Saguaro Solar Power Plant, Red Rock, Arizona

B. Scott Canada and Jeff Lee, Arizona Public Service

Pages: 1 2 3 4

Solar energy projects over the past few years have been predominantly based on photovoltaic (PV) cells. But given enough land and flat plate collectors, just about any size plant could be constructed. Developers are still pushing the limits on PV plants, with the world's largest PV-based plant now rated at 10 MW (see profile of the Bavaria Solarpark) and larger plants being actively considered. Perhaps the most well-known solar thermal projects are the Solar Electric Generating Systems (SEGS) III–VII plants built beginning in the mid-1980s and now owned by Kramer Junction Co. Each of the five 33-MW systems continues to operate reliably, selling its output to Southern California Edison.

Together, all of the SEGS plants (I–IX) have a capacity of about 354 MW. One unique aspect of the SEGS design is its ability to supplement generation to meet peak load demands by firing with natural gas during periods of low solar energy intensity. Since the SEGS installations, advances in parabolic trough solar technology and organic Rankine cycle (ORC) power technology have made small parabolic trough plants more economically feasible.

Desert developments

Arizona Public Service (APS) is an equally familiar name in solar energy development; the utility owns an extensive portfolio of over 5.6 MW of fixed, tracking, and concentrating PV systems across Arizona. The company's interest in solar project development literally "comes with the territory"—among U.S. states, Arizona gets more than its fair share of sunshine. These projects all have helped APS develop a keen sense of which solar technologies provide the most bang for the buck. In fact, the APS STAR facility is a world-class solar research facility whose primary mission is understanding how these technologies perform in utility and customer applications.

The Saguaro Solar Power Plant (SSPP) was designed to solve a number of pressing problems for APS and others interested in developing solar energy. At the corporate level, the project will help satisfy some of APS's obligation under the Arizona Environmental Portfolio Standard (EPS) to generate a portion of its electricity from solar resources. A corollary objective is to evaluate the cost and performance of concentrating solar power (CSP) and ORC technologies for use in future renewables projects. In addition, the U.S. DOE's Solar Technology Program will use the site to help baseline the cost and performance of the current generation of parabolic trough technology and evaluate the design, installation, O&M, and performance of CSP designs (see box).

Concentrating solar power technologies

Solar thermal or concentrating solar power (CSP) plants have a marked resemblance to conventional steam plants. The obvious difference is the fuel source: A CSP system concentrates solar radiation to either heat an organic working fluid or to superheat steam, which then is expanded in a turbine-generator to produce electricity. In both cases, the working fluid is condensed after its expansion and returned to the collector to close the cycle.

Existing CSP plants use one of three alternative collector designs (Table 1). Parabolic troughs are used by the APS 1-MW demonstration plant described in this article. In the central receiver approach, large mirrors track the sun and concentrate solar energy on a central tower to heat a working fluid. A working fluid also is heated in the third approach, but by parabolic dish reflectors that concentrate solar energy at the focal point of the individual dish.

Table 1. Comparing solar thermal power technologies. Source: Concentrated Solar Thermal Power—Now! (Greenpeace International, European Solar Thermal Industry Association, and IEA/SolarPACES, 2005). Photos courtesy of National Renewable Energy Laboratory

Pages: 1 2 3 4