U.S. patent application number 11/740707 was filed with the patent office on 2008-10-30 for solar collector with hydrophilic photocatalytic coated protective pane.
Invention is credited to Gerald D. Beranek.
Application Number | 20080264411 11/740707 |
Document ID | / |
Family ID | 39682521 |
Filed Date | 2008-10-30 |
United States Patent
Application |
20080264411 |
Kind Code |
A1 |
Beranek; Gerald D. |
October 30, 2008 |
Solar Collector with Hydrophilic Photocatalytic Coated Protective
Pane
Abstract
A solar collector which is illuminated by the sun through a
glass panel wherein the glass panel is constructed of glass without
low-e coatings with a first surface coating of a magnetron
sputtered vapor deposition coating consisting primarily of titanium
dioxide. The titanium dioxide achieves a hydrophilic photocatalytic
surface to produce a solar collector which is self-cleaning for
increased solar energy transmittance with less cleaning cost.
Inventors: |
Beranek; Gerald D.; (Lone
Rock, WI) |
Correspondence
Address: |
STIENNON & STIENNON
612 W. MAIN ST., SUITE 201, P.O. BOX 1667
MADISON
WI
53701-1667
US
|
Family ID: |
39682521 |
Appl. No.: |
11/740707 |
Filed: |
April 26, 2007 |
Current U.S.
Class: |
126/710 |
Current CPC
Class: |
C03C 2217/71 20130101;
F24S 40/20 20180501; F24S 80/52 20180501; C03C 17/2456 20130101;
C03C 2218/156 20130101; C03C 2217/212 20130101; C03C 2217/75
20130101; Y02E 10/40 20130101 |
Class at
Publication: |
126/710 |
International
Class: |
F24J 2/50 20060101
F24J002/50 |
Claims
1. A solar collector comprising: a box having a means for
collecting and removing useful solar energy from the box, and an
opening in the box arranged to receive solar radiation; and a glass
pane without a low-E coating with a pre-installation solar energy
transmittance of greater than 85% and having an outer surface
coated with a photoactive, photocatalytic titanium dioxide coating
of less than 100 angstroms in thickness applied by Magnetron
Sputter Vapor Deposition, the titanium dioxide coating of the type
which when exposed to ultraviolet light activates the outer surface
to a hydrophilicity to the extent of having a water droplet contact
angle of 0-25.degree., and to be photocatalytic to degrade organic
matter in contact with the outer surface, the glass pane covering
the opening in the box.
2. The solar collector of claim 1 wherein the means for removing
solar energy from the box comprises collecting tubes containing a
fluid.
3. The solar collector of claim 1 wherein the means for removing
solar energy from the box comprises an array of solar cells.
4. The solar collector of claim 1 wherein the titanium dioxide
coating is such that when activated by ultraviolet light the
surface achieves a water droplet contact angle of less than
20.degree..
5. The solar collector of claim 1 wherein the glass pane solar
energy transmittance is greater than 88%.
6. The solar collector of claim 1 wherein the glass pane solar
energy transmittance is greater than 89%.
7. The solar collector of claim 1 wherein the glass pane
transmittance of visible light is greater than 89%.
8. The solar collector of claim 1 wherein the glass pane is
translucent tempered glass.
9. The solar collector of claim 1 wherein the glass pane is
constructed of low iron glass of less than 0.1% iron oxide computed
on Fe.sub.20.sub.3.
10. A photovoltaic or thermal solar collector comprising: an
enclosure; a solar cell or a thermal collecting tube arrangement
within the enclosure; and a protective glass cover pane overlying
the enclosure, the cover pane having a Magnetron Sputter Vapor
Deposition coating with a primary element of TiO.sub.2 less than
100 angstroms in thickness which is photocatalytic and super
hydrophilic, the cover pane having a transmittance of greater than
85 percent.
Description
CROSS REFERENCES TO RELATED APPLICATIONS
[0001] Not applicable.
STATEMENT AS TO RIGHTS TO INVENTIONS MADE UNDER FEDERALLY SPONSORED
RESEARCH AND DEVELOPMENT
[0002] Not applicable.
BACKGROUND OF THE INVENTION
[0003] The present invention relates to solar energy devices in
general, and more particularly to the protective glass coverings of
such devices through which solar radiation enters.
[0004] Solar radiation striking the earth's surface can be utilized
in various fashions to provide for heating and electrical needs.
Solar thermal collectors expose a working fluid to solar radiation,
and then transport that liquid for use either directly or for
heating some other fluid in a heat exchanger. Solar photovoltaic
cells convert the solar radiation to electricity which is then
either immediately used, stored in some fashion, or returned to the
power grid. For purposes of this application, "solar collectors"
encompasses both solar thermal collectors and solar photovoltaic
cells. Typically solar collectors have a cover which allows solar
radiation to pass through, but which blocks wind, precipitation,
dust and debris from attaching to or degrading the solar
device.
