Note: Descriptions are shown in the official language in which they were submitted.
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PHOTOVOLTAIC DEVICES INCLUDING COVER ELEMENTS, AND
PHOTOVOLTAIC SYSTEMS, ARRAYS, ROOFS AND METHODS USING THEM
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims priority under 35 U.S.C. 119(e) to U.S.
Provisional Patent
Application serial no. 60/946,881, filed June 28, 2007, which is hereby
incorporated herein
by reference in its entirety.
BACKGROUND OF THE INVENTION
1. Field of the Invention
[0002] The present invention relates generally to photovoltaic devices. The
present
invention relates more particularly to photovoltaic devices having cover
elements providing
control of the power generation of the photoelectric cells used therein.
2. Summary of the Related Art
[0003] The search for alternative sources of energy has been motivated by at
least two
factors. First, fossil fuels have become increasingly expensive due to
increasing scarcity and
unrest in areas rich in petroleum deposits. Second, there exists overwhelming
concern about
the effects of the combustion of fossil fuels on the environment due to
factors such as air
pollution (from NOX, hydrocarbons and ozone) and global warming (from C02). In
recent
years, research and development attention has focused on harvesting energy
from natural
environmental sources such as wind, flowing water, and the sun. Of the three,
the sun
appears to be the most widely useful energy source across the continental
United States; most
locales get enough sunshine to make solar energy feasible.
[0004] Accordingly, there are now available components that convert light
energy into
electrical energy. Such "photovoltaic cells" are often made from semiconductor-
type
materials such as doped silicon in either single crystalline, polycrystalline,
or amorphous
form. The use of photovoltaic cells on roofs is becoming increasingly common,
especially as
device performance has improved. They can be used to provide at least a
significant fraction
of the electrical energy needed for a building's overall function; or they can
be used to power
one or more particular devices, such as exterior lighting systems.
[0005] Radiation generates voltage in a photovoltaic cell regardless of
whether the cell is
fully integrated into a photovoltaic power system. The voltage of a single
photovoltaic cell
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generally is insufficient to cause an injury hazard for an installer. However,
in use on a roof,
tens or even hundreds of photovoltaic cells are electrically connected in
series in order to
build up a desirably high voltage; and multiple groups of series-connected
photovoltaic cells
are electrically-connected in parallel, in order to build up a desirably high
current.
Accordingly, installers can be subject to dangerous electrical hazards when
installing
photovoltaic cells on roofs during daylight hours.
SUMMARY OF THE INVENTION
[0006] The inventors have realized there is a need for photovoltaic devices
that can be
installed safely and can more controllably address variable illumination and
excessive
photovoltaic cell temperature.
[0007] One aspect of the present invention is a photovoltaic device
comprising:
a photovoltaic element having an active face, an active area on the active
face and an
operating wavelength range; and
a cover element attached to the photovoltaic device and disposed over the
active area
of the active face of the photovoltaic element, the cover element having an
opacity
of at least about 25%.
[0008] In another aspect of the invention, the photovoltaic device described
above further
includes a roofing substrate having a top face and a bottom face, and the
photovoltaic element
is disposed on or within a roofing substrate.
[0009] Another aspect of the invention is an array of photovoltaic devices as
described
above.
[0010] Another aspect of the invention is a roof comprising one or more
photovoltaic
devices as described above attached to a roof deck.
[0011] Another aspect of the invention is a method of installing a roof,
comprising:
first,
attaching one or more photovoltaic devices to a roof deck, each photovoltaic
device comprising:
a photovoltaic element having a photovoltaic cell, a first electrical lead
and a second electrical lead attached to the photovoltaic cell, an
active face and an operating wavelength range; and
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a high opacity cover element removably attached to the photovoltaic
device and disposed over the active face of the photovoltaic
element; and
connecting the first electrical lead and second electrical lead of each
photovoltaic device to an electrical system; and
then, removing the high opacity cover sheet from each photovoltaic device.
[0012] Another aspect of the invention is a photovoltaic system comprising:
one or more photovoltaic devices, each photovoltaic device comprising:
a photovoltaic element having an active face and an operating wavelength
range, and
a cover element attached to the photovoltaic device and disposed over the
active area of the active face of the photovoltaic element, the cover
element comprising an electrochromic material disposed over the active
area of the active face of the photovoltaic element, a first electrode and a
second electrode wherein the electrochromic material is disposed between
the first electrode and the second electrode, and wherein the
electrochromic material has at least 25% opacity in an electric field-free
state or in the presence of an electric field; and
an electrical switching system connected to each cover element through its
first
electrode and second electrode, and configured to adjust the opacity of the
electrochromic material.
[0013] Another aspect of the invention is a roof comprising the photovoltaic
system
described above attached to a roof deck.
[0014] The photovoltaic devices, photovoltaic systems, arrays, roofs and
methods of the
present invention result in a number of advantages over prior art methods. For
example,
photovoltaic devices of the present invention can allow for installation and
repair without
subjecting the worker to hazardous electrical conditions. Moreover,
photovoltaic devices and
photovoltaic systems of the present invention can be adjusted so that they
operate at or near
the maximum power condition of their photovoltaic cells, thereby maximizing
efficiency and
power generation.
