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WORL D OVERVIEW OF BUILDING-INTEGRATED PHOTOVOLTAICS
Steven J. Strong, President
Solar Design Associates, Inc., Harvard, MA 01451-0242 USA
ABSTRACT
There is a growing consensus that distributed photovoltaic
(PV) systems will be among those applications to first
reach widespread commercialization in the generation of
power on the utility grid. Chief among these distributed
applications are PV power systems for individual buildings.
Interest in the building integration of photovoltaics, where
the PV modules actually become an integral part of the
building, often serving as the exterior weathering skin, is
growing world-wide. With reduced installation costs,
improved aesthetics and all the benefits of distributed gen-
eration, building-integrated PV systems are a prime candi-
date for early market penetration. Product development is
proceeding in three general areas: Integral roof modules;
roofing tiles and shingles; and integral modules for vertical
facades. This paper will cover residential and commercial
applications with examples of the direct integration of PV
elements into residential and commercial buildings using
built examples from the US, Europe and Japan.
INTRODUCTION
The last two decades have brought significant changes to
the building design profession. Economic, environmental,
and aesthetic pressures have converged to point up the
critical role design professionals play in the developmentof the physical infrastructure and its ultimate impacts on
the global environment, national security, local health and
safety, and the corporate bottom line. By designing build-
ings to minimize waste and generate power rather than
just consume it, architects aire moving beyond the goal ofsimply creating buildings that are aesthetically pleasing,
toward an ethic of environmentally and socially responsible
design. These buildings, rather than merely using less con-
ventional fuel and creating less pollution, will rely on
renewable resources to produce some and, ultimately, all
of their own energy without creating any pollution (see
Figs. 1 and 2).
PHOTOVOLTAIC TECHNOLOGIES
While the solution to problems as complex as energy gen-
eration and security requires the integration of many
diverse resources, one technology, photovoltaics (PV),
offers the chance to produce that most universal energy,electricity, through a semiconductor process using no mov-
ing parts, no fuel other than sunlight, and creating no pol-
lutants. Ultimately modular, PV systems can be expanded
over time without losing the investment in earlier installa-
tions, and they can be physically distributed over a wide
geographical area and fielded on both new and existing
structures, minimizing their installation impact and cost of
land and power transmission and distribution systems.
Architectural use of PV typically involves crystalline silicon
PV modules and amorphous thin-films deposited on glass,
ceramic, stainless steel, or other appropriate materials.
Crystalline silicon PV has the advantage of higher conver-
sion efficiencies of light energy to electricity, and the draw-
back that it is rigid and not always architecturally appropri-
ate. Thin-film PV has advantages that include deposition
on unusually shaped materials and selective deposition
that allows varied transmission of light-looking much like
architecturally tinted glazings-making it an ideal replace-
ment for conventional building materials. The drawback of
thin-film PV, particularly amorphous silicon, is that its con-
version efficiencies are much lower than those of crys-
talline silicon. However, in building-integrated systems,
where the PV materials replace conventional building
materials, this may not necessarily be a disadvantage.
There is a growing consensus that distributed PV systems,
providing electricity at the point of use, will be the first PV
application to reach widespread commercialization. Chief
among these distributed applications are PV power sys-tems for individual buildings. Interest in the building inte-
gration of PV, where the elements actually become an inte-
gral part of the building, often serving as the exterior
weathering skin, is growing worldwide.
HISTORY
Following on the heels of the major energy cost and sup-
ply disruptions of the 1970s, designers, engineers, and
policy makers began looking seriously at renewable ener-
gy and conservation as solutions to problems of cost and
security. These same concerns helped mobilize the gener-
al public. Then, as conventional energy supplies stabilized
and prices dropped, public and political support to pursuethese solutions waned, and the anticipated market pene-
tration for these technologies was slowed. However, in the
late 1980s and early 199Os, public and political concerns
over pollution and global climate change produced a
renewed interest in these technologies. Groups associated
with utility power production and commercial and residen-
tial building energy use took particular interest.
