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