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The glass-and-steel structure employs a panelized construction system with photovoltaic panels. Rated at about 200 kilowatts, the solar installation is among the largest in the U.S. This was a first-of-its-kind application, where low-cost, thin-film photovoltaic panels were combined with clear glass in custom glazing units to provide the right balance among shelter, daylighting, and electricity generation.

The Stillwell Avenue Terminal is used by thousands of commuters daily, but it is better known for its weekend use, since Coney Island is a popular beach destination for city dwellers. Several thousand visitors reach Coney Island every day without using cars — almost three million per year. Thousands more use the station to transfer between trains and buses to reach other destinations.

The intricate pattern of light and shade created by the differing transparencies of glass and photovoltaic panels enlivens the project while optimizing daylighting conditions.

The design team considered active ventilation to counteract heat buildup under the roof, but instead designed a roof geometry that maintains acceptable ambient temperatures at the platform, even on a still day with trains idling in the station.

Concept and Design

The shed was originally conceived in 1998 as part of the capital planning studies to reconstruct the station. The photovoltaic function followed the idea of covering the platforms with a shed, a desirable feature in its own right.

Many discussions on the implications of the shed structure and the solar technology were held with various groups within New York City Transit — design, construction, operations, and maintenance — over a period of four years. These included an industry "peer assembly" in which many major players in the photovoltaics industry presented their products and visions.

Designed Simplicity

The design process was driven by a desire to simplify and standardize the systems, in order to make them easier to evaluate and service. From the initial designs, which featured dozens of panel sizes according to the demands of structure and geometry of the existing platforms, the design was simplified to use just two panel types: one photovoltaic and one sheet metal. At the same time, ventilation and daylighting functions performed by specialized elements in the original design were incorporated into the standard panels.

Construction

Ease of construction was a major requirement of New York City Transit, particularly since the terminal would be closed for very limited periods to minimize interruption and loss of train service. In the end, the modular photovoltaic roof was installed faster than the structural steel could be brought to the site.

The support structure consists of arched steel trusses mounted to steel columns. Steel tubes were selected both for structural efficiency and for aesthetics. Connection design was critical due to construction phasing constraints and New York City Transit's standards, which require bolted connections. In order to avoid mid-span plate splice connections and field welds, the project team relocated all structural connections to the columns, substantially reducing the structure weight.

The project team produced a detailed computer model of the structure using loads developed from a wind-tunnel analysis of the structure and building code requirements. The team also developed seismic load cases based on analysis of soil conditions and formulation of spring constants. This detailed analysis enabled the team to reduce the amount of cross bracing, which further reduced the weight of the structure.

Strategic Energy

The project's principal energy strategy is photovoltaic (PV) power generation. The system generates approximately 210,000 kilowatt-hours of electricity per year, enough to meet the electricity needs of about 30 average single-family homes in the northeastern United States. In New York City, on-site electricity generation has special value, as transmission constraints force 80% of energy to be generated within city limits. The grid is stressed, and summertime peak loads are becoming increasingly difficult to meet.

This system is one of the largest thin-film building-integrated PV (BIPV) systems in the world. It consists of 2,730 custom BIPV modules—each approximately five feet (1.5 meters) square, with the PV in the center and a clear glass strip around the edge. The photovoltaics are connected in series strings of five modules each. The wiring is combined in special boxes under the roof, where monitoring sensors were installed, and the DC power is fed to two redundant inverters in the lower-level BIPV room.

The area of the entire roof is 80,000 square feet (7,430 square meters): the arched BIPV section makes up 76,000 square feet (7,060 square meters), and the fritted glass transition shed to the north adds 4,000 square feet (370 meters). The active area of the PV modules is 41,000 square feet (3,810), and the rated output is 199 kilowatts at peak. The actual peak output is approximately 160 kilowatts.

Although the shed is open-sided, it was not a given that good daylight would reach the center of the platform area, which is 360 feet by 420 feet (110 meters by 128 meters). Daylight analysis was conducted early in the design process. Design criteria called for enough daylight transmission that artificial light would be unnecessary on the platforms from sunrise to sunset 98 percent of the time. The analysis led to a design that provides an average of 12 percent transparency under the shed. The structure accounts for 36 percent of the total shed roof surface area, the glass for 14 percent, and the photovoltaics for 50 percent. The glass is 95 percent transparent, and the PV panels are 5 percent transparent.

Ongoing Use

The Stillwell Avenue Terminal is already more than 90 years old. New York City Transit projects are designed to standards of durability, constructability, and maintainability well beyond those typical in the private sector.

Because trains run continuously year-round, the team designed the project to be maintainable without interrupting train service. The photovoltaic modules are fitted with quick-release connectors, and all service can be done from above. Three rolling gantries permit modules to be lifted up and replaced from above. The bolted steel connections and the panelized glass modules will allow the entire shed to be disassembled at the end of its useful life.

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Special thanks to Kiss + Cathcart, Architects for the material used in this report.

Lighting designer: Domingo Gonzalez, Domingo Gonzalez Associates, Inc., New York, New York

SUBSCRIPTION SAMPLE The Stilwell Avenue Terminal train shed project combined a new photovoltaic roof and supporting trusses with parts of the existing 90-year-old facility. Photo: Courtesy Kiss + Cathcart, Architects The Stillwell Avenue Terminal train shed roof comprises three arches, each finished with glass-embedded photovoltaic panels, which together produce a total of 210,000 kilowatt-hours of electricity per year. Photo: Adam Friedberg The exposed steel structure of the new roof trusses at the Stillwell Avenue Terminal are intended to recall the amusement park vernacular traditions of Coney Island. Photo: Adam Friedberg The Stilwell Terminal's eight tracks and four platforms are covered by the new roof by Kiss + Cathcart, Architects. Photo: Maki Isayama Axonometric drawing of the train shed roof. Image: Kiss + Cathcart, Architects Extra Large Image Detailed roof section and gantry plan drawings. Image: Kiss + Cathcart, Architects Extra Large Image Detailed drawings of the photovoltaic panels. Image: Kiss + Cathcart, Architects Extra Large Image Carefully placed transparent zones within the glazing panels, between the photovoltaic portions, help provide appropriate daylighting on the platforms. Photo: Courtesy Kiss + Cathcart, Architects   Click on thumbnail images to view full-size pictures.