fossil power plants

Assessing the Environmental Impacts of Solar/Fossil Power Plants Carolyn T. Hunsaker, Donald B. Hunsaker, Jr., Harlan H. Hashimoto, Michael M. Simpson, Richard L. Perrine, and Robert G. Lindberg

Carolyn Hunsaker is a Research Associate with the Environmental Sciences Division, Oak Ridge National Laboratory (ORNL). Donald Hunsaker, Jr., is a Research Associate with the Energy Division, O R N L . Michael Simpson is an Environmental Health Fellow with the Congressional Research Service, Washington, DC and Harlan Hashimoto is with the Department of Health, Honolulu, Hawaii. Richard Perrine and Robert Lindberg are faculty members in the Environmental Sciences and Engineering Program, University of California, Los Angeles.

statement or similar document to provide data for the setting. T o do this, one must have some idea of the type of region (coastal, desert, etc.) in which the technology would most likely be sited. One criterion for the suitability of an environmental assessment is the size of the project for which the assessment was done. Typically, thorough environmental analyses are performed for large projects that are expected to have maj or impacts on the environment. These analyses often contain a wealth of environmental setting data. The third step in the process is to t describe the environmental setting. The purpose of this step is to define the existing environment so that the magnitude of the environmental impacts resulting from the construction and operation of the technology can be gauged. Lastly, the resource demands of the technology and the available supply of resources are computed to determine what impacts might be expected. Significant impacts identified by the assessment method should be considered in greater detail. Impacts not significant for the study site should also be evaluated with regard to generally suitable sites. The results of the detailed studies would then form the basis for making any changes in the design or operation of the technology to mitigate negative impacts.

Hybrid solar/fossil power plants have been proposed as a technology that would minimize the disadvantages and maximize the advantages of solar and fossil power plant technologies. T h e development of hybrid solar/fossil power plants is in its infancy (Yokomizo, C.T.V. 1981. System Review: Central Receiver System. Livermore, California: Energy Systems S t u d i e s D i v i s i o n , S a n d i a N a t i o n a l Laboratories). T h i s p a p e r presents an assessment method to quickly i d e n t i f y the m a j o r e n v i r o n m e n t a l impacts of this new technology, and to d e t e r m i n e w h e t h e r it offers a n y advantages or disadvantages over either an exclusively solar or coal-fired plant. There are five steps to follow in identifying the environmental impacts and engineering issues (hereafter referred to collectively as "impacts") associated with hybrid solar/fossil power plant technology. The first step is to define the resource demands of the technology. T h e second step in the process is to locate an environmental impact

The hybrid solar/fossil system designed by Rockwell International et al. was chosen for this study primarily because it ~ s the largest g e n e r a t i n g c a p a c i t y h y b r i d solar/fossil p l a n t described in the literature at the time of this study (Rockwell International, University of Houston, McDonnell-Douglas, Salt River Project, Stearns-Roger, Babcock and Wilcox, and SRI International. 1980. Solar Central Receiver Hybrid Power Systems, Sodium-cooled Receiver Concept. Final R e p o r t , Vols. I-III. C a n o g a Park, California: Rockwell International). I m p a c t s i d e n t i f i e d for the largest commercially feasible plant were assumed to represent the worst potential problems to be faced by the technology. The completeness of design was also an important consideration in selecting the Rockwell configuration. Discussions in

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this paper are intended neither as an endorsement nor as a criticism of the Rockwell design. Figure 1 presents a map view and illustrates the major components of the Rockwell design of the hybrid technology. The system utilizes a fluid-cooled receiver located atop a tower. Surrounding the tower is a circular field of heliostats (mirrors) that direct the sun's energy onto the receiver surface. This energy is conducted away by molten sodium pumped through the receiver. The heated fluid is then used in steam production to drive turbines that generate electricity. Part of the fluid's thermal energy is stored and used to maintain power production during brief interruptions in insolation, such as occur with transient cloud cover. Coal is burned to heat the working fluid at night, when operation of the solarpowered system is impossible (e.g., during storms), or when peak insolation is temporarily mismatched with peak electrical demand. Table 1 summarizes pertinent engineering data for the plant.