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[0015] The accompanying drawings are not necessarily to scale, and sizes of
various
elements can be distorted for clarity.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] FIG. 1. is an i-V curve for a typical photovoltaic cell;
[0017] FIG. 2 is a set of i-V curves for a typical photovoltaic cell at a
variety of
temperatures;
[0018] FIG. 3 is a schematic cross-sectional view of a photovoltaic device
according to
one aspect of the invention;
[0019] FIG. 4 is a graph showing the relative spectral response of three
silicon-based
photovoltaic materials as well as the spectral content of solar radiation;
[0020] FIG. 5 is a schematic top perspective view of a photovoltaic device
according to
one embodiment of the invention; and
[0021] FIG. 6 is a is a schematic cross-sectional view of a photovoltaic
device according
to one aspect of the invention.
DETAILED DESCRIPTION OF THE INVENTION
[0022] The voltage and, hence, power output of a photovoltaic cell depends
strongly on
the intensity of the radiation to which it is exposed. Accordingly, as
illumination conditions
fluctuate with cloud cover, season, time of day and the appearance or
disappearance of shade-
providing structures, the power output of the photovoltaic cell will
fluctuate. Such
fluctuation is often undesirable from the perspective of electrical system
design.
[0023] Moreover, as the temperature of a photovoltaic cell increases, its
power output
drops. The graph of FIG. 1 is an i-V curve for a typical photovoltaic cell,
showing the
approximate location of the maximum power point. The graph of FIG. 2 shows a
series of i-
V curves for a typical photovoltaic cell; the skilled artisan will appreciate
that as the
temperature of the photovoltaic cell increases, the maximum power point shifts
to lower
voltages. Because the power generated by a photovoltaic cell is the product of
its operating
voltage and its operating current, as the maximum power point shifts to lower
voltages the
maximum power generated by the cell decreases.
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[0024] One aspect of the invention is a photovoltaic device. One example of a
photovoltaic device according to this aspect of the invention is shown in
schematic cross-
sectional view in FIG. 3. Photovoltaic device 300 includes a photovoltaic
element 302,
which has an active face 304 and an operating wavelength range. Photovoltaic
element 302
has one photovoltaic cell or multiple photovoltaic cells that can be
individually electrically
connected so as to operate as a single unit.
[0025] Photovoltaic element 302 can be based on any desirable photovoltaic
material
system, such as monocrystalline silicon; polycrystalline silicon; amorphous
silicon; Ill-V
materials such as indium gallium nitride; II-VI materials such as cadmium
telluride; and more
complex chalcogenides (group VI) and pnicogenides (group V) such as copper
indium
diselenide. For example, one type of suitable photovoltaic element includes an
n-type silicon
layer (doped with an electron donor such as phosphorus) oriented toward
incident solar
radiation on top of a p-type silicon layer (doped with an electron acceptor,
such as boron),
sandwiched between a pair of electrically-conductive electrode layers.
Photovoltaic element
302 can also include structural elements such as a substrate such as an ETFE
or polyester
backing; a glass plate; or an asphalt non-woven glass reinforced laminate such
as those used
in the manufacture of asphalt roofing shingles; one or more protectant or
encapsulant
materials such as EVA or ETFE; one or more covering materials such as glass or
plastic;
mounting structures such as clips, holes, or tabs; and one or more optionally
connectorized
electrical cables. Thin film photovoltaic materials and flexible photovoltaic
materials can be
used in the construction of photovoltaic elements for use in the present
invention. In one
embodiment of the invention, the photovoltaic element is a monocrystalline
silicon
photovoltaic element or a polycrystalline silicon photovoltaic element.
[0026] Photovoltaic element 302 can include at least one antireflection
coating, disposed
on, for example, the very top surface of the photoelectric element or between
individual
protectant, encapsulant or protective layers.
[0027] Suitable photovoltaic elements can be obtained, for example, from China
Electric
Equipment Group of Nanjing, China, as well as from several domestic suppliers
such as Uni-
Solar, Sharp, Shell Solar, BP Solar, USFC, FirstSolar, General Electric,
Schott Solar,
Evergreen Solar and Global Solar.
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[0028] Active face 304 of photovoltaic element 302 is the face presenting the
photoelectrically-active areas of its one or more photoelectric cells. The
active face can be
the top surface of the one or more photovoltaic cells themselves or can be the
top surface of a
series of one or more protectant, encapsulant and/or covering materials
disposed thereon.
During use of the photovoltaic device 300, active face 304 should be oriented
so that it is
illuminated by solar radiation. The active face 304 has on it an active area
306, which is the
area in which radiation striking the active face will be received by the
photovoltaic cell(s) of
the photovoltaic element 302.
[0029] The photovoltaic element 302 also has an operating wavelength range.
Solar
radiation includes light of wavelengths spanning the near UV, the visible, and
the near
infrared spectra. As used herein, the term "solar radiation," when used
without further
elaboration means radiation in the wavelength range of 300 nm to 1500 nm,
inclusive.
