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Solar Power Plants, Water, and Climate

January 22, 2011

Solar Power Plants, Water, and Climate Change

This blog is a critique of environmental impact assessments for 17 solar power plant projects in the southwestern U.S. Thirteen of the projects are on the Department of the Interior’s fast track renewable energy developments list for public lands.1 CEQA (for projects in California) and NEPA environmental impact assessments were fast-tracked to meet the December 31, 2010 deadline for securing stimulus funding for these expensive projects.2 Data sources and annotated background information on the projects can be downloaded from our website’s Resources page as a pdf (see Endnote 2).

Whether or not enough water will be available for power plant projects in the arid southwest is a subject of controversy. The southwestern U.S.’s surface waters are already over-allocated and the various states of groundwater overdraft in many basins have not curtailed approval of further groundwater allocation for solar power plants. All of the solar projects must use water for construction in the short term, and for operations over the life of the plants. Air-cooled photovoltaic and heat-engine technologies use least, and solar thermal technologies use the most. Table 1 lists estimated water use in these categories and total use for the construction phases, which vary in duration.

Table 1. Solar Power Plant Summary of Plant Type and Projected Water Use

_________________________________________________________________________

Amargosa Farm Road. Parabolic trough, 464 MW capacity. Dry cooled, auxiliary equipment wet cooled. Operational** water use 400 acre-feet per year (afy). Construction, 39 month duration; water use, 1,950 af.

*Blythe Solar Project. Parabolic trough, 1000 MW capacity. Dry cooled, auxiliary equipment wet cooled. Operational water use 600 afy. Construction, 69 months duration; water use, 5,890 af.

*Genesis Solar Project. Parabolic trough, 250 MW capacity. Dry cooled. Auxiliary equipment wet cooling (no water use estimate given). Operational water use 218 afy total. Construction, 39 months duration; water use, 2,440 af

*Palen Solar Project. Parabolic trough, 500 MW capacity. Dry cooled, with auxiliary equipment wet cooled. Operational water use 300 afy. Construction, 39 months duration; water use, 1,500 af.

*Ridgecrest Solar Project. Parabolic trough, 250 MW capacity. Dry cooled, with auxiliary equipment wet cooled. Operational water use 150 afy. Construction, 28 months duration; water use, 1,470 af.

*Ivanpah Solar Project. Power tower, 400 MW capacity. Dry cooled, with auxiliary boiler operated during transient cloudy days or at night, water use not specified. Operational water use 100 afy. Construction, 72 months [based on assumed 6 work days/week]; water use, 2,255 af.

Rice Solar Project. Power tower, 150 MW capacity. Dry cooled. Operational water use 150 afy. Construction, 30 months duration; water use, 780 af.

*Sonoran Solar Project. Parabolic trough, 375 MW capacity. Wet cooled, 3,000 afy (assumes 25% energy production from gas co-firing); Operational water use for dry cooled alternative 150 afy (assumes 25% energy production from gas cofiring). Construction, 39 months duration, no water use estimate.

Abengoa Solar Project.  Parabolic trough, 250 MW capacity. Wet cooled. Operational water use 2,160 afy. Construction, no estimates available.

Beacon Solar Project. Parabolic trough, 250 MW capacity. Wet cooled. Operational water use 1,388 afy. Construction, 5 years duration; water use, 3,765 af.

Nevada One Solar Project. Parabolic trough, 64 MW capacity. Wet cooled. Operational water use ~400 afy. Construction, no duration or water use figures available.

*Crescent Dunes Solar Project. Power tower, 110 MW capacity. Hybrid wet/dry cooled. Operational water use 600 afy. Construction, 30 months duration; water use, 725 af.

*Imperial Valley Solar Project. Heat engine, 750 MW capacity. No generation cooling. Operational water use 33 afy. Construction, 39 months duration; water use, 166 af.

*Calico Solar Project. Heat engine, 850 MW capacity. No generation cooling. Operational water use 20 afy. Construction, 52 months duration; water use, 600 af. Rights to this land have been sold, may be used for PV installation.

*Desert Sunlight Solar Farm. Thin film PV, 550 MW capacity. No generation cooling. Operational water use 29 to 1,460 afy. Construction, 26 months duration; water use, 1,400 af

*Lucerne Valley Solar Project. Thin film PV, 45 MW capacity. No generation cooling. Operational water use 0.07 to 0.1 afy. Construction, 270 days duration; water use, 10 af.

*Silver State Solar, N & S.  Thin film PV, 327 MW capacity. No generation cooling. Operational water use 21 afy. Construction, 4 years duration; water use, 600 af.

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* Fast-track project

** Operational water use figures are given in acre feet per year (afy) for the life of the projnect, Construction uses are given in total acre feet (af) estimated to be used for the period of construction only.

Estimates of operational water consumption range from 100 to 600 afy for dry cooled solar thermal projects, from 400 to 3,000 afy for wet cooled solar thermal, and from 0.07 to 33 afy for heat engine and photovoltaic arrays (although one inexplicably ranges from 29 to 1,460 afy). Water use and project size are only slightly correlated for each type of plant.