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Environmental Setting Ses~eral environmental assessment and impact documents dealing with large power plant sites in desert locations were scanned for this study. We considered the e n v i r o n m e n t a l report ( c o n s t r u c t i o n permit stage) prepared for the Sundesert nuclear plant (San Diego Gas and Electric Company. 1977. Environmental Report, Construction Permit Stage, Sundesert "Nuclear Plants, Units I and 2. San Diego, California) to be the most suitable to the purposes of this study. The Sundesert nuclear plant, which was never built, was to have been located near the town of Palo Verde in eastern Riverside County, California. Site resources for a hybrid solar/fossil power p l a n t necessarily require solar radiation of appropriate quantity and quality. Solar radiation data (daily solar radiation averages 2.1 x 107 J / m ~) and cloud cover data (27% average cloudcover) collected at Yuma, Arizona, indicate the suitability of the Palo Verde area for s o l a r e n e r g y c o l l e c t o r s . (Department of Water Resources. 1978.

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Calilornia Sunshine - Solar Radiation Data. Bulletin No. 187. Sacramento, California: State of California Resources Agency).

Major Impacts Unique to a Hybrid Solar/Fossil Power Plant Impacts were considered in a broad context which included the effects of the environment on the facility, and of the facility on itself (intraplant or engineering issue). An initial screening identified air quality, land use, water use and quality, hydrology, geology and soils, o c c u p a t i o n a l h e a l t h a n d safety, meteorology, socioeconomics, vegetation and wildlife, aesthetics, and solid waste disposal as impact categories we felt would be most important or unique to a hybrid solar/fossil power plant, and these were analyzed in the most detail (Environmental Science and Engineering. 1981. Environmental E l # a s ol Solar Thermal Power Systems, Environmental Considerations in Siting a Solar-Coal H y b r i d P o w e r P l a n t , V o l u m e 1: Environmental Assessment. University of California, Los Angeles: Environmental Science a n d E n g i n e e r i n g P r o g r a m , Laboratory of B i o m e d i c a l a n d Environmental Sciences). This paper reports on the impact categories that were determined to be of major significanceand uniquely associated with a hybrid/fossil plant or to be of major significance to a solar power plant - - land use, air quality, hydrology, geology and soils, and aesthetics. Land Use The major land-use impact from a solar power plant is the large land area requirement (12 km ~ for a 430-MW plant without an exclusion area) compared to other c o n v e n t i o n a l power plants (Sundesert would have required 2.6 km 2 for two 950-MW nuclear plants). An exclusion or limited access area might be warranted for safety or security reasons or to limit dust and aerosol deposition on heliostats. An exclusion area would significantly increase the land area required by a solar facility; however, the exclusion area could also serve a secondary use as a wildlife reserve. The large land area requirement for a solar power plant is

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considered to be a significant impact unique to a solar facility that requires large land areas covered by solar collectors, whether they are heliostats, photovotaie cells, or trees. The amount of land required for a hybrid solar/fossil or solar plant was not considered to be a major constraint for the Palo Verde study site or other desert locations where a large amount of similar o p e n l a n d exists. H o w e v e r , the construciton of a hybrid solar/fossil plant could significantly exclude or constrain other land uses such as agriculture, as well as limit present uses of open space (offr'oad recreational vehicles). Availability of land at the Palo Verde site does not appear to be a problem for the hybrid study plant. Changes in zoning would be required. Disturbance (grading and clearing) of the land for construction is certain, and an increase in the h u m a n p o p u l a t i o n is expected d u r i n g the construction phase. Nearby lands to the east support an intensive agricultural industry. Open space would be used for urban development as the demand for public services and housing in the area increases. The exact impact of building a hybrid solar/fossil plant on local land uses is uncertain, but, as a minimum, urban development would increase primarily to accommodate workers during the five-year construction phase.

