Incorporating Building Integrated Photovoltaic (BIPV)

Technology

into

New York City Transit’s

BMT Stillwell Avenue Terminal Train Shed

Rich Miras, PE, Program Manager, New York City Transit

Fazla Hassan, Project Manager, New York City Transit

Tony Daniels, RA, Associate Principal, Kiss + Cathcart

Architects

ABSTRACT

New York City Transit’s BMT Stillwell Avenue Terminal Train

Shed will be one of the largest building integrated

photovoltaic roofs in the world. In this paper, we will

explore the special concerns arising from the design,

installation, operation, and maintenance of the BIPV

system. After a brief discussion of the Stillwell Terminal

reconstruction project, we will highlight the environmental

benefits of the BIPV system. We will describe BIPV systems

and their components and discuss how the technology was

successfully applied in this project, and how the design of

the system met unique maintenance and operations

requirements of New York City Transit.

INTRODUCTION

The BMT Stillwell Avenue Terminal is the largest in New

York City Transit’s system, and by some measures, the

largest rapid transit terminal in the world. (See Fig. 1)

The terminal is located in Coney Island, home to Nathan’s

original hot-dog stand, the world famous Cyclone

rollercoaster, the beach and boardwalk, and Brooklyn’s

minor-league baseball team, also called the Cyclones.

Coney Island has been a popular tourist destination since

the late 1800’s, but its popularity declined in the 1970’s.

It is currently undergoing a revitalization, and is once

again becoming a popular transit destination.

The terminal is a functionally critical node in New York

City Transit’s system. In addition to being the terminal

station for four of the BMT subway lines, the terminal is a

primary base of operations for the BMT Southern Division.

Trains are locally controlled and dispatched; subway car

interiors are cleaned; and Rapid Transit Operation (RTO)

train crews report to work daily. The terminal also

controls and facilitates non-revenue train movements to and

from the mainline, and the Coney Island Yard and Shop

complex, in support of scheduled car maintenance and

inspection operations. The terminal is also an intermodal

transfer point for several bus routes. The consolidation

of operational functions and personnel at the terminal

achieves economies of scale and other functional benefits

and efficiencies.

Stillwell Avenue Terminal is fully above ground, with fare

control and service areas at grade, and platforms on an

elevated concrete-encased steel viaduct structure. It was

built in 1916, and had deteriorated over the years. As

part of New York City Transit’s routine inspection cycle,

it was determined that the structure should be

reconstructed.

The Stillwell Terminal reconstruction project includes:

• Replacement of the steel viaduct structure

• Four new platforms

• Seven new tracks

• New circulation elements like elevators and Americans

with Disabilities Act compliant ramps

• A new fare control area,

• A new Rapid Transit Operations (RTO) facility and

other ancillary operations and crew facilities

• A restored historic façade along Surf Avenue

• A new “Portal Building” which includes retail spaces.

• And a New train shed spanning all 8 terminal tracks

and four platforms, which incorporates Building

Integrated Photovoltaic (BIPV) technology.

The Rehabilitation of the Stillwell Terminal is the largest

capital project in New York City Transit’s current budget

cycle.

The initial proposed phasing of the terminal reconstruction

project permitted only one track to be taken out of service

at any given time. This would have resulted in a project

duration of approximately 9 years. Through coordination

with the numerous stakeholders in the project, the project

duration was shortened to 43 months, with a major portion

of the terminal closed for only 19 months. The main

construction impact began in September 2002 and will

conclude in May of 2004. The entire project is scheduled

for completion in the Winter of 2005. These dates are

significant, because Coney Island’s economy depends heavily

upon tourists and summer day trippers who use the subway to

travel. The substantially reduced train service will be

limited to the summer of 2003.

New York City Transit took several actions to achieve this

abbreviated construction schedule. First, several off-site

operations facilities had to be constructed. These

temporary facilities take the place of those facilities at

the terminal displaced by construction. In addition, a

two-step RFP process was used to select the project’s

general contractor. By selecting a low bid from pre-

qualified contractors, the nightmare of an under-qualified

low bidder was avoided. Finally, temporary bus service and

facilities have been provided in order to preserve public

transit service in the Coney Island area.