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Fig. 1. The Lord residence, on the coast of Maine, USA
includes a utility-intertied, roof-integrated 4.25 kWp PV
array, comprising 16 large-area modules. This system is
exchanging power with the utility under a “Net Metering”
agreement.
Early projects integrating PV into residential and commer-
cial buildings involved mostly government-financedor sup-
ported opportunities to field-test and demonstrate the tech-
nology. In the United States, projects included the Carlisle
House 7.5 kWp), the Georgetown University Intercultural
Center (325 kWp), and the three regional Residential
Experimental Stations, which served as test beds for
numerous technologies and innovative designs. On a more
ambitious scale, electric utilities have followed with several
projects, including the 100 kW of distributed PV systems
on existing homes and commercial buildings in Gardner,
Massachusetts 1985), the many programs of the
Sacramento Municipal Util ity District, and the projects of
other utilities, including Delmarva Power and Light, the
New York Power Authority, Southern California Edison, and
the City of Austin TX) municipal electric utility.
TlAL BlPV SYSTEMS
The first building-integrated market envisioned for PV was
on residential roof tops. In the United States in the 197Os,
there was a rush to install solar domestic hot water sys-
tems, encouraged by tax credits, and many assumed that
the PV market would follow suit. So, in the late 1970s and
early 1980s, much research and commercial development
effort focused on this market The US . Department of
Energy (US-DOE) sponsored the development of threeregional Residential Experimental Stations-in
Massachusetts, New Mexico, and Florida-to test proto-
type systems in varied climates. Based on results from
these research stations, the US-DOE and the
Massachusetts Institute of Technology (MIT) commis-
sioned Solar Design Associates to design the first utility-
interactive, building-integrated, PV-powered residence-
the Carl isle House. However, in the early 1980s,
Fig. 2 A commercial building in Freiburg, Germany, with a
faGade of “structural glazing” elements incorporating PV
modules and operable view glass in a prefabricated
assembly; the roof and faGade modules total 18.5 kWp.
government and corporate support for this market wanedwith the loss of the tax credits. Interest has only recently re-
emerged in the United States, as designers and architects,
often supported by forward-thinking utilities or philosophi-
cally inclined private clients, have begun to take advantage
of technology advances. Recent examples of systems of
this type include the PV Pioneer program, in Sacramento,
California (see Fig. 3); and the Lord residence, on the
coast of Maine (see Fig. I , respectively.
The SMUD PV program has installed more than 4.3 MWof
PV through early 1996, and its plan is to obtain at least half
of its energy from energy efficiency and renewables by the
end of the decade. SMUD’s residential PV Pioneers
receive SMUD-installed and owned PVroofs and pay a monthly premium for p
Fig. 3. The Sacramento Municipal Utility District’s “Solar
Pioneers” program installs PV systems on the homes of
volunteer util ity customers.
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program. There is a long wailing list of customers who wish
to participate, even thought they receive no direct benefit
from the electricity generated, because the connection is
made on the utility side of the meter.
In Europe and Japan, where interest in energy security and
concerns about the environrnent have increased over the
past decade, interest in renewable energy in general, and
PV in particular, has also increased. Japan and most coun-tries in Europe are land-limited, so distributed PV systems
on buildings proved a very attractive path to pursue. In
Japan, the Ministry of International Trade and Industry
(MITI) began a -/-year program in the fall of 1993 to subsi-
dize the price (up to 2.7 million yen [approximately
US 27,000] in the first 3 years, dropping to zero after the
seventh year) of residential PV systems up to kWp per
home. The goal is 62,000 homes and 185 MWp of installed
residential systems.