[0005] A conventional solar device cover will comprise a sheet of
glass. The glass may or may not be transparent in the visible
spectrum, but should be substantially transparent in the
wavelengths being used by the solar device. Because of the
protective function of the solar device cover, it will be exposed
to contamination which can gradually obstruct the glass covering,
resulting in a diminution of the solar energy passing through the
cover to the solar device. To restore the performance of the solar
device it is then necessary to periodically clean the glass covers,
something that may be cumbersome, time consuming, and costly and
potentially unsafe.
[0006] Various coatings have been applied to glass panels to reduce
the obstruction occurring over time due to exposure to the
elements. What is needed is a glass panel for a solar collector
cover which contributes to optimal transmission of solar energy and
which addresses the problem of dirt build-up thereon.
SUMMARY OF THE INVENTION
[0007] The solar collector of this invention comprises an array of
solar cells or fluid containing heat absorbing channels which are
illuminated by the sun through a glass panel wherein the glass
panel is constructed of thin high transmissive low iron glass with
a first surface coating of a magnetron sputter vapor deposition
coating consisting primarily of titanium dioxide. The titanium
dioxide coating achieves a hydrophilic photocatalytic surface. The
hydrophilic surface has a contact angle of 25.degree. or less,
preferably 20.degree. or less. The back surface is preferably not
coated.
[0008] It is a feature of the present invention to provide a solar
collector with improved collection efficiency in the face of
obscuring dust or dirt on the collector's glass cover.
[0009] It is a further feature of the present invention to provide
a glass cover for a solar cell array or a solar absorption box with
lower maintenance costs.
[0010] Further objects, features and advantages of the invention
will be apparent from the following detailed description when taken
in conjunction with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] FIG. 1 is side elevational cross-sectional view of a solar
cell array module and glass cover of this invention.
[0012] FIG. 2 is a side elevational cross-sectional view of a solar
absorber and glass cover of this invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0013] Referring more particularly to FIGS. 1-2, where like numbers
refer to similar parts, a solar cell array module 20 is shown in
FIG. 1. The solar cell array module 20 comprises a plurality of
solar cells 22 positioned beneath a glass pane 24. The glass pane
24 together with an enclosure or box 26 protects the solar cells 22
from the environment. The glass pane 24 prevents rain, moisture and
possibly corrosive elements from contacting the solar cells 22
which may corrode or short out in the presence of moisture. However
to function, that is to generate power from the sun's rays, the
glass pane is necessary in order to allow the sun's rays to reach
the photoelectric surface 30 of the solar cells. The cost of solar
cells, while continuing to decline, is still substantial.
Therefore, to minimize the total cost and the number of solar cells
needed it is important to maximize the amount of sunlight reaching
the photoelectric surface 30 of the solar cells 22.
[0014] Although the module 20 may be fixed in place, to maximize
the amount of sunlight falling on the solar cells the module 20 may
be made be to track the sun, or may be adjusted seasonally. For
example a solar cell array module located at 35 degrees north
latitude such as in Albuquerque, N. Mex., will in the winter be
oriented at an angle of about 60.5.degree. from the horizontal and
facing south. During the summer the optimum angle is closer to
8.degree.. For latitudes at 45 North the optimal angle in the
winter will be 67.5.degree., and 17.degree. in the summer. Thus it
is apparent that for solar collectors the orientation of the glass
pane of the module 20 with respect to horizontal will often be
closer to horizontal than to vertical, with the result that
atmospheric dust may build up on the glass pane 24 blocking
sunlight from reaching the solar cells 22 within the enclosure 26.
Of course the build up of dust and dirt on the glass pane 24 of the
module 20 could be dealt with by frequent washing, however this can
involve considerable expense, especially when it is considered that
solar collectors are often located on the roof of buildings or
other relatively inaccessible locations.
[0015] Titanium dioxide coated windows have been developed which
take advantage of the properties of titanium dioxide to achieve a
hydrophilic photocatalytic surface. The titanium dioxide may be in
the anatase form, and in some cases can be doped with carbon. When
windows employing such a titanium dioxide coating are exposed to
ultraviolet light the surface becomes hydrophilic and
photocatalytic so as to oxidize organic dirt, dust, and films which
are in contact with the titanium dioxide coating. When rain or wash
water is applied to the windows they are readily washed clean.
Windows with titanium dioxide coating are normally supplied with
other coatings, particularly low-E coatings which block ultraviolet
and infrared rays in order to produce a window with less heat loss
and less heat gain which is normally desirable in a window. Because
the low-E coatings may give the glass an undesirable color,
additional coatings are added in order to achieve a neutral color
for aesthetic reasons.
[0016] The glass pane 24 is preferably thin tempered glass, having
a thickness of about 3-6 mm (1/8 to 1/4 inches), and preferably of
very clear glass such as can be achieved with a low iron content
glass i.e., less than 0.1% iron oxide calculated on the basis of
Fe.sub.20.sub.3, such as is available, for example from Guardian
Industries Corporation under the trademark Guardian UltraWhite.TM..
