#Trends Over Time

The scenario results presented so far have focused on the configuration of the energy system in 2050 when the net-zero target has been achieved. The modeling also describes the transition path over time, subject to the linearly declining constraint imposed on economy-wide emissions. Technology deployment dynamics depend on several factors, including the increasing stringency of the target, technology improvements over time, and capital stock turnover. Figure 42 shows technology trends over time. The graphs in this figure do not convey relative scale of deployment (vertical axes reflect different units and scales), rather they provide a snapshot of the timing of deployment across scenarios for key decarbonization technologies. A key observation is that the timing of deployment varies across technologies within a given scenario based on relative economics. In the earlier part of the time horizon, emissions reductions strategies with lowest marginal costs are deployed first. As the emissions target becomes more stringent over time, mitigation effort shifts to increasingly costly options. Additionally, assumed cost and performance improvements over time change trade-offs between technologies and create new opportunities.

In the electric sector, wind and solar capacity increases steadily throughout the time horizon, accelerating in the Limited Options case to support hydrogen production from electrolysis. Conventional gas capacity also increases over time in all scenarios, as it transitions from high to low capacity factors will providing firm balancing for increased renewables. Gas with CCS begins to deploy by 2030 and increases further as the target tightens in the scenarios where it is available. In the Limited Options scenario, new nuclear capacity also comes online by 2030 and continues to grow. Hydrogen-fired capacity does not deploy until after 2035 in the Limited Options case, when rising prices of CO₂ and falling costs of electrolysis make it competitive with gas as a capacity option.

In the end-use sectors, the deployment of electric vehicles is similarly cost-effective in all scenarios, with the timing of adoption driven mainly by capital stock turnover and modeling assumptions about lags in customer behavior. Heat pump adoption also grows steadily across scenarios, accelerating slightly in the Higher Fuel Cost and Limited Options cases. Hydrogen for used for energy directly at the end-use grows steadily in all cases through 2040, mainly in fuel cell vehicle applications in industrial non-road segments. After 2040 it increases rapidly in the Limited Options case, reflecting shifting economics versus gas as the emissions target and CO₂ price become more stringent. A similar pattern can observed with respect to industrial electrification (not shown in figure).

In the non-electric fuels sectors, hydrogen production begins to shift to gas with CCS (and bioenergy with CCS in the All Options case, not shown) around 2030, gradually displacing conventional SMR production. Electrolysis does not being to deploy until after 2035 in the Limited Options case but grows rapidly afterwards to meeting increasing hydrogen demands in this scenario, particularly from synthetic fuel production. Hydrogen blending does not occur until after 2040 in any scenario, as a relatively high carbon price is needed to make such a substitution economic. Biofuels production begins to increase earlier in the time horizon, but saturates in the scenarios with limited biomass feedstock supply. Renewable natural gas is deployed in small volumes based on the lower cost waste methane pathway, but does not expand in scale to higher cost options until after 2040 and only in the Limited Options case. Finally, direct air capture deploys only beginning in 2050 in the Higher Fuel Cost case, at which point its cost (which is assumed to have declined significantly over time) sets the marginal cost of achieving the target.