THE TRAIN SHED

While glass-roofed train sheds have been constructed since

the 19th century, the terminal’s train shed is unique and

innovative in several respects. It is New York City

Transit’s first BIPV roof, and will be the largest of its

type ever built. While the Terminal’s facilities, viaduct,

and fare control areas were designed in-house by New York

City Transit’s engineers and architects, an outside

consultant team led by Jacobs Engineering and Kiss +

Cathcart Architects was brought in to complete the design

of the train shed.

The shed is a triple-arched skylight set on a system of

trusses constructed from Hollow Structural Section (HSS)

members (see figure 2). The trusses, in turn are set on top

of the steel viaduct structure. When complete, it will be

the visual signature of the terminal. In addition, it will

demonstrate New York City Transit’s commitment to

environmentally sustainable and responsible design.

New York City Transit has developed and Environmental

Management System certified under ISO 14001. This

certification program requires that New York City Transit

monitor the integration of environmentally responsible

aspects into design and development of all projects. The

shed and the other aspects of the terminal are therefore

subject to conformance with New York City Transit’s Design

for the Environment program. The train shed helps the

Stillwell Terminal Reconstruction project achieve these

integration goals by providing an on-site source of

renewable energy for the facility.

In addition, there will be several other benefits to the

train shed. First, it will generate approximately 260,000

kilowatt hours of electricity for terminal facility, mostly

at peak hours. This energy is the equivalent of the power

required for 40 single family homes in one year. This is a

tremendous environmental benefit, since this energy is

produced on-site, without burning fossil fuels. There is

also a financial benefit, since New York City Transit will

not have to buy this electricity from the utility.

The magnitude savings can also be measured in terms of the

time of energy production. The Stillwell BIPV system will

provide approximately 11% of the peak facility demand, and

approximately 30% of the energy used at the facility.

Since most of this production will be at times of peak

demand, the financial benefit will be even greater. On-

site solar energy production displaces the most polluting

and expensive power.

The annual environmental benefits from PV can be quantified

in terms of reduction of greenhouse gas emissions. Each

year, the PV array at Stillwell will result in avoided

emissions of approximately 125 tons of Carbon Dioxide, 500

pounds of sulfur dioxide, and 350 pounds of nitrogen oxide.

These figures are specific to the mix of power delivered

through Con Edison’s power grid in New York, approximately

40% of which is generated through nuclear power. In other

areas, where electrical supplies are generated more through

fossil fuel combustion, greater reductions in greenhouse

gas emissions are likely.

There are several other benefits to the train shed. It

will provide improved maintenance and durability for the

terminal, by covering the track and platforms. It will

protect rail passengers from the elements. Finally, it

will create an architecturally significant public

structure, and contribute to the revitalization of Coney

Island.

Building Integrated Photovoltaics

Photovoltaic (PV) technology is a means of converting

energy from sunlight into DC power. The “photovoltaic

effect” has been scientifically investigated since 1839

when Henri Becquerel noticed that shining a light onto

certain chemical compounds could generate an electric

current. In essence, light energy causes chemical and

ionic reactions, which free electrons. The movement of the

free electrons can be directed by combining materials of

varying chemical compositions. This controlled movement of

electrons creates an electrical current. Thus, sunlight

can generate electrical power.

PV technology has developed and matured, and applications

of the technology today range from wristwatches to

satellites. The market for PV panels as building

materials is growing, and the number of manufacturers of PV

Panels continues to increase. The production capacity of

the PV industry has been increasing each year, with the

manufacturing capacity reaching some 400 Megawatts in 2003.

Worldwide, PV solar-electric sales totaled approximately $2

billion in 2002. The U.S. Department of Energy’s National

Center for Photovoltaics estimates that the U.S. PV

industry will grow at a rate of approximately 25% per year.

PV modules are typically fabricated from silicon or other

semi-conductive materials applied to glass panels.

