCS is deployed, the hatched area refers to the captured portion of the carbon contained in the primary resource. The fossil component of primary energy, particularly petroleum and coal, declines over time in all scenarios due to efficiency gains, electrification, and other forms of fuel-switching. Natural gas retains a significant share in the Net-Zero All Options scenario, the majority deployed with carbon capture. Primary supply from low-carbon resources (in particular, renewables, nuclear, and bioenergy) increases significantly relative to today and relative to the Reference Scenario—though the contribution of bioenergy is sensitive to the assumptions around biomass feedstock supply. Because of the significant thermal losses in bioenergy conversion to liquid fuels, total primary energy in the Net-Zero All Options scenario increases relative to the Reference Scenario. In the Net-Zero Higher Fuel Cost scenario, fossil and bioenergy resource use is lower, with higher shares of renewables, leading to lower total primary energy, partly due to the convention of denoting renewable electricity generation using direct equivalent (i.e., primary energy input equal to secondary generation output). In the Net-Zero Limited Options scenario, primary supply from non-fossil sources expands greatly, with 80% of primary energy coming from renewables and nuclear. Total primary energy increases because of the conversion losses associated with hydrogen production and fuel synthesis, despite increased end-use-efficiency in response to higher costs. Note that carbon capture is still deployed with bioenergy, with the captured carbon flow utilized for fuel synthesis, denoted as carbon capture and utilization (CCU).
Final energy declines over time in all scenarios, primarily due to the trends in structural change in the economy, efficiency improvements, and electrification described above in the context of the Reference scenario. As shown in Figure 16, the contributions of efficiency and electrification increase in the net-zero scenarios, resulting in lower final energy and higher shares of electricity. The more restrictive the scenario in terms of supply-side low-carbon technology costs and availability, the larger the contribution of efficiency and electrification.
Figure 17 shows final energy by fuel type across scenarios. The bottom panel of this figure shows final energy organized in terms of liquid fuels, pipeline gas, and alternative energy carriers, as in the Sankey diagrams shown in the Scenario Summaries section. The top panel of Figure 17 provides a complementary view, breaking out delivered final energy in terms of the fuel supply pathway, i.e., fossil, bioenergy, hydrogen and hydrogen-derived fuels, and direct use of electricity. In the Net-Zero All Options Scenario, roughly one-third of delivered final energy is from fossil fuels, around 20% is bioenergy, 5% is hydrogen (produced from natural gas and bioenergy), and 43% is electricity. In the Net-Zero Limited Options Scenario, these shares are significantly different. Fossil represents only 5% of delivered energy, with bioenergy representing 15%, electrolytic hydrogen and hydrogen-derived fuels 21%, and electricity 59%. In this scenario, around 80% of final energy is provided either directly or indirectly by the electric sector. These comparisons illustrate the sensitivity of the potential role and value of hydrogen and hydrogen-derived synthetic fuels (so-called “e-fuels” when the source of the hydrogen is electricity) to assumptions about competing carbon management technologies, namely CCS and bioenergy.