Different photovoltaic elements have different power generation efficiencies
with respect to
different parts of the solar spectrum. FIG. 4 is a graph showing the relative
spectral response
of three commonly-used photovoltaic materials as well as the spectral
distribution of solar
radiation. Amorphous doped silicon is most efficient at visible wavelengths,
and
polycrystalline doped silicon and monocrystalline doped silicon are most
efficient at near-
infrared wavelengths. As used herein, the operating wavelength range of a
photovoltaic
element is the wavelength range over which the relative spectral response is
at least 10% of
the maximal spectral response. According to certain embodiments of the
invention, the
operating wavelength range of the photovoltaic element falls within the range
of about 300
nm to about 2000 nm. Preferably, the operating wavelength range of the
photovoltaic
element falls within the range of about 300 nm to about 1200 nm. For example,
for
photovoltaic devices having photovoltaic cells based on typical amorphous
silicon materials
the operating wavelength range is between about 375 nm and about 775 nm; for
typical
polycrystalline silicon materials the operating wavelength range is between
about 600 nm and
about 1050 nm; and for typical monocrystalline silicon materials the operating
wavelength
range is between about 425 nm and about 1175 nm.
[0030] As shown in FIG. 3, photovoltaic device 300 also includes a cover
element 308.
The cover element is attached to the photovoltaic device 300 and is disposed
over the active
area of the active face of the photovoltaic element. The cover element has an
opacity of at
least 25%. As used herein, "opacity" refers to the fraction of solar energy
within the
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operating wavelength range that the cover element prevents from reaching the
active area of
the active face of the photovoltaic element. For example, a cover element that
allows 52% of
solar energy within the operating wavelength range to reach the active area of
the active face
of the photovoltaic element (e.g., by reflecting 30% and absorbing 18%) has an
opacity of
48%. The opacity at every wavelength within the operating wavelength range
need not be at
least about 25%, as long as the total energy within the operating wavelength
range prevented
from reaching the active area is at least about 25%. In certain embodiments of
the invention,
the cover element has an opacity of at least about 50%. In certain especially
desirable
embodiments of the invention, the cover element has an opacity of at least
about 90%, or
even at least about 95%.
[0031] In certain embodiments of the invention, the cover element
substantially covers
the active area of the active face of the photovoltaic element. However, in
other
embodiments of the invention, the cover element only partially covers the
active area of the
active face of the photovoltaic element. For example, a completely opaque
cover element
that covers only 50% of the active area would have an opacity of 50%.
[0032] The cover elements of the present invention are desirably thick enough
to provide
the desired opacity as well as any other desired properties (e.g., mechanical
strength,
weatherproofness), but thin enough not to adversely affect the desired size
and shape of the
photovoltaic roofing device. For example, in one embodiment of the invention,
the cover
element has a thickness in the range of about 25 m to about 2 mm. In certain
desirable
embodiments of the invention, the cover element has a thickness in the range
of about 75 m
to about 1 mm.
[0033] In certain embodiments of the invention, the cover element has an
opacity of at
least about 25%, but no greater than about 98%. Such cover elements can be
useful in
situations where the skilled artisan desires to reduce but not completely
eliminate the power
output of the photovoltaic device (e.g., in order to equalize the power
performance of
photovoltaic devices on different parts of a roof or to balance power
generation and cell
temperature in accordance with the graphs of FIGS. 1 and 2). In such
embodiments of the
invention, the cover element can include, for example, a layer of a partially
transmissive
material. Examples of partially transmissive materials include polymeric
materials filled with
a small amount of carbon black, dye or opaque pigment, and glass materials
with metallic
particles formed therein. Alternatively, the cover element can include a
substantially
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transmissive material having a partially transmissive coating formed thereon.
For example,
the cover element can include a polymeric film or glass sheet having an
interference filter or
a very thin layer of metal formed theron. In other embodiments of the
invention, the cover
element does not completely cover the active area of the active face. The
cover element can
be made from any desirable material, and can include a single or multiple
layers. The cover
element can include one or more layers designed to provide other
functionality, such as
mechanical protection or weatherproofing.
[0034] According to one embodiment of the invention, the cover element has a
substantially neutral optical density over the operating wavelength. Such
cover elements can
be constructed, for example, using metallic particles, carbon black, or a thin
metallic layer.
According to another embodiment of the invention, the cover element has a
variable optical
density over the operating wavelength. For example, the cover element can have
different
opacity at the shorter wavelengths of the operating wavelength range than it
does at longer
wavelengths. Alternatively, the cover element can have a range of wavelengths
within the
operating wavelength range for which it has a substantially lower or higher
opacity than it
does over the remainder of the operating wavelength range. Cover elements
having variable
optical density can be constructed, for example, using a colored pigment or
dye or an
interference filter.
[0035] In one embodiment of the invention, the cover element is substantially
uniform in
optical density over its area. In other embodiments of the invention, the
cover element varies
in optical density over its area. For example, in one embodiment of the
invention, the cover
element has a pattern of regions of high and low opacity; the overall opacity
of the cover
element would be a function of the individual opacities and relative areas of
each. For
example, a checkerboard pattern of opaque and transmissive regions would have
an opacity
of about 50%.
