A variable transmittance double pane window includes an electrochromic material that has been deposited on one pane of the window in conjunction with an array of photovoltaic cells deposited along an edge of the pane to produce the required electric power necessary to vary the effective transmittance of the window. A battery is placed in a parallel fashion to the array of photovoltaic cells to allow the user the ability to manually override the system when a desired transmittance is desired.

BACKGROUND OF THE INVENTION 
1. Field of Invention 
The present invention relates to energy-saving windows, and more 
particularly to an apparatus for varying the light transmittance of window 
glazing. 
2. Description of the State of the Art 
Presently there exists approximately 19 billion square feet of windows in 
commercial and residential buildings, and another 600 million square feet 
of windows are being installed in new buildings throughout the United 
States each year, culminating in enormous cost and energy demands for air 
conditioning to negate unwanted solar heat gains through these windows. 
Static solar gain control coatings can be applied to windows; however, 
this practice is disadvantageous in that sunlight is blocked even when it 
is needed for lighting and heating during cold weather. 
There have been some apparatus and methods developed for controlling the 
transmittance of light through window panes. For example, U.S. Pat. No. 
4,768,865 to C. Greenberg et al., discloses a conventional electrochromic 
film on a window that is responsive to the application of an electric 
field to change from a high-transmittance, non-absorbing state to a 
lower-transmittance, absorbing or reflecting state. The Ito et al. patent, 
U.S. Pat. No. 4,832,468, discloses the use of an electrochromic coating 
for dimming automobile windows, including a plurality of solid 
electrochromic elements arranged in a horizontal abutting fashion and 
adhered to the glass window, each element being controllable independently 
of the others. C. Hashimoto et al., in his U.S. Pat. No. 4,958,917, 
discloses a specialized combination of two electrochromic cells which, 
together, are capable of reducing the transmittance of visible light to 
less than the usual lower limit of 7% for known electrochromic coatings. 
While Greenberg, Ito, and Hashimoto teach the use of electrochromic 
coatings or controlling the transmittance of light through window panes, 
these coatings require external power supplies and, to be practical, the 
need for wiring into a building's electrical system. These coatings also 
absorb substantial mounts of the incident light and then radiate large 
amounts of the absorbed energy as heat to the interiors of the buildings 
in which they are installed, thus decreasing the effectiveness of the 
devices for blocking heat gain in the buildings and partially defeating 
the purpose for which they are used. 
I. Mockovciak, in his U.S. Pat. No. 4,475,031, disclosed a self-contained 
sun-sensitive window made up of liquid nematic crystals (LC), sandwiched 
between two transparent sheets and powered directly by a solar cell. 
Liquid nematic crystals, however, are not effective in blocking heat 
radiation. Rather, they merely scatter light, thus making a window 
translucent, but not effectively blocking heat gain from the sun's rays. A 
further disadvantage of such liquid nematic crystal technology is that a 
constant source of energy is required to change the translucence of the 
window, thus requiring a substantial and continuous source of electric 
power as long as transparency instead of translucence is desired. 
SUMMARY OF THE INVENTION 
Accordingly, it is a general object of this invention to provide a variable 
transmittance window that does not require an external power supply. 
A more specific object of the present invention is to provide a variable 
transmittance window that further decreases the amount of radiant energy 
transmitted through a window. 
Another specific object of the present invention is to provide a variable 
transmittance window that can be activated and deactivated with 
consumption of power only at the transition between the activated state 
and the deactivated state or vice versa, but without requiring power to 
maintain it in either state after a transition from one state to the 
other. 
Additional objects, advantages and novel features of this invention shall 
be set forth in part in the description that follows, and in part will 
become apparent to those skilled in the art upon examination of the 
following or may be learned by the practice of the invention or may be 
realized and attained by means of the instrumentalities and in 
combinations particularly pointed out in the appended claims. 
To achieve the foregoing and other objects and in accordance with the 
purposes of the present invention, as embodied and broadly described 
herein, the apparatus of this invention may comprise two glass plates 
spaced apart in a parallel relationship to one another and forming an air 
tight cavity there between. The surface of one glass plate facing the 
cavity has deposited on it a coating comprising an array of photovoltaic 
cells in conjunction with electrochromic material. This coating may also 
be connected in parallel to a battery as an alternate power source. 
