The transition from coal-fired power plants to those fueled by natural gas in Texas is saving water and making the Lone Star state less vulnerable to drought, even when the large amount of water used for hydraulic fracturing (fracking) to stimulate gas wells is considered, according to a new study.
Even though gas production with fracking requires "significant water consumption in Texas, the new consumption is easily offset by the overall water efficiencies of shifting electricity generation from coal to natural gas," according to the University of Texas at Austin (UT) study, recently published in the journal Environmental Research Letters.
Researchers estimate that water saved by shifting a power plant from coal to natural gas is 25 to 50 times as great as the amount of water used in hydraulic fracturing to extract natural gas. Natural gas also enhances drought resilience by fueling peaking power plants, which complement increasing use of wind generation, which doesn't consume water, according to the research.
Texas is the U.S. state that annually generates the most electricity. In recent years it also has been ravaged by drought, which lasts throughout the year in some areas of the state and grips nearly the entire state during summer months (see Shale Daily, Nov. 7).
The researchers estimate that in 2011 alone, Texas would have consumed an additional 32 billion gallons of water -- enough to supply 870,000 average residents -- if all its natural gas-fired power plants were instead coal-fired plants, even after factoring in the additional consumption of water for hydraulic fracturing to extract the natural gas.
In Texas, concerns about water use for fracking are heightened because the use of fracking is expanding rapidly while water supplies are dwindling as the third year of a devastating drought grinds on. Because most electric power plants rely on water for cooling, the electric power supply might be particularly vulnerable to drought.
"The bottom line is that hydraulic fracturing, by boosting natural gas production and moving the state from water-intensive coal technologies, makes our electric power system more drought resilient," said Bridget Scanlon, a senior research scientist at the university's Bureau of Economic Geology who led the study.
To study the drought resilience of Texas power plants, Scanlon and her colleagues collected water use data for all 423 of the state's power plants from the U.S. Energy Information Administration and from state agencies including the Texas Commission on Environmental Quality and the Texas Water Development Board, as well as other data.
Since the 1990s, the primary type of power plant built in Texas has been the natural gas combined-cycle plant with cooling towers, These plants use fuel and cooling water more efficiently than older steam turbine technologies. About one-third of Texas power plants are combined-cycle gas plants, and these consume about one-third as much water as coal steam turbine plants.
The other major type of natural gas plant in the state is a natural gas combustion turbine plant, which can also help reduce the state's water consumption by providing peaking power to support expansion of wind energy.
The study focused exclusively on Texas, but the authors said they believe the results should be applicable to other regions of the country where water consumption rates for the key technologies evaluated -- hydraulic fracturing, natural gas combined-cycle plants with cooling towers and traditional coal steam turbine plants -- are generally the same.
The Electric Reliability Council of Texas, which manages the state's power grid, projects that if current market conditions continue through 2029, 65% of new power generation in the state will come from natural gas combined-cycle plants and 35% from natural gas combustion turbine plants, which use no water for cooling, but are less energy efficient than combined-cycle plants.
"Statewide, we're on track to continue reducing our water intensity of electricity generation," Scanlon said.
Hydraulic fracturing accounts for less than 1% of the water consumed in Texas, according to the researchers. But in some areas where its use is heavily concentrated, it strains local water supplies, as documented in a 2011 study by Jean-Philippe Nicot of the Bureau of Economic Geology. Because natural gas is often used far from where it is originally produced, water savings from shifting to natural gas for electricity generation might not benefit the areas that use more water for fracking.
UT researchers early this year found that oil and gas producers are using more water for fracking, but they're also recycling more, making it important to distinguish between water "use" and "consumption" (see Shale Daily, Jan. 18).
Operators developing shale plays use between two and six million gallons of water per well when they frack, said an official with the research and consulting firm Synapse Energy Economics recently. Frank Ackerman, an environmental economist with the Cambridge, MA-based firm, said fracking is one of the most water-intensive energy activities, along with coal-fired power generation and nuclear energy (see Shale Daily, Sept. 17).