Technology Roadmaps and R&D

There are a number of technologies that support water‐efficient energy systems or energy‐efficient water systems. These technologies are at various stages of research, development, demonstration, and deployment. Figure 9.8 illustrates a range of technologies optimizing water use for energy in waste heat recovery, cooling, alternate fluids, and process water efficiency.

Cooling for thermoelectric generation is an important target for water efficiency because it withdraws large quantities of water for cooling and dissipates tremendous amounts of primary energy. 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 the waste heat, such as through thermoelectric materials, enhancements in heat exchanger technologies, or low‐temperature co‐produced geothermal power. A third approach to improve the water efficiency of cooling systems is through advancements in technologies, including air flow designs, water recovery systems, hybrid or dry cooling, and treatment of water from blowdown.

Opportunities to optimize water use also exist in other parts of the overall energy system. With further research, alternative fluids may replace freshwater in hydraulic fracturing, geothermal operations, and power cycles. Process freshwater efficiency can be improved in carbon capture, bioenergy feedstock production, and industrial processes. Many of the technologies that improve water efficiency are enhanced by advances in materials, including thermoelectric properties, heat‐driven state change, scaling/fouling resistance, and temperature and pressure tolerance.

Figure 9.9 shows water treatment technologies that can potentially enhance energy efficiency of water systems and enable the productive, economical, and safe use of nontraditional water resources for energy and nonenergy applications. Such improvements in water treatment and management have particular use for treating oil‐ and gas‐produced waters, as well as saline aquifers, brackish groundwater, brines, seawater, and municipal wastewater. For saline sources, promising water treatment technologies include membrane distillation, forward osmosis, evaporation, nanomembranes, and capacitive deionization. For municipal wastewater, treatment technologies include anammox systems, anaerobic pretreatments, and anaerobic membrane bioreactors. In addition, the biosolids contained in wastewater can be a source of methane energy.

Table 9.2 Comparison of the water withdrawal and water consumption factors (in gal/MWh) for fuel‐based electricity‐generating technologies.

Source: From National Renewable Energy Laboratory (NREL) (2011).