Does the use nuclear power help or hinder the use of intermittent renewables in a near-zero-emission energy system? Mengyao Yuana, Fan Tonga, Lei Duana, Nathan S. Lewisb, Ken Caldeiraa aCarnegie Institution for Science, bCalifornia Institute of Technology USAEE 2018 | Sep 24, 2018 I’d like to share with you my work on the relationship between nuclear power and renewable energy in a near-zero energy system

Motivation: perceived tension between nuclear power and renewable energy This study is motivated by the perceived tension between nuclear power and renewable energy such as wind and solar PV While the answer may seem clear to most of you in the audience, there still is much public debate over whether nuclear power, wind, and solar can coexist in a near-zero energy system Some people believe that nuclear power and renewables compete for market share in a carbon-constrained world Some argue that nuclear power could potentially help wind and solar by providing a low-carbon baseload, especially when the sun is not shining and the wind is not blowing

Central question Would increased penetration of nuclear power compete with or facilitate the penetration of intermittent renewables such as wind and solar PV? If driven by cost reduction, nuclear power and renewables tend to substitute each other If driven by increased cost of carbon emissions, nuclear power and renewables could together drive out fossil fuels Motivated by this debate, we ask the following question Our analysis shows that the answer is two-part If driven by cost reduction, nuclear and renewables tend to substitute each other If driven by increased cost of carbon emissions, nuclear and renewables could work together to substitute fossil fuels

Overview of simple energy model Goal: understand fundamental system dynamics Model relies on fundamental physical principles Idealized assumptions: perfect foresight, zero-loss transmission, perfectly efficient energy market Objective function: minimize overall system cost Decision variables Capacity and hourly generation for each technology Simultaneously optimized based on levelized costs To arrive at this answer, we developed a simple energy model Our goal is to understand fundamental system dynamics that are independent of details Model relies on fundamental physical principles such as energy balance We further assume perfect foresight, zero-loss transmission, and a perfectly efficient energy market Capacity and hourly generation for each system component are optimized based on the levelized cost of each technology

Overview of simulations for nuclear vs. renewables analysis System components: natural gas, wind, solar PV, nuclear Natural gas with carbon capture and storage (CCS), constant nuclear generation Data input (detailed in Shaner et al., Energy Environ. Sci., 2018) Aggregated hourly electricity demand for CONUS Aggregated hourly wind and solar availability for CONUS (MERRA-2) Cost and performance assumptions from US Energy Information Administration (EIA, Annual Energy Outlook 2018) Varying costs of renewables (wind + solar) and nuclear Fixed and variable costs are varied together System cost optimized hourly for one year (2015) We performed simulations for a wide range of cost and technology assumptions For the purpose of this talk, we consider a system consisting of natural gas, wind, solar PV, and nuclear In particular, we assume that natural gas has carbon capture and storage facilities installed, which corresponds to a higher cost for natural gas, and nuclear generation is constant at full capacity The input data are detailed in a recent publication by my colleagues. They include hourly electricity demand for the US and historical wind and solar data Nate: emphasize reliability; we have used wind and solar data from across the U.S. with no spatial selection or bias to understand the best case of correlation and averaging across the whole continent We used cost and performance assumptions from the most updated EIA estimates In our analyses, we varied both the costs of renewables and costs of nuclear and solved for the optimal system cost hourly for one year

Examples of optimized generation mix 0.5× renewable costs 1× nuclear costs Demand or generation (1 = average demand) Baseline case (NGCC / CCS, constant nuclear generation) Model optimizes hourly generation Plots showing daily average of demand and generation 0.5× renewable costs 0.5× nuclear costs Demand or generation (1 = average demand) 0.5× renewable costs 0.25× nuclear costs This plot shows an example of the optimized generation mix for a year Generation is optimized for each hour but is shown here as daily averages At these cost assumptions, the system consists mostly of wind and natural gas with a small amount of solar – wind generation is curtailed at times with low demand – natural gas fills the gap between high demand and low renewable generation As the costs of nuclear decrease, we see more nuclear in the system – nuclear generation is curtailed when demand is low – and natural gas is still needed for peak demand hours As the costs of nuclear further decrease, nuclear becomes the dominant generation source – the system consists of a very small amount of solar – nuclear capacity is sized to meet peak demand, and nuclear generation is curtailed at most times

