NREL. 2014. Modeling climate-water impacts on electricity sector capacity expansion. To be presented at the ASME 2014 Power Conference Baltimore, Maryland July 28–31, 2014. National Renewable Energy Laboratory. 12 pages.
Excerpts follow:
ABSTRACT Climate change has the potential to exacerbate water availability concerns for thermal power plant cooling, which is responsible for 41% of U.S. water withdrawals. This analysis describes an initial link between climate, water, and electricity systems using the National Renewable Energy Laboratory (NREL) Regional Energy Deployment System (ReEDS) electricity system capacity expansion model.
Average surface water projections from Coupled Model Intercomparison Project 3 (CMIP3) data are applied to surface water rights available to new generating capacity in ReEDS, and electric sector growth is compared with and without climate-influenced water rights.
Climate impacts are notable in southwestern states, which experience reduced water rights purchases and a greater share of rights acquired from wastewater and other higher-cost water resources.
Thermal power plants require water for operations. Water use includes both “withdrawal” and “consumption,” where withdrawal is the amount of water removed from the water source for use (but then returned to the source, often at a higher temperature), whereas consumption is the amount of water that is evaporated, transpired, incorporated into products, or otherwise removed from the immediate water environment [1]. Water withdrawals for thermal power plant cooling account for 41% of total U.S. water withdrawals, making electric sector withdrawals the largest of any sector [1]. The electric sector consumes a smaller portion (~3%), but this consumption can have important regional implications in areas of water stress [2]. Thermal power plants account for 80% of U.S. electricity, meaning any short- or long-term disturbance in water resources can impact the reliability of electricity supply
[3]. Already, this vulnerability has caused power plant shutdowns or output reductions on several occasions, primarily during heat waves and drought [4–6].
Climate change has the potential to exacerbate power plant water availability problems by altering spatial and temporal distributions of freshwater resources and their thermodynamic properties, most importantly temperature [7]. Temperature is especially important because higher cooling water inlet temperature leads to less efficient cooling and potentially higher outlet temperatures, which are limited by Environmental Protection Agency (EPA) regulation.
Less water available for thermal cooling could produce operational difficulties or instigate legal disputes over water rights. The expectation of lower water availability could impact decisions on what types of power plants to install, where to install new capacity, and regulatory decisions on water rights availability to proposed power plants. Thermal power plant lifetimes vary greatly, but they are generally expected to be 30–60 years; new power plant construction decisions can therefore have lasting impacts
All major generating technologies are represented in the model, including nuclear, coal, natural gas combined cycle (GasCC), natural gas combustion turbine (GasCT), hydro, wind, solar, geothermal, biopower, and storage. Technology types are differentiated by costs and operating characteristics, and renewable resources have region-specific quantities and costs that comprise regional supply curves. Variable renewable resources such as wind and solar are further described by statistically calculated capacity value at peak for supplying planning reserves, induced operating reserve requirements, and curtailments. Existing fossil and nuclear capacity is retired based on proposed and lifetime-based retirements from Ventyx, and renewable technologies with lifetimes within the study period are assumed to be automatically rebuilt when their expected project lifespans are reached [16].
Thermal power generating technologies (nuclear, coal, GasCC, CSP-concentrating solar power) are distinguished by the following cooling technology types: once-through, cooling pond, recirculating tower, and dry (air cooling). Geothermal technologies are currently assumed to use dry cooling, but later model versions will allow alternative cooling technologies. Each power-cooling technology combination has a specific capital and operating cost, water withdrawal and consumption rate, and heat rate.
Water withdrawal rates determine the quantity of water rights that must be purchased when new capacity is installed. Water rights must be purchased in the balancing area where capacity is built, and each balancing area has a water rights supply curve with quantity and cost of the following water rights types: unappropriated fresh surface water, appropriated fresh surface water, shallow groundwater, wastewater, and brackish groundwater.
Existing data have not yet been transformed to physical water availability data necessary to inform such a constraint, and doing so is the subject of ongoing work.
| Technology | 2010 capital cost ($/kW) |
| Coal | 2,940 |
| GasCC | 970 |
| GasCT | 830 |
| Nuclear | 4,800 |
| Solar photovoltaic | 4,210 |
| Onshore wind | 1,770 |
Table 1: Capital cost projections for select technologies in $/kW for the initial ReEDS solve year, 20102.
Water withdrawal and consumption rates for select technologies are shown in Table 4. Once-through systems withdraw 1 to 2 orders of magnitude more water than recirculating cooling, though recirculating cooling consumes substantially more water through evaporation. Water withdrawal and consumption rates for dry cooling are negligible. Generally, systems that withdraw less water are more costly and less efficient.
Power technology Nuclear Coal GasCC Water withdrawal/costs. Figure 1 provides a sense of national water rights availability and cost. Available rights are primarily unappropriated surface water in regions outside the southwest, groundwater in the eastern half of the country, and groundwater between the Pacific Northwest and Rocky Mountains. Wastewater and brackish groundwater resources are substantially more expensive but are well distributed across the country. Appropriated water is defined only for the western half of the country and has intermediate costs and relatively low availability in western states except California, where there is no available appropriated water. One model limitation is the omission of saltwater resources for coastal regions; the SNL work does not include salt water resources, and no other salt water resource assessment exists, so water rights estimates for coastal regions are likely lower than actual.