Another structural embodiment includes the same coating as discussed above 
deposited on a thin, flexible, transparent polymer material. The polymer 
material may then be adhesively applied to existing windows.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
The stand-alone photovoltaic powered electrochromic window 10 assembly 
according to the present invention is best seen in FIGS. 1-4. The window 
assembly 10 is comprised of two plates 12 and 42 of glass or other 
transparent material are placed parallel and spaced apart in relation to 
one another, separated by spacers 46 and sealed around their peripheral 
edges to form an air tight cavity 50 between plates 12 and 42. Deposited 
on the inside surface 14 of glass plate 12 and facing cavity 50 is an 
array 60 of photovoltaic cells and an electrochromic coating 16. The array 
60 of photovoltaic cells and a battery 36 (not shown in FIGS. 1-4, but 
described below) are connected in parallel to electrochromic coating 16 
via appropriate switching (not shown in FIGS. 1-4, but described below) to 
allow selective activation of the electrochromic coating 16 to either a 
substantially transparent state or a substantially opaque state. It can 
also be set for any desired state of partial transparency or opacity 
between those two limits. 
When the electrochromic coating 16 is in the substantially transparent 
state, radiation 70 from the sun is substantially transmitted through both 
plate 12 and plate 42 of window assembly 10 into the interior of the 
building. Of course, some amount of the radiation 70 is always reflected 
and some is absorbed by the plate 12 and 42, but, with the electrochromic 
coating 16 in the substantially transparent state, most of the radiation 
70 in the near infrared, visible light, and ultraviolet portions of the 
spectrum is admitted into the interior of the building. Inside the 
building, the sun's radiation 70, of course, provides light and is 
eventually absorbed by interior walls, floors, furnishings, and the like, 
where the electromagnetic radiation is converted to heat energy. In colder 
ambient weather conditions, such heat inside the building is, of course, 
usually desired and welcomed. However, in hotter ambient weather 
conditions, it is not desired and often has to be dissipated or removed by 
ventilation, air conditioning, or the like to maintain the interior of the 
building at temperatures that are comfortable to humans. 
The window assembly 10 of the present invention is effective in 
substantially decreasing such undesirable heat gain inside a building from 
the sun's radiation by a combination of features. The electrochromic 
coating 16 on the inside surface 14 of exterior plate 12 of the window 
assembly 10 can be changed to its substantially opaque state, thus 
blocking rather than transmitting the sun's radiation. With most of the 
sun's radiation blocked in this manner, it does not reach the interior of 
the building to be absorbed and converted to interior heat. Instead, a 
substantial amount of the radiation is either reflected or absorbed by the 
electrochromic coating 16. At the same time, however, inside plate 42 and 
sealed space 50 prevent heat energy from the light radiation absorbed by 
coating 16 from being transmitted into the building interior by either 
conduction or convection. The glass of interior sheet 42 does not transmit 
significant amounts of infrared radiation, thus blocking heat entry by 
radiation, and the space 50 is sized wide enough to minimize molecular 
conduction of heat, but narrow enough to prevent convection. At the same 
time conduction of heat by the exterior plate 12 from the electrochromic 
layer 16 and infrared radiation, as well as ambient air and convection or 
breeze currents adjacent to the outside surface of plate 12, will 
dissipate the absorbed heat energy to the exterior atmosphere. Therefore, 
this combination and design of window apparatus 10 are very effective at 
blocking energy from the sun from entering the building through a window. 
Of course, as mentioned above, when heat gain in the building is desired, 
the electrochromic coating 16 can be changed back to its substantially 
transparent state to admit the sun's radiation into the building. Of 
course, as mentioned above, the extent of opacity or transparency of the 
electrochromic coating 16 can be varied and set at any desired state 
between the two limits, so, for example, enough light can be admitted to 
be able to see through the window assembly 10 while minimizing the mount 
of energy transmitted. 
Referring now primarily to FIG. 4, the stand-alone photovoltaic powered 
electrochromic window 10 according to the present invention also includes 
an array of photovoltaic cells 60 of a type well known in the art, 
deposited on the inner surface 14 of the glass plate 12 or other 
transparent substrate. In accordance with standard practice, an n-type 
conductivity region 62 is created on the front side 64 of a p-type 
polycrystalline silicon substrate 66. A plurality of front surface 
metallic contacts 68 are disposed on the front surface 64 and adjacent to 
the inner surface 14 of glass plate 12. Both the front surface 64 and 
metallic contacts 68 are covered by an anti-reflective coating (not 
shown). Each solar cell is connected in a series/parallel manner to the 
others to form a photovoltaic array 60. 
An electrochromic (EC) coating 16 is deposited on the substrate 12 
immediately adjacent to photovoltaic array 60 and substantially covering 
the remaining inner surface 14. Electrochromic coating 16 can be composed 
of five layers, including two transparent electrically conductive layers 
(TE) 18 and 26, which function as electrodes; an electrochromic layer 20; 
an ion-conductive electrolyte layer 22; and an ion storage layer 24 or 
counter-electrode layer. 
Generally, the EC coating 16 is deposited on the inner surface 14 of glass 
plate 12 one layer at a time, such as by physical vapor deposition, 
sputtering, chemical vapor deposition, i.e., heat stimulated or radio 
frequency discharge or the like. For example, the first layer deposited on 
the substrate 12 can be the transparent conductor (TE) layer 18 made of 
highly doped metal oxides, such as tin oxide, zinc oxide, indium oxide, or 
mixtures thereof. This TE layer can be about 1000 to 5000 angstroms thick. 
