Alternative Energy

Phoenix, Arizona, USA


Phoenix, Arizona, USA



* There were a lot of firsts with this project and that can be very scary for even the most talented project team.

—Barbara Lockwood, Arizona Public Service

The Saguaro solar trough power plant in Phoenix, Arizona, USA is fairly small. It only has a 1 megawatt generating capacity—enough to provide power to about 250 to 300 customers. But it's having a big impact in reviving a long-dormant type of solar technology.

Instead of using mirrors to generate electricity directly from sunlight, the Saguaro plant concentrates the sun's light through a trough of mirrors to heat mineral oil within tubes, which is then used to create steam to run a turbine. Traditionally, solar trough power plants have required tens of megawatts of generating power to run massive turbines. And because of that, the technology had largely yielded to photovoltaic solar panels that can be built and installed more cost-effectively in individual households.

That's where Phoenix-based utility Arizona Public Service (APS) saw its opportunity. Staff at the company's research facility spotted the potential for large-scale implementations.

“Around 2001 or so we started to take a serious look at how to get solar beyond the ‘onesie twosie’ rooftop stage,” says Scott Canada, APS project manager and construction manager on the Saguaro project.

To do that, the company launched a project to combine solar trough thermal technology with organic rankine cycle (ORC) engines that require less steam. That means they can leverage commercially available, smaller turbines instead of the huge ones used in previous incarnations.

And unlike traditional solar plants, which can't store energy, solar trough thermal technology can easily be combined with a storage facility, allowing sites to provide electricity whenever it's needed—not just when the sun is shining.

But Saguaro was to be the first solar thermal trough farm built since 1991—and, in many ways, that meant starting from scratch.

“Twenty years of intellectual knowledge had gone away, and the supply chains were not real strong,” Mr. Canada says. “In the last three to five years, solar construction has made a quantum leap forward, but back then there were only a handful of folks to talk to, and none had contracting experience. They were all technologists.”


Getting Up to Speed

Faced with limited industry expertise, as well as a moribund supply chain, APS knew this project would come with a steep learning curve. So it chose partners eager to gain construction and implementation skills while sharing their technical expertise.

APS selected what is now known as Acciona Solar Power, a subsidiary of Spain-based Acciona Energía, to provide the parabolic solar trough technology as well as serve as the chief coordinator on the construction of the farm itself. And Ormat International, Reno, Nevada, USA, signed on as the provider of the ORC power plant.

From the start, APS drew on its in-house expertise for the project. Doing so allowed Acciona Solar Power to get early feedback on design and conceptual details from APS and the contractor team.

110,000 square feet (10,219 square meters) The total area of mirrors on the Saguaro site

Still, Mr. Canada acknowledges the increased role was something of a risk for APS. “If you dictate too much to somebody you're paying to design and build something, it can open you up to having hard conversations about scope creep and change orders,” he says.

“But [the team was] great at recognizing that we could bring something to the party, too.”

Because solar trough technology hadn't been used for nearly 20 years, the team wrestled with finding parts, too. For example, the tubes that hold the mineral oil came from Schatt, a company just “tooling up to supply these,” Mr. Canada says.

The use of the new ORC engine also added a few twists to the construction process. “It had never been used for solar,” Mr. Canada says, which necessitated some changes in building and implementation processes.

“Solar projects are not done near a fabrication shop, for example, and idling a workforce while you drive two hours to a supply house can cost a lot of money,” he says. In the case of the engine, manufacturer Ormat addressed the issue by prefabricating as much as possible at their plant in Israel to make sure everything lined up before shipping.

APS and its partners began construction of the $6 million plant in June 2004 and completed it 15 months later. Although building a small plant wasn't the quickest route to ROI, the company felt the project was worthwhile as both a testing ground and a way to revitalize the still-nascent technology.

“APS and industry partners have a unique platform to explore new innovation opportunities, including new collector designs, thermal storage for plant dispatch ability and production forecasting,” says Barbara Lockwood, manager of renewable energy at APS.

“These innovations will further reduce the cost of solar generation and improve the value of the energy delivered from the plants.”

The bellwether project has already sparked renewed interest in a long-overlooked solar technology.

“There were a lot of ‘firsts’ with Saguaro—many that came up when we encountered challenges—and that can be very scary for even the most talented project team,” Ms. Lockwood says. “But we forged ahead. We learned and we grew. The results were a proof of concept for our company and to the industry that projects such as these could be done successfully on a large scale.”

Acciona Solar Power has already tapped into its expertise to build Nevada Solar One, a $250 million, 64-megawatt solar thermal plant that opened in June in Boulder City, Nevada, USA. Meanwhile, Saguaro has spawned larger APS projects as well, including the Solana generating station, a 280-megawatt solar thermal plant serving about 70,000 customers slated to debut in 2011.

“If online today, it would be the largest solar plant in the world,” Ms. Lockwood says. “That would not have happened without the success of the Saguaro solar trough project.” –Carol Hildebrand




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