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A man tests water with scientific equipment near a large commercial power plant.

NREL's Jordan Macknick tests water by the Excel Zuni Power Plant in Commerce City, Colorado.
Photo by Dennis Schroeder, NREL

Connecting the Moving Dots

Systems-level thinking illuminates the connections among energy, the environment, and the economy as NREL analysts help find a path to a "water smart" future.

NREL analysts provide insights into the nexus between energy and water use issues. Their work has supported federal and local agencies, as well as other stakeholders, as the nation transitions into a future where the energy-water nexus will become integral to both the nation's power system and environment. This work plays into NREL's and the U.S. Department of Energy's (DOE's) missions in a number of ways, including through a project with the U.S. Department of Interior (DOI) meant to address economic, energy, and water-use issues at the Navajo Generating Station (NGS) in Arizona.

The three massive chimneys rising up from NGS appear almost serene against the backdrop of the desert on the Navajo Indian Reservation near Page, Arizona. But a closer look reveals that there is more than meets the eye in this picture.

"It is a microcosm of everything you could imagine going on in one plant," said Scott Haase, an NREL senior engineer and the lab's liaison to the DOI.

Haase, who is among a number of NREL staff providing support for DOI and its Bureau of Reclamation, said the issue is complex. Power sector, transmission, and environmental concerns are in play; there are people who want renewables to be transitioned into the mix; in the arid Southwest, energy-water nexus challenges are paramount; economic development demands and tribal interests remain present; and a carbon emission ruling challenges the status quo.

The 2,250-megawatt coal-fired power plant was built in the 1970s, partially by the federal government, which retains about a quarter share of ownership in the plant—as do a number of partners, including several utilities. The plant has a major impact on the region. NGS provides electricity to Arizona, California, and Nevada, and is vital to the economies of the Navajo Nation and Hopi Tribe by using tribal coal and providing many well-paying jobs. It also supplies low-cost power for pumping water from the Colorado River into the vital Central Arizona Project, or CAP. The CAP was designed and built by the Bureau of Reclamation to supply water to customers in Arizona, and is an integral part of legal settlements with Indian tribes over water rights.

However, because the plant is near 11 national parks or wilderness areas—the Grand Canyon is only 15 miles away—there are concerns that it contributes to haze. Parks are designated as high priority visibility under the Clean Air Act, and as a result, the U.S. Environmental Protection Agency (EPA) has taken a series of actions to help improve air quality. Those measures involve new standards for nitrogen oxide (NOx) emissions at the plant, leading to a series of negotiations about the plant's future —a process that has highlighted the complex connections linking energy, the environment, and the economy in the area.

While it might seem helpful to try to "connect the dots" to find a solution, NGS presents a situation where the dots are more like three dimensional objects, evolving and moving.

"It's very complicated," said David Hurlbut, a senior analyst with NREL's Strategic Energy Analysis Center (SEAC). "You have to be mindful of how these connections will change over time as the economy and technologies change."

Hurlbut and others have been tapped by the Bureau of Reclamation to find what's referred to as a "glide path" for the plant to be modified in the short-term or possibly closed by 2044. "We're looking for a reasonable transition path to switch from coal to clean energy alternatives in a way that minimizes the economic disruption," he said.

No Easy, or Simple, Answers at NGS

A large power plant with three towering smokestacks in the desert.

The Navajo Generating Station is the focus of energy/water nexus issues that radiate far beyond its setting in Pace, Arizona, near the Grand Canyon.
Photo provided by SRP

Yet there are no easy answers, as Hurlbut noted, because "you can't just unplug the coal plant. That's overly simplistic."

Following the EPA's notice of intent to set a new NOx standard for the plant, DOI asked NREL in 2011 for an objective assessment of the coal plant in terms of EPA's then-proposed new NOx emission standards.

"The Bureau of Reclamation has enlisted NREL to assist the agency in the development of low-emitting energy alternatives as part of a long-term and incremental replacement approach for the federal interest in the NGS," said Kevin Black, the Bureau's NGS program manager for energy development.

Bureau of Reclamation Deputy Regional Director David Palumbo said the alternatives will be determined through a "rigorous analysis combining energy, environmental, and economic factors." He added that the Bureau and NREL are working with stakeholders who must prepare for changes in future NGS operations by understanding the effect on energy generation, environment impacts, and related economies.

"What we're doing is taking everything we've been doing generally throughout the lab in terms of analysis of solar, wind, and renewable technologies, and focusing on a particular question in a particular situation," Hurlbut said.

After the 2011 request, NREL analysts burned a different kind of fuel—midnight oil—to complete a study in a matter of months to help inform EPA while the agency drafted a new proposed NOx rule. Their work helped attract wide support from stakeholders—utilities, non-government agencies, Indian tribes, and others—for the final EPA rule. NREL analysts also provided technical support to DOI for subsequent negotiations with key parties involved in the plant.

NREL continued to provide key systems-level thinking, enabling stakeholders to move forward with an arrangement that essentially reduces NGS output by a third, enabling EPA to issue its final rule in 2013 with stakeholder backing.

"Even if the coal plant continues to operate, things are going to change," Hurlbut said. "We're looking at where the sector is heading regardless of what happens to NGS by taking trends we can observe or expect, and then following them to 2020, to 2030—and providing a plausible range of outcomes."

Also in 2013, the EPA, DOI, and DOE jointly released a statement outlining goals and acknowledging how difficult the intertwined set of issues surrounding NGS will be to solve, committing themselves to developing a road map. NREL analysts are "providing a knowledgebase they can draw upon to make these agency-level decisions," Hurlbut said.

The Energy-Water Nexus as Part of Systematic Change

As unique as the NGS situation appears—a microcosm of challenges in one case—it illustrates the increasingly commonplace collisions between water use and energy demands nationally—a crunch that NREL analysts are studying. NREL is prepared to provide insights into the nexus between energy and water use issues.

"The energy-water nexus is a foundational element of our work here," said NREL's Jordan Macknick, another SEAC analyst who studies the energy-water nexus. "Something that most people don't recognize is 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, he said. "In order to ensure that we have sustainable sources of energy, we need to use water wisely."

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.

Systems Approach to Gain Insights into New Patterns

As NGS and many other examples show, the issues of connecting energy, the environment, and the economy are complex and becoming more frequent. "The decisions have multiple dimensions," said Associate Laboratory Director Robin Newmark. "If we only fix one part of the problem, we may exacerbate another." She explained that such multifaceted challenges are what drive the analysis team because helping stakeholders around the globe gain a more complete understanding of all the moving parts ultimately leads to better solutions.

Newmark, who leads NREL's Energy Analysis and Decision Support organization, including SEAC and the Joint Institute for Strategic Energy Analysis, was a key contributor to the 2014 National Climate Assessment, which recognized that water quality and quantity are being affected by climate change. This, in turn, overlaps with energy and economy.

"Whether with federal or state agencies, utilities, or other organizations, NREL's systems-level thinking is illuminating the links among energy, the environment, and the economy," Newmark said. "In this way, we're not only connecting the dots for decision-makers, we're connecting the present with a more sustainable future."

Learn more by reading NREL's technical reports, Navajo Generating Station and Clean-Energy Alternatives: Options for Renewables and Navajo Generating Station and Air Visibility Regulations: Alternatives and Impacts.

NREL Analysis: Reimagining What's Possible for Clean Energy

Summer 2015 / Issue 8

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