“Building-Integrated” refers to the practice of

incorporating PV modules directly into building façade and

roof systems, rather than mounting them to the building

enclosure. BIPV materials replace other building

components, resulting in extremely cost effective

applications. For example, an opaque PV panel can take the

place of a spandrel glass panel. The costs of the two

panels are frequently comparable, but only the PV panel

produces electricity

While building integrated PV systems are potentially the

most cost effective installations, stand-alone PV power

generation systems are quite effective under some

conditions. PV has always been a sensible choice for power

generation in areas far removed from the power grid. For

example, a PV system with batteries large enough to power a

home can cost less than extending electrical power lines by

just a few hundred yards. These applications have proven

useful in remote areas and throughout the developing world.

In the developed world, extensive PV arrays can be

installed where real-estate costs are low and solar

insolation is high, such as along highway or railway

rights-of-way. Power from such installations can be stored

and used for lighting, or for DC current regulation in

traction power systems, or for other uses. This area is a

candidate for further research.

DESIGN CHALLENGES

The project team faced many challenges in the design of the

PV array and balance of system. Some of these challenges

were specific to the New York City Transit Authority’s

operations and maintenance requirements, but others were

typical challenges encountered on projects of this type.

In order to better understand the potential benefits and

issues with the different types of PV modules and system

configurations, New York City Transit requested that the

design team develop detailed design and maintenance

criteria for the system. With input from NYCT’s

maintenance and operations groups, the design criteria were

refined and the team was able to develop a biddable,

constructable, and maintainable design.

The design criteria developed for the Stillwell BIPV system

addressed several concerns, which can be grouped into the

following general categories:

• BIPV design and Maintenance Parameters

• Electrical Configuration and Utility Interconnection

BIPV Design and Maintenance Parameters

Due to the configuration of the shed, PV modules had to

meet several requirements. The panels had to meet building

code structural requirements for overhead glazing. In

addition, the roof had to be designed to provide enough

daylighting to virtually eliminate the need for artificial

light on the platforms from sunrise to sunset. (See Fig.

3) While the BIPV system is a “first-of-its-kind”

installation, cost was also a major consideration.

Perhaps most significantly, the system had to be designed

to be maintained from above the roof by NYCT personnel.

NYCT operates trains continuously, at all times. A track

in NYCT’s system can be taken out of service only through a

“General Order” (GO.) Each GO request is reviewed and

approved prior to implementation, to address safety and

security concerns. The GO process is involved and

expensive. By requiring maintenance to be performed from

above, GO’s can be avoided. These maintenance

considerations were the most important design drivers on

the project.

The solution to these various parameters resulted in a

design based on a single modular PV panel size and type

incorporated into a conventional skylight system, (see

Fig. 4.) The PV panel size was designed to be flexible, in

order to accommodate products from several manufacturers.

In order to ensure that PV power output requirements were

met, drawings indicated minimum PV area parameters for the

modules. In addition, minimum transparent area was also

indicated to ensure proper daylight levels at the platform.

This solution allows the contractor to exploit efficiencies

and economies of scale in production. The result is a

project that is easier to deliver and construct within the

short window of available time.

PV modules have no moving parts, and their service life is

quite long, with most manufacturers offering 20 and 25 year

warranties. In fact, PV modules have been in service in

some of the most demanding climates on earth for periods of

25 years or more. However, the PV panels at Stillwell were

designed to meet stringent requirements for loading and the

skylight system allows for replacement with relative ease.

The Stillwell PV panels consist of PV modules and clear

glass laminated between two plates of partially hardened

glass. (See fig. 5) The total thickness of this triple-

laminated panel is approximately 3/4”. Each panel is

attached to an aluminum perimeter frame by factory

application of a structural glazing sealant. The aluminum

perimeter frame is then mechanically attached to an

aluminum subframe, which in turn is mounted to the steel

structure. Once the PV panel is mechanically secured, a

waterproof seal is applied to complete the system. In

order to remove a PV panel, one cuts the waterproofing, and

unscrews the panel perimeter frame from the subframe.

This operation can be performed from above the shed roof.

There is no need to disturb the structural glazing sealant

or approach the PV panels from below.

The design also includes a maintenance gantry system which

moves on rails. The gantry system will permit access for

maintenance to every part of the roof. The gantry system

will be equipped with special equipment for lifting,

moving, and setting PV panels along the curve of the roof.

