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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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