[0036] According to another embodiment of the invention, the cover element is
colored.
As used herein, an item that is "colored" is one that appears colored
(including white, black
or grey, but not colorless) to a human observer. According to one embodiment
of the
invention, the cover element includes (either at one of its surfaces or within
it) a near infrared
transmissive multilayer interference coating designed to reflect radiation
within a desired
portion of the visible spectrum. In another embodiment of the invention, the
cover element
includes (either at one of its surfaces or within it) one or more colorants
(e.g., dyes or
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pigments) that absorb at least some visible radiation but substantially
transmit near-infrared
radiation. The color(s) and distribution of the colorants can be selected so
that the
photovoltaic device has an appearance that matches, harmonizes with and/or
complements a
desired type of roofing material, such as asphalt shingles of a given color
and design. The
pattern of colorant can be, for example, uniform, or can be mottled in
appearance. Ink jet
printing, lithography, or similar technologies can be used to provide a
pattern of colorant that
approximates the appearance of the roofing materials to be used in conjunction
with the
photovoltaic device (e.g., granule-coated asphalt shingles). Photovoltaic
devices made with
colored polymer structures are described in further detail in U.S. Patent
Application serial no.
11/456,200, filed on July 8, 2006 and entitled "Photovoltaic Device"
(published as US
2008/0006323 Al on Jan. 10, 2008), which is hereby incorporated herein by
reference in its
entirety. Moreover, the use of granules on the top surface of the cover
element can also help
provide the desired opacity and approximate the appearance of roofing
materials to be used in
conjunction with the photovoltaic device. The granules can be, for example,
ceramic-coated
inorganic particles optionally colored with metal oxides, such as those used
on asphalt
roofing shingles. The use of granules is described in further detail in U.S.
Patent Application
serial no. 11/742,909, filed on May 1, 2007 and entitled "Photovoltaic Devices
and
Photovoltaic Roofing Elements Including Granules, and Roofs Using Them," which
is hereby
incorporated herein by reference in its entirety.
[0037] In another embodiment of the invention, the cover element has a high
opacity to
solar radiation in the operating wavelength. For example, in certain
embodiments of the
invention, the cover element has an opacity of at least about 95%, at least
about 98%, at least
about 99%, or even at least about 99.5% to solar radiation in the operating
wavelength. Such
a cover element would not allow solar radiation to illuminate the photovoltaic
element, and
therefore would prevent the photovoltaic element from generating power. Such a
cover
element could be desirable for use during the installation or repair of
photovoltaic elements
because it would prevent the exposure of the installer/repairperson to
dangerous electrical
conditions. Such cover elements can be made, for example, using a polymer
layer made
substantially opaque with pigment or dye; a polymer layer coated with a layer
of metal thick
enough to be substantially opaque; a metal sheet or foil; or some other
substantially opaque
material such as paper or fabric. The cover element can include one or more
layers designed
to provide other functionality, such as mechanical strength or protection or
weatherproofing.
For example, in one embodiment of the invention, the cover element includes a
protective
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polymer layer over an opaque layer such as a metal foil. In another embodiment
of the
invention, the cover element can provide mechanical protection to the
photovoltaic element,
enabling more robust or rugged handling than a similar photovoltaic element
not so equipped.
[0038] Of course, a cover element having a high opacity would not be desirable
during
normal operation of the photovoltaic element; accordingly, such a cover
element would be
removably attached to the photovoltaic device. The high opacity cover element
can be
removably attached to the photovoltaic element itself, for example using a non-
permanent
adhesive. In another embodiment of the invention, the high opacity cover
element has a
plastic surface, and is removably attached to the photovoltaic element by
static electricity
forces. In one embodiment of the invention, the high opacity cover element can
be attached
to the photovoltaic element on the active area of the active face. However, in
certain other
embodiments of the invention, it is not attached directly to the active area
of the active face of
the photovoltaic element itself, but rather is attached to another part of the
photovoltaic
element, or even another part of the photovoltaic device (e.g., a roofing
substrate on which
the photovoltaic element is disposed, described in more detail below). Such
embodiments of
the invention may be desirable in that they keep the active area of the active
face of the
photovoltaic element free of adhesive that might discolor or otherwise
interfere with
illumination of the photovoltaic element. One or more layers of the cover
element can
provide mechanical strength to the cover element to keep it from tearing or
breaking during
its removal, described below.
[0039] In some embodiments of the invention, the cover element is flexible,
and includes
a graspable tab not attached directly to the photovoltaic device. After
installation, the
installer can grasp the graspable tab and peel the flexible cover element away
from the
photovoltaic element, exposing it and thereby starting the generation of
power. The tab can
be made from the same material(s) as the rest of the cover element, or can
alternatively be
made from a separate material such as plastic. The high opacity cover elements
of the
present invention can be printed, for example, with a decorative pattern,
installation or
advertising information, or a trademarked name, image or device.
