Alteris Renewables: Ferrisburgh Solar Farm

The 1.047 MW Ferrisburgh Solar Farm (FSF) is currently the largest solar installation in the state of Vermont. Located along a highly trafficked road in close proximity to a local high school, it includes a significant educational component. The project also supports the local economy. Alteris Renewables and the entire FSF team were proud to make this project the first PV system commissioned under Vermont’s Standard Offer Program, a rebate structure designed to encourage the development of renewable energy projects.

The state obligated the team to acquire a Certificate of Public Good (CPG) for this project. Obtaining a CPG necessitates following a rigorous permitting process—the same required of electric transmission facilities, electric generation facilities and certain gas pipelines. Because a project of this size had never been done in Vermont, the team had to show local residents and town and state officials that the project would not adversely impact the community. They had to address concerns raised by state agencies relating to module reflectivity, inverter noise levels and storm water impact, among others. The team also worked closely with the electric utility, Green Mountain Power, to address interconnection and protection issues relating to MW-size PV installations.

One of the realities of designing a ground-mounted PV system in Vermont is that the significant annual snowfall must be taken into account. This presented the design challenge of balancing the optimal array tilt angle for snow shedding while avoiding significant inter-row shading. In addition, ample clearance under the array was necessary to attempt to prevent accumulated snow from obscuring the array’s lower edge. The final design specifies a 30° module tilt with 48 inches of clearance between the ground and the bottom of the array.

This system was instantly put to the test by a series of record snowfalls. The project was commissioned in late November 2010, at the beginning of one of the snowiest winters on record. Three months after commissioning, as the snow kept piling up, the owners had doubts as to whether the system would meet its energy production forecast. During many winter days, the modules were covered with deep snow or with snow and ice. However, as anticipated, they cleared off relatively quickly when the sun came out. Despite the record snowfall, the system is right on target for producing the projected annual energy generation.

“During the month of October, we received double the normal rainfall. As the clay field on which the system was being installed became saturated, machines were no longer an option for rack and module assembly. The majority of the array construction had to be managed with ladders. In spite of this significant obstacle, the job was brought in on time and on budget.”

—Jay Myrto, project manager, Alteris Renewables


DESIGNER: Adam J. Smith, director of electrical engineering, Alteris Renewables,
LEAD INSTALLER: Ken Mayer, Alteris Renewables
DATE COMMISSIONED: November 30, 2010 
LOCATION: Ferrisburgh, VT, 44.3°N
SOLAR RESOURCE: 4.24 kWh/m2/day

Equipment Specifications

MODULES: 3,806 Suntech STP275- 24/Vd, 275 W STC, -0/+5 W, 7.84 Imp, 35.1 Vmp, 8.26 Isc, 44.7 Voc
INVERTERS: 3-phase, 277/480 Vac service, two Advanced Energy Industries Solaron 500 kW, ±600 Vdc maximum input, ±330 to ±550 Vdc MPPT range
ARRAY: 11 modules per source circuit (3,025 W, 7.84 Imp, ±386.1 Vmp, 8.26 Isc, ±491.7 Voc). Inverter One: 186 source circuits total, with 93 positive and 93 negative-to-ground (562,650 W, 729 Imp, ±386.1 Vmp, 768 Isc, ±491.7 Voc). Inverter Two: 160 source circuits, with 80 positive and 80 negative-toground (484,000 W, 627 Imp, ±386.1 Vmp, 661 Isc, ±491.7 Voc).
ARRAY INSTALLATION: Fixed-tilt ground mount, Schletter FS System rack, 180° azimuth, 30° tilt
ARRAY STRING COMBINERS: 22 Cooper Crouse-Hinds model CCBF16F15DS200, 15 A fuses
ARRAY RECOMBINERS: Two Controls Engineering and Services model 27600, 225 A fuses
SYSTEM MONITORING: Draker Laboratories Sentalis 1000 Base Station, SHARK Energy Meter, weather station including plane-of-array irradiance, cell temperature and ambient temperature


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