Throughout Europe, governments are supporting the
installation of residential PV systems. In Germany, the gov-
ernment has implemented its “1,000 Roofs” program, sub-
sidizing 70% of the cost of residential PV systems of
between 1 and 5 kWp. The program, begun in 1990, soonexpanded its goal to 2,500 roof-top installations. In
Switzerland, even before the Germans instituted the “1,000
Roofs” program, a privately funded program was devel-
oped that resulted in 333 3-kWp grid-connected PV sys-
tems, using private, long-term financing with low interest
rates and volume purchases. The Dutch government plans
to field 250 MWp of PV by tlhe year 2010, including an ini-
tial 1,000 homes by the year 2000. In Austria, the govern-
ment modeled a plan after tlhe German “1,000 Roofs” pro-
gram, with the goal of subsidizing the installation of 200
kWp of PV. This program is nearly completed, and discus-
sions are now under way to expand it by an additional 100
kWp. In Finland, more than 20,000 vacation homes are
currently powered by PV, and estimates indicate that thereare approximately 200,000 vacation homes that are ideal
candidates for using PV. Nearby, Sweden has more than
20,000 vacation homes powered by PV, with more than
5,000 new installations each year, while Norway has more
than 50,000 vacation homes powered by PV, with more
than 8,000 new installations annually.
As for residential PV technologies, companies in the
United States, Japan, and Europe are actively pursuing
module designs that lend tlhemselves to easy installation
and provide an aesthetically pleasing substitute for tradi-
tional residential roofing materials. The Japanese compa-
ny Sanyo and the Swiss company Alpha Real are working
on roofing tiles, while Sanyo and the US. companyUSSC
are developing amorphous silicon thin-film roofing shinglemodules.
Another area of importanceto the commercialization of dis-
tributed PV systems is the work with utilities and federal
authorities to establish uniform utility interconnection stan-
dards and “Net Metering” policies. Net Metering is a sys-
tem where the utility credits a user, on a one-to-one cost
Fig. 4. The Bavarian Environmental
Ministry’s amorphous-silicon fagade and
crystalline PV sun-controlling eyebrows pro-
vide a total output of 53.4 kWp.
basis, for the power produced versus the power con-
sumed. Any power produced in excess of the amount con-
sumed is typically repurchased by the utility at the lower
“avoided cost” rate, while any power consumed beyond the
level of the power produced is sold to the customer at the
utility’s standard rate. This system is a win-win proposition,
with the utility’s offsetting its peak loads with customer-sup-
plied power, while the PV-system owner benefits by using
the utility as a backup, avoiding the cost of a battery stor-
age system. Currently, Japan, Switzerland and twelvestates in the United States mandate Net Metering.
INTEGRATED COMMERCIAL BlPV SYSTEMS
Architects and engineers in Europe and Japan have, with
the convergence of strong public interest and significant
government support, become very creative in the integra-
tion of PV elements into commercial building fagades.
Other building applications include using PV as a sun
screen, a light monitor, a semi-transparent window, and as
sloped glazing or a roofing material. Each element can use
either crystalline silicon or thin-film PV, depending on the
needs of the architect and the client. More recently, archi-
tects in the United States have begun to field some excep-
tional examples of BlPV in commercial buildings.
Examples of PV integrated into commercial structures
include the Bavarian Environmental Ministry (see Fig. 4), in
Germany, with both a fagade of amorphous silicon modules
and sun-controlling “eyebrows” over the south-facing win-
dows, using thick-crystal modules, with a total generating
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Fig. 5. The Aerni Fenster, AG, industrial plant and office
building, in Arisdorf, Switzerland. The roof- and fa ade-
integrated systems total 62 kWp.
capacity of 53.4 kWp; the soon-to-be-constructed Science
Park Gelsenkirchen, near Essen, Germany, which, at 300
kWp, will be the largest building-integrated PV system inEurope; the faqade and roof systems, totaling 62 kWp, of
the window manufacturer Aerni Fenster, AG, in Arisdorf,
Switzerland (see Fig. 5); the APS factory, in Fairfield,
California, with its “entry cube,” 3.2-kW amorphous silicon
curtain wall (see Fig 6); the Olympic Natatorium, in Atlanta
Georgia, with its 340-kWp roof-top crystalline array (see
Fig. 7); the Mataro Library, in Mataro, Spain, with its 53-
kWp crystalline faGade (see Fig. 8); and, a Tsukasa
Electric Industry Company building, in Japan, featuring a
full south faGade of Sanyo amorphous silicon modules,
with opaque modules used in non-view areas and semi-
transparent modules used as view glass (see Fig. 9).
