Utility-scale with a capital ‘U’: First Solar’s Agua Caliente PV project pushes toward initial power

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Tom Cheyney
Tom Cheyney
Tom Cheyney, former senior editor of PV-Tech and Photovoltaics International, is now chief curator of SolarCurator.com and director of Impress Labs’ solar practice.

The deserts of southwestern Arizona include a whole lot of empty terrain, interrupted occasionally by one of a handful of small towns, both alive and ghostly, as well as patches of irrigated farmland and mineral excavation sites. The rugged, scrubby landscape stretches for miles on either side of Interstate 8, the main west-east artery in that part of the US. The scale of the vast expanse swallows up thousand-acre parcels like a rattlesnake gobbling up a baby field mouse.

But something impressive and historic is rapidly taking shape on 2,400 acres of former agricultural lands and military proving grounds up the road a piece from the tiny burg of Dateland in Yuma County, within spitting distance of the high-strung wires of the Hassayampa-North Gila 500kV #1 power transmission line. Agua Caliente Solar Project, the largest utility-scale photovoltaic power plant currently in advanced construction, soon will be generating electricity from an area nearly three times the size of New York’s Central Park.

If all goes according to plan, the first “chunk” of what will eventually be a dozen power “blocks,” each comprised of hundreds of thousands of First Solar cadmium-telluride thin-film PV modules installed on specially designed fixed ground-mounted arrays, will be coming online and delivering energy to transmission operator Arizona Public Service by the end of 2011. At least 40–50MW (AC) of Agua’s eventual 310–320MW (AC) total capacity – a number that has risen since the decision to add a 12th block – will be commissioned by the end of the year.

Sometime in 2012, when the next series of blocks are plugged in and energized, Agua will become the first PV power farm in North America to reach triple-digit installed capacity, signaling the beginning of the era of true utility-scale solar PV. By the time the plant is completed in 2014 and other similarly large (or larger) operations are either online or close to it, the now-impressive 10, 20, and 40MW farms, even Sarnia’s 80MW, may be regarded nostalgically as boutique utility scale.

Over the course of the 25 years of NRG Energy’s power purchase agreement with Pacific Gas & Electric (PG&E) and First Solar’s operations and maintenance deal with the owner, Agua will generate hundreds of thousands of gigawatt-hours of power per annum. In such a classically insolated location, benefiting from well over 300 sunny days per year and DNIs in the upper ranges, the power plant should actually pass the terawatt-hours mark within several years.

Whether viewing the massive project from the observation tower next to the air conditioned mobile-home main offices of developer/EPC/O&M lead First Solar and owner NRG or driving around on the miles of roads criss-crossing the acreage for a close-up look, it was readily apparent during my late September visit that Agua, albeit in various stages of construction, was proceeding at maximum velocity toward that terawatt future. Close to a million modules were already installed and the first power generation systems neared “substantial completion,” while scores more boxes of the CdTe panels were being offloaded from trucks for imminent deployment. Containers of combiner-box components and man-size spools of wire waited for assembly or placement.

Although several areas were already under glass, construction was still in its early stages in other zones, as Buesing’s earth movers and other heavy equipment cut, filled, and graded the earth and water trucks did their part to spray down the ever-present dust. Across the access road in another block, thousands of galvanized-steel posts were being driven into the ground by First Solar teams, while alongside that stretch of dirt, various tilt brackets, tables, and other racking elements were being installed.

Dozens of power conversion station (PCS) vaults, each containing a pair of SMA inverters, had already been deployed, with a couple more resting on the back of flatbed trucks and others being craned into position. Similar looking PVCS structures (short for “photovoltaic combining switchgear”) had also started to proliferate along the edges of the blocks, where the juice coming out of the inverters will be collected and then sent via power poles to the substation and eventually out to the APS grid.

The main substation, located on the south side of the acreage a few hundred meters from the Hassayampa-North Gila transmission line, looks the part of a large utility-scale structure. Its transformers and various subsystems were in full horizon-blocking effect, waiting for the day when the system steps up the 34.5kV of juice coming from the field to 500kV and jumps it over to APS.

Site manager and tour guide Raymond Christian provided some specifics of the project’s current status as well as a broader view of the activities swirling around the location. The veteran construction hand and former US Marine was obviously energized about the goings-on at Agua, but also careful not to reveal too much about the distinctive methods and specially designed gear that First Solar uses in its build-outs of solar farms.

He exhibited some of this discretionary caution when I asked him about an unusual design element on the inner edge of the arrays along each side of an access road, where single rows of posts and tilt brackets sat empty next to completed or nearly completed racks of modules. But he wouldn’t explain why they were set that way, calling the layout an “IP design feature.”

“It’s part of the method behind our madness,” he said. “Things like that are proprietary from a design standpoint and proprietary in the way that First Solar conducts business on a day-to-day basis. We’re very proud of the fact that we can go ahead and put one of these [projects] together in short order. We think it has to do with the special way we do sequencing of construction and these types of things, so we would like to keep those things secret.”

Christian did share an impressive factoid about the rapid installation of the tables that sit on top of the posts and brackets and help support the 25-degree-tilted modules as part of the racking system. “Those tables are about 20 feet long when they’re expanded, and their dead weight is 155 pounds plus. They come in packages of 18, and one crew of three can actually install a rack of 18 of them in about eight minutes. Not necessarily lock them in their final position, but actually install them. For the most part, they look pretty clean, straight, and uniform.”

