IRC Solar Roof Systems: Belmont Hill School
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IRC Solar Roof Systems, an affiliate of IRC Industrial Roofing Companies, was contracted to develop a 186 kW PV installation at Belmont Hill School, a private school located in Belmont, Massachusetts. The 14,000-square-foot array is installed on the roof of the school’s Jordan Athletic Center and generates enough electricity to offset approximately 20% of the facility’s electrical demand.
The 778-module system is one of the largest school-based projects in eastern Massachusetts and the first commercial PV interconnection for the municipalowned local utility, Belmont Municipal Light Department (BMLD). An initial challenge was working with BMLD’s existing regulations for commercial solar production. While Massachusetts requires investor-owned utilities to support distributed generation and system net metering, municipal-owned utilities need participate only voluntarily. This required IRC to work with the BMLD board to gain approval of the project’s net metering program.
In the design phase, a single central inverter was considered. However, the only available location was not ideal because the inverter would have been located in a high-traffic area near the school’s delivery entrance. Multiple string inverters were the preferred solution based on an available exterior wall surface at the second-floor level. An adjacent low-slope roof provided the installation crew and future maintenance crews a safe and convenient working surface. School administrators also favored the location since the inverters are not visible from ground level.
The structure supporting the main standing-seam metal roof over the Jordan Athletic Center’s ice rink is composed of light-gauge purlins with 4.5-foot on-center spacing. Utilizing an attachment method such as the railless S-5! PV Kit would have streamlined the attachment to the metal roofing seams but would have resulted in excessive point loading between the structural purlin members. The engineered solution uses IronRidge XRS extruded aluminum rails in conjunction with S-5! mounting clamps to span the structural members while transferring the collateral loads created by the PV array directly to the purlins.
The PV source circuits are combined at the array to minimize the number of conductors from the roof to the inverter location. This design approach required 14 disconnecting combiners that are mounted on the roof surfaces in close proximity to the array. The location of the combiners assisted with PV source-circuit wire management by allowing an easy transition to conduit for the output circuits. The inverters’ 277 Vac circuits are combined in a panelboard at the inverter location to simplify the conductor run to the facility’s main distribution panel.
IRC worked with the school’s faculty and staff to integrate an educational component that allows students, teachers and parents to view real-time and historical performance and environmental data. A 40-inch flat-screen monitor installed in the athletic building displays continuously updated system information that highlights the environmental benefits of Belmont Hill School’s solar project. An online classroom supplements the on-site learning opportunities.
“Engineering a solution at Belmont Hill School was made easier by the partnership of the school, the local energy committee and the support of the Belmont Municipal Light Department. IRC Solar Roof Systems is contracted to provide ongoing O&M for both the PV and the metal roofing systems.”
—Kurt Penney, business development, IRC Solar Roof Systems
DESIGNER: Steven J. Strong, president, Solar Design Associates, solardesign.com
LEAD INSTALLER: Michael Donnelly, director of electrical operations, IRC Solar Roof Systems, ircmaine.com
DATE COMMISSIONED: January 16, 2012
INSTALLATION TIME FRAME: 45 days
LOCATION: Belmont, MA, 42.5°N
SOLAR RESOURCE: 4.3 kWh/m2/day
HIGH/LOW DESIGN TEMPERATURES: per Solar ABCs solar reference map: 90°F/1°F
ARRAY CAPACITY: 186.7 kW
ANNUAL AC PRODUCTION: 232 MWh
MODULES: 778 Sharp ND-240QCJ, 240 W STC, +5/-0%, 8.19 Imp, 29.3 Vmp, 8.75 Isc, 37.5 Voc
INVERTERS: 3-phase, 277/480 Vac service; 14 Fronius IG Plus V 12.0-3WYE277, 12 kW, 600 Vdc maximum input, 230–500 Vdc MPPT range
ARRAY: 14 modules per source circuit (3,360 W, 8.19 Imp, 410.2 Vmp, 8.75 Isc, 525 Voc); four source circuits per inverter typical (13.4 kW, 32.8 Imp, 410.2 Vmp, 35 Isc, 525 Voc); 186.7 array capacity total
ARRAY INSTALLATION: Roof-mount, steel standing-seam roofing panels, IronRidge XRS racking, S-5! mounting clamps, 210° azimuth, 18.4° tilt
ARRAY STRING COMBINERS: 14 Bentek six-pole Integrated Disconnect Combiners, 15 A fuses
SYSTEM MONITORING: DECK Monitoring production and environmental monitoring; Obvius AcquiSuite server, dashboard and Modbus communication