Air Quality The air quality impact assessment focused on impacts of one p l a n t component on another and on effects of the environment on the plant because available literature suggested that these effects could be potentially the most significant impacts u n i q u e to the facility (King, D.L., and Meyers, J.E. 1978. Environmental Reflectance Degradation o / C R T F Heliostats. Albuquerque, New Mexico: Sandia Laboratories; Peterson, J.T. and Flowers, E.C. 1977. Interactions Between Air P o l l u t i o n and Solar Radiation. Solar Energy 19:23-32). It was important to assess whether air pollution generated at or near the plant would compromise, in any way, the operation of the solar components of the power plant. Interactions between solar energy and air pollution have been studied extensively

(Bird, R.E. and Hulstrom, R.L. 1979. Aerosols and Solar Energy. Paper presented at the Workshop on Artificial Aerosols, sponsored by the Institute for A t m o s p h e r i c Optics and R e m o t e Sensing, and the Naval Research Laboratory SERI Report No. T P 36-309. Golden, Colorado: Energy Research Institute. Microfiche; Peterson and Flowers 1977), and the results of these and other studies indicated that air pollution could affect the operation of the solar component in two ways: 9 pollutants could settle out of the air onto the heliostat surfaces, thereby degrading the reflectivity of the heliostats; . pollutants could remain suspended in the air and could reduce the intensity of incoming sunlight to the plant's heliostats. A preliminary emissions inventory compiled for the hybrid plant identified the following major sources of air pollution: coal handling and combustion, cooling tower operation, vehicular travel, and land disturbance. Two other sources of air pollution that could be significant but which were not evaluated are crop dusting and d u s t storms. The most commonly used technical tool in air quality impact assessment is the numerical model that translates atmospheric emissions into ambient concentrations. F o r the air quality impact assessment done in this study, models were used to r e h t e - p o l l u t a n t emissions to the impacts of interest - pollutantdeposition on heliostat surfaces and insolation attenuation. For pollutant depositon, the major pollutants of concern were those with a large e n o u g h mass to deposit on heliostat surfaces; thus we were primarily interested in solid and liquid aerosols. The Aerosols on the Surface of Heliostats model (ASH) was developed during this study as a tool to relate emissions of aerosols from a variety of sources to aerosol accumulation rates on heliostat surfaces ( H u n s a k e r , D., Hunsaker, C.T. and Perrine, R.L. 1981.

Environmental E]lects o] Solar Thermal Power Systems, .Vol. 11: Air Quality and Meteorology Impacts. Los Angeles,

California: UCLA Environmental Science and Engineering Program, Laboratory of B i o m e d i c a l a n d Environmental Sciences; Perrine, R.L. 1981. Some Environmental Consideration in Siting a Solar/Coal Hybrid Power Plant. In Beyond the Energy Crisis,

Opportunity and Challenge, R. A. Fazzolare and C.F. Smith, eds. New York: Pergamon Press). Basically, the ASH model multiplies ambient concentrations of particles (in g / m ~ ) as predicted by a Gaussian dispersion model (e.g., Turner, D.B. 1970. Workbook o/ Atmospheric Dispersion Estimates. PHSP No. 999-AP2~. Washington, DC US Department of Health, Education and Welfare) by the surface wind speed (in m/s) to arrive at a particle deposition rate expressed as grams per square meter-second. Ten percent of the total mass of particles colliding with heliostat surfaces is assumed to stick to and accumulate on the surface, thereby degrading heliostat efficiency. T h e exact m i n i m u m mass of accumulated aerosols that will begin to degrade heliostat efficiency is not currently known. There is a definite lack of research and published results in the a r e a of q u a n t i f y i n g reflectance degradation as a function of quantitative measurements of physical changes to heliostats (e.g., reflectance as a function of percent surface covered, etc.). Data describing the effects of deposition of particles of different sizes and chemical compositions on heliostat performance :are also lacking. Those data would permit a more rigorous analysis of the negative air quality impacts of aerosolgenerating a c t i v i t i e s at h y b r i d solar/fossil plants. The ASH model was applied to emissions from coa! h a n d l i n g and combustion, cooling tower operations, and vehicular uavel. As an upper limit, worst-case estimate, approximately 2 to 4 kg of coal particulates and salt particles' from cooling towers could accumulate on a heliostat in a 30-day period; fugitive dust can increase this byanother I to 2 kg, and coal handling and intraplant vehicle travel may also contribute significantly to this total. Dust storms and crop dusting could add additional quantities of particulate matter to the heliostat s u r f a c e s . T h e exact q u a n t i t i e s of EIA REVIEW

