When New York’s Metropolitan Transit Authority (MTA) decided in 1999 that the 86-year-old Stillwell Avenue Station, the city’s busiest subway station, was due for a major overhaul, it also decided to set an example of “green” building in public transportation.

The highlight of the reconstructed station is a solar roof made of building-integrated photovoltaic panels (BIPV) and covering the full width of the station, the largest installation of its kind. This multi-arched roof, which was designed to recall the great rail terminals of the 19th and early 20th centuries, offers effective weather protection for travellers and station facilities while contributing significantly to the station’s non-traction power needs.

Its 2,730 solar panels, custom-made by RWE SCHOTT Solar (RSS), give the station its unique new appearance and are expected to generate approximately 250,000 kilowatt hours a year, contributing significantly to the station’s power needs. This performance is enough to power 40 single-family homes and will provide up to 65 percent of the station’s electricity during sunny days and 15 percent over the course of the year.

The 5’ x 20’ thin-film amorphous silicon (ASI) solar panels were chosen after a rigorous evaluation process based on a variety of criteria, including price, cost of installation, efficiency and aesthetics. “This technology offers unique possibilities for integration into buildings,” says Donald Press, SCHOTT Solar. “It gives architects and engineers an outstanding degree of flexibility.”

With more than 7 million daily passengers, longevity and easy maintenance were primary concerns for the project. New York’s subway system operates around the clock. Wear and tear is constant and shutdowns are expensive. Combining the ecological vision for the station with the rigorous requirements of the MTA made the project especially challenging for the architects. “The integration of high standards of appearance and performance with detailed operational requirements makes this project unique,” says Tony Daniels, project manager at the architectural firm Kiss+Cathcart. “People are more willing to embrace a project when it is beautiful and environmentally positive, as well as functional.”

To facilitate easy maintenance and repair, a 192-point supervisory and control data acquisition (SCADA) system was set-up for monitoring the roof. Prior to installation, the individual solar panels were coded and tested for size, weight and wattage. Programming these specifications into the monitor system allows for quick detection of any deviation. Once identified, a problematic panel can be tested right on the shed and then replaced, if necessary.

This is made easy by a design that allows for maintenance and replacement of panels from above via catwalks integrated into the roof. Additionally, an arched gantry, which can be moved over the roof, offers easy access to the individual solar panels. The use of a single type of panel simplifies replacement and reduces spare storage needs.

The MTA mandates specific light levels for platforms, based on perceptions of safety and security. By offering 20 - 25 percent light transmission, the solar panels help to meet these requirements while holding down costs for daytime lighting. Based on a computer daylighting analysis, clear glass strips were integrated into the panels to allow the right amount of natural light to flow through the roof, giving the station an open and airy feel. “It would be a shame to have to turn on the lights during the day under a solar energy roof,” says Daniels.

These features turned the storied station, originally constructed between 1915 and 1919, and today, the world’s largest rapid transit terminal, into a state of the art transportation hub that makes a strong statement for the use of solar energy in public building projects. Besides showcasing a vanguard solar system, the Stillwell Avenue Station shows that a large public agency can lead the way in environmentally sound construction projects. “For the first time, New York’s subway system will have a clean and efficient source of energy to keep this terminal up and running round the clock, year round,” said Donald Press, SCHOTT solar.