Power of the Sun

April 18, 2013

When completed, the BrightSource Energy-designed Ivanpah Solar Electric Generating System (ISEGS) in California’s Mojave Desert will look striking. Its innovations will provide much needed power during the peak hours of the day to more than 140,000 homes in California.

ISEGS is a 392-MW gross solar complex using more than 300,000 garage-door-size mirrors to focus the power of the sun on solar receivers atop power towers. The solar receivers are like traditional boilers, turned inside out. The project is located about 5 miles from the California-Nevada border on federal land managed by the Bureau of Land Management.

Photo: Caterpillar
The Hercules Machinery Co.’s custom-built vibratory hammer is mounted on a Cat 336E.

BrightSource Energy’s proprietary solar thermal energy system is engineered to produce predictable, reliable, and cost-competitive clean energy. BrightSource’s solar thermal energy systems generate power the same way as traditional power plants, by creating high-temperature steam to turn a turbine. However, instead of using fossil fuels or nuclear power to create the steam, the system uses the sun’s energy. BrightSource’s headquarters are in Oakland, CA.

The ISEGS complex is comprised of three separate plants to be built in phases between 2010 and 2013, and will use BrightSource Energy’s Luz Power Tower solar thermal technology. The Ivanpah facility is the first BrightSource solar power plant of this type of technology. It will also be the smallest in scale, compared to what is currently on the company’s drawing board.

It’s almost an understatement to describe the ISEGS project as being large and complex. It is unique. It is unusual. And it is a challenge.

San Francisco-based Bechtel, the giant engineering, construction, and procurement firm, is responsible for managing the construction process of the unique project. It has more than 2,000 employees working on the site.

“I had worked with grade control technology in the past and felt comfortable soliciting input early in the process to see if there might be an efficient GPS machine-control solution for building the solar fields,” states Mark Wagner, lead area superintendent with Bechtel. “We were looking at the precision placement of 173,500 pylons scattered over 3,600 acres, so traditional staking would be incredibly time consuming and very costly.”

It was clear that the ISEGS project would be more than a typical machine-control system project, so Dave George, commercial manager-worldwide with Trimble, brought in the local Trimble dealer and appropriate product and machine experts from within Trimble, including personnel from the US, New Zealand, and Holland. The project would require a highly customized solution.

The three parties-Bechtel, Trimble, and the local Trimble dealer-determined that an excavator-mounted vibratory hammer could work if the Trimble technology and custom attachment could work together. They traveled to the headquarters of the Hercules Machinery Co. (HMC), in Fort Wayne, IN, to create a custom vibratory hammer that could be mounted to a long-reach excavator, with the ability to traverse the ephemeral washes of the site and still meet the tight tolerances required for the pylon insertion.

Trimble experts recognized that determining the exact location points for the pylons with the machine-not with surveyors-had to be the solution. And the solution was found in an unconventional source.

“We were looking at 173,500 holes that needed to be drilled and 173,500 pylons that needed to be inserted,” Wagner says. “The rigs had to have the accuracy of a surveyor’s rod and the ability to collect the pylon’s “˜as-built’ data.” The answer came from Trimble, who had experience with Trimble HYDROpro Construction Software, a software package for specialized waterway and coastal construction tasks that require precise point positioning.

HYDROpro Construction’s pile feature is used for precise pile positioning applications for bridge and wharf construction. Trimble engineers were able to modify this powerful construction software for use on the Mojave Desert site where water is scarce and the average annual rainfall is less than 5 inches.

There was a tremendous amount of testing-three different rounds-before the custom approach was adopted for implementation. BrightSource has stringent requirements for its outcome and how the project would be completed.

“BrightSource had tested and rejected four other pile-driving systems from other suppliers,” states Wagner. “We were happy to provide a creative solution that would work, while accommodating the stringent environmental concerns we needed to operate within.”

Because of environmental impact concerns regarding disruption of soil, plant, and animal life, the site was not graded before the pylons were placed. The ISEGS site is under the jurisdiction of the California Bureau of Land Management and requires minimal environmental impact. The site’s three solar fields have alternating bands of “drive zones” and “no-drive zones.” Thanks to their innovative design, the excavators are allowed to maneuver and operate in the 130-foot-wide no-drive zones.

The excavators are equipped with shortened masts customized by HMC, so that they can safely reach multiple pylons from one location within the no-drive zones. The excavators have wide tracks with triple grousers for low impact. Their long reach and multiple degrees of freedom of the mast mean that they don’t have to drive up to each pylon, as a traditional pile-driving rig would have to do. Since the drill and the vibratory hammer are interchangeable on the mast, the same make and model excavators are used for both drilling and insertion. That means they travel in the same tracks with each pass through the solar field, reducing impact to the desert even further.

The Trimble HYDROpro Construction system is used strictly for its positioning and data collection capabilities, which saved Bechtel approximately 10 to 30 minutes of surveyor time per pylon, to lay out the holes, lay out the pylons, and collect the as-built data after the pylon was inserted.

“Our excavators with the HYDROpro systems provide precise XY location as well as verticality and orientation,” states Wagner. “Trimble also helped us collect Z (sea level) elevation of the top of the pylon, which is fed into and collected by HYDROpro.”

The BrightSource Ivanpah Solar Electric Generating System has 14 excavators working on the site, and all are equipped with Trimble HYDROpro Systems. The Bechtel crews are averaging between 75 and 125 pylons per day, per machine.

Each excavator cab is outfitted with a Trimble Tablet handheld computer running HYDROpro System software. The machines have two receivers-a Trimble SPS852 GNSS Modular Site Positioning System Receiver and a Trimble SPS552H Heading Add-on GNSS Receiver, which is designed to calculate the precise heading of the machine, so that all the pylons can be oriented per specification.

Additionally, the Trimble system was instrumental because GPS was required by BrightSource for converting the latitude and longitude into an ECEF or Earth Center, Earth Fixed location. BrightSource uses a center-of-earth location in relation to the sun so that each mirror in its solar generating system is precisely aligned.

The environmental impact concerns are tremendous and govern how work is completed. At any given point, there are 60 to 90 biologists and botanists onsite making sure that endangered plant life and wildlife are not harmed. Rare plants, snakes, jackrabbits, lizards, and the endangered desert tortoise are moved offsite or into nurseries until the project is complete. If a desert tortoise wanders into a work area, everything must stop until a biologist can safely remove it from harm’s way.

BrightSource’s Ivanpah Solar Electric Generating System is on schedule and becoming a reality in California’s Mojave Desert. It is currently the largest concentrated solar plant under construction in the world. According to BrightSource, the ISEGS site will become a success story for solar electric generating facilities to be built all over the world. 
About the Author

Jeff Winke

Jeff Winke is a business and construction writer.

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Photos courtesy Chino Basin Water Reclamation District.
From left: Matt Hacker, Metropolitan Water District of Southern California; Marco Tule, Inland Empire Utilities Agency Board President; Gil Aldaco, Chino Basin Water Conservation District Board Treasurer; Curt Hagman, San Bernardino County Supervisor; Elizabeth Skrzat, CBWCD General Manager; Mark Ligtenberg, CBWCD Board President; Kati Parker, CBWCD Board Vice President; Teri Layton, CBWCD Board member; Amanda Coker, CBWCD Board member.