Renewable Energy Cannot Substitute for Nuclear:
A Perspective on Meeting Power Generation Needs in Georgia, USA
The often-discussed issue of replacing nuclear with solar or wind is a false choice—solar and wind energy cannot substitute for nuclear energy. With respect to how we should move forward in our energy policy, everyone is entitled to their own convictions, but not their own math and not their own science and engineering.
BACKGROUND ON U.S. NUCLEAR POWER PLANT CLOSINGS
This perspective is focused on the state of Georgia and issues currently being discussed about the expansion of nuclear power in the state. However, some background on the broader issues threatening nuclear power in the U.S. is included as context for Georgia citizens and decision-makers as they deliberate the future of power generation for the state.
The U.S. has announced the closing of 11 nuclear power plants totaling 11,993 MW of power and 100,882,068 MWhrs of actual generation with the most recent being Diablo Canyon (Table 1).
Table 1. Nuclear power plant closings announced in the U.S. with each plant’s respective capacity, annual generation, and year of generation. (Data Source: U.S. EIA)
This is enough electricity to supply:
- The total power generation needs for any one of 37 states, exclusive of Texas, Florida, Pennsylvania, Illinois, California, Alabama, New York, North Carolina, Georgia, Ohio, Arizona, Michigan, and Washington;
- The residential electricity needs for any one of 48 states (excluding only Texas and Florida);
- The residential electricity needs of 23,191,280 U.S. citizens (based on 2015 residential sales of 1,399,883,717 MWhr for 322 million people (4.35 residential MWhr/capita); or
- The overall power generation needs of 8,262,249 U.S. citizens (total U.S. generation in 2015 was 3,930,579,000 MWhrs for 322 million people (12.21 MWhr/capita total power generation needs).
From an emissions perspective, this level of generation has avoided any one of the following CO2 emission scenarios:
- 98.9 million metric tons of CO2 if the power had been generated by coal, or
- 60.9 million metric tons if the power had been generated by natural gas combustion turbines or
- 41 million metric tons if the power had been generated by natural gas combined cycle.
The predominant reason for the announced closings is economics and most if not all of the plants are located in merchant markets. However, with carbon emission reductions and global climate issues being such a great concern, the loss of this much zero-carbon power generation is deeply concerning given the reality that this generation must be made up with some other resource. The most often proposed non-hydro, zero-carbon options are solar and wind while the quickest and cheapest option is natural gas, but both have shortcomings compared with nuclear. As the state of Georgia is currently in a position to expand its nuclear base, this presents an opportunity to offer some perspective based on a comparison of these power generation options for Georgia and address the issue of whether solar or wind can be considered as substitutes for nuclear power.
POWER GENERATION PROFILE: GEORGIA AND THE U.S.
The resource portfolios and 15-year trends for the electric power sector (utilities and independent power producers) in Georgia and the U.S. are given in Figures 1a and 1b and Table 2. Recent trend data for 2015 and 2016 year-to-date (YTD) are given in Figures 2a and 2b and Table 3.
Long-term Trends: 15-Year Period from 2001-2015
The most relevant resources are presented here, those being coal, natural gas, nuclear, hydroelectric, utility-scale solar PV, wind, biomass/wood and geothermal. The focus is on coal, natural gas, nuclear, solar PV and wind as they represent the resources that will likely undergo the greatest change over the next 20-30 years.
Figures 1a and 1b. 15-year trend for power generation by resource for the electric power sector in Georgia and the U.S. This is limited to utilities and independent power producers. (Data Source: U.S. EIA)
Table 2. A comparison of the respective percent shares of power generation resources for Georgia and the U.S. over the 15-year period from 2001-2015. (Data Source: U.S. EIA)
Observations of 15-year trends:
- From 2001 to 2015, power generation in the U.S. and Georgia shifted from predominantly coal to a more evenly distributed portfolio of coal, natural gas, and nuclear, with renewables comprising the remaining share;
- Georgia transitioned from a coal/gas/nuclear percent share of 65.1/2.9/29.9 in 2001 to 29.9/40.2/27.4 in 2015, compared with the U.S. which transitioned from a 52.6/15.5/21.5 percent share in 2001 to 34.2/31.6/20.3 in 2015;
- Solar constituted 0.7% of U.S. power generation in 2015 and 0.1% of Georgia’s power generation;
- In Georgia, nuclear accounts for 88.4% of the overall zero-carbon generation (down from 92.6% in 2001), whereas for the U.S. nuclear accounts for 59.4% of overall zero-carbon generation (down from 73.4% in 2001);
- Hydroelectric generally held steady for both Georgia and the U.S. from 2001-15;
- The U.S. increased its overall zero-carbon resource base by 4.9% from 2001-15 whereas Georgia’s decreased 2.3% during the same period;
- A notable change in zero-carbon resources in the U.S. came from wind generation, which increased from a 0.2% share in 2001 to a 4.9% share in 2015.