Such a glass has visible light transmittance of 91% to 90% and a
solar energy transmittance of 89 to 86% for glass thicknesses of 3
mm, or 6 mm (1/8 or 1/4 inches) respectively. The glass is coated
with a layer of less than 100 angstroms of titanium dioxide which
is expected to reduce solar energy transmittance by less than 1% so
that a suitable glass pane 24, will transmit 89 to 90% of visible
light and have a solar energy transmittance of 85% to 88%. The
titanium dioxide coating is deposited with the Magnetron Sputter
Vapor Deposition (MSVD) process (also known as Magnetron Sputter
Vacuum Deposition) (for purposes of this application, Magnetron
Sputter Vapor Deposition will be used to include Magnetron Sputter
Vacuum Deposition) which results in a smooth surface of controlled
composition, which upon activation with ultraviolet light has a
water droplet contact angle of 25.degree. or less, preferably
20.degree. or less, achieving even super hydrophilicity with a
contact angle of near zero, i.e. less than 2-3.degree.. This low
contact angle allows rainwater or wash water to sheet off the
titanium dioxide pane surface 32.
[0017] The photocatalytic properties result in a gradual
destruction of organic materials in contact with the titanium
dioxide surface 32 in the presence of ultraviolet light. A suitable
coating may be obtained from Cardinal Glass Industries, for example
the titanium dioxide coating sold under the trademark Neat.TM.
glass. With this applied coating, there is little or no affect on
the solar transmittance or the solar reflectance. Conventional
Cardinal window glass with this coating is not suitable for use
with solar collectors because of its relatively low light
transmission i.e., in addition to the photoactive hydrophilic
titanium dioxide coating, other coatings, namely silver-based low-E
coatings, are used which reduce total energy transmission through
the glass. Moreover, silver-based low-E coated surfaces must be
hermetically sealed to avoid oxidation, and thus are not suitable
for the single pane of a solar collector. The glass pane of the
present invention does not have low-E coatings. However the
Cardinal Glass Neat.TM. coating, which contains metallic and
nonmetallic layers but consists primarily of titanium dioxide, if
applied to a suitable glass with high light transmissive properties
provides a suitable glass for application in solar collectors. The
benefit of the photoactive hydrophilic and photocatalytic titanium
dioxide coated glass is that more light reaches the solar cells
over time, because the glass pane is less obscured by soiling, due
to the self-cleaning properties of the photocatalytic surface. The
cost of maintenance of solar panels is also reduced because of the
speed and ease of cleaning, and the relative infrequency of
cleaning.
[0018] The Magnetron Sputter Vapor Deposition (MSVD) process is
distinct from pyrolytic hydrophilic coatings inasmuch as the
surface coating is substantially less rough, see for example the
comparison on page 2 of Cardinal glass technical bulletin CG 05 of
June 2006 which is incorporated herein by reference, which shows
surface variations of over 20 nanometers on a short scale for a
pyrolytic hydrophilic coating whereas the MSVD coating has few and
lower peaks.
[0019] As shown in FIG. 2, a thermal solar collector module 34 has
an insulating box 36 with a glass pane 24 with a titanium dioxide
outer surface 32 and an uncoated inner surface 38. Inside the
insulated box 36, thermal collecting tubes 40 or passageways are
arranged to allow a fluid 42 moving through the passageways to
gather solar heat which enters through the glass pane 24. As with
the solar cell array module 20, the thermal solar collector module
34 employs the glass pane 24 to isolate and protect from the
environment the solar collecting structures, such as the collecting
tubes 40 and any light baffles and absorbers present. Furthermore,
the glass panel acts to limit convective cooling of the interior of
the insulated box 36. At the same time, the glass pane 24 provides
over time greater solar incidence, and therefore greater solar
energy because of the degrading of obscuring organic particles and
film through the photocatalytic action of the titanium oxide
coating. The photoactive hydrophilic properties allow the ready
removal by rainwater or washing of all contaminants which obscure
the glass pane 24 outer surface 32.
[0020] It should be understood that because the glass pane 24 need
not transmit images, the glass pane 24 may have a texture such that
it is only translucent i.e., transmitting light but sufficiently
diffuse as to prevent perception of distinct images, while still
having the visible light transmittance and solar energy
transmittance of clear glass.
[0021] It should be understood that the glass pane 24 of the device
of FIG. 1 is not laminated to or directly affixed to the solar
cells 22, but rather spaced a short distance from the solar cells,
and that similarly in the device of FIG. 2, the glass pane 24 is
not laminated or directly affixed to the collecting tubes 40.
[0022] It should be understood that the visible light and solar
energy transmittance is defined with respect to low iron content
glass such as is available for example from Guardian Industries
Corporation under the trademark Guardian UltraWhite.TM. such that
visible light transmittance of 91 to 90% and a solar energy
transmittance of 89 to 86% pertain for glass thicknesses of 3 mm,
or 6 mm (1/8 or 1/4 inches) respectively.
[0023] It is understood that the invention is not limited to the
particular construction and arrangement of parts herein illustrated
and described, but embraces all such modified forms thereof as come
within the scope of the following claims.
* * * * *