Sun Light and Power: Clif Bar and Company
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Clif Bar & Company, a leading maker of energy and nutritional foods and drinks, recently moved into its new headquarters in Emeryville, California. Clif Bar contracted with Sun Light & Power (SLP) of Berkeley, California, to provide a turnkey design/build 531 kW PV system as part of a substantial renovation.
Clif Bar consultants initially rejected using the existing roof of the building for modules due to its broken-up nature and limited structural capacity, and focused instead on the top level of the existing parking garage for the placement of the proposed PV system. However, since Clif Bar wanted to offset as much electrical usage as possible, SLP designed an expanded system on the garage and took on the challenge of using the building roofs as well. The resulting system of 1,968 Suntech 270 W modules, plus Tigo Energy Maximizers, is predicted to offset more than 80% of the anticipated electrical loads at the facility.
One of the biggest challenges of this project was determining how to create a structure that would interface with the existing parking garage. SLP was constrained by irregularly placed columns and a post-tensioned slab that could not accept any additional load. The final design used a custom long-span framework topped with C-channels to which the modules were directly mounted. Installing this framework required retrofitting the parking garage’s column anchors. This phase of construction required weeks of ground-penetrating radar scanning and very careful coring for exact anchor placement.
The Tigo Energy Maximizer system allows increased production, modulelevel monitoring and control, and very detailed information that will be utilized to assist in the array’s operation and maintenance. This system was installed under California’s performance-based incentive; therefore, the additional energy production and granular monitoring justified the additional hardware expense.
Each Maximizer unit communicates wirelessly with a hardwired gateway, so additional communications cables are not required throughout the array. Setting up the gateways and Tigo wireless network required substantial troubleshooting and support from Tigo. This was the largest Maximizer system ever built. However, by the final project phase, SLP and Tigo had worked out all the kinks. Everything went smoothly with the installation of the last 1,500- plus Maximizers.
Since interconnecting on the line side of the service disconnect would have required rebuilding the entire 3,000 A, 480 V switchgear, a load-side connection was used. This required SLP to procure some specialty parts from the switchgear manufacturer and position them, along with the incoming conductors, into a tight space.
The SLP project manager for the job, Randy Haberl, was challenged in planning a project that involved a lot of custom work, a large SLP crew and many subcontractors for areas including steel design, fabrication and erection; priming and painting; striping; wire rope; scanning; coring; roofing; lighting design; communications; trenching; concrete and doweling; various crane lifts; forklifts and scissor lifts; scaffolding; and more.
The on-site challenges were a major contributor to the relatively long installation time frame. However, the contractor considers the project a huge success and the customer calls it a “great job.”
“The Clif Bar project was extremely challenging and satisfying. We had to work with the existing structure of the building and parking garage, around building tenants and during business hours, installing only surface conduit and electrical equipment. Almost every aspect of the build is unique.”
—Koralie Hill, foreperson, Sun Light & Power
DESIGNERS: Yun Lee and Ben Bachelder, project engineers, Sun Light & Power, sunlightandpower.com
LEAD INSTALLER: Koralie Hill, foreperson, Sun Light & Power
DATE COMMISSIONED: August 2011
INSTALLATION TIME FRAME: 10 months
LOCATION: Emeryville, CA, 37.8°N
SOLAR RESOURCE: 4.9 kWh/m2/day
HIGH/LOW DESIGN TEMPERATURES: per solarabcs.org/permitting/map: 77°F/34°F
ARRAY CAPACITY: 531 kW
ANNUAL AC PRODUCTION: 800 MWh
MODULES: 1,968 Suntech STP270- 24/Vd, 270 W STC, +2/-0%, 7.71 Imp, 35.0 Vmp, 8.2 Isc, 44.5 Voc
INVERTERS: 3-phase, 277/480 Vac service, Satcon PVS-500, 500 kW, 600 Vdc maximum input voltage, 320–600 Vdc MPPT range
ARRAY: 12 modules per string (3,240 W, 7.71 Imp, 420 Vmp, 8.2 Isc, 534 Voc); 12 strings per combiner (38.9 kW, 92.5 Imp, 420 Vmp, 98.4 Isc, 534 Voc); 164 strings total (531.4 kW, 1,264 Imp, 420 Vmp, 1,345 Isc, 534 Voc), one Tigo MM-ES50 Energy Maximizer installed per module
ARRAY INSTALLATION: 420 modules installed on five modified bitumen low-slope roofs, custom pipe-racking structure with ProSolar rail and module clamps; 1,548 modules installed on new custom steel superstructure above existing parking garage top level; 165° azimuth, 5° tilt (all modules)
ARRAY STRING COMBINERS: 14 AMtec Prominence 12, 15 A fuses
ARRAY RECOMBINERS: Satcon Powergate Combiner, 160 A fuses
SYSTEM MONITORING: 1,968 Tigo Maximizer units communicate wirelessly to 25 Tigo Gateways connected to seven Tigo Maximizer Management Units; includes revenue-grade ac output metering and performance monitoring and reporting services