There are several pathways to accomplish the decarbonizing of the U.S. electric grid by 2035, but they all come with their own sets of challenges, according to a new report from the National Renewable Energy Laboratory (NREL).
The report, Examining Supply-Side Options to Achieve 100% Clean Electricity by 2035, examines the types of supply side clean energy technologies and the scale and pace of deployment needed to achieve 100 percent clean – defined as zero net greenhouse gas emissions – power grid by 2035, which NREL says could put the United States on a path to economy wide decarbonization by 2050.
The authors noted that the report comes on the heels of the enactment of the Inflation Reduction Act (IRA), which, with the Bipartisan Infrastructure Law (BIL), aims to reduce economy wide greenhouse gas emissions in the United States to 40 percent below 2005 levels by 2030. The reductions are expected to be more pronounced within the electric power sector with initial estimates of declines of 68 to 78 percent below 2005 levels by 2030. Nonetheless, the authors say the laws are likely not sufficient to bring the country all the way to 100 percent carbon dioxide free electricity by 2035.
In the study, which as done in partnership with the Department of Energy (DOE) with funding support from the DOE’s Office of Energy Efficiency and Renewable Energy, the authors evaluated four core scenarios that were each compared with two reference scenarios, one with current policy electricity demand and the other with higher load growth as a result of accelerated electrification.
The authors noted that the most cost effective pathway to large-scale decarbonization likely involves electrification of buildings and much of the transportation and industrial sectors, as well as “aggressive” energy efficiency and demand management measures. However, they also noted that electrification “will dramatically increase demand, which in turn makes it more difficult to decarbonize the electricity system due to the rate of deployment needed.”
The four core scenarios used in the study are:
- All Options, in which all technologies continue to decline in cost while reaching higher levels of performance, including development and deployment of direct air capture (DAC) technology, which removes carbon dioxide directly from the atmosphere. (The other three scenarios assume DAC does not achieve cost and performance targets needed to be deployed at scale.)
- Infrastructure Renaissance, which assumes improved transmission technologies as well as new permitting and siting approaches that allow greater levels of transmission deployment with higher capacity.
- Constrained, in which additional constraints to deployment of new generation and transmission capacity increases costs and limits deployment of certain technologies.
- No CCS, in which carbon capture and storage (CCS) technologies do not achieve needed cost and performance targets for cost-competitive deployment.
Beyond the four core scenarios, NREL also analyzed 142 additional sensitivities in the study in order to capture future uncertainties related to technology cost, performance, and availability.
None of the scenarios in the study include the IRA and BIL energy provisions, but NREL said their inclusion is not expected to significantly alter the 100 percent systems explored.
In all the core scenarios, the 100 percent requirement is met on a net basis, meaning gross emissions can be offset through negative emissions technologies, such as DAC, that can capture carbon dioxide from the air.
In all scenarios, as much as 5 percent of 2035 generation is from fossil fuel technologies. The All Options scenario includes about 660 gigawatts (GW) of fossil capacity of all types in 2035.
Only the No CCS scenario precludes the use of fossil fuel generation; it also has the greatest use of seasonal storage. In the other three scenarios, fossil generators continue to contribute through 2035, but their emissions must be offset by technologies including DAC and bioenergy with carbon capture and storage. Fossil plants with carbon capture and storage would have to have emissions offsets because their capture rates are assumed to be 90 percent and upstream methane leakage from natural gas production must also be offset.
In all the modeled scenarios, NREL said new clean energy technologies would be deployed at an “unprecedented scale and rate” to achieve 100 percent clean electricity by 2035.
The models call for wind and solar energy to provide between 60 and 80 percent of generation in the least-cost electricity mix in 2035, with overall generation capacity growing to roughly three times the 2020 level by 2035. That would require the installation of between 40 and 90 GW of solar on the grid per year and 70 to 150 GW of wind power per year by the end of the decade. That growth in renewable generation would represent a fourfold increase in the current annual deployment levels of wind and solar power, NREL noted.
Across the four scenarios, 5 to 8 GW of new hydropower and 3 to 5 GW of new geothermal capacity would also need to be deployed by 2035, as well as 120 to 350 GW of diurnal storage, that is, storage capable of discharging from to 2 to up to 12 hours.
Seasonal storage would also have to play an important role in reaching 100 percent clean energy by 2035, NREL said, because there would be a multiday-to-seasonal mismatch of variable renewable supply and demand if clean electricity comprises 80 to 95 percent of generation. Across the scenarios, seasonal storage capacity in 2035 would need to range from 100 to 680 GW, which would require “substantial development” of infrastructure such as fuel storage, transportation and pipeline networks.
In the Constrained scenario, nuclear capacity more than doubles, reaching 27 percent of generation, while limited growth in the other three core scenarios results in a contribution of 9 to 12 percent, largely from the existing nuclear fleet, NREL said.
Differences in energy contribution among the four core scenarios are largely driven by constraints in transmission and renewable siting, NREL said. In all scenarios, a “significant” amount of new transmission would be needed to deliver energy from wind-rich regions to load centers in the eastern United States. Total transmission capacity in 2035 would need to be 1.3 to 2.9 times current capacity, requiring 1,400 to 10,100 miles of new high-capacity transmission lines per year, NREL said.
Technologies being deployed today “can provide most of U.S. electricity by 2035 in a deeply decarbonized power sector,” but achieving a net-zero electricity sector at the lowest cost will take advances in research and development into emerging technologies, including the “potentially important role of several technologies that have not yet been deployed at scale, including seasonal storage and several CCS-related technologies,” NREL said in the study.
In addition, a growing body of research has demonstrated that the cost of transitioning to 100 percent carbon dioxide free electricity increases steeply as the 100 percent mark is approached. The higher costs of the so-called “last 10% challenge” are driven largely by the seasonal mismatch between variable renewable energy generation and consumption, NREL said.
NREL said it has been studying how to solve the last 10 percent challenge, including outlining key unresolved technical and economic considerations and modeling possible pathways and system costs.
“There is no one single solution to transitioning the power sector to renewable and clean energy technologies,” Paul Denholm, principal investigator and lead author of the study, said in a statement. “There are several key challenges that we still need to understand and will need to be addressed over the next decade to enable the speed and scale of deployment necessary to achieve the 2035 goal.”