Frederickson Electric: Poulsbo Middle School

Sandwiched between Seattle and the Olympic Peninsula, picturesque Poulsbo, Washington, is home to the state’s first fullcapacity community solar project. The 75 kW array was developed by Washington Solar Incentives (WSI) and was installed by Frederickson Electric. WSI secured the host facility, negotiated all contracts, organized investors and oversaw the installation.

A first-in-the-nation Washington state incentive program that includes a community solar provision made the project at Poulsbo Middle School possible. The model allows community members to fund up to a 75 kW system on a public facility and receive a production incentive of $1.08/kWh. At the end of the incentive period in June 2020, the investors transfer ownership to the facility and are projected to have earned an average double-digit annual return.

The incentive requires the use of modules and inverter systems manufactured in Washington. The Silicon Energy modules feature frameless construction with a glass backsheet. The modules mount in a cascading fashion, which increases air circulation and effectively uses rainfall to clean the array. Silicon Energy developed the module racking system, which also serves as a raceway for the array conductors. The entire assembly is listed and has a Class A fire rating.

The 15 single-phase inverters take up an entire wall adjacent to the electrical service room. Inverter input and output wiring is organized in a gutter system surrounding the inverters and disconnects. The inverter outputs are combined five per phase in a dedicated distribution panelboard, which connects to the electrical service on the supply side to avoid backfeeding an existing GFI device on the main disconnect.

“It was an interesting challenge to design a 75 kW system with equipment manufactured in Washington. I’m pleased with the result, which combines very durable modules with an efficient inverter system.”

Hans Frederickson, Frederickson Electric

Overview

DESIGNER: Hans Frederickson, Frederickson Electric, fredelectric.com
LEAD INSTALLER: Bret Ortlieb, Frederickson Electric
PROJECT DEVELOPER: Rick Lander, Washington Solar Incentives, wa-solar-incentives.com
DATE COMMISSIONED: March 2011
INSTALLATION TIME FRAME: 60 days
LOCATION: Poulsbo, WA, 47.7°N
SOLAR RESOURCE: 3.7 kWh/m2/day
HIGH/LOW DESIGN TEMPERATURES: per solarabcs.org/permitting/map: 84°F/18°F
ARRAY CAPACITY: 74.1 kW
ANNUAL AC PRODUCTION: 72.2 MWh

Equipment Specifications

MODULES: 390 Silicon Energy SiE- 190, 190W STC, ±3%, 7.5 Imp, 25.3 Vmp, 7.9 Isc, 30.5 Voc
INVERTERS: 3-phase, 277/480 Vac service, 15 Power-One PVI-4.2- OUTD-US, 4.2 kW, 600 Vdc maximum input, 90–580 Vdc operating MPPT range, 200–530 Vdc full power MPPT range; Silicon Energy prewired inverter system assemblies with dc and ac disconnects
ARRAY: 13 modules per string (2,470 W, 7.5 Imp, 328.9 Vmp, 7.9 Isc, 396.5 Voc), two parallel strings per inverter (4,940 W, 15 Imp, 328.9 Vmp, 15.8 Isc, 396.5 Voc)
ARRAY INSTALLATION: Silicon Energy mounting hardware secured to custom-built galvanized steel rack. Aluminum racking components isolated from galvanized steel with rubber tape. 182° azimuth, 5° tilt
SYSTEM MONITORING (fredelectric.com/pms.html): Fat Spaniel inverterdirect monitoring with environmental sensors

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