Specifications

Since the New York City Transit Authority is a public

agency, proprietary specifications are not permitted in

construction contracts. This limitation poses special

challenges for unique projects, such as Stillwell Terminal.

On the one hand, it is necessary to specify performance

requirements for systems and assemblies. On the other

hand, it is necessary to validate designs on the basis of

whether they can be procured and constructed. While there

is no “off the shelf” system capable of meeting the unique

requirements for Stillwell’s BIPV system, it is possible to

construct the system from fairly conventional components.

The specifications make use of several techniques to

indicate the requirements for the BIPV system. Since the

terminal is located less than 1000 feet from the ocean,

structural loading requirements were developed through wind

tunnel testing and analysis during design. In order to

ensure acceptability of the system for installation by

union labor, a UL label was required. Mock-ups and samples

of the system were required to verify that the maintenance

criteria could be met. Finally, the contractor was

required to perform structural load and impact tests on the

mock-up. Large and small missile impact tests and cyclical

pressure tests were specified in accordance with ASTM

E1886. (see fig. 6) These are the most stringent specified

performance standards in use today.

Electrical Configuration

There are two major components of every PV system: PV

modules and the electrical “balance-of-system,” which

includes all of the wiring and devices necessary to

transport the power generated by the modules. The second

category of design challenge is centered on the electrical

configuration of the BIPV system. Issues addressed in

this area include

• Estimating the power output from the PV system for

purposes of design,

• Configuring the electrical balance of system

• Designing the intertie with utility power.

Estimates of PV power output are critical in the design of

any system. For one, the entire electrical balance of

system design, including equipment sizes and wire sizes,

depends upon the amount of power produced. There are also

frequently incentives and benefits sponsored by utilities

and by the government that depend upon the system’s output.

Finally, once you are producing power, you need to figure

out how to use it. The estimate is therefore a critical

first step in the system design.

PV Power estimates depend on a number of factors, including

local solar radiation conditions, the type of PV modules

to be used, and the orientation and location of PV modules.

Since PV’s will produce power even in low-light conditions,

estimates should take into account every available hour of

sunlight. In the Northern Hemisphere, South facing PV’s

generally produce the most power. However, it may be well

worth installing PV’s at other orientations, as well,

depending upon factors including the location of the site,

the demand profile of the building, and local utility rate

structures.

The function of PV module type in PV power estimates

deserves special mention. PV modules are rated based on

their efficiency at creating power under a standard test

condition (1000 watts per square meter.) Depending on the

technology used, commercially available PV module

efficiency ranges from 5-6 percent to about 15 percent.

The efficiency of PV modules as a class has been steadily

rising, as the photovoltaic effect becomes better

understood through research. Within 15 years, we expect to

see efficiencies in the 12 to 20 percent range.

With the initial estimates of power output from the PV

arrays in hand, the balance of system and utility

interconnection can be designed. The first critical

decision to make is whether the PV array will be connected

to the grid. If the system is to be grid-independent, as

in a rural application, it is likely that a battery back-up

system will be required. If the installation is to be

grid-tied, there are a number of utility power conditioning

and special metering requirements to consider.

PV balance of system components are somewhat less

specialized than PV modules. Many devices and controls

used in PV power systems are similar to those used in

conventional power generation systems. However, the single

most important electrical device used in a system is the

inverter, which turns DC current into AC current, and

sometimes conditions power to allow for interconnection

with the utility grid. In coordination with transformers

and other devices, inverters are critical to the interface

of PV power with utility power.

At Stillwell, NYCT decided to tie the PV output into the

main feeder system for the facility. This solution does

not include a battery storage system, which would require a

substantial amount of space, and would also require annual

maintenance, and eventual replacement after about 15 years.

However, the array will still substantially reduce the draw

on the local power grid, especially during times of peak

power consumption, when the risk of brownouts and blackouts

is highest.

In the case of a grid power failure, this arrangement can

result in the potentially dangerous situation where the PV

array is energizing the grid, exposing Con Edison system

maintainers to the risk of working with live wires. Con

Edison therefore requires that independent power generation

systems comply with a strict set of interconnection

protocols. The Stillwell PV balance-of-system is therefore

equipped with a number of “reverse power relays” and other

devices to prevent the export of power to the grid.