Optimized generation mix for varying nuclear costs at 0 Optimized generation mix for varying nuclear costs at 0.5× wind and solar costs Nuclear costs (1 = EIA 2018 cost estimates) The same trend is found across an array of nuclear costs In these simulations, we fixed the costs of wind and solar and varied the costs of nuclear from 0 to 1 The plot here shows the optimized generation mix averaged over a year at each nuclear cost Slices correspond to the generation profiles we saw on the previous slide As the costs of nuclear decrease, nuclear pushes out wind, solar, and natural gas to become the dominant generation source When nuclear becomes extremely cheap, the optimized system with the lowest cost consists only of nuclear

Optimized shares of generation mix for all cost assumptions simulated Decreasing renewable costs Wind + Solar Nuclear Natural gas 0.5× nuclear costs 0.5× nuclear costs 0.5× nuclear costs (1 = EIA 2018 cost estimates) Wind and solar costs 0.5× renewable costs We see this substitution relationship when we expand the analysis to vary both the costs of renewables and costs of nuclear Plots show the optimized generation shares of wind and solar, nuclear, and natural gas x-axis shows costs of nuclear varied from 0 to 1, y-axis shows costs of wind and solar varied from 0 to 1 Colormap represents shares in the generation mix At a fixed cost for wind and solar, as the costs of nuclear decrease, the penetration of nuclear increases, and the penetration of wind and solar decreases – the same is true for the other levels of wind and solar costs At a fixed cost for nuclear, as the costs of wind and solar decrease, the penetration of wind and solar increases, and the penetration of nuclear decreases – the same is observed at the other levels of nuclear costs Nuclear costs (1 = EIA 2018 cost estimates) Decreasing nuclear costs

Revisit central question Would increased penetration of nuclear power compete with or facilitate the penetration of intermittent renewables such as wind and solar PV? If driven by cost reduction, nuclear power and renewables tend to substitute each other Possible scenarios where this conclusion can change?  Example: increasing cost of carbon emissions Therefore, in a cost-optimized solution, nuclear and renewables tend to compete with each other This conclusion can change, of course – for example, when the cost of carbon emissions is raised

Demand or generation (1 = average demand) Increasing natural gas costs (~ carbon price) 1× natural gas costs (equivalent) 2× natural gas costs (equivalent) 4× natural gas costs (equivalent) Demand or generation (1 = average demand) 1× renewable costs 1× nuclear costs 0.5× renewable costs 0.5× nuclear costs To illustrate this, we revisit some optimized generation profiles In these plots, the costs of renewables and costs of nuclear are lowered at the same time This is equivalent to raising the costs of natural gas or cost of carbon emissions We see that nuclear and renewables are working together to push out natural gas generation, and the system eventually consists only of nuclear, wind, and solar 0.25× renewable costs 0.25× nuclear costs

Concluding remarks We have presented results of an idealized model that considers a bulk energy market with an ideal grid over a large domain When driven by cost reduction of nuclear power relative to renewables, nuclear power tends to replace intermittent renewable resources When driven by increasing natural gas costs (increasing carbon price), nuclear and renewables could potentially coexist Factors that could potentially change the qualitative results from this model include: Spatial heterogeneity Dynamic evolution of energy system Ancillary service Policy and public perception To summarize, we used a simple energy model to study the relationship between nuclear power and renewable energy in a near-zero energy system We found that when the system is driven by cost reduction, nuclear and renewables tend to compete with each other When the system is driven by emissions reduction, nuclear and renewables could potentially coexist Real energy systems are of course much more complex, and there exist factors that could change our conclusion, such as differences in regional markets, dynamic interactions between technologies, and market and policy feedback

Thank you! Mengyao Yuan Postdoctoral Research Scientist, Carnegie Institution for Science myuan@carnegiescience.edu | @yuan_mengyao

References Shaner, M. R., Davis, S. J., Lewis, N. S. & Caldeira, K. Geophysical constraints on the reliability of solar and wind power in the United States. Energy & Environ. Sci. 11, 914– 925 (2018). US EIA. Electric Power Annual. (Washington, DC, 2017). US EIA. Annual Energy Outlook 2018. (Washington, DC, 2018).