An electrochromic (EC) layer 20 is next deposited on the TE layer 18. An 
electrochromic material is one that takes on or losses a color, i.e., 
becomes opaque or transparent, in response to an electric potential or 
current therethrough. Typical examples of EC materials or so-called 
cathodic electrochromic materials, which take on color in a reduced state, 
which can be induced by a DC electric current, include WO.sub.3, 
MoO.sub.3, TiO.sub.2, U.sub.2 O.sub.5, Bi.sub.2 O.sub.3, PbO.sub.2, and 
CuO.sub.x. This EC layer can be about 1000 to 5000 angstroms thick. An 
ion-conductive electrolyte layer 22 can then be deposited on the EC layer 
20. Electrolyte layer 22 may be a liquid, a polymer gel, or a solid film. 
For most applications, the liquid electrolyte is not practical. Polymer 
gels in which the polymer acts like a sponge to hold the liquid 
electrolyte may be practical when the polymer gel is also used as the 
bonding layer between two sheets of glass or two sheets of plastic onto 
which the other layers have been deposited. Typical polymer gels are made 
of polyethylene oxide, polypropylene oxide, or a silicone imbibed with a 
lithium salt solution such as lithium perchlorate dissolved in propylene 
carbonate. Solid thin film electrolytes are made of so-called fast-ion 
conductor materials in which either lithium or hydrogen ions diffuse 
readily. Examples of such fast-ion conductor materials include Li.sub.3 N, 
Li.sub.2 NH, and Li.sub.1-x M.sub.x Ti.sub.2-x (PO.sub.4).sub.3, where M 
represents another metal, such as aluminum, chromium, gallium, or the 
like. A solid thin film electrolyte layer 22 may be, for example, 1000 to 
5000 angstroms thick. Next, the ion storage layer 24 is deposited on the 
electrolyte layer 22. The materials used in this ion storage layer 24 can 
be a complementary electrochromic material, or anodic electrochromic 
materials which take on color in an oxidized state. A typical example of 
such a material is Prussian blue, and other practicable examples include 
Ni(OH).sub.2, IrO.sub.2, and CuO.sub.x. This ion storage layer 24 can be 
about 1000 to 5000 angstroms thick. Finally, a second transparent 
electrically conductive layer 26 is deposited for the second electrode, 
thus completing electrochromic (EC) coating 16. 
Two leads 32 and 33 are connected respectively to the transparent 
conducting electrode layers 18 and 26 to provide the electric potential 
and circuit across the EC coating 16, which is necessary to cause the EC 
coating 16 to convert from transparent to opaque and vice versa The leads 
32 and 33 are in turn connected to polarity reversing switch 39 housed 
within control box 90, as illustrated in FIG. 5. Switch 39 allows for the 
polarity of the charge across the EC coating 16 to be reversed, thereby 
changing the opacity of the EC coating 16, as discussed in more detail 
below. A power source selection switch 38 is connected in series to 
polarity reversing switch 39. The two alternate power sources available to 
operate the present invention are a battery 36, also housed within control 
box 90, and the array of photovoltaic cells 60, which are connected in 
parallel with the EC coating 16. Switch 38 is used to select between these 
two alternate power sources 36 and 60. Leads 34 and 35, which are 
connected to the array of photovoltaic cells 60, are then connected to 
leads 34' and 35' originating in control box 90 to complete the circuit, 
as shown in FIG. 5. 
The second or interior glass plate 42 or other transparent material is 
placed parallel and spaced apart in relation to exterior glass plate 12. 
This spatial separation between plates 12 and 42 is maintained by aluminum 
spacer 46 around the perimeter edges of plates 12 and 42, thereby forming 
an air tight chamber 50 between plates 12 and 42, which encloses EC 
coating 16. Aluminum spacer 46 functions not only to maintain glass plates 
12 and 42 in a spaced apart relation, but also as a container for a 
desiccant material 54. The desiccant material 54 is in communication with 
chamber 50 through apertures 52, so it can absorb any water vapor within 
chamber 50, thus retarding the formation of condensation on the inside 
surfaces of glass plates 12 and 44. 