Only in regions lacking unappropriated water, where climate effects are imposed on appropriated and retired surface water rights, would the modifications to water rights be expected to alter electric sector development.
States where the modeled impacts on water rights are important include California, Nevada, Arizona, and New Mexico, which have no unappropriated water, and Texas, where unappropriated water is limited or unavailable in the southern and western portions of the state. Figure 4 plots cumulative rights purchased over time in these states, subsequently referred to as the southwest, for the baseline scenario along with the 2050 total for all scenarios. Unappropriated rights make up a notable fraction of the total, but these are all in Texas. Groundwater resources are an important source of electric sector water in the southwest, representing nearly a quarter of all new water rights, split primarily between Texas, New Mexico, and Nevada. Retired rights are most often used for new capacity, but 97% of retired rights are purchased in Texas and California. Outside of Texas and California, groundwater dominates, with lesser contributions from retired rights and wastewater..
In a given balancing region, GasCC capacity in 2050 differs across scenarios by less than 1 GW, which is generally small compared to total generating capacity in a region. Though expected water availability falls in climate change scenarios, there remains sufficient water rights at low enough cost such that even water-stressed regions experience little change in capacity expansion. New GasCC capacity might resort to wastewater under modeled climate change scenarios, but the costs of these alternative water resources are still very small compared to total capital costs; hence, they are not large enough to drive major changes in capacity expansion decisions.
Assumptions made to simplify this preliminary analysis tend to underestimate changes in water availability, particularly in the western states.
References
[1] Kenny, J. F., N. L. Barber, S. S. Hutson, K. S. Linsey, J. K. Lovelace, and Maupin, M. A., 2009, “Estimated use of water in the United States in 2005,” US Geological Survey Circular1344.
[2] Solley, W. B., Pierce, B. R., and Perlman, H. A., 1998, “Estimated Use of Water in the United States in 1995,” US Geological Survey Circular 1200.
[3] USEIA, 2013, “Annual Energy Outlook 2013 with Projections to 2040,” DOE/EIA-0383(2013).
[4] Averyt, K.., Fisher, J., Huber-Lee, A., Lewis, A., Macknick, J., Madden, N., Rogers, J., and Tellinghuisen, S., 2011, “Freshwater use by U.S. power plants: Electricity’s thirst for a precious resource,” Union of Concerned Scientists: A report of the Energy and Water in a Warming World Initiative, Cambridge, MA.
[5] Rogers, J., Averyt, K., Clemmer, S., Davis, M., FloresLopez, F., Frumhoff, P., Kenney, D., Macknick, J., Madden, N., Meldrum, J., Overpeck, J., Sattler, S., Spanger-Siegfried, E., and Yates, D., 2013, “Water-smart power: Strengthening the U.S. electricity system in a warming world,” Union of Concerned Scientists, Cambridge, MA, 2013.
[6] Department of Energy (DOE), 2013, “U.S. Energy Sector Vulnerabilities to Climate Change and Extreme Weather,” DOE/PI-0013. [7] Karl, T., Melillo, J.,
[9] Tidball, R., Bluestein, J., Rodriguez, N., and Knoke, S., 2010,“Cost and Performance Assumptions for Modeling Electricity Generation Technologies,” NREL/SR-6A20-48595. National Renewable Energy Laboratory, Golden, Co.
[10] Chandel, M. K., Pratson, L. F., and Jackson, R. B., 2011, “The potential impacts of climate-change policy on freshwater use in thermoelectric power generation,” Energy Policy, 39, pp. 6234–6242.
[11] Macknick, J., Sattler, S., Averyt, K., Clemmer, S., and Rogers, J., 2012, “The water implications of generating electricity: Water use across the United States based on different electricity pathways through 2050,” Environmental Research Letters, 7(045803).
[12] Roy, S. B., Chen, L., Girvetz, E. H., Maurer, E. P., Mills, W. B., and Grieb, T. M., 2012, “Projecting Water Withdrawal and Supply for Future Decades in the U.S. under Climate Change Scenarios,” Environ. Sci. Technol, DOI:10.1021/ES2030774.
[13] Tidwell, V. C., Kobos, P. H., Malczynski, L. A., Klise, G., and Castillo, C. R., 2012, “Exploring the water-thermoelectric power nexus,” J. of Water Planning and Management. 138(5), pp. 491–501.
[14] Macknick, J., Cohen, S. M., Woldeyesus, T., Martinez, A., and Newmark, R., “Water constraints in an electric sector capacity expansion model,” In preparation.
[15] Short, W., Sullivan, P., Mai, T., Mowers, M., Uriarte, C., Blair, N., Heimiller, D., and Martinez, A., 2011, “Regional energy deployment system (ReEDS),” NREL/TP-6A20-46534. National Renewable Energy Laboratory, Golden, CO.
[16] Ventyx Energy Velocity Suite, 2013.
[17] Tidwell, V. C., Zemlick, K., and Klise, G., 2013, “Nationwide Water Availability Data for Energy-Water Modeling,” SAND2013-9968, Sandia National Laboratories, Albuquerque, NM.