Independent Power Systems: Boulder Valley Christian Church
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Acting as guides to their community, the Boulder Valley Christian Church leaders place a strong emphasis on environmental stewardship. As a reflection of this commitment, they contracted Independent Power Systems (IPS) to install a turnkey PV system that would both promote the Church’s stewardship commitment and reduce its operating expenses.
Because the public utility, Xcel Energy, limited the system capacity eligible for the Colorado incentive program, IPS’s final design needed to maximize energy production. The Church’s roof was initially proposed for the array location. However, after modeling various array configuration scenarios, IPS designers determined that the roof ’s low angle, combined with sections that faced southwest and southeast, would not allow for the desired energy yield. A ground-mounted array located adjacent to the Church’s community garden was proposed as an alternative. This would increase installation costs per kW but result in an estimated 20% increase in annual energy production that would more than offset the upfront costs.
IPS researched several ground-mount racking systems to compare material and installation costs. The specified product needed to be robust enough to meet the site’s 120-mph wind-load and 30-psf snowload requirements. The Conergy Solar- Linea D driven-pile solution was selected for the project. The dual-post mounting system offered reduced pile-driving time and was less expensive in material and labor costs compared to other products that IPS evaluated because it required only a 4-foot pile ground-penetration depth. Each racking section was configured to support 26 modules, resulting in a streamlined aggregation of 13-module source circuits. This design facilitated the use of a single 36-circuit combiner box and one circuit to the inverter, lowering BOS costs.
“Pile location was critical for the racking system. If a pile contacted an obstruction before the refusal point, or the angle was out of tolerance, the options would have been limited. Fortunately, we did not hit anything serious and our posts went in the ground as planned.”
—Simon Wood, Independent Power Systems
DESIGNERS: George Vaughan, project engineer; Simon Wood, project manager; Independent Power Systems, solarips.com
LEAD INSTALLER: Jonah Coles, installation manager, Independent Power Systems
DATE COMMISSIONED: September 2011
INSTALLATION TIME FRAME: 26 days
LOCATION: Boulder, CO, 40.0°N
SOLAR RESOURCE: 5.6 kWh/m2/day
HIGH/LOW DESIGN TEMPERATURES: per Solar ABCs solar reference map: 93°F/-13°F
ARRAY CAPACITY: 110 kW
ANNUAL AC PRODUCTION: 168.9 MWh
MODULES: 468 SunPower SER-235P, 235 W STC, +5/-3%, 7.91 Imp, 29.7 Vmp, 8.45 Isc, 36.8 Voc
INVERTER: 3-phase, 480 Vac service, Satcon PVS-100-UL, 100 kW, 600 Vdc maximum input voltage, 315–600 Vdc input voltage range
ARRAY: 13 modules per string (3,055 W, 7.91 Imp, 386.1 Vmp, 8.45 Isc, 478.4 Voc); 36 source circuits terminated in single combiner box (109.98 kW, 284.8 Imp, 386.1 Vmp, 304.2 Isc, 478.4 Voc)
ARRAY INSTALLATION: Conergy SolarLinea D ground mount, 180° azimuth, 40° tilt
ARRAY STRING COMBINER: Sun- Power 36-string combiner, 15 A fuses
SYSTEM MONITORING: SunPower SMS 2.0 web-based commercial monitoring