Stretching from Fourth to Fifth Streets, the Bourse attracts nearly one million visitors a year, many of them tourists in town to see the Liberty Bell, Independence Hall, and the National Constitution Center. The Bourse itself is on the National Register of Historic Places and now joins a growing list of local properties of significance embracing the green movement.
The Strawbridge & Clothier building at Eighth and Market has been renovated to the U.S. Green Building Council's LEED (Leadership in Energy and Environmental Design) silver-certification status, as has the former U.S. Post Office at 30th Street. The Philadelphia Free Library's venerable Central Library now has a green roof.
"Historical buildings are typically energy hogs," said Michael R. Tilghman Jr., director of commercial-property management for Bourse owner Kaiserman Co. Inc., and chairman of its year-old green council. "Being able to put solar at the Bourse gives us the ability to improve the energy efficiencies that is not typical of historical buildings."
For instance, Tilghman said, older buildings traditionally have lower ceilings, limiting natural light.
Even in its early days, the Bourse was unique. A 1915 graphite sketch of the ornate, columned edifice shows a series of skylights in what was then a roof on a much shorter building, about three stories.
The seven floors of offices that now rise above the Bourse's food court, and the arched skylights that now top that airy space, were added by Kaiserman.
Out on the Bourse's 30,000-square-foot roof, the solar panels are arranged in five separate sections, to avoid the skylights and the shadows cast by two hulking mechanical penthouses. The building itself is surrounded by structures of similar height or shorter, so it is not in any shadows.
The solar panels are attached to a patented racking system created from recycled aluminum by SolarDock, of Wilmington, that requires no roof penetration. The Bourse's racks are held down by 1,700 ballast blocks, each weighing 33 pounds.
The no-penetration factor was one of the major selling points for Kaiserman, Tilghman said, given that the Bourse is a building of historic significance.
The system was installed over three weeks in May and June by five employees of the solar division of Union Electric Contracting Co. in Fort Washington. Among those doing the work was Ammon G. Morgan Jr., who was grateful it was not scheduled for last week in the 100-degree-plus heat.
The job was tricky enough, Morgan said in an interview last week. It required hoisting 30,000 tons of equipment with a 250-foot crane that was parked in the middle of Fourth Street on weekends.
With Kaiserman expecting $8,000 in energy savings in the first year of going solar - and likely more in subsequent years, when electric-rate caps are no longer in effect - Tilghman said the system should pay for itself within five years. About 3.5 percent of the building's consumption will be covered by the solar system.
He would not disclose the cost of the 43-kilowatt system, but said it would be offset as much as 60 percent by federal and state solar incentives, among other things. The company also will be able to sell energy credits to utilities.
Finishing touches are being made to a display in the Fifth Street lobby that will enable visitors to view pictures of the solar panels and to monitor their energy output.
Daniel E. O'Brien, SolarDock's vice president of business development, described as "truly impressive" Kaiserman's decision to "make the jump [to solar] on a historical building."
At the Philadelphia Historical Commission on Friday, Randal Baron, a preservation planner, said he was not familiar with the Bourse's solar project and was unable to establish whether the agency had formally reviewed it and issued permits for it.
Based on a description provided to him by a reporter, including that the panels cannot be seen from street level, Baron said, "I don't think there's a conflict."
"We truly believe that historic preservation is at the heart of the green movement, in a way," Baron said. "The whole idea of preservation is not to throw things away - to conserve materials, to conserve infrastructure."
But there are limits, said Mike Rosen, director of the Green Studio at Martin Architectural Group P.C., of Philadelphia.
"The aesthetic concept is something that is strongly debated," Rosen said. "You have to do it very sensitively to do it right."
In other words, do not expect solar panels on Independence Hall, Rosen said: "The roofs are visible from everywhere."
Contact staff writer Diane Mastrull at 215-854-2466 or firstname.lastname@example.org.