1. 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

2. 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

3. 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

4. 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

5. 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

6. 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

7. 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

8. 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

9. 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

10. 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

11. 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

12. Thank you!
Mengyao Yuan
Postdoctoral Research Scientist, Carnegie Institution for Science

13. 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 (Washington, DC, 2018).

14. 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

15. 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

16. 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

17. 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

18. 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

19. 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

20. 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?

21. 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

22. 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