Recent Trends: 2015 and 2016 YTD
Figures 2a and 2b. Recent trends (2015 and 2016 YTD) for power generation by resource for the electric power sector in Georgia and the U.S. This is limited to utilities and independent power producers. (Data Source: U.S. EIA)
Table 3. A comparison of total generation and respective percent shares of power generation resources for Georgia and the U.S. for 2015 and 2016 YTD. (Data Source: U.S. EIA)
Observations of recent trends:
- Solar PV power generation in Georgia increased from a 0.1% share in 2015 to 0.5% for 2016 YTD while in the U.S. it increased from 0.7% to 0.8%;
- Georgia’s zero-carbon generation for 2016 YTD is at 33.5% (83.6% of which is nuclear), which is up from the 31% level of 2015 and also up from the 32.3% level of 2001;
- Zero-carbon generation in the U.S. is at 40% for 2016 YTD (55% of which is nuclear), which is up from the 34.2% level of 2015 and also up from the 29.3% level of 2001;
- According to EIA-860, the U.S. had 11,924.9 MW of installed solar PV capacity in 2015, and based on 2015 generation of 25,890,000 MWhr this calculates out to a capacity factor of 24.8%.
- According to EIA-860, the U.S. had 73,395.2 MW of installed wind capacity in 2015, and based on 2015 generation of 190,748,000 MWhs, this calculates out to a capacity factor of 29.7%.
The state of Georgia currently has over 4,000 MW of nuclear capacity in two plants (Plant Edwin I. Hatch and Plant Vogtle) with two new units under construction at Plant Vogtle that will add 2.2 GW. In addition, as part of its 2016 Integrated Resource Plan, Georgia Power Company is considering a 7,000 acre site in Stewart County, Georgia as a potential location for an additional nuclear facility. The property is located on the western side of the state and Georgia Power has already begun preliminary geological and water studies. The property is owned by Southern Company, Georgia Power’s parent company. Consideration of the 7,000 acre site as a potential location for a new nuclear plant has raised the question of whether other options should be considered for building additional capacity in Georgia. In particular, some have proposed that Georgia’s solar resource be developed more aggressively and that the land would serve as a prime location for a large solar PV farm.
To develop a general idea of the pros and cons among available options a brief analysis of four power plant technologies (nuclear, natural gas combined cycle (NGCC), utility-scale solar PV, and wind turbines) is presented here. Initially, each technology is evaluated based on a capacity-equivalent basis of 1,000 MW in order to evaluate costs, land requirements and annual generation on a normalized capacity-equivalent basis. It is conceded up front that a significant amount of preliminary work must be done before initiating construction of a nuclear plant. This is offered only as an overview to compare key characteristics associated with each technology, highlight some of their respective challenges, and begin framing some of the trade-offs and limits associated with each option. Sources for all data used in this analysis are given in the reference section. Results are presented in Table 4.
Table 4. Comparative analysis of nuclear, NGCC, solar PV and onshore wind on a 1,000 MW capacity-equivalent basis. (Data Sources: U.S. EIA; Other Data Sources: See Reference Section)
Observations of capacity-equivalence:
- A 1,000 MW nuclear plant has an annual generation that is 1.64 times that of a 1,000 MW NGCC plant, 2.79 times that of a 1,000 MW offshore wind system, and 3.28 times that of a 1,000 MW solar PV system;
- On a total cost basis, the least cost option is NGCC, followed by onshore wind, solar PV and then nuclear;
- On both a land requirement basis and productivity per acre (GWhr/acre) basis, the best option is NGCC, followed by nuclear, solar PV and wind;
- On a carbon emission basis, only NGCC emits CO2;
- On a cost per MWhr basis, NGCC is the least cost option followed by nuclear, wind and solar PV;
- If the entire proposed 7,000 acre site in Stewart County, Georgia was covered with solar PV, the annual generation would be 2,452,800 MWhrs, which is equivalent to what Plant Vogtle Units 1 & 2 currently generate in about 46 days.
The differences in actual annual generation across the four technologies highlight the inadequacy of using capacity alone as a metric to compare power generation technologies and the extent to which each is contributing to overall power demands. In fact, on a capacity-equivalent basis, these plants are far from operational equivalency as indicated by the differences in their respective annual generation levels.
Since actual power generation must be considered in deciding among technology options, a generation-equivalent analysis was done to determine the installed capacity, land and cost requirements for matching the 8,059,200 MWhr output from a 1,000 MW nuclear plant with a 0.92 capacity factor.
Table 5. Comparative analysis of nuclear, NGCC, solar PV and onshore wind on an 8,059,200 generation-equivalent basis (equivalent to the annual generation of a 1,000 MW nuclear power plant with a 0.92 capacity factor).
