A book entitled “Solar Farms for Dummies” would never sell. Once constructed, solar farms are so simple to maintain that the biggest job is cutting the grass.
by James A. Bacon
Does anyone wonder how a solar farm works? From an electro-mechanical standpoint, it’s remarkably simple — nothing like a gas-fired power plant with its profusion of ducts, pipes, fans and vents. But there’s more to it than is evident to the casual observer. I got a primer this morning at the unveiling of Dominion Virginia Power’s “Solar Partnership Program” plant outside the Philip Morris USA manufacturing facility in Chesterfield County.
The 11-acre facility produces two megawatts of electricity at peak output, enough to power 500 homes. Though small by utility-scale standards, the solar farm is the biggest producer of solar electricity in Virginia today. That distinction won’t last long, for bigger solar farms are in the project pipeline. Still, it was large enough to give me an education.
That’s Brett Crable, director of the utility’s new technologies program, in the photo above. He took me on a quick tour — it was quick because, frankly, there is not much to see — and instructed me in solar farm basics.
The most complex part of the farm is the solar panel, which converts sunlight to electricity. There are 8,000 panels, each one generating about 36 volts of electricity under prime conditions. The panels are mounted on stationary aluminum frames, tilted at an angle to optimize exposure to the sun. In some solar farms the panels are mounted on mechanisms that rotate to track the movement of the sun even more closely, squeezing out more energy production but incurring more up-front capital expense and maintenance issues. Dominion decided in this project to keep things simple.
So, where does the electricity go after the panels create it? Wires from the panels (seen at left) feed the low-voltage electricity to a collector box underneath the panel array (below). Those boxes consolidate the flow of electricity into a single underground electric line, which feeds the inverter boxes.
Each of Philip Morris solar farm’s inverters handles about 500 kilovolts; there are four in all. Their job is convert Direct Current (DC) from the solar panels into Alternating Current (AC) that we use in our homes and businesses. The four inverters feed into the transformer (below), the function of which is to step up the voltage to 35,000 volts so it can be fed into the local distribution system.
Under the terms of the arrangement with Philip Morris, Dominion owns and operates the solar farm, leasing the land for nominal fee. Although the solar farm is less than a hundred yards from a major sub-station, the underground line from the transformer plugs into the local distribution network some distance away. That’s because the purpose of the facility is to gather data on how the intermittent generation of solar power effects the quality and reliability of electric current on a lightly loaded circuit. (More on that in another post.)
The solar farm, which has been up and running for several months, largely takes care of itself. Dominion expects to send over people periodically to cut the grass and maybe twice a year to inspect the panels. The utility monitors electricity flows remotely. While the $4.9 million up-front expense of buying and installing the panels and other equipment is high per kilowatt of generating capacity compared to large, gas-fired facilities, the ongoing cost of maintaining the facility is almost nil.
The only thing he can think of that might make the solar farm less labor-intensive, says Crable, is to bring in goats to graze on the grass. Some people actually do that. His main reservation, he says, tongue-in-cheek, “I don’t know how you tell the goats they missed a spot.”
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