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Table 1

Summary of the Major Characteristics of the Hybrid Solar/Fossil Plant

Design power level Operating lifetime Thermal storage capacity at 100% load Land area Number of heliostats Heat rejection methods Central tower height Distance to cooling towers Water consumption Heliostat cleaning Cooling towers Flue gas desulfurization Coal consumption at 100% load Coal storage capacity (52 d of 1OO% capacity) Dead Live Air pollutant emission controls Sulfur dioxide

Nitrogen oxides Particulates

420 MW 30 years 3h 12.3 km = 60,680 2 mechanical-draft, wet cooling towers 3300m 1,570 m 1.5 x 10 lo m3/year 7.7 x 101=m3/year 4.0 x 1Ol~m3/year 203,000 kg/h 258 x 106 kg 20 x 106 kg Dry flue gas desulfurization system Dual register burners: no excess air Fabric filter

Source: Rockwell International et aL 1980. deposited material are not important because the relationship between particle loading a n d reflectance degradation is not well u n d e r s t o o d a n d because u n c e r t a i n t i e s a r e - i n h e r e n t in the modeling exercises. T h e p o t e n t i a l a t t e n u a t i o n of insolation by pollutants suspended in the air was evaluated using a Rockwell International et al. (1980) computer p r o g r a m ( S O L A R ) . B a s i c a l l y , the S O L A R p r o g r a m uses a dispersion model (US EPA. 1977. User's Manual/or the Single Source (CRSTER) Model. EPA450/2-77-013. Research Triangle Park, North Carolina: Office of Air Quality P l a n n i n g and Standards) to predict ambient pollutant concentrations, and then uses these concentrations with Beer's Law to estimate the intensity of available insolation below the plume. T h e model

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produces a conservative estimate of the potential reduction in radiation intensity that could occur.The S O L A R program was run only for emissions from coal combustion. Results indicated that a 25% reduction in insolation intensity could be caused by the coal plume. Studies conducted at Denver, Colorado, showed that a 25% reduction in insolation can cause a 40% reduction in annual energy collection (Bird and Hulstrom 1979). One major ramification of the aerosol deposition modeling exercise is that not all of the heliostats are expected to require the same washing schedule. Mass deposition rates, and therefore cleaning frequency, are expected to depend on the location of the heliostat in the field in relation to the emission s o u r c e s a n d the p r e v a i l i n g w i n d direction.

Hydrology Solar technolog,y such as the Rockwell design requires a large site for the heliostat field. Construction of the p l a n t would alter surface water runoff patterns over a large area (13 km~), and surface runoff would be significantly increased if the site were paved. Impacts could be decreased if the heliostat field is not paved. Conceivably the soil surface could be stabilized with vegetation to maintain and possibly increase rainwater infiltration, decrease erosion, and reduce fugitive dust emissions. Sediment basins should be constructed to retain eroded sediments and thus reduce discharges of suspended solids to streams. T h e alteration of hydrological patterns for such a large desert area is considered significant and also a function of the large land area requirement of the solar plant component.

