Water Consumption of Energy Resource Extraction, Processing, and Conversion

Water as a Factor in the Energy Supply Chain

Water and energy are closely linked. The water industry is energy-intensive, consuming electricity for desalination, pumping, and treatment of wastewater. The energy industry is also water-intensive, which is the focus of this report. Water is used for resource extraction (oil, gas, coal, biomass etc.), energy conversion (refining and processing), transportation and power generation. Energy accounts for 27% of all water consumed in the United States outside the agricultural sector (Electric Power Research Institute 2008). Water, like energy, is a commodity but with very different characteristics. Water is almost always local where energy tends to be more of a global sector, linked to fungible commodities.

Constraints on water availability often influence the choice of technology, sites, and types of energy facilities. For instance, water has always been a potential constraint for thermal electricity generation, given the large volumes of water typically required for cooling. Water availability is thus of paramount importance when deciding on a suitable location of a power plant.

This paper provides an overview of water consumption for different sources of energy, including extraction, processing, and conversion of resources, fuels, and technologies. The primary focus of this paper is to summarize the consumptive use of water for different sources of energy. Where appropriate, levels of water withdrawals are also discussed, especially in the context of cooling of thermoelectric power plants.

The most comprehensive review of water consumption and energy production is a December 2006 report to Congress by the U.S. Department of Energy (DOE), titled "Energy Demands on Water Resources" (U.S. Department of Energy 2006). The DOE report was the starting point for this research effort, with additional sources used to increase the coverage of fuels (notably improved estimates for biofuels and shale gas production), additional processing technologies (coal-to-liquids and gas-to-liquids), and a more extensive review of water use in electricity from renewable sources, and carbon capture and sequestration (CCS). The data compiled in this analysis is based on an extensive review of available literature for the U.S. market, with particular emphasis on capturing recent trends where there may have been significant changes (e.g., biofuels, shale gas, and solar technology) and further studies completed. To the best of the authors' knowledge, there are no individual reports that have integrated information of resource extraction, processing, and conversion since the 2006 DOE report.

U.S. water consumption for energy

Water is becoming increasingly important in several aspects of U.S. energy production, including the expansion of biofuels, some sources of renewable energy, and cooling technologies for large power plants.

Absolute water consumption for energy production has been increasing in the United States, a trend that may continue if reliance on water-intensive fuels continues. Charts ES-1 and ES-2 summarize water consumption for fuel extraction and processing, and electricity production, respectively.

Thermoelectric power plant cooling accounts for between 3 and 4% of all U.S. water consumption, and has been increasing its share of total water use. New or modernized steam turbines and combined cycle gas turbine power plants being built predominantly use closed-loop cooling, a technology which has lower water intake but substantially higher net water consumption. Old power stations with once-through cooling are being updated or replaced with closed-loop cooling systems, (Chart ES-2). Consequently, water consumption from electricity production is likely to continue to increase even if production were to stay the same.

Biofuels are by far the most water-intensive source of fuel in the United States because of the extensive use of irrigation for corn production. The current generation of corn-based ethanol is particularly water intensive, consuming in excess of 1,000 gal/MMBtu on average, a water consumption one or two orders of magnitude greater than that of alternative sources of liquid fuels. A mandated move to advanced biofuels (cellulosic ethanol) could bring biofuels water-usage closer to other fuels, but these technologies are unproven on a commercial scale.

The recent shale gas transformation of the U.S. natural gas industry has also focused attention on the water-energy nexus, although the water consumption for the production of shale gas appears to be lower (0.6 to 1.8 gal/MMBtu) than that for other fossil fuels (1 to 8 gal/MMBtu for coal mining and washing, and 1 to 62 gal/MMBtu for U.S. onshore oil production). The increased role of shale gas in the U.S. energy sector could result in reduced water consumption (Chart ES-1). The water used for releasing the gas (hydraulic fracturing), however, has to be carefully managed at a local level. Concerns about potential contamination of freshwater supplies with hydrofracking fluids also need to be addressed. Natural gas-fired combined cycle power plants (CCGT) also have some of the lowest consumption of water per unit of electricity generated, helped by the relatively high thermal efficiency of CCGT plants (Chart ES-2).

Increased reliance on nuclear power, which has the highest water consumption of the thermoelectric technologies, and the potential for wide-scale CCS deployment, could also significantly increase water consumption (Chart ES-2). In contrast, some of the renewable energy technologies, in particular wind and solar photovoltaic, which have practically no water consumption (Chart ES-2), could contribute to reducing water consumption for the energy sector.

Finally, it is worth emphasizing that the wide range of water intensity estimates for the different processes investigated shows that, for each process, there are typically alternative technologies, which could reduce water consumption, albeit at a higher cost, with lower efficiency and/or reduced reliability.