Bella Energy: Salt Palace Convention Center
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Salt Lake County and Bella Energy recently commissioned a 1.652 MW rooftop PV system on the Calvin L. Rampton Salt Palace Convention Center in downtown Salt Lake City. The array is the largest roof-mounted system in the state of Utah and covers approximately 170,000 square feet of the convention center, offsetting 17% of the building’s annual energy consumption. The New Markets Tax Credit Program in part financed the project, which is one of a small number of PV projects financed using this mechanism. Bella Energy and CarbonFree Technology were joint developers, and Bella acted as the EPC contractor on the system. Bella Energy employed local contractors Clark’s Quality Roofing and Rydalch Electric to complete the physical installation.
Bella Energy initially proposed a 2 MW system. However, given uncertainty surrounding the financing mechanism, the developers decided to design and engineer the system in scalable sections prior to the financial closing, so that they could quickly scale it down should the available funding be reduced. To accommodate the final available project funding, they reduced the system to 1.652 MW by removing 348 kW of array capacity and the associated inverter and BOS requirements.
The large size of this PV system, coupled with a requirement to make a low-voltage interconnection, required two new electrical services for the building— and the initial plan connected those services to the inverters only. In an effort to have the building consume all of the generated energy instead of exporting it, the developers opted to connect the services to the existing utility transformers that historically experienced the largest loads. Rocky Mountain Power, the local electric utility, completed impact studies on the effects of interconnection and provided support during interconnection and protective relay programming.
One of the major challenges in implementing the system was the installation of attachments to the roof that the site’s seismic classification required. The need for more than 700 attachments created challenges for both design and implementation. Because the building had been designed to be built in multiple phases, careful consideration and verification was required to ensure that the attachments were positioned correctly over the building’s purlins based on the size and the wind loading imposed on each subarray. Installers used Unirac FastFoot assemblies for the attachments, which they assembled off-site and installed as weather allowed throughout the project’s winter installation time frame. After removing insulation, the installers secured wood blocking to the roof ’s metal deck to build up to membrane level, where they attached the FastFoot assemblies. They sealed each penetration with a hotair– welded TPO boot to satisfy the roof warranty holder’s requirements.
“One of the most arduous phases of the design was creating an accurate model of the building. The Salt Palace was constructed in several stages across decades. Creating a model of the 635,000-squarefoot rooftop required sifting through a plethora of architectural and structural drawings from several different plan sets, extracting relevant information, recreating and stitching together dozens of small sections into a single drawing, and then reconciling the result with actual on-site measurements and a professional survey of the roof. This up-front effort was crucial to ensuring the completeness and accuracy of the final layout and racking design.”
—Leif Cook, Bella Energy
DESIGNER: Leif Cook, design engineer, Bella Energy, bellaenergy.com
INSTALLATION TEAM: Andy Blakeslee, site superintendent; Shannon Welch, construction project manager; Dana Mosman, operations manager, Bella Energy; Clark’s Quality Roofing, racking and module installation, clarkroof.com Rydalch Electric, electrical installation, rydalch-electric.com
DATE COMMISSIONED: May 1, 2012
INSTALLATION TIME FRAME: 145 days
LOCATION: Salt Lake City, UT, 40.8°N
SOLAR RESOURCE: 5.3 kWh/m2/day
HIGH/LOW DESIGN TEMPERATURES: per Solar ABCs solar reference map: 97°F/3°F
ARRAY CAPACITY: 1.652 MW
ANNUAL AC PRODUCTION: 2,347 MWh
MODULES: 6,006 Suntech STP275- 24/Vd, 275 W STC, +5/-0%, 7.84 Imp, 35.1 Vmp, 8.26 Isc, 44.7 Voc
INVERTERS: 3-phase, 480 Vac service; two Solectria SGI 500, 500 kW, 625 Vdc maximum input, 300–500 Vdc MPPT range; one Solectria SGI 300, 300 kW, 625 Vdc maximum input, 300–500 Vdc MPPT range
ARRAY: 11 modules per source circuit (3,025 W, 7.84 Imp, 386.1 Vmp, 8.26 Isc, 491.7 Voc); 15 source circuits per combiner, typical (45.4 kW, 117.6 Imp, 386.1 Vmp, 123.9 Isc, 491.7 Voc); 500 kW inverters with 210 source circuits per inverter (635.3 kW, 1,646 Imp, 386.1 Vmp, 1,735 Isc, 491.7 Voc); 300 kW inverter with 126 source circuits total (381.2 kW, 988 Imp, 386.1 Vmp, 1,041 Isc, 491.7 Voc)
ARRAY INSTALLATION: TPO roofing, Unirac ISYS Roof 1.5 racking, 180° azimuth, 10° tilt
ARRAY STRING COMBINERS: 37 SolarBOS Disconnect Combiners, 15 A fuses
SYSTEM MONITORING: Draker Sentalis 800 base station with zone monitoring, environmental sensors and Shark revenue-grade meters