HTF Spills/Leaks: The current heat transfer fuid (Monsanto Therminol VP-1) is an aromatic hydrocarbon, biphenyl-diphenyl oxide. The oil is classified as non-hazardous by U.S. standards but is a hazardous material in th e state of California. When spills occur, contaminated soil is removed to an on-site bio-remediation facility that utilizes indigenous bacteria in the soil to decompose the oil until the HTF concentrations have been reduced to acceptabl e levels. In addition to liquid spills, there is some level of HTF vapor emissions from valve packing and pump seal s during normal operation [11]. Although the scent of these vapor emissions is often evident, the emissions are wel l within permissible levels.

Water: Water availability can be a significant issue in the arid regions best suited for trough plants. The majority o f water consumption at the SEGS plants (approximately 90%) is used by the cooling towers. Water consumption i s nominally the same as it would be for any Rankine cycle power plant with wet cooling towers that produced the sam e level of electric generation. Dry cooling towers can be used to significantly reduce plant water consumption; however, this can result in up to a 10% reduction in power plant efficiency. Waste water discharge from the plant is also a n issue. Blowdown from the steam cycle, demineralizer, and cooling towers must typically be sent to a evaporation pond due to the high mineral content or due to chemicals that have been added to the water. Water requirements are shown in Section 5.

Land: Parabolic trough plants require a significant amount of land that typically cannot be used concurrently for other uses. Parabolic troughs require the land to be graded level. One opportunity to minimize the development o f undisturbed lands is to use parcels of marginal and fallow agricultural land instead. A study sponsored by th e California Energy Commission determined that 27,000 MWe of STE plants could be built on marginal and fallo w agricultural land in Southern California [12]. A study for the state of Texas showed that land use requirements fo r parabolic trough plants are less that those of most other renewable technologies (wind, biomass, hydro) and also les s than those of fossil when mining and drilling requirements are included [13]. Current trough technology produce s about 100 kWh/yr/m2 of land.

Hybrid Operation: Solar/fossil hybrid plant designs will operate with fossil fuels during some periods. During thes e times, the plant will generate emissions consistent with the fuel.

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