When it comes to the environmental impacts of burning coal and natural gas, we tend to focus most of our attention on carbon dioxide emissions. But generating electricity from fossil fuels is also a pretty water-intensive process, a new analysis shows.
The ongoing transition from coal to natural gas electricity is easing the water use associated with power generation somewhat. But much bigger savings could be achieved by switching to solar- and wind-generated electricity.
Researchers from Duke University gathered data from various U.S. government databases to calculate how much water each megawatt hour of electricity generated from either coal or natural gas uses. Water is needed for both production of fossil fuels and for electricity generation in power plants.
Coal production requires water for mining, cleaning, and transportation. Hydraulic fracturing or “fracking,” a form of natural gas extraction in which fluid is forced into a well to create cracks through which natural gas trapped in the rock can flow, requires a lot of water. Water is used in processing and transporting natural gas as well.
Despite the increased reliance on fracking, natural gas production is still less water-intensive than coal, the researchers report in Environmental Research Letters. Coal production uses about 0.60 cubic meters of water per megawatt hour of electricity eventually generated, while natural gas requires just 0.18 cubic meters.
Both coal and natural gas power plants use water in cooling towers. Modern power plants tend to recirculate cooling water, but even so, about 40% of all water taken from rivers and groundwater reservoirs in the United States is used for cooling at power plants.
And again, coal-fired power plants require substantially more water for cooling compared to natural-gas plants. Overall, generating electricity from coal is more than twice as water intensive as natural gas, the researchers found.
The good news is that most coal and natural gas electricity generation takes place in areas that have abundant water. But 37% of coal mining and 50% of natural gas extraction in the United States takes place in water-stressed regions, the researchers point out.
At fossil fuel power plants, there tends to be a tradeoff between carbon emissions and water use. So-called “dry” cooling technology can reduce water demand, for example, but at the expense of reducing efficiency – in other words, resulting in greater carbon emissions per megawatt hour of electricity generated.
Carbon capture and sequestration has been suggested as a way to control emissions from fossil fuel power plants. But this technology is itself water intensive – to a greater degree for coal than for natural gas – and would increase the amount of water used by power plants.
But it’s possible to have low-carbon electricity that’s water efficient too, the researchers point out. Solar and wind energy require very little water – mostly just for washing the solar panels and turbine blades every once in a while. A previous study estimated that solar energy uses about 0.02 cubic meters of water per megawatt hour of electricity generated, and wind energy just 0.001 cubic meters. That’s only 1 or 2 percent of the water required for coal and natural gas electricity generation.
“The growing contribution of renewable energy technologies such as wind and solar will reduce water consumption at an even greater magnitude than the transition from coal to natural gas, eliminating much of water withdrawals and consumption for electricity generation in the U.S.,” the researchers write.
Source: Kondash A.J. et al. “Quantification of the water-use reduction associated with the transition from coal to natural gas in the U.S. electricity sector.” Environmental Research Letters 2019.
Image: via pxhere.