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| Fig. 1: Diagram of a coal-fired power station, illustrating the process to produce high-pressure steam, which then drives a turbine. (Source: Wikimedia Commons) |
Between 2011 and 2024, the United States electric power sector experienced a dramatic fuel transition driven by quantifiable physical and economic advantages. Natural gas generated 1,870,000 gigawatt-hours (GWh) of electricity in 2024, representing 42.7% of total U.S. power generation, while coal fell to just 652,760 GWh (14.9%). [1] This reverses the situation in 2001, when coal provided 51% of electricity and natural gas only 17%. Coal-fired capacity collapsed from a 2011 peak of 318,000 megawatts (MW) to 172,000 MW in 2025, with utilities planning to retire an additional 27,000 MW by 2028. [2] In 2025 alone, 8,100 MW of coal capacity will retire4.7% of the remaining fleet. The fundamental driver is economics; when adjusted for thermal efficiency, natural gas at $3.01/MMBtu costs $24.11 per megawatt-hour to generate electricity, while coal at $3.37/MMBtu costs $36.37/MWh: a 34% price disadvantage for coal. [3]
Coal and natural gas plants convert thermal energy into electricity but use very different physical systems. A coal plant burns pulverized coal in a boiler to produce high-pressure steam, which drives a turbine connected to a generator through a Rankine cycle. Coal-fired plants require extensive fuel handling infrastructure, including coal storage areas, conveyor systems to transport coal to pulverizers, and pollution control equipment such as electrostatic precipitators to remove ash particles. Plants also need cooling systems to condense steam back into water for reuse, and ash removal systems to handle solid combustion waste. Fig. 1 illustrates this process, showing how coal combustion creates high-pressure steam that drives the turbine-generator system.
Natural gas plants operate differently. In a modern combined-cycle plant, natural gas burns in a combustion chamber, directly driving a gas turbine (Brayton cycle). The hot exhaust gases from this turbine then pass through a heat recovery steam generator (HRSG), which creates steam for a second turbine (Rankine cycle). This two-stage process extracts more useful work from the same fuel. Combined-cycle systems achieve an average operating heat rate of 7,146 Btu/kWh compared with 10,000 Btu/kWh for simple-cycle gas systems. [1] Gas plants are smaller and cleaner than coal plants because natural gas arrives by pipeline and burns completely, leaving no ash or solid waste. They require no coal storage yards, no ash removal systems, and minimal pollution controls.
The carbon emissions differential reinforces the economic case. Coal-fired plants produce 2,257 pounds of CO2 per megawatt-hour, compared to 976 pounds for natural gas plants. This is a 57% reduction, and the difference arises from both fuel chemistry (natural gas produces 117 lbs CO2/MMBtu versus coal's 209 lbs CO2/MMBtu) and thermodynamic efficiency (gas combined-cycle plants achieve 7,731 Btu/kWh versus coal's 10,551 Btu/kWh). [3]
Between 2005 and 2019, total U.S. power sector CO2 emissions fell by 819 million metric tons, with 532 million metric tons (65% of the total) resulting from coal-to-gas switching. [3] Kentucky illustrates this transition at the state level. Kentucky, a state historically reliant on coal as a means of electricity generation, found that state-wide, coal's share of electricity fell from over 90% a decade ago to 67% in 2024, while natural gas surged from 3% to 26%: a nine-fold increase. [1] Kentucky's coal production collapsed from 121 million tons in 2008 to just 24.3 million tons in 2024, an 80% decline. [4] The state's utilities are now planning $2.7 billion in new natural gas combined-cycle plants. [1]
The displacement of coal by natural gas represents one of the largest energy transitions in U.S. history, driven fundamentally by numbers: 532 million metric tons of CO2 avoided, $12/MWh cost advantage at current prices, and 27 percentage points of market share shifted in just 23 years. These quantitative factors explain why coal generation fell from 2,000,000 GWh in 2007 to under 700,000 GWh in 2024. [1] Rapidly, we're beginning to see how the physics of thermodynamic efficiency and the economics of fuel costs are reshaping American electricity generation, with natural gas emerging as the bridge fuel that both displaced coal and enabled renewable energy expansion.
© Anne Liang. The author warrants that the work is the author's own and that Stanford University provided no input other than typesetting and referencing guidelines. The author grants permission to copy, distribute and display this work in unaltered form, with attribution to the author, for noncommercial purposes only. All other rights, including commercial rights, are reserved to the author.
[1] "Electric Power Annual 2024," U.S. Energy Information Administration, October 2025.
[2] "Electric Power Monthly, September 2025," U.S. Energy Information Administration, September 2025.
[3] "Monthly Energy Review, Nobember 2025," U.S. Energy Information Administration, DOE/EIA-0035(2025/11), November 2025.
[4] "Annual Coal Report 2024," U.S. Energy Information Administration, November 2025.