[0040] An example of a photovoltaic device according to one embodiment of the
invention is shown in FIG. 5. The photovoltaic device 500 includes a roofing
substrate 520
having four photovoltaic elements 502 disposed thereon. The photovoltaic
device also
includes a cover element 508 having a graspable tab 510. The cover element 508
can be
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made from, for example, plastic-coated paper. In the embodiment of the
invention shown in
FIG. 5, the roofing substrate 520 is a dual-layer asphalt roofing shingle. In
the embodiment
of the invention shown in FIG. 5, each of the photovoltaic devices has a pair
of connectorized
electrical cables 522 that remain disposed on top of the roofing substrate
520; they can be
connected into an electrical system and covered by a next course of shingles.
The skilled
artisan will recognize that electrical cables in the photovoltaic elements can
be routed in
many different ways. For example, the electrical cables can run through a hole
in the roofing
substrate and be potted in by roofing compound; or they can be integrated into
the roofing
substrate itself. The photovoltaic element can be attached to the roofing
substrate using
adhesive, or alternatively they can be screwed, clipped, or nailed to the
roofing substrate or to
the roof deck, as would be appreciated by the skilled artisan.
[0041] In one embodiment of the invention, the roofing substrate is an asphalt
roofing
shingle. In another embodiment of the invention, the roofing substrate is a
plastic tile. In
another embodiment of the invention, the roofing substrate is a plastic or
metal panel.
[0042] In some embodiments of the invention, the high opacity cover element
does not
cover the entire photovoltaic device. In many situations, an installed
photovoltaic device
would not have its entire surface presented to the environment, for example
because it is
partially covered by one or more other photovoltaic devices. This is
especially common
when the photovoltaic device is constructed to include a roofing substrate
such as a roofing
shingle, tile, panel, membrane or shake. Such photovoltaic devices would be
installed
analogously to standard roofing materials, with some overlap between the
roofing substrates.
Accordingly, it is desirable for only the areas of the photovoltaic device
that are ultimately
exposed to the environment to be covered by a high opacity cover element, so
that the
installer can remove all such cover elements only after an entire set of
photovoltaic devices is
installed. For example, as shown in FIG. 5, the cover element covers only the
photovoltaic
elements themselves; it does not extend to cover the headlap area of the
asphalt shingle.
Accordingly, when many such photovoltaic devices are installed on a roof, none
of the cover
elements would themselves be covered by other photovoltaic devices, and
therefore would be
easily removable by the installer.
[0043] In certain embodiments of the invention, the high opacity cover element
has a
skid- or slip-resistant surface. For example, the high opacity cover element
can have an
upper layer of a grit affixed thereon, for example as described in U.S. Patent
5,124,178,
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which is hereby incorporated herein by reference in its entirety. In another
embodiment of
the invention, the high opacity cover element has surface relief formed in its
top layer, for
example using polymer molding or embossing techniques, or has a top surface
formed from a
skid- or slip-resistant material. A skid- or slip-resistant surface can
provide added safety to
the installer, as it provides a surface that is less likely to be slick than
the surface of the
photovoltaic elements.
[0044] According to another embodiment of the invention, the cover element
comprises
an electrochromic material disposed over the active area of the active face of
the photovoltaic
element. In certain embodiments of the invention, the electrochromic material
substantially
covers the photovoltaic element. The electrochromic material has at least 25%
opacity in the
presence of an electric field or in the absence of an electric field (i.e., in
its switched on or
switched off state). As used herein, an electrochromic material is one that
changes its opacity
in response to an electric field; it can achieve the change in opacity through
any mechanism,
such as color change or an increase in scattering. As described in further
detail below, the
use of an electrochromic material can allow the skilled artisan to passively
or actively adjust
the photovoltaic power generation of the photovoltaic device in order to
balance power
output and provide electrical safety during installation and/or repair.
[0045] An example of a photovoltaic device according to this embodiment of the
invention is shown in cross-sectional view in FIG. 6. Photovoltaic device 600
includes
photovoltaic element 602, which has an active face 604 and an active area 606
on its active
face 604. The photovoltaic device also includes a cover element 608 on the
active face of the
photovoltaic element. The cover element includes a top electrode 632, a bottom
electrode
634, and an electrochromic materia1630 disposed therebetween and substantially
covering
the active area of the active face of the photovoltaic element. The first and
second electrodes
can be substantially transparent, and can be made, for example, from materials
such as
indium tin oxide. As shown in FIG. 6, the cover element can also include a
protective layer
636 (e.g., a polymer layer) on top of the top electrode. In this embodiment of
the invention,
the top and/or bottom electrodes can be electrically connected into a control
system
configured to adjust the opacity of the electrochromic material, for example
by adjusting the
voltage difference between the top and bottom electrodes.
[0046] According to one embodiment of the invention, the electrochromic
material has at
least 50% opacity in an electric-field free state and has less than 50%
opacity in the presence
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of an electric field. More desirably, the electrochromic material has at least
75% opacity in
an electric-field free state and has less than 25% opacity in the presence of
an electric field.
Electrochromic materials including liquid crystalline phases are examples of
materials
suitable for use in this embodiment of the invention.
