Scenarios for Low Carbon and Low Water Electric Power Plant Operations: Implications for Upstream Water Use

Abstract

Electric sector water use, in particular for thermoelectric operations, is a critical component of the water-energy nexus. On a life cycle basis per unit of electricity generated, operational (e.g., cooling system) water use is substantially higher than water demands for the fuel cycle (e.g., natural gas and coal) and power plant manufacturing (e.g., equipment and construction). However, could shifting toward low carbon and low water electric power operations create trade-offs across the electricity life cycle? We compare business-as-usual with scenarios of carbon reductions and water constraints using the MARKet ALlocation (MARKAL) energy system model. Our scenarios show that, for water withdrawals, the trade-offs are minimal: operational water use accounts for over 95% of life cycle withdrawals. For water consumption, however, this analysis identifies potential trade-offs under some scenarios. Nationally, water use for the fuel cycle and power plant manufacturing can reach up to 26% of the total life cycle consumption. In the western United States, nonoperational consumption can even exceed operational demands. In particular, water use for biomass feedstock irrigation and manufacturing/construction of solar power facilities could increase with high deployment. As the United States moves toward lower carbon electric power operations, consideration of shifting water demands can help avoid unintended consequences.

Figure 1

Electricity generation mix (PJ) by major fuel/technology type in 2015 and 2050 for BAU and seven scenarios: 30% reduction (30%), low carbon (LC), low carbon and low withdrawals (LCLW), low carbon and constant consumption (LCCC), and the same carbon and water constrained scenarios without biomass (LC-NB, LCLW-NB, and LCCC-NB). Results are shown at the nine-region (Census Divisions) and national level.

Figure 2.

(a) National water withdrawals (T liters yr–1) by life cycle stage in 2015 and 2050 for the BAU and seven scenarios. The dashed boxes show the 2050 water withdrawal reductions relative to BAU. (b) National water consumption (B liters yr–1) by life cycle stage in 2015 and 2050 for the BAU and seven scenarios.

Figure 3.

Regional water consumption (B liters yr⁻¹) by life cycle stage in 2015 and in 2050 for the BAU and seven scenarios. The fuel cycle water use (yellow) is divided into biomass water use and other fuel cycle (coal, natural gas, and uranium) water use. The markers show operational (i.e., cooling system) consumption in 2005 for each region. For the LCCC and LCCC-NB scenarios, the operational stage is constrained to meet those levels out to 2050. If the green bar for the operational water use for the LC scenario is above those regional operational water constraint markers, it means that the region has to make cuts in operational stage water use under the LCCC scenario.

Figure 4.

Regional water consumption (B liters yr⁻¹) under the LC scenario in 2015 and 2050 for (a) the fuel cycle stage and (b) the power plant manufacturing stage. For the fuel cycle stage, biomass is shown on a separate scale; for the power plant manufacturing stage, solar PV and CSP are shown on a separate scale, as these are orders of magnitude higher