In another Agua zone, where scores of rows of dusty thin-film panels were already installed a few feet off the desert floor, with native ground-cover starting to take root underneath the glass, he pointed out a more-pronounced-than-normal dip and crown in one of the arrays, something that will be taken care of before that block is signed off.

“We will come back with a remediation team and take the kick out of it,” he said. “We’ll go in underneath the table and tilt brackets, loosen the brackets, and reset the rest of the mount. It’s an aesthetics thing, as long as we meet our torque threshold for retorquing the title brackets back down.”

During an impromptu briefing on the tower, the project boss listed the latest – and largely at or over goal – completion percentages for certain parts of the site, culled from that day’s latest EPC construction dashboard data presented at the morning meeting. Some 67% of dirt work was completed and ready for the surveyors to lay out the “structurals.” As for those pieces of steel, about 49% of the posts were driven and 38–39% of the tilt brackets, tables, and the like had been set up. Eighty-five of the planned 246 PCS vaults had been built and placed. 

The teams were in “push” mode as the end-of-quarter goals were fast approaching, and nowhere was that more apparent than the status of CdTe panel deployment. With 879,000 modules installed to date, the target was to boost that number to 1.4 million by month’s end. Christian said that the crews placed 70,000–75,000 modules per day (night actually, since that’s when the glass is attached to the arrays at the 24/7 work site for safety reasons related to Agua’s superheated desert location).

The daily installation rate translates to well over 5MW (DC), since the Series 3 modules used have ratings in the 75–77W range. The 1.4 million pieces of PV glass set to be in place by September 30 represent at least 105MW (DC); using an updated 1.26:1.0 DC:AC conversion ratio, that translates to approximately 83MW (AC).

The original nameplate for the entire plant was 290MW (AC), but Christian said that a 12th block is in the engineering stage and should start early construction soon. The additional set of arrays would add another 20–30MW (AC), bringing the total to 310–320MW (AC), or about 397MW (DC) after conversion – an amount estimated to require in the neighborhood of 5.2 million PV panels.

At ground level, all of that solar power is broken down into 20,940-module arrays, currently specified at 1.26MW (AC), according to the site manager. This represents an upgrade from the 1MW array size found at the 21MW (AC) Blythe plant not too far north (at least as the turkey vulture flies) of Agua. Another obvious difference between the arrays at the two sites: the newer racks sport four modules vertically, compared to three up at the older power plant. A close look also revealed new types of module clamps holding the glass in place.

In addition, the pair of SMA inverters converting the DC to AC at each array are rated at about 630kW versus the 500kW Siemens units found at Blythe. The PCS vaults that house the inverters have also been redesigned with a proprietary venting and cooling system that eliminates the need for HVAC – and dramatically lowers the parasitic power load as a result, said Christian.

While not mentioning other specifics, he noted there were many improvements in system design since Blythe and even Sarnia were built, including fewer pieces to assemble and more factory preassembly, as well as more efficient installation/construction practices, plus what he called a “changing footprint” as far as what’s required to build bigger system like Agua.

He also cited some other project statistics, which although nontechnical, underscored the scope of the job. Each of the 1400–1600 workers is required to drink at least three liters of water per day, and a range of safety personnel, procedures, and equipment are in place to make sure people are properly hydrated and cooled down if they start to suffer from the heat. The equivalent of a small berg’s worth of ice, nearly 2,500 pounds, is also delivered each week.

Between 60 and 80 trucks come to the worksite daily, with about 7,000 expected to pass through during the course of the project, according to Christian. While the speed limit throughout much of Agua is 10.5mph, certain internal roads have been paved to mitigate the dust raised by the trucks and also allow for a faster limit of 25mph so the vehicles can complete their deliveries and leave the site as quickly as possible.

Some of those  trucks transport PV modules (coming from First Solar’s manufacturing facilities in Ohio, Germany, and Malaysia), but the loads don’t stay in inventory for long. Christian said a “buffer” of about 65,000 panels “above and beyond what is consumed daily” is available onsite – although the actual breakage/damage rate for modules is 0.25%, well under the allowable level of 2–3%. Noting they don’t want to build up stock, he said the goal is “just-in-time deliveries and just-in-time consumption.”

Throughout the site, teams collect and transport pallets, cardboard boxes, plastic, and other materials back to a dedicated recycling yard for processing so that no spoilage in its raw form leaves Agua. He expects 2,500 tons of cardboard to be used and recycled over the course of construction.

Although proud of the recycling effort, First Solar’s Agua Caliente project point man has more important things on his mind, like meeting the deadlines for “substantial completion” of the first three power blocks and making the handoff to the commissioning, start-up, and operations and maintenance teams by year’s end.

A critical step to putting the power on the grid will take place sometime toward the end of November or beginning of December, when a planned outage on the APS line will allow for a tie-in at the utility’s switchyard, he said. After that, there’s “a lot of functional testing, load testing, and the like that go over a timeline before the actual release [of electricity] back through the substation and then to the APS (Hoodoo Wash) switchyard, and ultimately out on the grid.”

If the interconnection timeline holds, the first dozens of megawatts of photovoltaically-generated power will wend their way through the APS transmission lines to offtaker PG&E’s customers less than five months after the finalization of the Department of Energy’s US$967 million loan guarantee for Agua and NRG’s subsequent acquisition of the project from First Solar, offering a robust, real-world counterpoint to those who have questioned the program’s effectiveness.

(This blog-feature also appears in the new PVI Lite edition, which is available in digital format here and will be distributed in a print version at the Solar Power International 2011 show in Dallas, TX.)

 

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