Fig. 7. The roof-top PV system at the 1996 Olympic
Natatorium, in Atlanta, Georgia, USA, employees 2,832
modules to produce 340 kWp. In addition, a custom arched
glass PV canopy was designed for the entrance to the
complex. At 3,043 m2, this is the largest system of its kind
in the world.
~
1200
Fig. 6. The APS factory’s “entry cube” comprises a 3.2
kWp amorphous silicon PV curtain wall, replacing conven-
tional faGade materials.
In the United States, in 1992, the US DOE launched a 5
year cost-shared program, called “Building Opportunities in
the U.S. for Photovoltaics (PV:BONUS), to encourage the
development of building-integrated PV systems. Under
this program, Solarex Corporation, of Frederick, Maryland,
a division of Amoco/Enron Solar, has developed a line of
building-integrated components for
faSades and sloped glazing
PowerWallm, in conjunction with architectural curtain wall
giant Kawneer of Atlanta.
There are several factors driving ation of PV with
commercial buildings. One is the surface area of
the buildings with the proper orientation, much of which
could receive PV materials, either in new construction or in
retrofit. Another factor is the coincidence of the building
power loads with the peak production of PV-the buildings
are occupied during the day, when the PV system pro-duces power. Another is financial, in that part of the cost of
the PV module components will be offset by the cost of the
materials they replace, whether roofing materials, fagade
materials, or shading elements. Commercial building
developers and owners often consider the “value” of an
architectural element as much as its “cost”-otherwise,
why would a building be finished in granite or marble? And,
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Fig. 8 The Mataro Library, in Mataro, -Spain, uses a
facade- and roof-integrated crystalline PV system to pro-
duce 53 kWp of power
initial experience shows that BlPV provides an image thatappeals to potential tenants, helping to lease the building
space.
SYSTEM COMPONENTS
The most obvious components in building-integrated PV
systems are the modules. These can vary from thick-crys-
tal modules, with opaque backings, to semi-transparent
thin-film-on-glass modules, and include any combination in
between, with sizes ranging up to 2 square meters. Or
they might be designed into shingle or tile elements. The
most architecturally and aesthetically pleasing modules
include, in addition to the shingle or tile modules, the crys-
talline glass-on-glass modules and the thin-film-on-glassmodules. These crystalline modules can be integrated into
structures in such a way that. the light entering the building
will have the feel of that passing through the leaves of a
tree-providing elegant patterns of light and shade (see
Fig. 10. A view from the interior of the Mataro Library,
showing the diffuse lighting effects of using glass-on-glass
PV modules used in building faqades.
Fig. 10). The thin-
film modules, i f ’opaque, can be
used as faqade ele-
ments for non-view
areas, or if semi-
transparent, can
replace tinted glass
in view areas.Because the mod-
ules are made
semi-transparent
by laser-cutting
evenly spaced
microscopic holes
in the PV material
to allow light to
pass through, a
process developed
at Sanyo, their
efficiency is less
than the opaque
modules.
Fig. 9 The Tsukasa Electric
Industry Company building, in
Japan, with a Sanyo amorphous
silicon module facade.
A critical balance-of-system component for BlPV systems
is the power electronics used to transform the dc power
generated by the modules into the ac power used in virtu-
ally all applications. These inverters also synchronize the
power from the system with that of the utility grid and mon-
itor the power flow for faults. They vary from individual
large central inverters to the newly developed Module-
Integrated Inverters, which convert the dc output of each
individual module to ac (see Fig. 10). Additional compo-
nents could include storage batteries, for stand-alone sys-
tems, and the required mounting and connecting hardware.
INTERNATIONAL ACTIVITIES
In 1990, under the leadership of Prof. Jurgen Schmid, a
working group was created within the International Energy
Fig. 11. A module-integrated, 250-W inverter measuring
21.6 cm x 18.4 cm x 3.2 cm (shown with a pencil or scale).
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