[0047] According to one embodiment of the invention, the electrochromic
material has
less than 50% opacity in an electric-field free state and has at least 50%
opacity in the
presence of an electric field. More desirably, the electrochromic material has
less than 25%
opacity in an electric-field free state and has at least 75% opacity in the
presence of an
electric field. Electrochromic materials based on ion transfer among multiple
layers of
ceramic materials, such as those made by SAGE Electrochromics, Inc., are
examples of
materials suitable for use in this embodiment of the invention.
[0048] The use of electrochromic materials can allow the skilled artisan to
configure
photovoltaic power generation systems that can be switched on or off. An
electrical control
system can be included in the electrical system into which the photovoltaic
devices according
to this embodiment of the invention are interconnected. The electrical control
system would
be interconnected with the top and/or bottom electrodes of the electrochromic
materials and
could be configured to adjust the opacity of the electrochromic material. For
example, the
electrical control system can be configured to provide between the top and
bottom electrodes
both a low-to-no voltage difference and a voltage necessary for switching the
electrochromic
material between its low- and high-opacity states. The power used to drive the
electrical
control system could come from the photovoltaic power generation system itself
in the form
of direct connection and/or storage batteries. The electrical control system
could be
configured to address individual photovoltaic devices, or groups of individual
photovoltaic
devices, or alternatively switch all photovoltaic devices in the system. In
certain
embodiments of the invention the electrical control system is controlled by a
system that
monitors the electrical performance of the photovoltaic power generation
system. If output
unexpectedly drops in part of the photovoltaic power generation system, the
electrical control
system can switch the corresponding electrochromic materials to their high-
opacity states,
thereby preventing them from generating electricity and providing the repair
personnel a
greatly reduced electrical hazard while they investigate and repair the fault.
In other
embodiments of the invention, the electrical control system is configured to
provide
continuous adjustment of the opacity of the electrochromic material. In this
embodiment of
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the invention, the photovoltaic devices can be tuned so that they operate at
or near the
maximum power condition of their photovoltaic cells, thereby increasing
efficiency and
power generation.
[0049] In other embodiments of the invention, the electrochromic material is
in its low
opacity state in the presence of an electric field, and the photovoltaic
device provides the
power necessary to keep its associated electrochromic material in its low
opacity state during
normal use. For example, in one such embodiment, the photovoltaic element
includes a first
electrical lead and a second electrical lead. These electrical leads would be
used to connect
the photovoltaic device into a photovoltaic power generation system. These
electrical leads
could take many forms; they can be two separate wires, a single, dual-
conductor wire, or even
a pair of terminals or system of internal circuitry to which external wires
are connected.
Alternatively, one of the leads can be an electrical ground. In this
embodiment of the
invention, the top electrode is electrically connected to the first electrical
lead, and the bottom
electrode is electrically connected to the second electrical lead. If the
photovoltaic element is
operating correctly, in the illuminated state there would be a voltage
difference between the
first and second electrical leads; this voltage difference would be sufficient
to sustain the
electrochromic material switched in its low opacity state. When the
photovoltaic element is
in a fault state, there would be very little voltage difference between the
first and second
electrical leads, and the electrochromic material will revert to its high
opacity state. While
photovoltaic devices according to this embodiment of the invention would
require an external
power source to provide the electric field necessary to initially switch their
electrochromic
materials into their low opacity state, they would otherwise sustain the low
opacity state with
a fraction of the power generated by the photovoltaic device itself. The
external power
source can be provided, for example, by a control circuit coupled to a light
sensor; when the
light sensor senses that the photovoltaic devices have just begun to be
illuminated enough to
switch their electrochromic materials from high opacity to low opacity, (e.g.,
at sunrise), the
control circuit can provide a pulse of electrical power to the electrochromic
materials. The
electrochromic materials will switch to their low opacity states and part of
the power
generated by the photovoltaic device can then sustain that low opacity state.
[0050] The photovoltaic devices of the present invention can include a bypass
diode that
connects the electrical terminals of the photovoltaic element. The bypass
diode allows
current to flow between the electrical terminals when a fault, a loss of
illumination or a
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malfunction occurs in the photovoltaic cell(s) of the photovoltaic element or
photovoltaic
roofing element, or when the cover element is in a substantially opaque state.
The bypass
diode serves to cut a photovoltaic element or photovoltaic roofing element out
of the
photovoltaic power generation system when it malfunctions, and can also allow
for testing of
electrical connectivity before the photovoltaic power generation system is
activated.
[0051] Because the photovoltaic devices of the present invention can be used
on a roof, it
may be desirable for them to have the properties of a roofing material.
Accordingly, in one
aspect of the invention the photovoltaic device includes a roofing substrate
having a top face
and a bottom face, and the photovoltaic element is disposed on or within a
roofing substrate.
Roofing substrates suitable for use in this aspect of the invention include
shingles, tiles,
panels, membranes and shakes. As used herein, a photovoltaic device disposed
"on" a
roofing substrate is disposed on a top surface of the roofing substrate, while
a photovoltaic
device disposed "within" a roofing substrate is disposed on a bottom or side
surface of the
roofing substrate, with the active area of its photovoltaic element being
exposed to face the
same direction as the top surface of the roofing substrate. While the
embodiment described
with reference to FIG. 5 has a two-layer shingle as its roofing substrate, the
skilled artisan
will appreciate that more or fewer layers can be used. For example, more
layers can help
improve stability and help better accommodate the thickness of the
photovoltaic element.