With smaller, residential PV arrays rated up to 10 kW, Con

Edison permits “net metering” arrangements. These

arrangements are mini power purchasing agreements, which

allow customer owned PV arrays to feed excess power back

into the grid when local demand is less than the power

produced. In effect, net metering permits the customer to

“spin the meter backwards.” Unfortunately, this

arrangement is not currently available to larger producers

of power.

Another key design decision for the PV balance of system is

the number and location of inverters. Commercially

available inverters can be sized as small as a few hundred

watts, and as large as 225 kW. At Stillwell, we

considered several arrangements of inverters. With 2,730

PV modules in the array, we studied arrangements with as

many as 546 inverters and as few as one. Most of the

schemes with smaller inverters were located near the PV

array, at the roof level. These schemes were dismissed due

to the difficulty in access for maintainers, and potential

complications in the detailing of waterproofing.

A two-inverter solution was finally selected, with the

inverters and related electrical balance of system located

in an electrical room below the platform level. Under

normal operations, each inverter handles output from half

of the PV array. The two inverters are connected by a

tandem circuit breaker, which allows for either half of the

PV array to be shunted to either inverter or taken off

line. In the event that one of the inverters needs to be

taken off line for servicing, on all but the brightest and

sunniest hours of the days, PV power output will not be

reduced.

The last major subsystem that we will consider is the

Supervisory Control and Data Acquisition (SCADA) system.

In order to monitor the output and continued proper

functioning of the PV installation, a SCADA system was

specified. The system will monitor PV output at 182 points

in the array, as well as at the inverter in and out

locations, and other critical points in the electrical

balance of system. The SCADA system will also track

weather and insolation data in order to validate the

system’s performance.

Construction on the project began in the fall of 2001, and

the PV system is scheduled for installation this fall. The

process of testing and validating the design of the system

has gone smoothly, and the Contractor has been able to

deliver the specified design. Stillwell will open at the

end of 2004, (See Fig. 7.)

CONCLUSION

Renewable energy technologies can be successfully

incorporated into rail transit facilities if design teams

pay heed to maintenance and operations concerns. At the

same time, design teams must work with the developing

parameters of the PV industry. While there are many unique

components and subsystems in BIPV power systems, design

solutions can be found by combining conventional assemblies

and equipment with new technologies. The environmental

benefits of BIPV systems are indisputable, and installation

of these systems becomes more feasible every day, as the

industry continues to grow and the systems are better

understood. The Stillwell Terminal Train Shed BIPV roof

will set a new standard for functional and aesthetic

integration of photovoltaic panels in one of the most

demanding environments anywhere.

ACKNOWLEDGEMENTS

The authors wish to credit Mike Kyriacou, P.E., and New

York City Transit’s design management team for their

leadership in the design of this first-of-its-kind

installation. But for their efforts, the project would not

have been built. In addition, we received valuable input

from several other members of the design team. Tom Reed,

P.E., and Jay Mehta, P.E., of New York City Transit, and

Robert Harvey, Jr., P.E. of Jacobs read the paper and

provided comments. Gregory Kiss, R.A., and Robert Garneau,

R.A. also provided input and assistance.

Table of Figures

Fig. 1 Aerial View of Stillwell Avenue Terminal

Fig. 2 Axonometric View of the Stillwell Terminal

Train Shed

Fig. 3 Interior View of the Train Shed

Fig. 4 Typical BIPV Panel

Fig. 5 BIPV Panel Glazing Detail

Fig. 6 Structural Testing of the Skylight System

Fig. 7 Visualization of the Completed Roof

Fig. 1 Aerial View of Stillwell Avenue Terminal

Fig. 2 Axonometric View of the Stillwell Terminal

Train Shed

Fig. 3 Interior View of the Train Shed

Fig. 4 Typical BIPV Panel

Fig. 5 BIPV Panel Glazing Detail

Fig. 6 Structural Testing of the Skylight System

Fig. 7 Visualization of the Completed Roof