To Transition to Net-Zero, it’s Helpful to Know What Net-Zero Energy Systems Look Like
This is the first blog in a series examining net-zero energy systems, drawing upon the results of our Meta-Analysis of U.S. Economy-Wide Decarbonization Studies (Meta NZ).
How do we move with speed and scale to transition the U.S. economy to net-zero by midcentury? To begin to answer this question, it’s helpful to understand what net-zero energy systems look like. That’s what we set out to do in Meta NZ, a meta-analysis of prominent U.S. economy-wide, net-zero studies.
This collaborative effort builds upon rigorous modeling results from five independent, industry-leading studies,* bringing together a diversity of perspectives and analytical frameworks. By casting a wide net across some of the most comprehensive and granular studies performed to date, Meta NZ provides data-driven insight into the designs of net-zero energy systems — the common approaches, the range of possibilities, and the areas of differentiation.
I recently convened a few leading experts from the organizations behind these five decarbonization studies for a dialogue on the design of net-zero energy systems. We discussed our shared understanding of these systems and the variety of technologies, pathways, infrastructure, and integration that are leveraged to achieve economy-wide, net-zero emissions. Our conversation echoed a central theme from Meta NZ: consistently, across five independent studies and 23 different scenarios, a variety of solutions in electricity, fuels, carbon management, and efficiency are deployed in net-zero energy systems.
“One of the things that these studies brought to light was that there are multiple feasible technology pathways. We don’t know exactly what the future is going to look like. There is an importance around this diverse technology approach in order to maximize our chances of actually being able to succeed in any of these pathways to net-zero emissions by 2050.” — Lindsey Walter, Third Way
Electricity supplies roughly half of all energy delivered to end-use customers in net-zero energy systems — the other half is delivered in the form of gaseous, liquid, or solid fuels. Electricity is generated from a variety of low-carbon pathways. Wind and solar generation capacity grows significantly across all 23 net-zero scenarios to between 4- and 26-times that of today’s levels. Energy storage technologies, predominantly batteries, are deployed to balance short-duration variability (hourly, intraday). Fuel-based generation, especially from gas, is leveraged to balance long-duration variation (multiday, seasonal) in renewables and demand. Total installed capacity of fuel-based generation is comparable to today in most net-zero scenarios.
“Because wind and solar are so cheap, but also because they are variable, a lot of the rest of the system organizes itself around making use of those resources at the time they are generating electricity.” — Ryan Jones, Evolved Energy Research
Hydrogen arises as a versatile energy carrier in net-zero energy systems, offering the storability and transportability characteristics of a fuel, while emitting no carbon dioxide emissions at point of end-use. Hydrogen production increases sharply in all net-zero scenarios, growing to between 3- and 20-times that of today’s levels. A variety of low-carbon hydrogen production methods are deployed, including electrolysis, natural gas reforming with carbon capture, and biomass gasification. Hydrogen is used in a variety of ways, including direct use for industrial applications and heavy-duty vehicles, blending into the pipeline gas supply, and as a feedstock for fuels and chemicals production, including ammonia and synthetic hydrocarbon fuels.
“We see hydrogen used across a whole host of different sectors — in the areas of transport mostly around shipping or heavy-duty trucking. We also see it being used for synthetic fuel production as well. We see it in a few scenarios for the power sector. And we see hydrogen being used in industry.” — Lindsey Walter, Third Way
Pipeline Gas continues to be leveraged in net-zero energy systems, supporting power generation, and delivering energy to the industrial and buildings sectors across all 23 net-zero scenarios. While the total level of gas consumption declines from today’s levels across most scenarios, the infrastructure throughput capacity remains relatively high to meet peak demands (e.g. peak power generation loads, peak winter space heating demands). The gas composition evolves in net-zero energy systems, with increased levels of low-carbon gas supplied through bioenergy and synthetic pathways (e.g. anaerobic digestion, gasification, methanation), and hydrogen blending.
“Gas infrastructure that can serve both electric and non-electric — for example, building space heating — peak loads, remains important even as the utilization of gas could potentially go down” — Geoff Blanford, EPRI
Liquid Fuels, including liquid hydrocarbons and ammonia, continue to be used in net-zero energy systems as well, serving as transportation fuels and industrial energy feedstocks across all 23 net-zero scenarios. As with pipeline gas, liquid hydrocarbon fuels are increasingly produced through low-carbon bioenergy and synthetic pathways, offering drop-in fuel substitutes that can leverage existing infrastructure networks and mature end-use technologies.
“Fuels are still maybe half of final energy use in the system… as there are some things that are just difficult to electrify, such as air travel for example, or high temperature industrial processes.” — Eric Larson, Princeton University
Carbon Management solutions are integrated throughout net-zero energy systems. Carbon capture and sequestration technologies are coupled with fossil fueled activities (e.g. gas-fired power generation) to abate emissions. Carbon sequestration is also coupled with direct air capture or carbon captured from bioenergy processes, providing a pathway to remove CO2 from the atmosphere. These negative emissions flows balance remaining positive emissions from costly-to-abate activities in other parts of the economy. Captured CO2 is also leveraged as a feedstock to produce synthetic fuels. Across net-zero scenarios, carbon sequestration accounts for up to 2 billion metric tons of CO2 per year. This is a significant scale of deployment given that a total of 5 billion metric tons of CO2 are emitted annually across the U.S. economy today.
“If you look at biofuel with carbon capture and sequestration pathways… you are producing both a fuel and a negative emission offset… having two value streams from this process.” — Geoff Blanford, EPRI
Efficiency improvements drive down energy consumption and associated emissions. Efficiency gains across the variety of ways we source, make, move, store, and use energy are consistently adopted as part of least-cost pathways to reach economy-wide, net-zero emissions.
So, what do net-zero energy systems look like? There is no single solution and there is no single design. Least-cost approaches for net-zero energy systems build upon the energy systems we have today, leveraging a variety of solutions in electricity, fuels, carbon management, and efficiency.
