What does an Expanded Electric Grid Look Like in Net-Zero Energy Systems?
This is the third 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).
I have recently written about the variety of solutions leveraged in net-zero energy systems, and the expanded role of electricity in achieving economy-wide decarbonization. In this blog, I unpack the electricity generation mix across the 23 different net-zero scenarios contained within the five net-zero studies evaluated in our meta-analysis.*
What power plants are built in net-zero energy systems?
Studies evaluating least-cost pathways to achieve U.S. economy-wide, net-zero emissions consistently point to considerable growth in low-carbon electricity through a variety of sources and generation technologies.
Wind and solar power dominate generation capacity in all scenarios, increasing significantly to between four to 26 times that of today’s level. Hydropower generation capacity remains largely unchanged relative to today across scenarios. Geothermal power remains at low levels, exceeding 5 GW in only two scenarios. Storage capacity is dominated by batteries across all scenarios. Other storage technologies, such as pumped hydro and compressed air energy storage, have relatively little new deployment. The substantial increase in battery capacity complements the substantial increase in wind and solar capacity, serving to balance the short-duration (hourly, intraday) variability of these resources.
Fuel-based generation — fossil, nuclear, biomass, and hydrogen — provides firm capacity to balance long-duration (multiday, seasonal) variations in renewable generation and electricity demand. Total fuel-based power capacity varies across net-zero scenarios, ranging from 40% to 117% of today’s fuel-based generation capacity. Nuclear power generation is deployed in all net-zero scenarios, except the two scenarios where nuclear sources are explicitly excluded (scenarios 11 and 16). Gas-fired power generation is deployed in every net-zero scenario, even the three scenarios where fossil fuel, and therefore natural gas, is explicitly excluded (scenarios 11, 16, and 22). In these no-fossil scenarios, gas-fired generators leverage low-carbon fuels in the pipeline gas mix.
Why do least-cost pathways to net-zero consistently point to a variety of generation sources?
Different generation pathways have different attributes. This can be highlighted by considering the way in which these various generators are dispatched in net-zero energy systems. The figure below shows the fleet-average capacity factor values for each type of generator in net-zero systems.** Capacity factor values provide an indication of the relative level to which the full capacity of a given generator is used. For example, a capacity factor of 100% would indicate that a generator is used at its full rated capacity (GW) over the entire course of the year. A capacity factor of 50% could indicate that a generator is used at its full rated capacity for half of the year, or it could indicate that a generator is used at 50% of its rated capacity over the entire year, or it could indicate a multitude of other possibilities in between.
Wind and solar are among the lowest-cost pathways to generate low-carbon electricity, and because of this, there is tremendous growth in the deployment of these resources to reach net-zero. However, the wind doesn’t always blow, and the sun doesn’t always shine. These regional, seasonal, intraday, and weather-related variations constrain the achievable capacity factor for these resources in the range of ~40–50% for wind and ~20–30% for solar.
Much of the rest of the electricity mix serves as firm generation to balance variations in energy demand and supply (especially wind and solar) over a range of timescales. Storage technologies offer a cost-effective means to address short-duration variability (hourly, intraday). Fuel-based generation, which leverages the energy stored in fuels and their supporting infrastructure, provides the ability to address long-duration variability (multiday, seasonal). Whereas nuclear and biomass power plants tend to operate as baseload generators (high capacity factors), gas-fired power plants offer flexible operation, providing a cost-effective means to meet peak demands across both short- and long-duration variabilities. While gas-fired generators may be dispatched infrequently (low capacity factors), their peak generation capacity is consistently leveraged across net-zero scenarios with and/or without carbon capture (CC).
Yes, Electricity. Yes, Fuels. Yes, Infrastructure.
Each of these 23 different scenarios have considered least cost pathways to reach net-zero emissions across the entire U.S. economy. Throughout these net-zero scenarios a considerable amount of new power generation capacity is built — especially wind, solar, and batteries. In addition to building these power plants, the electricity transmission and distribution network is greatly expanded. Yes, electricity. Yes, infrastructure.
Fuel-based power generation continues to play an important role in net-zero energy systems. Accordingly, the infrastructure that supports those fuels plays a similarly important role. For example, gas-fired generation is used in all 23 net-zero scenarios. And, the total installed gas-fired generation capacity is similar to today’s levels in most of those scenarios. To provide this power capacity, the pipeline gas infrastructure that supplies these power plants must be maintained at levels similar to today as well. Yes, fuels. Yes, infrastructure.
There is no single solution for net-zero energy systems. Rather, economy-wide, net-zero studies consistently point to a variety of technologies and pathways involving electricity, fuels, and the infrastructure that supports them.
* Net-Zero 2050: U.S. Economy-Wide Deep Decarbonization Scenario Analysis | An Open Energy Outlook: Decarbonization Pathways for the USA | Annual Decarbonization Perspective 2022 | Net-Zero America: Potential Pathways, Infrastructure, and Impacts | Pathways to Net-Zero Emissions
** The fleet-average capacity factors reported here have been calculated by dividing the total generation output (GWh) for a given generator type by its total annual generation capacity (GW) and taking that quotient as a ratio to the total number of hours in a year. All capacity factor data is adapted from Meta NZ, except for today’s simple cycle and combined cycle gas turbine data, which is adapted from EIA data.