Water use estimates for construction vary from 10 to 3,765 af for duration periods of 9 months to 6 years. Water use estimates for comparable projects vary so widely that many must be little more than guesswork, heavily influenced by project proposers. The public is not likely to see accurate figures until the projects have been in service over a substantial period. Wet cooling strategies clearly are far more water-consuming than dry cooled designs, but substantial amounts of groundwater likely will be consumed by both over the prolonged construction periods.

Wet cooling is preferred by project developers because it costs less to install and is more efficient than dry-cooling, but its use in water-scarce arid regions is discouraged both by agency and public pressure. Potentially significant operational problems might force greater reliance on wet cooling after these expensive power plants have been built, however.

The disadvantages of dry cooling include: higher capital costs (6 to 10 times the cost of wet cooling),3 higher auxiliary operating requirements (high energy use to operate fans and pumps),4 fan noise, and lower plant performance, especially on hot days, when the peak power is most in demand. Lower plant performance translates directly to higher electricity costs.

Model studies show about 5% lower performance for dry cooled parabolic trough plants, and under 2% for power tower plants. During hot periods, however, the performance penalties are more than triple: 17.6% for parabolic trough plants and 6.3% for power tower plants. Lowered generation of electricity can add significantly to the cost of the electricity produced.4 Efficiency penalties might be even greater: a technical study of hybrid air cooled power plants of the type used with geothermal sources and parabolic-trough solar thermal, discovered a 37% output reduction on hot days with air cooling than with wet (evaporative) cooling.5

A critical concern that is not assessed by any of the environmental documents I have reviewed is the potential impact of climate change on the operation of these solar facilities. The environmental assessments focus solely on the climate effects from greenhouse gas releases in plant construction and operation. Climate warming is already happening, as has been abundantly demonstrated in the scientific literature, and the predicted effects include extended drought in the southwestern U.S.6 Considering both the existing temperature and precipitation trends and the potential for abrupt climate change,7 it would be wise to assess the potential problems affecting the solar thermal power plants now being considered for installation. Prolonged hot periods are likely to bring pressure from plant operators to shift to wet cooling with a risk of depleting aquifers. Operation permits already allow night time make up of reduced solar insolation from transient cloudiness, but it is not clear that a shift to wet cooling could replace full days of hot weather. If permits do not cap permissible levels of water use, there may be trouble ahead.

Endnotes

1. U.S. Department of the Interior, Bureau of Land Management, Fast-Track Renewable Energy Projects, January 6, 2011. http://www.blm.gov/wo/st/en/prog/energy/renewable_energy/fast-track_renewable.html

2. Howard Wilshire, Fast-Tracking Solar Energy in the Desert, 2010 www.theamericanwestatrisk.com, click on Resources

3. EPRI, Palo Alto, CA, and California Energy Commission, Comparison of Alternate Cooling Technologies for California Power Plants: Economic, Environmental, and Other Tradeoffs, 2002, the initial capital costs of dry cooling systems exceed the costs of wet cooling systems by 6 to 10 times, and the fan power required for cooling is 4-6 times higher. Such penalties would substantially increase the costs of solar electricity.

4. U.S. Department of Energy, Concentrating Solar Power Commercial Application Study: Reducing Water Consumption of Concentrating Solar Power Electricity Generation, U.S. Department of Energy, Report to Congress [2008] http://www.nrel.gov/csp/pdfs/csp_water_study.pdf; U.S. Department of Energy, Estimating Freshwater Needs to Meet Future Thermoelectric Generation Requirements, 2008 Update, DOE/NETL-400/2008/1/339, 2008. http://www.netl.doe.gov/technologies/coalpower/ewr/pubs/2008_Water_Needs_Analysis-Final_10-2-2008.pdf

5. Written communication from John Rosenblum, Rosenblum Environmental Engineering,  November 30, 2010; Greg Mines, Evaluation of Hybrid Air-Cooled Flash/Binary Power Cycle, Idaho National Laboratory, October 2005

6. U.S. Global Change Research Program, Climate Change Impacts in the United States, A State of Knowledge Report from the U.S. Global Change Research Program, 2009; Richard Seager and G.A. Vecchi, Greenhouse Warming and the 21st Century Hydroclimate of Southwestern North America, Proceedings of the National Academy of Sciences, vol. 107, no. 50, 2010; Seth Shulman, Dust Bowl 2: Drought Detective Predicts Drier Future For American Southwest, Grist, 12 August 2010

7. U.S. Geological Survey, Abrupt Climate Change, Final Report, Synthesis and Assessment Product 3.4, U.S. Climate Change Science Program and the Subcommittee on Global Change Research, 2008; G.T. Narisma and others, Abrupt Changes in Rainfall During the Twentieth Century, Geophysical Research Letters, vol. 34, L06710, doi:10.1029/2006GL028628, 2007

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One Comment leave one →
  1. Ehren Evans permalink
    February 22, 2011 4:16 am

    This blog post was very informative, thank you. I speculate that another possible impact of solar power plants on water and climate in the desert is the diversion of insolation to electricity, reducing evaporation and daytime highs locally. The soils immediately in and around the solar plants might become progressively moister, year after year as the power plants divert sunlight to electricity production. This might create grassland or savannah microenvironments in the desert that will affect the local ecology.

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