Additional layers (and partial layers) of shingle material can be used for
other purposes, such
as to meet aesthetic, mechanical, or weatherproofness requirements. Of course,
a single layer
of asphalt shingle material can be used as the roofing substrate. In other
embodiments of the
invention, the roofing substrate is a plastic tile.
[0052] In certain embodiments of the invention, the roofing substrate has an
exposed area
(i.e., not covered by the photovoltaic element) on its top face, and the cover
element is
attached to the exposed area of the roofing substrate. The exposed area can,
for example, at
least partially surround the photovoltaic element. As described above,
attachment of the
cover element to an exposed area on the top face of the roofing substrate can
keep the active
area of the active face of the photovoltaic element free of adhesive.
[0053] The photovoltaic devices of the present invention may be used in a
variety of
applications. As described above, they can be integrated with roofing
substrates to provide
photovoltaic roofing elements. However, the person of skill in the art will
appreciate that the
photovoltaic devices of the present invention can be used in other
applications. For example,
CA 02693028 2009-12-23
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they can also be used in photovoltaic modules, using, for example, the
commonly-used rack-
mounted array architecture. The photovoltaic devices of the present invention
can be used in
any photovoltaic applications, especially those in which
installer/repairperson safety,
photovoltaic cell temperature and/or adjustability of photovoltaic response is
desirable.
[0054] The photovoltaic devices described above are generally installed as
arrays of
photovoltaic devices. Accordingly, another aspect of the invention is an array
of photovoltaic
devices as described above. The array can include any desirable number of
photovoltaic
devices, which can be arranged in any desirable fashion. For example, the
array can be
arranged as partially overlapping, offset rows of photovoltaic devices, in a
manner similar to
the conventional arrangement of roofing materials. The photovoltaic devices
within the array
can be electrically interconnected in series, in parallel, or in series-
parallel. In one
embodiment of the invention, the array of photovoltaic devices is fixed in a
frame system
similar to that used in conventional rooftop photovoltaic modules.
[0055] One or more of the photovoltaic devices described above can be
installed on a
roof as part of a photovoltaic system for the generation of electric power.
Accordingly, one
embodiment of the invention is a roof comprising one or more photovoltaic
devices as
described above disposed on a roof deck. The photovoltaic elements of the
photovoltaic
devices are desirably connected to an electrical system, either in series, in
parallel, or in
series-parallel, as would be recognized by the skilled artisan. There can be
one or more
layers of material, such as underlayment, between the roof deck and the
photovoltaic devices
of the present invention. The photovoltaic devices of the present invention
can be installed
on top of an existing roof, in such embodiments, there would be one or more
layers of
standard (i.e., non-photovoltaic) roofing elements (e.g., asphalt coated
shingles) between the
roof deck and the photovoltaic devices of the present invention. Electrical
connections are
desirably made using cables, connectors and methods that meet UNDERWRITERS
LABORATORIES and NATIONAL ELECTRICAL CODE standards. Even when the
photovoltaic devices include roofing substrates as described above, the roof
can also include
one or more standard roofing elements, for example to provide weather
protection at the
edges of the roof, or in any hips, valleys, and ridges of the roof.
[0056] Photovoltaic devices of the present invention can be fabricated using
many
techniques familiar to the skilled artisan. The cover elements can be made,
for example,
using methods such as doctor blading, laminating, molding, extrusion, vapor
deposition, roll
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coating, curtain coating, spray coating and/or other techniques familiar to
the skilled artisan.
When making photovoltaic devices including as a roofing substrate an asphalt
shingle or an
asphalt non-woven glass reinforced laminate, the methods described in U.S.
Patents
5,953,877; 6,237,288; 6,355,132; 6,467,235; 6,523,316; 6,679,308; 6,715,252;
7,118,794;
U.S. Patent Application Publication 2006/0029775; and International Patent
Application
Publication WO 2006/121433 can be used. Each of the patents and publications
referenced
above is hereby incorporated herein by reference in its entirety. Photovoltaic
devices can be
fabricated in a continuous process and then cut into individual elements as is
done in the
fabrication of asphalt shingles. When a continuous process is used, it can be
necessary to
individually prepare any electrical cables running between elements, for
example by cutting
the cables between elements and connectorizing the cut ends.
[0057] Another aspect of the invention is a method of installing a roof. The
method
includes attaching one or more photovoltaic devices to a roof deck, each
photovoltaic device
comprising a photovoltaic element, a first electrical lead, a second
electrical lead, an active
face and an operating wavelength range; and a high opacity cover element
removably
attached to the photovoltaic device and disposed over the active area of the
active face of the
photovoltaic element. In certain embodiments of the invention, the high
opacity cover
element substantially covers the active area of the active face of the
photovoltaic element. As
described above, there can be one or more layers of material between the roof
deck and the
photovoltaic devices. The method also includes connecting the first electrical
lead and the
second electrical lead of each photovoltaic element to an electrical system.
