Texas, the U.S. state that annually generates the most electricity, has transitioned from coal to natural gas for electricity generation and that has not only reduced CO2 emissions but is saving water and making the state less vulnerable to drought.
Hydraulic fracturing - fracking - is a process in which water, sand and chemicals are pumped at high pressure into a well to fracture surrounding rocks and allow oil or gas to more easily flow. Hydraulic fracturing and horizontal drilling are the main drivers behind the current boom in U.S. natural gas production and the resulting drop in CO2 emissions from energy back to early 1990s levels. Environmentalists have adapted a 'plead the alternative' approach in their war on natural gas, claiming that the amount of water that is consumed means that, because most electric power plants rely on water for cooling, the electric power supply might be particularly vulnerable to drought if fracking isn't banned.
Exploration for natural gas through hydraulic fracturing obviously requires significant amounts of water also, but that consumption is easily offset by the overall water efficiencies of shifting electricity generation from coal to natural gas - to the tune of 25 to 50 times better by shifting a power plant from coal to natural gas. Natural gas also enhances drought resilience by providing so-called peaking plants to complement increasing wind generation, which doesn't consume water.
The University of Texas at Austin
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.
Since the 1990s, the primary type of power plant built in Texas has been the natural gas combined cycle (NGCC) plant with cooling towers, which uses fuel and cooling water more efficiently than older steam turbine technologies. About a third of Texas power plants are NGCC. NGCC plants consume about a third as much water as coal steam turbine (CST) plants.
The other major type of natural gas plant in the state is a natural gas combustion turbine (NGCT) plant. NGCT plants can also help reduce the state's water consumption for electricity generation by providing "peaking power" to support expansion of wind energy. Wind turbines don't require water for cooling; yet wind doesn't always blow when you need electricity. NGCT generators can be brought online in a matter of seconds to smooth out swings in electricity demand. By combining NGCT generation with wind generation, total water use can be lowered even further compared with coal-fired power generation.
The study focused exclusively on Texas, but the authors believe the results should be applicable to other regions of the U.S., where water consumption rates for the key technologies evaluated — hydraulic fracturing, NGCC plants with cooling towers and traditional coal steam turbine plants — are generally the same.
The Electric Reliability Council of Texas, manager of the state's electricity grid, projects that if current market conditions continue through 2029, 65 percent of new power generation in the state will come from NGCC plants and 35 percent from natural gas combustion turbine plants, which use no water for cooling, but are less energy efficient than NGCC plants.
"Statewide, we're on track to continue reducing our water intensity of electricity generation," says Scanlon.
Hydraulic fracturing accounts for less than 1 percent of the water consumed in Texas. 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 hydraulic fracturing.
Source: University of Texas at Austin