Observations of generation-equivalence:
- The total cost for NGCC is less than all other options;
- The total cost for nuclear is less than solar PV and wind and requires less land;
- The land required for matching the output of solar PV to that of a 1,000 MW nuclear plant is greater than that of any other option and would cover the city of Atlanta, Georgia—twice over;
Even though a system can be designed so that each technology quantitatively matches the generation of a 1,000 MW nuclear plant, the systems are not operationally equivalent as daily generation from solar and wind is constrained by the inherent variabilities in resource availability and NGCC emits CO2. Solar and wind are at a particular disadvantage because of their respective capacity factors which are governed not only by inherent characteristics of each technology, but also by the inherent characteristics of nature and resource availability. Solar PV is dependent on irradiance while wind turbines depend on wind speed. Figure 3 and Figure 4 illustrate the daily intermittency of the solar resource in Stewart County, Georgia, the location for the proposed nuclear plant, and the wind resource in the coastal area of Brunswick, Georgia, where wind resource has some potential. These graphs represent inherent characteristics of nature as to the availability of solar and energy resources, which aren’t subject to human manipulation. While enhancements to solar PV and wind turbine technologies can improve efficiencies by capturing a greater share of the resource that’s available, no enhancement to the respective technology can change the natural law that solar and wind are intermittent. Meaning, there are recurring periods of time when these energy resources simply aren’t available and power can’t be generated regardless of installed capacity levels. Moreover this intermittency fluctuates daily, monthly and seasonally.
Figure 3. Solar resource available at the Stewart County, Georgia proposed location (latitude 32.1o, longitude -84.1o). Graph generated using NREL’s System Advisor Model.
Figure 4. Wind resource in Brunswick, Georgia (latitude 31.2o, longitude -81.4o). Graph generated using NREL’s System Advisor Model.
Intermittency is a constraint unique to renewables compared with nuclear, coal, natural gas, and hydroelectricity. Moreover, there are key differences in the storage, flow and dispatchability characteristics of each energy resource and their respective impacts on reliability and availability. Here, the term dispatchability characterizes power generation that can be reduced without a loss of available energy resources or increased on demand up to capacity limits; in other words, the energy resource itself is storable and can be controlled and managed at the power plant. The term storable is in reference to the energy resource itself and not electricity storage (Table 6). In addition, on an operational basis and within the context of climate issues, carbon reduction represents another operational criterion that must be considered in the selection of power generation technologies. It’s also noted that flexibility is included as a desirable and necessary characteristic of natural gas.
Table 6. Operational characteristics of nuclear, coal, natural gas, hydro, solar and wind resources.
Observations of operational-equivalence:
- Nuclear is the only energy resource that can substitute for any of the other resources;
- Coal cannot substitute for nuclear, natural gas, hydro, solar or wind due to carbon emissions;
- Natural gas cannot substitute for nuclear, hydro, solar or wind due to carbon emissions;
- Natural gas cannot substitute for coal due to storability;
- Hydro cannot substitute for nuclear, coal or natural gas due to weather-dependency;
- Solar and wind cannot substitute for nuclear, coal, natural gas, coal or hydro due to storability, weather dependency and dispatchability;
On a capacity-equivalence basis only, any power generation system can be designed to mathematically match another system, meaning that the capacity of a solar PV or wind power generation system can be designed to match the capacity of a nuclear power system. However, this is a wholly inadequate and misleading basis for comparison as power generation systems must also be designed to meet requirements for total generation, reliability and availability as well as the long-term objectives of carbon reduction. Therefore, the overall operational characteristics of each energy resource constrain system design. Consequently, based on capacity-equivalence, generation-equivalence, and operational-equivalence, nuclear energy is the only energy resource that can substitute for any other energy resources, whereas no other energy resource can substitute for nuclear.
The often-discussed issue of replacing nuclear with solar or wind is a false choice. By the laws of nature and the principles of science and engineering that govern power generation, solar and wind energy resources cannot substitute for nuclear energy. With renewables, intermittency is a constraint, not a problem. Problems arise when the wrong approach is taken for the wrong reasons. And the wrong approach is to expand renewable energy capacity to the exclusion of nuclear energy in order to satisfy a misplaced belief that renewables can substitute for nuclear. In particular, solar and wind cannot serve as substitutes or replacements for nuclear; they’re alternatives with alternative operational characteristics. With respect to how we should move forward in our energy policy, everyone is entitled to their own convictions, but not their own math and not their own science and engineering.