Summary of cases simulated Non-dispatchable nuclear (constant generation) Dispatchable nuclear (flexible generation) Natural gas (NGCC) Natural gas with carbon capture & storage No natural gas NGCC / CCS, Constant nuclear generation NGCC, No NGCC, Flexible nuclear generation Two dimensions for nuclear Three dimensions for natural gas In total 6 cases

Baseline cost assumptions (EIA, 2018) NGCC NGCC/CCS Nuclear Wind Solar PV Technology description Conv gas / oil combined cycle Adv CC with CCS Adv nuclear Solar PV, fixed tilt Total overnight capital cost [$/kW] 982 2175 5946 1657 1851 Fuel cost [$/MMBtu] 3 - Fuel cost [mills/kWh] 7.45 nth-of-a-kind heat rate [Btu/kWh] 6350 7493 10460 9271 Fixed O&M cost [$/kW-yr] 11.11 33.75 101.28 47.47 22.02 Variable O&M cost [$/MWh] 3.54 7.20 2.32 0.00 Project life [yrs] 20 40 30 Fixed cost [$/kW-h] 0.012 0.027 0.062 0.021 0.020 Variable cost [$/kWh] 0.023 0.030 0.025 0.000

Nuclear costs (1 = EIA 2018 cost estimates) Optimized shares of generation Case: NGCC + CCS, constant nuclear generation Wind + Solar Nuclear Natural gas Nuclear costs (1 = EIA 2018 cost estimates) (1 = EIA 2018 cost estimates) Wind and solar costs

Nuclear costs (1 = EIA 2018 cost estimates) Optimized shares of generation Case: NGCC + CCS, flexible nuclear generation Wind + Solar Nuclear Natural gas Nuclear costs (1 = EIA 2018 cost estimates) (1 = EIA 2018 cost estimates) Wind and solar costs

Optimized shares of generation Case: NGCC, constant nuclear generation Wind + Solar Nuclear Natural gas Nuclear costs (1 = EIA 2018 cost estimates) (1 = EIA 2018 cost estimates) Wind and solar costs

Optimized shares of generation Case: NGCC, flexible nuclear generation Wind + Solar Nuclear Natural gas Nuclear costs (1 = EIA 2018 cost estimates) (1 = EIA 2018 cost estimates) Wind and solar costs

Optimized capacity shares of nuclear and renewables (wind + solar) for all cost assumptions simulated Baseline case (NGCC / CCS, constant nuclear generation) Nuclear costs scaled from 1 × 10−8 to 1 (1 = EIA estimates) Wind and solar costs scaled from 1 × 10−8 to 1 (1 = EIA estimates) Renewable costs 1e−8× 0.25× 0.5× 0.75× 1× Nuclear costs 1e−8× 0.4× 0.5× 0.6× 1× Shows color bins rather than lines?

Value of dispatchable nuclear generation Cases: NGCC / CCS, constant vs. flexible nuclear output Relative difference in total system cost Constant vs. flexible nuclear generation Assume as dispatchable as natural gas combined cycles Results represent maximum possible difference (1 = EIA 2018 cost estimates) Wind and solar costs Nuclear costs

Value of dispatchable nuclear generation Cases: NGCC, constant vs Value of dispatchable nuclear generation Cases: NGCC, constant vs. flexible nuclear Relative difference in total system cost Constant vs. flexible nuclear generation Assume as dispatchable as natural gas combined cycles Results represent maximum possible difference (1 = EIA 2018 cost estimates) Wind and solar costs Nuclear costs