In operation, the array of photovoltaic cells 60 outputs a DC electric 
current in proportion to the intensity of the sunlight 70 incident upon 
it. The DC voltage produced by the photovoltaic array 60 is then applied 
between TE layers 18 and 26 of EC coating 16, which serve as the positive 
and negative electrodes, respectively. As the voltage is applied across 
the two electrodes 18 and 26, ions are removed from the counter-electrode 
24, conducted through the ion-conducting layer 22, and inserted into the 
electrochromic material 20, so that the two layers 24 and 20 are 
simultaneously oxidized and reduced, respectively. In this "on" state, 
both materials 24 and 20 become more opaque. When the desired light 
transmittance level or opaqueness is reached, switch 38 can be mined to an 
"off" position, thus removing the voltage being applied. When there is no 
voltage across the EC coating 16, it will hold whatever state of opacity 
or transparency it was in when the voltage was removed. Over time the ions 
will migrate back to their original state without the assistance of 
electric voltage, thus increasing the transparency of the EC coating 16. 
However, migration is a very slow process, and, for practical purposes a 
voltage is not required to maintain an opaque state. 
When the EC coating 16 of the present invention is turned "on," i.e., 
opaque, most of the solar energy is absorbed and radiated or conducted 
back toward, the exterior, as described above. A small percentage of solar 
heat 72 can, however, reach chamber 50. However, because chamber 50 is 
quite narrow, preferably about 10 to 15 mm, very little convection occurs 
in air tight chamber 50, thus a negligible amount of heat reaches the 
interior of the building. Reversing and applying the DC polarity across TE 
layers 18 and 26 by way of switch 39 causes a reversal of the 
electrochromic properties, and the EC coating 16 reverts to its high 
transparency or radiation transmittance state. Switch 38 can also activate 
battery 36 as an alternate power source when the conditions are such that 
the incident sunlight 70 is not sufficient for the photovoltaic array 60 
to produce energy. The photovoltaic array 60 can also be used to charge 
the battery 36 when not otherwise in use. Since electric power is only 
required during transition from one state of opacity or transparency to 
another, but not to hold any particular state, this combination window 
assembly 10 provides a very effective, controllable, yet efficient 
energy-saving apparatus that is self-contained and operates to reduce or 
enhance heat gain in a building with no need for an external power source. 
In alternate embodiments 100 and 200, as shown in FIGS. 7-11, the array of 
photovoltaic cells 60 and electrochromic coating 16 are deposited on a 
thin, flexible, transparent polymer material 112, as opposed to a glass 
sheet 12 as in the preferred embodiment 10, thus forming an integral 
photovoltaic powered electrochromic film 100 that can be applied 
adhesively to the inner surface of existing windows. 
An array of photovoltaic cells 60 is deposited on a portion of the surface 
114 of the polymer material 112 along one end, as shown in FIG. 7. An 
electrochromic coating 16 is then deposited on the remaining surface 114, 
thus completely surrounding the photovoltaic array 60, as shown in FIG. 7 
and more clearly in FIG. 8. Leads 32-35 are connected to the photovoltaic 
array 60 and electrochromic layer 16 in the same fashion as described 
above for the preferred embodiment, and similarly to leads 32'-35', 
respectively, that originate from control box 90. 
Alternate embodiment 200 is constructed in the same manner as alternate 
embodiment 100 except that the photovoltaic array 60 is deposited in a 
continuous loop a spaced distance inward from the perimeter of the surface 
114 of polymer material 112. Depositing photovoltaic array 60 in this 
manner creates two separate surface areas, the inner surface area 114 and 
the outer perimeter surface area 114' on which electrochromic coatings 16 
and 16' are deposited, respectively. In turn, leads 32 and 33, which are 
connected to terminals 28 and 30, respectively, are also connected to 
terminals 28' and 30', respectively. Terminals 28' and 30', are in turn 
connected to the electrochromic coating 16' deposited on the outer 
perimeter surface 114'. Alternate embodiment 200 is advantageously used 
where, due to architectural design, the incidental sunlight 70 is 
obstructed from falling on the entire window surface at one time. 
Photovoltaic array 60, when laid out in a rectangular loop configuration, 
increases the probability that some incidental sunlight 70 will strike a 
portion of the photovoltaic array 60, even when another portion of the 
same is shaded. 
As discussed above, the photovoltaic arrays 60 of the above-described 
embodiments are set off from the edges so that the outer perimeter of the 
surface area 114' may be trimmed to fit an existing window. Once trimmed 
to a desired window size, the electrochromic panel 200 can be adhered to 
the surface of the window (not shown). Well-known adhesives can be used, 
including those that are typically provided with peel-off protective 
sheets during storage and transportation. Control box 90 can be placed in 
an accessible position, and leads 32'-35', which run from control box 90, 
can be connected to leads 32-35, respectively. Once adhered in place on a 
window and hooked up as described above, the electrochromic panel 200 can 
be used to selectively vary opacity or transparency of the window. 
The foregoing description is considered as illustrative only of the 
principles of the invention. Further, since numerous modifications and 
changes will readily occur to those skilled in the art, it is not desired 
to limit the invention to the exact construction and process shown as 
described above. Accordingly, all suitable modifications and equivalents 
may be resorted to falling within the scope of the invention as defined by 
the claims which follow.