Commercial Grid-Direct Photovoltaic System: Colorado Rocky Mountain School Solar Farm

A collaborative effort between the Colorado Rocky Mountain School (CRMS), the Aspen Skiing Company and Xcel Energy, the CRMS Solar Farm broke ground only after lengthy negotiations. The numerous approvals involved made the design challenges seem simple by comparison.

The main electrical design challenge was proper wire and conduit sizing on the ac side of the system. CRMS, like many schools, has a 3-phase 208 service. In order to run a relatively low ac volt- age over a long distance with minimal voltage drop, 3/0 copper was used from each Sunny Tower to the utility interconnection. This increased costs and posed minor logistical hassles. Meridian Energy Systems in Austin, Texas, provided consultation services to the Sunsense design team.

Infrastructure requirements for the project were considerable. These included trenching and burying conduit, as well as laying down service roads. A fencing contractor provided both the perimeter fence and the array’s struc- tural foundation. Only after the infra- structure was complete could the instal- lation team begin its work.

The Sunny Towers provided for more than a clean and convenient installation; they also make detailed performance monitoring easy. Referring to the online SMA Sunny Portal allows the owners, operators or maintenance personnel to verify performance for each inverter and subarray.

"Thanks to our crafty installation team, the project went even smoother than expected. Columns of modules were assembled on the ground. Using a custom harness and an extension reach forklift, each six-module panel was lifted into place. This innovation dramatically improved installation efficiency."

--Scott Ely, Sunsense

Overview

DESIGNER: Scott Ely, President, Sunsense, sunsensesolar.com
LEAD INSTALLER: Jeff Lauckhart, Operations Manager, Sunsense
DATE COMMISSIONED: July 2008
INSTALLATION TIMEFRAME: 90 days
LOCATION: Carbondale, CO, 39.6º N
AVERAGE SOLAR RESOURCE: 5.36 kWh/m2/day
RECORD LOW/AVERAGE HIGH TEMPERATURE: -39º F / 89º F
ARRAY CAPACITY: 147.42 kW STC
AVERAGE ANNUAL AC PRODUCTION: 208 MWh

Equipment Specifications

MODULES: 756 BP Solar SX3195S, 195 W STC, +9%/-9%, 7.96 Imp, 24.4 Vmp, 8.6 Isc, 30.7 Voc
INVERTERS: 3-phase, 208 Vac system, 3 SMA Sunny Towers, 42 kW each, 6 SB7000US per tower, 600 Vdc maximum input, 250–480 Vdc MPPT range.
ARRAY: Eighteen 42 module subarrays—14 modules per string (2,730 W, 7.96 Imp, 341.6 Vmp, 8.6 Isc, 429.8 Voc), 3 strings per inverter (8,190 W, 23.9 Imp, 341.6 Vmp, 25.8 Isc, 429.8 Voc)
ARRAY INSTALLATION: Nine Direct Power & Water Large Ground Mount, 84 modules each, 180º azimuth, 35º tilt
ARRAY COMBINER: 15 A fuses in Sunny Towers
SYSTEM MONITORING: Revenue grade meter from Xcel Energy; SMA Sunny WebBox with sensor package monitored via Sunny Portal

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