Sandy Allison, a partner with Alma Properties LLC, stands on the roof of 436 Market St. in Chattanooga. Allison is one of several people responsible for the instillation of solar panels on the roof of the building where The Johnson Group is located.

• What: Workers finished installing a 50-kilowatt solar array on the roof of The Johnson Group, a public relations company. The 217 panels each produce 230 watts of power during peak hours, which is fed back into TVA's grid.

• Companies: The Johnson Group, Tennessee Solar Solutions and Alamo Properties

• Location: The Johnson Group, 436 Market St.

• How it's green: The panels feed power back into TVA's grid during peak usage hours, saving an estimated $1,200 per month on the company's electric bill, and helping to offset heavy demand for electricity in the region.

• Why do it this way? The wind doesn't blow hard enough in Chattanooga to support a windmill, said Anthony Roden, president of Tennessee Solar Solutions. That leaves solar energy as the most efficient method of on-site power generation.

• What's the cost: The 217 panels cost Sandy Allison of Alamo Properties just over $212,000 to install. Assuming a $1,200 per month cost reduction, the panels pay for themselves in about 15 years. A $75,000 state grant and a $63,750 federal grant help to offset some of the cost, while a $10,000 to $15,000 grant from Green Spaces helps pay interest on the loan. TVA also kicks in $1,000 when the array is commissioned, and buys the power at 12 cents above the retail rate.

• Advice for others: Roden says that any building owners interested in commissioning a solar array should comparison shop for the best price. It's also important to act quickly, as state and federal grants run out at the end of 2011, he said.

• How is environmen-talism a part of the business? The idea for the panels originated when The Johnson Group undertook a top-to-bottom review of it's level of environmental sustainability two years ago. They are part of a larger plan that includes recycling and reducing paper and other waste.