practical. This produces improved inverter efficiency and minimizes DC cable losses. The arrangement is such that _+ 5,200 V DC and 2,438 V AC are provided at the inverter input. The plant capacity factor can be highly variable, since it is critically dependent on the plant’s geographic location. Capacity factors have been estimated to range from nearly 25.8% in the Phoenix area to just under 18% in Boston. The Phoenix site was chosen for this analysis. The reference system is designed to occupy a 4-km2 (1000-acre) site, which houses the solar arrays, switch gear, transformer station, and personnel buildings. Excluding periodic maintenance crews, the staff requirement is about 26 persons. Environmental residuals from the plant site should be minimal under normal operating conditions. No gaseous emissions should result from the normal operation of the system, and any waste heat should be removed from the arrays by natural convection. Small amounts of waste and garbage would be generated by personnel on site and small amounts of combustion products would be produced by on-site maintenance vehicles. An unquantified but small amount of runoff would result from cleaning of the solar arrays. Some environmental residuals would be generated as a result of the cell manufacturing process, but these effects have not yet been characterized. 3.2.3 Conventional Coal-Fired Power Plant The reference, high-sulfur coal-combustion system is a single-unit facility. The steam plant uses a cross-compound turbine generator with two parallel shafts and has a net plant capacity of 1250 MW. The basic steam cycle is modeled after a 1232-MW concept designed by United Engineers and Constructors (UE&C), as described in their report "Commercial Electric Power Cost Studies."10 The UE&C design utilizes a conventional lime flue-gas desulfurization system for stack gas cleaning and a mechanical draft cooling tower for removing condensate heat. The characterization represents high-sulfur coal-combustion technology and SO2 removal as projected to be available in 2000. The plant capacity factor is assumed to be 70%. It is also assumed that all of the plant's stack gases are processed to remove 90% of the SO2 (recent EPA regulations). Thus the reference high-sulfur coal facility for the year 2000 is assumed to use a Wellman-Lord SO2 removal system. The Wellman-Lord process has recently been demonstrated by the EPA, H and it is expected that this or a similar technology will be the preferred option in the year 2000. The Wellman-Lord system reduces the area of land required, but the processing of all stack gases decreases the net plant efficiency. Therefore, the plant capital cost is higher than that for the UE&C design. 10 These factors have been fully accounted for in the characterization. Figure 3.5 is a simplified schematic of the functional plant components. The combustion boiler produces steam at 26.5 x 10$ N/m^ (3845 psi) and 543°C (1010°F). Turbine power is produced with throttle steam of 24.2 x 10$ N/m^ (3515 psi) at 540°C (1000°F) for the high pressure turbine and steam at 4.1 N/m^ (600 psi) at 540°C for the intermediate pressure turbine.
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