Water usage in cooling systems for electricity production: an event study of retrofitted coal-fired power plants in the United States

Abstract

Thermoelectric power plants account for approximately 40% of total U.S. water withdrawals each year. In 2022, 48.5 trillion gallons of water were withdrawn for cooling systems in electricity production, of which 962.9 billion gallons of water were consumed and no longer available for downstream use. Conventional steam coal plants, in particular, withdrew 18.3 trillion gallons of water for once-through and recirculating cooling systems in 2022 while contributing to 19.7% of total U.S. net electricity generation. As coal-fueled electricity production becomes less competitive, cases of coal-to-gas retrofits occur to avoid stranded assets. Two retrofitting methods are adopted in practice: coal-fired power plants are repurposed and replaced by natural gas combined-cycle plants, or the boiler of a coal plant is converted to burn natural gas. In this study, we construct panel data and employ an event study framework to examine changes in water withdrawal, water consumption, water discharge, and carbon emissions resulting from coal-to-gas retrofits in the continental United States from 2013 to 2022. Seventeen coal-fired power plants have been replaced with natural gas combined-cycle plants, and 167 coal steam units in 85 plants have undergone coal-to-gas boiler conversions. We find a sharp and sustained reduction in water withdrawal of 40.2–53.9 thousand gallons per megawatt-hour of net electricity produced when a coal plant transitioned to a natural gas combined-cycle plant. Water discharge was also reduced by 30.7 thousand gallons, and carbon emissions decreased by 0.59 short tons per megawatt-hour. Yet, boiler conversion did not lead to statistically significant changes in per megawatt-hour water withdrawal, water consumption, water discharge, or carbon emissions. Spatial assessment further informs resource planning of projected water-stressed regions, as 204.6 gigawatts of coal-fired power plants remain operable in the United States in 2022. Fuel transition should adopt a nexus approach and account for the interdependence between water resources and electricity production to realize sustainable development commitments.