Energy Water Nexus Examined

Water use and energy demands are starting to collide, nationally, a crunch that National Renewable Energy Labs (NREL) analysts are studying.

Most people don’t recognize that the energy sector is the largest user of water in the nation, withdrawing more of this resource than any other industry. Given the effects of climate change—shifting historical weather and precipitation patterns—water is becoming an energy-security issue.

In the past decade, dozens and dozens of power plants, both in the United States and elsewhere, have had to shut down temporarily or curtail generation because there’s simply not enough water to cool generators. In some cases, plants have had to suspend operations because the water returned to the river system from power plants is too warm, and therefore harmful to the river ecosystems.

NREL is equipped with systems-level modeling capabilities to analyze the energy-water nexus across a spectrum of conditions. For example, Macknick has finalized a journal article that characterizes how much water is used by different technologies over their entire life cycle. His work has demonstrated that one great character of renewable technologies such as photovoltaic (PV) and wind energy generation is that they require zero water for operation. “These are essentially drought-proof,” he said.

NREL is also examining how water resource constraints may affect the future development and operation of the U.S. energy sector. By implementing water resource constraints into the Regional Energy Deployment System (ReEDS) tool—an electricity system capacity expansion model allowing comparisons of scenarios—Macknick and his collaborators are able to look at how water can affect long-term capacity expansion through 2050. They ask questions such as, if there is a drought or there are legal constraints on freshwater resources, how much water would be available for the energy sector and how would electricity deployment change? The modified ReEDS model also allows analysts to examine if there are opportunities to use alternatives to freshwater, including municipal wastewater or brackish groundwater.

Another study published in a peer-reviewed journal looked at all 1,200 U.S. power plants that use freshwater for cooling. Macknick’s team determined that most of those plants could be retrofitted to have zero freshwater usage by using alternative water from wastewater or brackish groundwater sources or by using dry cooling for less than half a penny per kilowatt-hour.

“Water is local,” Macknick said. “We have to look at water resource trends happening on a local level.” And now, the ReEDS tool has the capacity to analyze the entire nation divided into 134 regions. The added capability allows NREL to see how the regions affect the overall picture of sustainability, and what steps are needed to ensure a “water smart” electricity future.

That overall picture is one that NREL is monitoring. As Macknick noted, although most of that water is for power plant cooling, water is used throughout the entire lifecycle of all energy technologies for manufacturing, the fuel cycle, and power plant operations. NREL studies are evaluating water usage and providing alternatives to some of those concerns, such as decreasing the amounts of water used in the manufacture of PV cells.

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