LightWave Solar: University School of Nashville

In December 2012, LightWave Solar commissioned a ground-mounted PV system at the University School of Nashville’s (USN) Athletic Campus. Potential sites for the array were constrained by a Tennessee Valley Authority easement for high-voltage electrical lines and an extensive irrigation system for the campus’s athletic fields. The array’s location within a flood plain added further complications.

To resolve permitting issues related to the flood plain, LightWave Solar worked closely with the Metro Nashville Codes Enforcement agency. The agency required the modules and power conditioning equipment to be installed 12 inches above the 100-year flood elevation. To meet these requirements, LightWave Solar specified an elevated array structure utilizing Unirac’s U-LA racking system.

The array’s location resulted in a 900-foot ac transmission distance to the point of interconnection. A REFUsol 024K-UL inverter was chosen due in part to its 3-phase 480 Vac output. The string inverter’s high-output voltage, coupled with the use of direct-burial ac cabling, minimized the cost of the ac transmission run. USN’s Athletic Campus grounds-keeping staff provided the excavation and trenching for the array installation.

USN plans to monitor system data in various science programs, and the project team was concerned about the lack of readily accessible Internet access for system monitoring. They used a cellular modem fed via direct-burial Cat 5 cable from the inverter to provide Internet connectivity.

“The staff at USN was wonderful to work with. The campus was in full use when the installation took place, and Bret Mash at USN was a huge help with on-site coordination during this busy time on campus.”

John Tickle, LightWave Solar

Overview

DESIGNERS: JP Plumlee, solar sales consultant, and Dan Stroh, PV design engineer, LightWave Solar, lightwavesolar.com
PROJECT MANAGER: John Tickle, project manager, LightWave Solar
LEAD INSTALLER: Chris Jader, lead solar technician, LightWave Solar
DATE COMMISSIONED: December 12, 2012
INSTALLATION TIME FRAME: 10 days
LOCATION: Nashville, TN, 36.2°N
SOLAR RESOURCE: 4.9 kWh/m2/day
HIGH/LOW DESIGN TEMPERATURES: per Solar ABCs solar reference map: 93°F/5°F
ARRAY CAPACITY: 24 kWdc
ANNUAL AC PRODUCTION: 30,015 kWh

Equipment Specifications

MODULES: 100 Canadian Solar CS6P-240P, 240 W STC, +5/-0 W, 8.03 Imp, 29.9 Vmp, 8.59 Isc, 37.0 Voc
INVERTER: 3-phase, 277/480 Vac service; one REFUsol 024K-UL, 23.2 kW, 500 Vdc maximum input, 125–450 Vdc MPPT range
ARRAY: 10 modules per source circuit (2,400 W, 8.03 Imp, 299 Vmp, 8.59 Isc, 370 Voc), 10 source circuits total (24 kW, 80.3 Imp, 299 Vmp, 85.9 Isc, 370 Voc)
ARRAY INSTALLATION: Ground mount, Unirac U-LA racking, 149° azimuth, 25° tilt
ARRAY STRING COMBINER: Inverter integrated, 15 A fuses
SYSTEM MONITORING: Inverter-integrated datalogger, REFUsol REFUlog monitoring platform

Article Discussion