Mitigating California’s greenhouse gas emissions
Williams et al. examine the challenges of mitigating emissions of heat-trapping gases in developed economies, via a case study of California’s goal of reducing emissions 80% below 1990 levels by 2050:
Three major energy system transformations were necessary to meet the target (Fig. 2). First, energy efficiency had to improve by at least 1.3% yr−1 over 40 years. Second, electricity supply had to be nearly decarbonized, with 2050 emissions intensity less than 0.025 kg CO2e/kWh [compared to about 1 kg/kWh for traditional coal power generation]. Third, most existing direct fuel uses had to be electrified, with electricity constituting 55% of end-use energy in 2050, compared to 15% today.
Results for a mitigation scenario including these and other measures are shown in Fig. 1. 28% of emissions reductions relative to 2050 baseline emissions came from energy efficiency; 27% from decarbonization of electricity generation; 14% from a combination of energy measures including smart growth, biofuels, and rooftop solar photovoltaics (PV); 15% from measures to reduce non-energy CO2 and non-CO2 GHGs; and 16% from electrification of existing direct fuel uses in transportation, buildings, and industrial processes….
Some studies suggest that 100% of future electricity requirements could be met by renewable energy, but our analysis found this level of penetration to be infeasible for California (20, 21). We found a maximum of 74% renewable energy penetration despite California’s high renewable resource endowment, even assuming perfect renewable generation forecasting, breakthroughs in storage technology, replacement of steam generation with fast-response gas generation, and a major shift in load curves by smart charging of vehicles. Using historical solar and wind resource profiles in California and surrounding states, the electricity system required 26% non-renewable generation, from nuclear, natural gas, and hydro, plus high storage capacity to maintain operability. It would be possible to forecast higher penetration in cases with a higher resource base and/or much lower energy demand, for example due to lower population growth or lower economic growth….
In our model, the largest share of GHG reductions from EE came from the building sector, through a combination of efficiency improvements in building shell, HVAC systems, lighting, and appliances. EE improvements were complemented by other measures to reduce new energy supply requirements for electricity, transportation, and heating. EE in combination with on-site distributed energy resources in the form of solar hot water and rooftop PV reduced the net consumption of grid-supplied electricity and fuels in new residential and commercial buildings to zero by 2030 (25). Structural conservation in the form of “smart growth” urban planning to reduce driving requirements was responsible for 5% of total emission reductions in 2050….
Achieving the infrastructure changes described above will require major improvements in the functionality and cost of a wide array of technologies and infrastructure systems, including but not limited to cellulosic and algal biofuels, CCS, on-grid energy storage, electric vehicle batteries, smart charging, building shell and appliances, cement manufacturing, electric industrial boilers, agriculture and forestry practices, and source reduction/capture of highGWP emissions from industry (35)….
Because mitigation measures reduce fuel use by investing in energy efficient infrastructure and low carbon generation, a much higher percentage of energy cost will go to capital costs; our model indicates a cumulative investment of $400-500 billion in current dollars (figs. S35 and S36) for electricity generation capacity in the mitigation case, a factor of about ten higher than the baseline case (37)….
The central role of electricity in our results suggests the importance of electricity sector governance as a tool of climate policy, but this has received relatively little attention until recently (47). Although some argue that regulation impedes innovation and increases implementation costs (43), state-level electricity regulation has existing tools for pursuing many climate policy goals, through both market mechanisms and direct regulation: requirements that utilities procure renewable generation, limit carbon intensities, and implement customer energy efficiency and distributed energy programs; and set rates that encourage conservation and electric vehicle charging, internalize pollution costs, and allocate the costs of these policies equitably (7, 48). Given the political challenges of achieving comprehensive federal climate legislation, it is worth further exploring decentralized electricity governance as a climate policy mechanism….
Assuming plausible technological advances, we find that it is possible for California to achieve deep GHG reductions by 2050 with little change in lifestyle (although the potential for lifestyle change deserves further study). The logical sequence of deployment for the main components of this transformation is energy efficiency first, followed by decarbonization of generation, followed by electrification. This transformation will require electrification of most direct uses of oil and gas. In California no single generation technology, RE, nuclear, or CCS, can be used to decarbonize all electricity; a mixed generation portfolio is required. If it is true that the low-carbon path features electricity, then the question is how best to mobilize investment and coordinate R&D and infrastructure roll-out to achieve this end, and what climate policy modalities will be most effective. If the oil economy is replaced by the electric economy, it is instructive to consider the implications of the price of a decarbonized kWh replacing the price of a barrel of oil as a benchmark for the overall economy.
