Wed January 29, 2014
Connecting the Drops: Water and Power
It takes water to produce electricity, but how much water varies a lot depending on the fuel source and the power generating technology.
In Colorado, around half a percent of our total water usage is used to generate electricity.
It’s a small percentage, says Stacy Tellinghusen, water policy analyst for Western Resource Advocates, a non-profit conservation group, but adds that it’s not inconsequential.
“The total volume is around 65,000 acre feet of water per year that’s consumed by power plants,” said Tellinghusen. “That’s about equal to the water that could be used otherwise by 500 to 600,000 Coloradoans.”
Tellinghusen adds that pretty much all of the water in Colorado is spoken for - so more water to make electricity means less water for agriculture or any other use.
“Most of our river systems are fully or over-allocated and fully used,” said Tellinghusen. “So any new water use for a power plant or for drilling or fracking is necessarily going to impact an existing water user in that basin.”
Hydraulic fracturing - or “fracking” - uses pressurized water and chemicals to crack shale and release deposits of oil and natural gas trapped deep underground. The technology has led to a rapid increase in oil and gas drilling in Colorado, especially in the northeastern part of the state and in Garfield County on the Western Slope. Energy companies buy the water for fracking from any willing seller and it’s often hauled by trucks to drilling sites. In 2011, the city of Greeley sold 500 million gallons of water to energy companies.
But the amount of water used to generate electricity at a natural gas-fired power plant is less than a coal-fired plant, even when factoring in the amount required for fracking. That’s according to James Meldrum, research associate for a project called the Western Water Assessment at CU-Boulder.
“This shift over to natural gas, the net is a reduction in the water use compared to coal,” says Meldrum. “With the hydraulic fracturing, you still have a net benefit from a water perspective if you’re looking at an overall level.”
But Meldrum is quick to echo Stacy Tellinghusen on the need to factor in water scarcity.
“One of the main points about water,” Meldrum said, “is that it’s not just how much water’s used overall, it’s where the water is used. So, one of the issues with hydraulic fracturing, of course, is that a lot of the places we have the shale gas, they don’t have as much water to begin with.”
A tight supply forces efficiency in power generation. In parts of the eastern United States with abundant water, as much as 50% of all water used may be to generate electricity - exponentially greater than the half a percent used here in Colorado. Meldrum says one big reason is inefficient cooling technology back East. In Colorado and most of the arid Western U.S., power plants recirculate cooling water.
An example is Xcel Energy’s Fort St. Vrain plant in Weld County. It saves water thru efficient cooling and by burning natural gas instead of coal. Xcel is the largest utility in Colorado, and Rich Belt is a Senior Water Resources Analyst for the company.
“With a natural gas power plant you have a turbine that is fired directly by natural gas, and that generates electricity as the turbine rotates,” says Belt. “But then there’s a waste heat stream that comes out the back end of that turbine. That’s also captured, and that’s used to generate steam, using water, which is used to drive another turbine. You get two whacks at the heat.”
Conventional coals plants are unable to do that - they’d first have to convert the coal into gas, which is an expensive and inefficient process.
Xcel is in the process of converting more of their coal plants in Colorado to natural gas, due in part to a mandate called the Clean Air Clean Jobs Act passed by the state legislature in 2010.
Many studies show that using natural gas instead of coal to generate electricity reduces air pollution and saves water. So does energy conservation at the individual level. Researcher James Meldrum says water use should also be factored into electricity use.
“A lot of the water that we as individuals use actually is indirectly through electricity that we use,” says Meldrum. “So if you want to conserve water or electricity, there can be benefits of one or the other, combined. Your personal water use is your toilet, your lawn, as well as turning on your lights and turning them off.”
And if the electricity powering your lights comes from renewable energy technologies –you’re probably way ahead when it comes to water use. Xcel’s Rich Belt says demand for Xcel’s electricity has increased over the past five years but the utility’s water use has remained flat, thanks to the addition of renewables and the conversion of big power plants from coal to natural gas.