A hybrid Sankey diagram shows the magnitude of energy and water flows on a national scale. The diagram illustrates that thermoelectric power generation both withdraws large quantities of water for cooling and dissipates tremendous quantities of primary energy due to inefficiencies in converting thermal energy to electricity (“withdrawn” water is diverted from a surface water or groundwater source). The intensity of water use and energy dissipated varies with generation and cooling technology. Significant aspects of water and energy flows do not appear in the diagram, the DOE notes. Flows will change over time, and anticipated changes in flows are important to consider when prioritizing investment in technology and other solutions. Future increased deployment of some energy technologies, such as carbon capture and sequestration, could lead to increases in the energy system’s water intensity, whereas deployment of other technologies, such as wind and solar photovoltaics, could lower it. Source: DOE. Click to enlarge.

When severe drought affected more than a third of the United States in 2012, limited water availability constrained the operation of some power plants and other energy production activities. Hurricane Sandy demonstrated the compounding ramifications of vital water infrastructure losing power. The recent boom in domestic unconventional oil and gas development has added complexity to the national dialogue on the relationship between energy and water resources.

The water-energy nexus is integral to two DOE policy priorities: climate change and energy security. DOE’s program offices have addressed the water-energy nexus for many years; however, this work has historically been organized on a program-by-program basis, where water has been considered among a number of other factors.

In the fall of 2012, DOE initiated a department-wide Water-Energy Tech Team (WETT) to increase cohesion among DOE programs and strengthen outreach to other agencies and key external stakeholders in the water and energy sectors. WETT developed The Water-Energy Nexus: Challenges and Opportunities to provide an analytical basis from which to address these objectives and to provide direction for next steps.

Trends. Water availability will affect the future of the water-energy nexus, DOE says. While there is significant uncertainty regarding the magnitude of effects, water availability and predictability will be altered by changing temperatures, shifting precipitation patterns, increasing variability, and more extreme weather.

Changes in precipitation and temperature patterns will likely lead to more regional variation in water availability for hydropower, bioenergy feedstock production, and other energy needs. Rising temperatures have the potential to both increase the demand for electricity for cooling and decrease the efficiency and capacity of thermoelectric generation. These changes and variations pose challenges for energy infrastructure resilience.

Population growth and migration patterns will also determine water and energy needs, as well as changes in fuels used and energy technologies deployed.

According to Energy Information Administration (EIA) data, planned retirements and additions of electricity generation units and cooling systems will decrease water withdrawals, will likely increase water consumption, and will increase the diversity of water sources used.

Challenges. The Water-Energy Nexus: Challenge and Opportunities lays out an array of technical and operational challenges across the water-energy nexus at local, regional, and national scales. The report notes that water scarcity, variability, and uncertainty are becoming more prominent, potentially leading to vulnerabilities of the US energy system.

The report identifies six strategic pillars that will serve as the foundation for coordinating R&D:

• Optimize the freshwater efficiency of energy production, electricity generation, and end use systems;

• Optimize the energy efficiency of water management, treatment, distribution, and end use systems;

• Enhance the reliability and resilience of energy and water systems;

• Increase safe and productive use of nontraditional water sources;

• Promote responsible energy operations with respect to water quality, ecosystem, and seismic impacts; and

• Exploit productive synergies among water and energy systems.

Technology RDD&D opportunities. The report identifies a number of opportunities throughout the stages of technology research, development, demonstration, and deployment:

• Recovery of dissipated energy;

• Advances in cooling systems;

• Alternatives to freshwater in unconventional oil and gas;

• Desalination and nontraditional waters;

• Net-zero wastewater treatment; and

• Efficient equipment and appliances.

As examples of the role technology can play, DOE report notes that one approach to reduce thermoelectric and other cooling requirements, along with associated water use, is to reduce the generation of waste heat through more efficient power cycles (e.g., the recompression closed loop Brayton cycle). Another option is to increase the productive use of waste heat, such as throughthermoelectric materials, enhancements in heat exchanger technologies, or low temperature co-produced geothermal power. There are also opportunities to optimize water use in other parts of the overall energy system. Alternative fluids can replace freshwater in hydraulic fracturing, geothermal operations, and power cycles. Process freshwater efficiency in carbon capture, bioenergy feedstock production, and industrial processes can be improved.

The water efficiency of cooling systems can also be improved through advancements in technologies such as air flow designs, water recovery systems, hybrid or dry cooling, or treatment of water from blowdown.

Representative problem/opportunity spaces in water for energy. Click to enlarge.		Representative problem/opportunity spaces in energy for and from water. Click to enlarge.

To pursue next steps, DOE will work with partners, including other federal agencies, state and local governments, foreign governments, private industry, academic institutions, non-governmental organizations, and citizens. This integration and collaboration will enable more effective research, development, and deployment of key technologies; harmonization of policies where warranted; shared robust datasets; informed decision-making; and public dialogue.