Geology and Soils T h e large l a n d area r e q u i r e m e n t s associated with solar power plants would result in a significant impact to the site terrain. Details concerning design requirements for the heliostat field were not available. T h e Rockwell report gives only one height specification for the heliostat pedestals, implying the need for a flat field. We assumed, therefore, that the heliostat field would require grading. Additionally, trenches would be dug for the underground control and power cables connecting the heliostats to the central control. Finally, a certain a m o u n t of grading and leveling of the site would remove vegetation a n d destroy the "desert pavement or crust," which is made up of densely p a c k e d pebbles a n d stones cemented or encrusted with salts, gypsum, limes, and silicates and which retards erosion and surface water runoff. Local hydrological patterns would be altered significantly, and wind erosion of soils could result in adverse impacts to neighboring land as well as to the solar facility's efficiency. Impacts from alterations of hydrological patterns and soil erosion could be reduced by limited grading on the site. Grading requirements could be greatly reduced by using heliostats with

variable pedestal heights calibrated for different positions on the field. Careful p l a n n i n g and execution might greatly reduce the number of temporary service roads a n d v e h i c u l a r a n d materials movements.

Aesthetics Reflections from the solar component might have a significant visual impact on nearby residents and travelers on local roads. T h e potential impact of reflections will not be quantifiable until a large solar power p l a n t using heliostats is operating. tt

Conclusions Air quality and land use were determined to be the significant engineering issues and environmental impacts (of the impact categories evaluated in this study) unique to a hybrid, solar/fossil power plant. T h e large land area requirement of a solar power plant could result in significant changes to surface runoff patterns and volumes and increased potential for soil erosion in desert areas. T h e diffuse nature of solar radiation makes the formulation of a strategy to m i t i g a t e land-use i m p a c t s difficult. Although water issues and impacts on vegetation and wildlife were not judged significant for the Palo Verde study site, these could be significant constraints to s i t i n g a h y b r i d s o l a r / f o s s i l facility 'elsewhere (e.g., a scarcity of appropriate quality water or the presence of rare, threatened, or e n d a n g e r e d species). Hybrid technology impacts in the areas of occupational safety and health, climate modification, and solid waste disposal were evaluated and found to be similar to those of a n y large p o w e r p l a n t . Socioeconomic impacts are expected to be s u b s t a n t i a l d u r i n g the c o n s t r u c t i o n phase, especially in rural areas such as the Palo Verde site. Because the facility would be highly visible in the local area, it could have a significant aesthetic impact. With regard to the expected effects of the environment on the facility, air quality was.of greatest concern. At issue was the question of degradation in heliostat performance resulting from fugitive dust and crop dusting. A substantial source of fugitive dust was

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determined to be residual material produced during construction that had blown off the site during construction but that had remained close enough to be blown back onto t h e site after plant operation had begun. A second fugitive dust source was associated with off-road recreational vehicles. This concern could be mitigated by an exclusion or controlled access area surrounding the facility, but a substantial increase in the facility's total land requirement would be involved. An additional source of particulate matter that was not addressed, but that could be significant, is cuhivation of nearby agricultural lands. The greatest concern in terms of intraplant or engineering issues was also for air quality. Attenuation of solar insolation by coal combustion emissions and impairment of heliostat efficiency from particulate deposition on heliostat surfaces were viewed as significant problems that could reduce the efficiency of the facility. Both problems could be mitigated by the use of cleaner b u r n i n g fossil fuels. Analysis of the potential degradation of heliostat surfaces was constrained by limited information on heliostat mass loading characteristics. The assessment method used in this study combined the detail of a sitespecific assessment with the broad

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coverage of a generic assessment, thus identifying issues and impacts that are significant a n d / o r unique to a new technology. Its major.value is to identify environmental impacts and engineering issues at an early stage in technology development and in a relatively short time so that the technology can be modified to mitigate potential problems. Acknowledgments Research for this study was sponsored by the US Department of Energy under Contract DE-AM03-76-SF00012 between the US Department of Energy and the University of California, Laboratory of Biomedical and Environmental Sciences, Los Angeles. Publication No. 2244, Environmental Sciences Division, Oak Ridge National Laboratory, operated b y U n i o n Carbide Corporation u n d e r contract W-7405-eng-26 with the US Department of Energy. For more information contact: Carolyn T. Hunsaker Environmental Sciences Division Oak Ridge National Laboratory P.O. Box X Oak Ridge, Tenn. 37830 (615) 574-7365