POLICY IMPLICATIONS FOR GEORGIA
With respect to zero-carbon power generation, Georgia is at a 31% zero-carbon share which is comparable with the U.S., which is at 34.2%. Since both Georgia and the U.S. have nuclear and hydro capacity, the 3.2% advantage the U.S. has over Georgia in zero-carbon power generation can be attributed to wind power generation, which constituted 4.9% of overall U.S. generation in 2015 and 6.7% for 2016 YTD. This, however, isn’t a broad national characteristic of wind energy in the U.S. as 67% of U.S. wind power generation in 2015 derived from only 8 states (Texas, Iowa, Oklahoma, California, Kansas, Illinois, Minnesota, and Colorado), with 23.6% coming from Texas alone. This trend is holding for 2016 YTD, as well.
It’s noted here again that while wind accounts for 6.7% of U.S. power generation, solar PV accounts for only 0.8%. For a variety of reasons that will not be explored here, wind is outperforming solar PV in the U.S. This is particularly relevant to Georgia because solar PV is the only geographically available renewable energy option in the state that has the potential to be economically feasible. Part of the bottom line here is that Georgia is at a natural disadvantage with respect to zero-carbon renewable energy because geography has picked the winners and Georgia isn’t high on the list, particularly with respect to the non-hydro renewable energy resource that currently leads the nation—wind. Georgia simply doesn’t have the wind resources to leverage at a scale that’s economically feasible.
Capacity Expansion in Georgia: Natural Gas
Power generation in Georgia has shifted from a storable resource (coal) to a flow resource (natural gas). While natural gas is dispatchable, abundant and lower-carbon than coal, it isn’t storable. Therefore, this shift decreases the state’s dependency on storable energy resources and increases its dependency on a flow resource that’s subject to impacts and disruptions from upstream weather conditions. Expanding Georgia’s power generation capacity on natural gas to the exclusion of nuclear will not only continue this trend away from a storable energy resource, but also will expose the state to price-related vulnerabilities likely to emerge from future federal regulatory actions related to carbon. These likely actions being EPA’s Clean Power Plan and a carbon tax. Residential electricity rates in Georgia for April 2016 were 11.16 cents/kWhr compared with the national average of 12.43 cents/kWhr (U.S. EIA), so price must be a key factor of consideration.
Capacity Expansion in Georgia: Solar PV
Increasing solar capacity to the exclusion of increasing nuclear and natural gas capacity would exacerbate the current shift away from storable energy resources by increasing the state’s dependency on a flow resource that not only can’t be stored, but is also intermittent and non-dispatchable. The analysis presented here concludes not only that solar PV cannot substitute for nuclear but also that installing utility-scale solar PV on the entire 7,000 acre site currently under consideration for nuclear expansion would generate only enough power to be equivalent to what Plant Vogtle Units 1 & 2 currently generate in about 46 days. Factual information such as this, which is based on generation-equivalency, should be shared with the general public as this decision is deliberated.
Capacity Expansion in Georgia: Nuclear
Given the state of Georgia’s geographic position with respect to renewable energy options, an unknown regulatory future that’s likely to include federal constraints on carbon emissions and the need to maintain reliability while keeping electricity prices affordable, nuclear energy is the only resource that meets all operational requirements for power generation. Nuclear power will provide a much-needed hedge against unknown regulatory carbon constraints. Therefore, based on operational-equivalency characteristics, solar PV cannot substitute for nuclear and should not be developed without an associated expansion in nuclear. As such, baseload nuclear power should be the foundation for expanding the state’s power generation capacity so that increased levels of renewables can be integrated into the resource portfolio along with the necessary increases in natural gas capacity for flexibility.
The robustness of Georgia’s electric power sector hinges on decisions that will be made over the next couple of years—decisions that must be made while hedging against the likelihood of a carbon-constrained energy future. If the state’s decision-makers don’t take advantage of expanding nuclear capacity now, the opportunity may not be available in the future in time to avoid an over-dependency on natural gas and to prevent the state’s solar resource from being underutilized due to an insufficient baseload of zero-carbon nuclear power to shore it up.
Generation, Emissions, Costs, and Capacity Factors: U.S. Energy Information Administration
- U.S. Energy Information Administration Electricity Data Browser
- Heat Rates
- CO2 Emission Rates
- Capital Costs
- Capacity Factors for Non-Fossil Fuels
- Capacity Factors for Fossil Fuels
References for Land Requirements:
- Nuclear: Nuclear Energy Institute; NEI (Power Plant Footprint)
- Solar: National Renewable Energy Laboratory; NREL Solar PV Land Requirements
- Wind: Tom Gray of the American Wind Energy Association has written, “My rule of thumb is 60 acres per megawatt for wind farms on land.” AWEO
- Natural Gas Combined Cycle: Duke Energy; A conservative estimate based on Duke Energy’s 1,640 MW Citrus County, Florida combined cycle plant that will sit on 400 acres. This calculates as 0.243 acres per MW, but was rounded up to 0.3 acres/MW (Duke Energy Citrus County)
National Renewable Energy Laboratory, System Advisor Model (NREL SAM)