advances in solar parabolic trough

Hank Price National Renewable Energy Laboratory, 1617 Cole Blvd., Golden, CO e-mail: henry – [email protected] Eckhard Lu ¨ pfert DLR Plataforma Solar de Almerı ´ a, Apartado 39, Tabernas E-04200 Almerı ´ a, Spain e-mail: [email protected] David Kearney Kearney & Associates, P.O. Box 2568, Vashon, WA 98070 e-mail: [email protected] Eduardo Zarza CIEMAT*—PSA, Apartado 22, Tabernas E-04200 Almerı ´ a, Spain e-mail: [email protected] Gilbert Cohen Randy Gee Duke Solar, 2101-115 Westinghouse Blvd., Raleigh, NC 27604 e-mail: [email protected] Rod Mahoney Sandia National Laboratories, P.O. Box 5800, Albuquerque, NM 87185 e-mail: [email protected] Advances in Parabolic Trough Solar Power Technology Parabolic trough solar technology is the most proven and lowest cost large-scale solar power technology available today, primarily because of the nine large commercial-scale sol ar power plan ts that are oper atin g in the Cali for nia Moj ave Des ert. Thes e plan ts, deve lope d by Luz Inte rnation al Limited and re fer re d to as Sol ar Elec tric Generating Sys tems (SEGS), ran ge in size from 14– 80 MW and repr esen t 354 MW of installed electric generating capacity . More than 2,000,000 m 2 of parabolic trough collector technology has been operating daily for up to 18 years, and as the year 2001 ended, these plants had accumulated 127 years of operational experience. The Luz collector technology has demonstrated its ability to operate in a commercial power plant environment like no other solar technology in the world. Although no new plants have been built since 1990, significant advancements in collector and plant design have been made possible by the efforts of the SEGS plants operators, the parabolic trough industry, and solar research laborat ories aroun d the world. This paper reviews the curr ent state of the art of parabolic tr ough sol ar power tech nolo gy and descri bes the R&D effort s that are in pr ogr ess to enhance this technology. The paper also shows how the economics of future parabolic trough solar power plants are expected to improve. DOI: 10.1115/1.1467922 Introduction Parabolic trough power plants consist of large fields of parabolic trough collectors, a heat transfer fluid/steam generation system, a Rankine steam turbine/generator cycle, and optional thermal storage and/or fossil-fired backup systems 1,2. The collector field is made up of a large field of single-axis-tracking parabolic trough solar collectors. The solar field is modular in nature and compri ses ma ny par al lel rows of solar col lec tor s, normal ly aligned on a north-south horizontal axis. Each solar collector has a line ar para bolic -shap ed reflec tor that focuses the sun’s direc t beam radiation on a linear receiver located at the focus of the parabola. The collectors track the sun from east to west during the day to ensure that the sun is continuously focused on the linear receiver. A heat transfer fluid HTF is heated up as high as 393°C as it circulates through the receiver and returns to a series of heat exchangers HX in the power block, where the fluid is used to generate high-pressure superheated steam 100 bar, 371°C. The superh eat ed ste am is the n fed to a conven tio nal reh eat ste am turbine/generator to produce electricity. The spent steam from the turbine is condensed in a standard condenser and returned to the heat exchangers via condensate and feed-water pumps to be trans- formed back into steam. Mechanical-draft wet cooling towers sup- ply cooling to the condenser. After passing through the HTF side of the sol ar hea t exc hangers, the cooled HTF is rec irc ula ted throu gh the solar field. The existing paraboli c trough plants have been designed to use solar energy as the primary energy source to produc e elec tric ity . Given sufficien t solar input, the plant s can operate at full-rated power using solar energy alone. During sum- mer months, the plants typically operate for 10–12 hr/day on solar energy at full-rated electric output. T o ena ble the se pla nts to achieve rated electric output during overcast or nighttime periods, the plants have been designed as hybrid solar/fossil plants; that is, a back up fossi l-fire d capab ilit y can be used to supple ment the solar output during periods of low solar radiatio n. In addit ion, thermal storage can be integrated into the plant design to allow solar energy to be stored and dispatched when power is required. Figure 1 shows a process flow schematic for a typical large-scale parabolic trough solar power plant. Background. Parabolic trough collectors capable of generating temp erat ures greater than 260°C were init iall y devel oped for indus tria l proce ss heat IPH appli cati ons. Several para bolic trough developers sold IPH systems in the 1970s and 1980s, but generally found three barriers to successfully marketing their tech- nologies. First, a relatively high marketing and engineering effort was required, even for small projects. Second, most potential in- dustr ial customers had cumbe rsome decision- makin g proce sses , which often resulted in a negat ive decision after considera ble effort had already been expended. Third, the rate of return for IPH projects did not always meet industry criteria. In 1983, Southern California Edison SCE signed an agreement with Luz Interna- tional Limited to purchase power from the Solar Electric Gener- ating System SEGS I and II plants. Later, with the advent of the California Standard Offer power purchase contracts for qualifying *Centro de Investigaciones Energe ´ ticas, Medioambientales y Tecnolo ´ gicas. Contributed by the Solar Energy Division of THE AMERICAN SOCIETY OF ME- CHANICAL ENGINEERS for publicati on in the ASME JOURNAL OF SOLAR ENERGY ENGINEERING. Manuscript received by the ASME Solar Energy Division, July 2001; final revision, January 2002. Associate Editor: R. Pitz-Paal. Copyright © 2002 by ASME Journal of Solar Energy Engi neer ing MAY 2002, Vol. 124 Õ 109 Downloaded 26 Feb 2008 to 129.74.250.197. Redistribution subject to ASME license or copyright; see http://www.asme.org/terms/Terms_Use.cfm

advances in solar parabolic trough

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