Cover Story. Renewable Top Plants: Nevada Solar One, Boulder City, Nevada

Power, Dec 2007 by Peltier, Dr Robert

face= Bold; Owner/operator: Acciona Solar Powerface=-Bold;

face= Italic; Concentrating solar thermal projects fell out of favor more than 15 years ago, when the last SEGS plant was commissioned. But advances in reflective mirror, thermal receiver, and tracking system technologies have significantly improved the systems' energy conversion efficiency at a much lower capital cost. POWER recognizes Nevada Solar One as a 2007 Top Plant for pushing the limits of solar thermal technology and for being the first of a new generation of concentrating solar projects now being developed around the world. face=-Italic;

By Dr. Robert Peltier, PE

Development of solar thermal projects in the U.S. was popular in the late 1980s, when nine plants were installed in California's Mojave Desert. The familiar family of Solar Electric Generating Station (SEGS) projects has a total capacity of 354 MW; the largest two plants, rated at 80 MW each, entered commercial service in 1990 and 1991, respectively. Even though all the SEGS plants are still operating and producing power for the electrical grid at around 99% availability, loss of tax credits, developer financial problems, and changes in the California energy market ended development of solar thermal plants of this design.

Lately, a confluence of improved technologies, higher energy prices, and state renewable energy mandates has created a much more favorable climate for solar thermal generation. So solar thermal has risen again--this time thanks to Acciona Energy.

Acciona Energy may be unfamiliar to you unless you're working in the wind or solar energy business. But the company's credentials are well established, especially outside the U.S. Its portfolio of 4,690 MW installed in 175 wind farms in 10 countries makes Acciona perhaps the largest wind developer in the world. In May, Acciona Windpower entered the competitive U.S. market when it began construction of a wind turbine manufacturing plant in West Branch, Iowa. The company expects to have the capacity to produce 250 1.5-MW turbines by the end of 2008. Wind is only part of Acciona's renewables business; solar energy plants, both photovoltaic and solar thermal, also play a major role.

face= Bold; The next generationface=-Bold;

Nevada Solar One builds on the experience derived from the SEGS projects and uses much of the same solar collection technology. The project was initially developed by Solargenix Energy in 2003, although it is now jointly owned by Acciona Energia and Solargenix Energy. (Acciona Energia purchased 55% of Solargenix Energy and formed Acciona Solar Power.) The only other utility-scale concentrating solar collector-style plant in the U.S. is the Saguaro Solar Power Plant, owned and operated by Arizona Public Service. That 1-MW project uses organic Rankine cycle technology and occupies a 25-acre site near the company's existing Saguaro Power Plant, close to Red Rock, Ariz., about 30 miles northwest of Tucson. (The Saguaro Solar Power Plant was a face= Bold; POWERface=-Bold; 2006 Top Plant.)

The 64-MW Nevada Solar One, touted as the largest solar thermal plant built in the world in the past 15 years, began commercial operation in June 2007. The $250 million project, located in the Nevada desert just 25 miles southwest of Las Vegas, broke ground on February 11, 2006, and was constructed in just 16 months. Solar One is the largest renewable generating facility in the state of Nevada (Figure 1). In fact, its immense size--350 acres--is, in the words of Green TV Productions' Shaine Ebrahimi, 'mind-blowing.' (You can watch Ebrahimi's podcast interview with project leaders at www.renewableenergyaccess.com/rea/news/story?id=47845.)

Power generated from the plant is purchased by Nevada Power Co. and Sierra Pacific Power under a 20-year power purchase agreement. Nevada's Renewable Portfolio Standard requires utilities to produce 20% of their electrical generation from renewables by 2013 and includes a so-called 'solar cut-out' that requires at least one-fourth of that power to come from solar sources. After all, the solar energy that shines on Las Vegas should stay in Las Vegas.

Solargenix has a 40-year lease with Boulder City for Solar One's site at a cost of $550,000 a year. The company also signed an option to lease another 650 acres in the future. Nevada Power Co. built a new 230-kV substation to interconnect the facility. Abilene, Texas-based Lauren Engineers & Constructors was the engineering procurement/construction contractor.

face= Bold; Collecting raysface=-Bold;

The solar collection system has more than 19,000 PTR 70 steel and glass, 12-foot-long receiver tubes, provided by Germany's Shott AG (www.schott.com), located on the focal line of the 219,000 parabolically shaped mirrors (Figure 2). These mirrors focus 30 to 60 times the sun's energy on the receiver tubes. The collectors, first manufactured for the 1-MW Saguaro plant, are aligned on an east-west axis. Each mirror panel is rotated by 760 individual sun trackers to maximize the energy input to the receiver tubes. The trackers can pick up the sun when it rises just 10 degrees above the horizon in the morning. Flabeg (www.flabeg.com), another German company, provided the mirror panels (Figure 3).