Darren Hill has powered his office computer and assorted peripheral equipment for two years from a solar panel mounted to the roof of his Old City business.

"I proved the model, now let's just do the whole building," said Hill, 40, the chief executive and cofounder of e-commerce platform provider WebLinc L.L.C.

On Tuesday, a contractor completed installation of a 12-kilowatt solar array on the roof of 100 Market St., one of three Old City locations where WebLinc's creative teams devise tools for online retailers.

Hill estimates that the 38 solar modules could provide up to 70 percent of the power needs of the 8,000-square-foot building. He hopes that the $38,000 system will pay for itself in less than six years with reduced electric bills.

Even if the financial returns fail to live up to expectations, the system provides WebLinc with other intangibles. The green credential gets a fist-bump in the tech world in which WebLinc operates. It was an instant hit with the company's 130 Center City employees, all but eight of whom commute to work by foot, bicycle, or public transit.

"This is definitely a corporate culture kind of thing," he said. "We sent out an email with pictures of the install and let our employees know what we're up to, and got back 25 emails about how cool it was. It's a smart thing."

WebLinc bought the Market Street building, once occupied by the Franklin Trust Co., out of bankruptcy for $1 million in 2013. The previous owners had prepared for the installation of a green roof, the water-absorbing vegetation that the Philadelphia Water Department promotes to reduce storm water runoff.

Hill thought a green roof was "interesting."

"But I thought that a solar system was cooler," he said. "It's badass."

Hill is currently obsessed with observing the output of the solar panels from his smartphone, and plans to devise a screen saver showing the system's status, which can be displayed for building visitors.

"We can show a client that most of the power we're using is coming from the roof," he said. "It will be a nice conversation piece, pretty cool."

The solar investment is part of a package of energy-conservation and waste-reduction measures WebLinc has taken, including low-wattage lighting, upgraded building insulation, and banishing plastic K-Cup pods.

"I would term this a smaller solar array," said Micah Gold-Markel, founder of Solar States L.L.C., the Northern Liberties installer that did the WebLinc job. "The footprint of the roof was not so large."

There were 10,341 solar systems in the state at the end of May, ranging from giant solar farms interconnected to the grid to smaller household installations. They have a combined capacity of 199,641 kilowatts, according to the Pennsylvania Public Utility Commission.

Solar output nationwide grew 42 percent from 2014 to 2015, according to the U.S. Energy Information Administration (EIA), as the price of the technology has declined. Gold-Markel said current prices are about half of the $5.70 a watt it cost in 2010 when his company installed an 82-kilowatt array on the roof of the Crane Arts Center in Northern Liberties. Combined with a 30-percent federal tax credit, solar has achieved "grid parity" in some installations, he said.

"We can make a very solid economic argument for folks like Darren, and that's why solar's exploding," said Gold-Markel. "This thing pays for itself in five years and is warrantied for 20 years. There's a powerful economic advantage to being clean. That wasn't the case in the past."

Solar has captured an outsize place in the public consciousness compared with its total power contribution. It still accounts for less than 1 percent of total electricity generation in 2015, and about 7 percent of the total of the 562 million megawatt hours of renewable power generated in 2015, according to EIA. Hydroelectric and wind turbines account for most renewable power.

According to experts, only about 25 percent of all residential rooftops are suitable for solar installations - the roofs may not get much sunlight or are in no condition to support solar modules.

But Hill thinks that still leaves a lot of opportunity. "It would be great if there were solar panels on every roof," he said. "What a difference that would make in the city."

amaykuth@phillynews.com

215-854-2947 @maykuth