By SETH MASIA December 30, 2012
On July 1, Constellation Energy commissioned a 16.1-megawatt photovoltaic installation (13 MW AC) on 100 acres leased from Mount St. Mary’s University in Emmitsburg, Md. A 1.6-MW solar power system on the same site supplies power directly to the university.
The largest solar array in the state, the $50 million project will supply about 20 million kilowatt-hours annually to Maryland’s Department of General Services and the University System of Maryland under a 20-year power purchase agreement. Constellation owns and operates the facility.
The ground-mounted solar power plant was built over six months by First Solar, using 165 workers to install 220,000 EPC 80-watt panels that feed 26 SMA Sunny Central 500-kilowatt inverters.
The main design challenge was the mixed nature of the soil. Rick Justice, Constellation’s construction manager, noted that bedrock slowed installation of some driven steel post. It normally takes one minute to drive a galvanized I-beam, but where crews encountered bedrock it could take up to 10 minutes.
Other parts of the tract lay in wetlands. “There were many government entities involved in permitting,” he said. “The Maryland Department of Environment determined we could only mitigate up to 2 acres of farmed wetland, and there was another 6 acres we couldn’t use. So we changed the azimuth to maximize the number of panels we could fit into the land we had.”
On the east side of the project, 4 MW of panels face 198 degrees (18 degrees west of south), and on the west side, 9 MW face 156 degrees (24 degrees east of south). Despite the variance, power performance met the design goal. Constellation installed a substation on site, and First Energy, the local utility company, put in some transmission upgrades to handle the grid connection.
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