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| Fig. 1: Share of cooling in electricity system peak loads across selected countries projected to 2050. The chart highlights the increasing contribution of cooling to peak electricity loads. (Image Source: G. DiBari, after the IEA. [4]) |
>By mid century, the National Climate Assessment projects that the U.S. will experience 20-30 more days over 90°F in most areas. [1] Currently heat causes more deaths annually than any other type of extreme weather disaster, including hurricanes, tornadoes, and floods in the U.S. [2] By 2050, the number of heat related deaths is expected to increase by 70% in U.S. cities with populations over 1 million. [3] On the global scale, the World Health Organization estimates that 250,000 people will die annually from heat related diseases by 2050. [3]
The International Energy Agency (IEA) projects that air conditioning demand will rise to help people adapt to this warmer world. By 2050, the global energy demand for air conditioning is projected to triple. [4]
This is due to the energy intensity of typical air conditioning. Twenty percent of a buildings energy consumption comes from air conditioners and electric fans, which represents 10% of global electricity consumption. [4] As the demand for AC rises, so too will its influence on peak load. Fig 1 shows the IEA's projections for the share of cooling demand in peak load. [4]
Since 2015, major blackout events, which are defined by the U.S. Energy Information Administration to last more than one hour and affect over 50,000 customers, have more than doubled between 2015 and 2021, the majority of which occur in the summer. [5] This rise in electricity load during the summer months, impacted by the increased demand for cooling, is coupled with reductions in generation and transmission capacity during higher temperatures. [6]
During high temperatures, combustion turbines that rely on water cooling become less efficient due to increased cold sink temperatures, which lower Carnot efficiency. As these temperatures rise and the inlet air flow mass decreases, more fuel is required to produce the same level of output, decreasing the efficiency of the power plants. [6]
On a summer day, the capacity of a combined-cycle gas turbine (CCGT) and simple gas turbines (GT) for the Eastern Interconnection decreases by 4.4 GW and 8.3 GW from their nominal value, respectively, due to increased temperatures according to Ke et al. [6] While regional variability impacts these exact values, during a heatwave, generation reductions become more significant. CCGT plants can decrease by 5.5 GW and GT by 10.2 GW. [6] Ke et al. further find that in the Eastern Interconnection the capacity decreases 4.6% for CCGT units and 9.5% for GT units. [6]
Nuclear plants can also be affected by rising temperatures. Due to the reliance on water cooling systems needed to prevent overheating, every 1.8°F increase can reduce output by over 2%, according to Linnerud et al.. [7] For solar generation, the impact of heat varies depending on the semiconductor material used. Typical c-Si cell temperature coefficients range from −0.25% to −0.45% per degree Celsius, excluding degradation rates. Thus, for each degree above industry standard (25°C), the cell efficiency decreases by 0.25% to 0.45%, based on the specific coefficient. [8] These generation losses are further compounded by reduced transmission thermal limits during high temperatures.
Transmission systems are also affected by rising temperatures. Higher ambient temperatures reduce the transmission system's thermal line rating by limiting the line's ability to dissipate heat through convection and radiation. Grid operators consequently lower the current to prevent the line from overheating. In addition, as the conductors heat up, they expand, causing the line to sag. To maintain safe clearance with the ground and prevent damage to equipment, operators may also reduce the power flow through the line. [9] Transformers, which regulate voltage levels across the transmission and distribution system, experience a 1% decrease in efficiency for every 1.8°F increase in temperature. [10] Considering these factors, network losses increase by 1% for every 5.4°F above industry standard. [10] While these values are regionally specific, increasing demand coupled with decreases in generation and transmission capacity even marginally can make the grid vulnerable to outages.
These impacts of rising temperatures on power generation and transmission systems are well-documented. Power generation sources face reduced efficiency under these higher ambient temperatures, while transmission and distribution systems face increased resistance, sagging lines, and reduced transformer efficiency. These capacity reductions, combined with rising electrical loads during warmer weather, emphasize the importance of adaptation measures such as demand-side management programs to prevent outages that can pose risks to public safety.
© Genevieve DiBari. 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] D. J. Wuebbles et al., "Climate Science Special Report," U.S. Global Change Research Program, 2017.
[2] T. Adams-Fuller, "Extreme Heat Is Deadlier Than Hurricanes, Floods, and Tornadoes Combined, Sci. Am. 239, No. 1, (July 2023).
[3] J. Worland, "Why Air Conditioning Is a Life-Saver and a Danger," Time, 10 Jul 18/
[4] "The Future of Cooling," International Energy Agency, 2018.
[5] B. Stone, Jr. et al., "How Blackouts During Heat Waves Amplify Mortality and Morbidity Risk," Environ. Sci. Technol. 57, 8245 (2023).
[6] X. Ke et al., "Quantifying Impacts of Heat Waves on Power Grid Operation," Appl. Energy 183, 504 (2016).
[7] K. Linnerud, T. K. Mideksa, and G. S. Eskeland, "The Impact of Climate Change on Nuclear Power Supply," Energy J. 32, 149 (2011).
[8] L. Xu, Lujia et al., "Heat Generation and Mitigation in Silicon Solar Cells and Modules," Joule 5, 631 (2021).
[9] S. Karimi, P. Musilek, and A. M. Knight, "Dynamic Thermal Rating of Transmission Lines: A Review," Renew. Sustain. Energy Rev. 91, 600 (2018).
[10] S. Aivalioti, "Electricity Sector Adaptation to Heat Waves" Columbia University Law School, January 2015.