Power plants continue to suck US dry
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New data from the US Geological Survey underline the need for fresh action on the water-energy nexus. The volumes of water withdrawn for cooling thermoelectric power plants remain stubbornly high.
New figures published at the end of October show that total water withdrawals in the US declined by 1% from 2000 to 2005 to reach 410 billion gallons per day (approximately 1.5 km3/d).
The data, compiled by the US Geological Survey (USGS), reveals that while the volume withdrawn for irrigation declined by 8% – partly due to more efficient sprinkler systems in the Southwest – the volumes of water required for cooling purposes in thermoelectric power plants rose by 3%, reaching 201 BGD (0.75km3/d), equivalent to 49% of total withdrawals in 2005.
Around 75% of the electricity generated in the US comes from thermoelectric power plants, which rely heavily on water for cooling. 43% use once-through cooling systems, while less than 1% use waterefficient methods such as dry cooling. An astonishing 92% of the water withdrawn for use in thermoelectric power plants is used for once-through cooling.
While the ratio of total water withdrawals to energy produced has decreased from an average of 63 gallons/kWh in 1950 to 23 gal/kWh in 2005, there are fears that a projected 15% rise in thermoelectric power generation capacity in the US between 2006 and 2030 could put a significant strain on remaining water resources.
“They are retiring once-through cooling thermal plants and replacing them with recirculation systems, but that’s a very slow cycle – you see it more on the 20-year numbers,” explains Nancy Barber, one of the coauthors of the USGS report.
While decommissioning may not be an economic option for many plants, retrofit retrofitting them is both difficult and expensive. “The expenses often outweigh the benefits,” explains Anu Mittal, co-author of a report published in October by the US Government Accountability Office (GOA), focussing on trends in power plant water use. She argues that some form of tax credit or relief at the federal level could encourage more power plant owners to reduce their water footprint by adopting alternative technologies, but believes the real issue lies in the inefficient pricing of water.
“The biggest problem is we don’t price water according to the reality of the situation,” she told GWI. “In those areas where there has been a huge shortage of water, you’ve seen some movement toward using alternative sources such as dry cooling, but where you don’t have those kinds of constraints, and water is cheaply priced, there’s no reason to move into an expensive technology,” Mittal explained.
“The demand for energy continues to increase, and as long as we rely on fresh water for cooling, I think we’re going to continue to see increases [in water withdrawals] unless we see a major shift in the use of alternative technologies.”
While technologies such as dry cooling are not new, the cost is only one factor behind the slow uptake. “If you use dry cooling in a hot climate, there’s too high an energy penalty,” says Mittal. “Dry cooling is more effective in certain climates than others, but even if the regional climate is appropriate, the cost of purchasing land to build dry cooling towers may be prohibitive.”
Using reclaimed water is another option, but one which comes with its own problems. “There are a number of disadvantages to using reclaimed water – one is that you’ve got to do more cleaning of your equipment, and more cleaning of the water that’s discharged.” She cites anecdotal evidence of power plant developers finding that the demand for reclaimed water already exceeds regional supply, and bemoans the lack of data relating to reclaimed water use by power plants in the US. “We really need that data, given how much water this sector consumes,” she observed. The USGS’s Barber agrees. “It’s one of those areas where we would love to do more, but the budget constrains us in what we’re able to collect.”
One issue not addressed by the USGS report is whether the current levels of water withdrawals in the US are sustainable. While volumes have remained more or less stable since 1975, despite a rising population and increased urbanisation, the volumes withdrawn for public supply and thermoelectric power continue to rise (see chart, left).
The vetoing of a number of power plant proposals due to insufficient water supplies is well documented, but not all legislatures treat the problem with equal severity. “There’s a huge amount of variability among the states as to how they’re handling this issue,” says Mittal.
The only way to effect a step-change reduction in the volume of water withdrawals for thermoelectric power cooling in the US is through legislation. Radical action will be required if the country is to manage its energy-water nexus responsibly in the face of demographic and climatic change.
The USGS report can be viewed at http://pubs.usgs.gov/circ/1344/pdf/c1344.pdf, while the GOA’s report is viewable at http://www.gao.gov/new.items/d1023.pdf.