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Sterling is home to the largest solar rooftop installation in Northern Va.

Project manager of the Sterling rooftop solar installation Rob Smith gives a tour of the panels at the July 9 unveiling. Times-Mirror/Anna Harris
That glint atop Prologis Concorde Distribution Center in Sterling isn’t clean windows.

It’s Northern Virginia’s largest collection of solar panels, and it sits on top of two Prologis rooftops. The industrial real estate developer partnered with Dominion Virginia Power for the $2.5 million solar project that’s part research and part practicality, according to Dominion.

Sun power collected from 3,000 solar panels generates 750 kilowatts of electricity, enough to power 185 homes in the area.

The Solar Partnership Program started after the General Assembly passed legislation in 2011 that opened the door for Dominion to create the research program studying the effects of rooftop solar on the power grid. The program itself was approved in 2012, and Dominion has been working out the kinks ever since.

The project spans multiple states, and the Sterling solar system was the gateway to the rest of Virginia. The first public unveiling and tour of this particular system was given July 9.

Rob Smith, the construction manager of the project, said the panels only need to be checked twice a year, but the relative easy maintenance comes after a harsh winter that made finishing the project difficult.

Ice and snow slowed the build that reached around 80 percent completion in December. It took them until March, when the system went online for the first time, to finish the remaining 20 percent.

The panels themselves are smaller than traditional ground systems, which are set in grassy clearings and angled at 30 degrees as opposed to the five-degree angles adopted for the rooftop systems.

The higher the tilt, the more weight is needed on the roof to secure the panels. Each panel weighs about 16 or 17 pounds. That’s 48,000-pound total on both roofs combined.

Less tilt means less efficiency and less energy produced overall. But, according to Dominion’s manager for New Technology and Renewable Programs Nate Frost, using pre-existing roof space keeps Loudoun land available for other purposes.

Sunlight hits the panels, which excites the materials inside and causes electron movement. The energy created from that movement is collected by wires strung between the panels. The direct current voltage then goes into inverters by the Prologis building where it’s converted to an alternating current. That energy goes to the transformer and then to the grid, where it is dispersed to homes and businesses in the area.

Exactly how the electrical grid is affected is what the study is for. The electrical grid is the network responsible for delivering electricity to consumers.

“The difference would be if you put something on the rooftop to power this particular building,” said Frost. “What we’re trying to do with this program is understand ‘what does that [dispersion] mean for the grid.”

Efficiency is still an issue with solar, and the rooftop solar makes gathering electricity more difficult.

The Virginia State Corporation Commission approved an $80 million cost cap for Dominion's overall project, money that Dominion said in its filing would be recovered as part of base rates in a future biennial review proceeding. The $2.5 million price to build Sterling's cost less than anticipated, though upkeep for the next roughly 15 years does mean recurring costs.

“In the three years that we’ve dealt in the process, we’ve seen project costs go down about a third,” Gurganus said. “So we definitely have increased the amount of electricity generated on our system through projects like this...It keeps rates economical for our customers and helps us balance our need to provide cost effective and reliable electricity with the desires of our customer base and the public at large to get a significantly higher portion of their energy from renewable sources. We’re finding that these projects have been well received in the community.”

While it may be a while before solar panels are on every rooftop, Dominion and Prologis see the partnership program as a step toward better understanding the effect of solar on consumers and the energy market.

This article has been edited to better reflect the relationship between Dominion and the project's funding source.


Hey Anna,

When you say $80 million from the “government,” you should say the Virginia tax payers.  Guess they didn’t teach out that in journalism school.  What’s the ROI on this project?????

Virginia Tax Payer

You know what’s easy to harness. The energy contained within hydrocarbons.

Solar Panels are caveman technology. Using photons to knock loose electrons and create electricity is inefficient. What we really need is to figure out how to harness the energy contained within a photon.

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