The electrical
system can be formed from, for example, a wiring array as described in U.S.
Patent
Application serial no. 11/743,073, filed on May 1, 2007 and entitled
"Photovoltaic Roofing
Wiring Array, Photovoltaic Roofing Wiring System and Roofs Using Them," which
is hereby
incorporated herein by reference in its entirety. The electrical system might
also be formed
by connecting the photovoltaic devices in series, and optionally connecting
the series-
connected groups of photovoltaic devices in parallel. The attaching and
connecting can occur
in any order, and can be performed at substantially the same time. After the
photovoltaic
devices are attached to the roof deck and connected to the electrical system,
the high opacity
cover element is removed from each photovoltaic device. According to this
embodiment of
the invention, the high opacity cover element can prevent the photovoltaic
devices from
generating electricity during installation, thereby helping to insure the
safety of the installer.
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Once the photovoltaic devices are installed, the high opacity cover element is
removed and
power generation begins.
[0058] Another aspect of the invention is a method of installing a roof. The
method
includes attaching one or more photovoltaic devices to a roof deck, each
photovoltaic device
comprising a photovoltaic element having a first electrical lead, a second
electrical lead, an
active face and an operating wavelength range; and a cover element comprising
an
electrochromic material disposed between a first electrode and a second
electrode, as
described above. The electrochromic material is at least 75% opaque, and more
desirably
substantially opaque, in the absence of an electric field. As described above,
there can be one
or more layers of material between the roof deck and the photovoltaic devices.
The method
also includes connecting the first electrical lead and the second electrical
lead of each
photovoltaic element to an electrical system. The electrical system can be
formed from, for
example, a wiring array as described in U.S. Patent Application serial no.
11/743,073, filed
on May 1, 2007 and entitled "Photovoltaic Roofing Wiring Array, Photovoltaic
Roofing
Wiring System and Roofs Using Them," which is hereby incorporated herein by
reference in
its entirety. The electrical system might also be formed by connecting the
photovoltaic
devices in series, and optionally connecting the series-connected groups of
photovoltaic
devices in parallel. The method also includes connecting the first electrode
and the second
electrode to an electrical control system. The attaching and connecting can
occur in any
order, and can be performed at substantially the same time, as the skilled
artisan would
appreciate. After the photovoltaic devices are attached to the roof deck and
connected to the
electrical system, the cover elements are rendered non-opaque by the
application of an
electric field through the electrical control system. According to this
embodiment of the
invention, the electrochromic cover element prevents the photovoltaic devices
from
generating electricity during installation, thereby helping to insure the
safety of the installer.
Once the photovoltaic devices are installed, the cover element is rendered non-
opaque and
power generation begins.
[0059] Another aspect of the invention is a photovoltaic system comprising one
or more
photovoltaic devices, each of which comprises a photovoltaic element and a
cover element.
As described above, the photovoltaic element includes an active face, an
active area on the
active face and an operating wavelength range. The cover element is attached
to the
photovoltaic device and disposed over the active area of the active face of
the photovoltaic
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element. In certain embodiments of the invention, the cover element
substantially covers the
active area of the active face of the photovoltaic element. The cover element
comprises an
electrochromic material as described above, as well as a first electrode and a
second
electrode, with the electrochromic material disposed between them. The
electrochromic
material has at least 25% opacity in an electric field-free state or in the
presence of an electric
field. The photovoltaic system also includes an electrical control system
connected to each
cover element through its first electrode and its second electrode, and
configured to adjust the
opacity of the electrochromic material. The adjustment of the opacity of the
electrochromic
material is achieved, for example, by changing the potential difference
between the
electrodes. The electrical control system can be designed to provide a
continuous adjustment
of the opacity of the electrochromic material, or alternatively to switch only
between a high-
opacity state and a low-opacity state. In certain embodiments of the
invention, the electrical
control system is configured to addressably switch or adjust the
electrochromic material of
each photovoltaic device individually. In other embodiments of the invention,
the electrical
switching system adjusts or switches all photovoltaic devices at once, or is
configured to
address groups of photovoltaic devices (e.g., all photovoltaic devices in a
given series of a
series-parallel connected photovoltaic power generation system). The
electrical control
system can be controlled manually, or can be automatically controlled by a
computing
system. The photovoltaic system according to this embodiment of the invention
can be used
to switch off photovoltaic power generation to allow workers to safely work on
a roof. In
embodiments having continuous adjustability, the photovoltaic system according
to this
embodiment of the invention can tune the photovoltaic devices so that they
operate at or near
the maximum power condition of their photovoltaic cells, thereby maximizing
efficiency and
power generation.
[0060] Another embodiment of the invention provides a roof comprising the
photovoltaic
system according to this aspect of the invention attached to a roof deck.
[0061] It will be apparent to those skilled in the art that various
modifications and
variations can be made to the present invention without departing from the
scope of the
invention. Thus, it is intended that the present invention cover the
modifications and
variations of this invention provided they come within the scope of the
appended claims and
their equivalents.
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