U.S. patent application number 13/821399 was filed with the patent office on 2013-07-11 for devices and methods for increasing solar hydrogen conversion efficiency in photovoltaic electrolysis.
This patent application is currently assigned to UNIVERSITY OF DELAWARE. The applicant listed for this patent is Robert W. Birkmire, Jingguang G. Chen, Daniel Esposito. Invention is credited to Robert W. Birkmire, Jingguang G. Chen, Daniel Esposito.
Application Number | 20130175180 13/821399 |
Document ID | / |
Family ID | 45893759 |
Filed Date | 2013-07-11 |
United States Patent
Application |
20130175180 |
Kind Code |
A1 |
Esposito; Daniel ; et
al. |
July 11, 2013 |
DEVICES AND METHODS FOR INCREASING SOLAR HYDROGEN CONVERSION
EFFICIENCY IN PHOTOVOLTAIC ELECTROLYSIS
Abstract
Devices and methods for photovoltaic electrolysis are disclosed.
A device comprises a photovoltaic cell element and an electrolysis
compartment. The photovoltaic cell element is configured to convert
a portion of solar energy into electrical energy and to pass
another portion of the solar energy. The electrolysis compartment
includes an aqueous electrolyte positioned to receive the other
portion of the solar energy and electrodes electrically connected
to receive the electrical energy produced by the photovoltaic cell
element. A method comprises receiving solar energy with a
photovoltaic cell element, converting a portion of the solar energy
into electrical energy, passing another portion of the solar energy
through the photovoltaic cell element, receiving with an aqueous
electrolyte the other portion of the solar energy, transmitting the
electrical energy generated by the photovoltaic cell element to a
pair of electrodes, and electrolyzing the aqueous electrolyte with
the pair of electrodes.
Inventors: |
Esposito; Daniel;
(Gaithersburg, MD) ; Birkmire; Robert W.; (Newark,
DE) ; Chen; Jingguang G.; (Hockessin, DE) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Esposito; Daniel
Birkmire; Robert W.
Chen; Jingguang G. |
Gaithersburg
Newark
Hockessin |
MD
DE
DE |
US
US
US |
|
|
Assignee: |
UNIVERSITY OF DELAWARE
Newark
DE
|
Family ID: |
45893759 |
Appl. No.: |
13/821399 |
Filed: |
September 30, 2011 |
PCT Filed: |
September 30, 2011 |
PCT NO: |
PCT/US2011/054138 |
371 Date: |
March 7, 2013 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61388055 |
Sep 30, 2010 |
|
|
|
Current U.S.
Class: |
205/340 ;
204/242; 204/274 |
Current CPC
Class: |
C25B 1/003 20130101;
H01L 31/048 20130101; Y02P 20/133 20151101; Y02E 10/50 20130101;
Y02P 20/134 20151101; C25B 9/04 20130101 |
Class at
Publication: |
205/340 ;
204/242; 204/274 |
International
Class: |
C25B 9/04 20060101
C25B009/04 |
Goverment Interests
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH
[0002] This invention was made with Government support under Grant
No. DE-FG02-00ER15104 awarded by the Department of Energy. The
Government may have certain rights in this invention.
Claims
1. A device for photovoltaic electrolysis comprising: a
photovoltaic cell element configured to convert a portion of solar
energy received into electrical energy, the photovoltaic cell
element configured to pass another portion of the solar energy; and
an electrolysis compartment including an aqueous electrolyte
positioned to receive the other portion of the solar energy passing
through the photovoltaic cell element, the electrolysis compartment
including electrodes electrically connected to receive the
electrical energy produced by the photovoltaic cell element.
2. The device of claim 1, wherein the photovoltaic cell element
comprises a thin film photovoltaic layer.
3. The device of claim 1, wherein the electrolysis compartment
comprises at least one transparent substrate, the transparent
substrate configured to pass the other portion of the solar energy
through to the aqueous electrolyte.
4. The device of claim 1, wherein the other portion of the solar
energy comprises infrared radiation; and the infrared radiation
heats the aqueous electrolyte.
5. The device of claim 4, wherein the electrolysis compartment
includes a flow of aqueous electrolyte passing between the
electrodes; and the aqueous electrolyte is heated by the infrared
radiation before flowing between the electrodes.
6. The device of claim 5, wherein a portion of the heated aqueous
electrolyte flows to a hot water storage chamber or a heat
exchanger.
7. The device of claim 1, wherein: the photovoltaic cell element
includes an encapsulant layer; and the aqueous electrolyte in the
electrolysis compartment contacts the encapsulant layer.
8. The device of claim 7, wherein: the electrolysis compartment
includes a first flow of aqueous electrolyte in contact with the
encapsulant layer and a second flow of aqueous electrolyte passing
between the electrodes.
9. The device of claim 8, wherein the first and second flows are
substantially opposite in direction.
10. The device of claim 8, wherein the first flow is positioned
between the photovoltaic cell element and the second flow.
11. The device of claim 1, wherein the photovoltaic cell element is
spaced from the electrolysis compartment by an air gap.
12. A method for photovoltaic electrolysis comprising: receiving
solar energy with a photovoltaic cell element; converting a portion
of the received solar energy into electrical energy with the
photovoltaic cell element; passing another portion of the received
solar energy through the photovoltaic cell element; receiving with
an aqueous electrolyte the other portion of the solar energy
passing through the photovoltaic cell element; transmitting the
electrical energy generated by the photovoltaic cell element to a
pair of electrodes; and electrolyzing the aqueous electrolyte with
the pair of electrodes.
13. The method of claim 12, further comprising the step of passing
the other portion of the solar energy to the aqueous electrolyte
through a transparent substrate of an electrolysis compartment.
14. The method of claim 12, wherein the other portion of the solar
energy comprises infrared radiation, and the step of receiving the
other portion of solar energy comprises heating the aqueous
electrolyte with the infrared radiation.
15. The method of claim 14, further comprising the step of flowing
the aqueous electrolyte between the pair of electrodes.
16. The method of claim 15, wherein the step of heating the aqueous
electrolyte with the infrared radiation comprises heating the
aqueous electrolyte before it flows between the pair of
electrodes.
17. The method of claim 16, further comprising one of the steps of
storing the heated aqueous electrolyte in a hot water storage
chamber; or flowing the heated aqueous electrolyte to a heat
exchanger.
18. The method of claim 12, wherein the step of receiving the other
portion of solar energy comprises receiving the other portion of
the solar energy with an aqueous electrolyte in contact with an
encapsulant layer of the photovoltaic cell element.
19. The method of claim 18, further comprising the steps of flowing
the aqueous electrolyte in contact with the encapsulant layer, and
then flowing the aqueous electrolyte between the pair of
electrodes.
20. The method of claim 12, wherein the step of passing the other
portion of the received solar energy through the photovoltaic cell
element comprises passing the other portion of the received solar
energy through an air gap to an electrolysis compartment.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims priority to U.S. Patent Application
No. 61/388,055, entitled "DEVICES AND METHODS FOR INCREASING SOLAR
HYDROGEN CONVERSION EFFICIENCY IN PHOTOVOLTAIC ELECTROLYSIS," filed
on Sep. 30, 2010, the contents of which are incorporated herein by
reference in their entirety.
FIELD OF THE INVENTION
[0003] This invention relates generally to electrolysis, and more
particularly to devices and methods for increasing solar hydrogen
conversion efficiency in photovoltaic electrolysis.
BACKGROUND OF THE INVENTION
[0004] Photovoltaic (PV) electrolysis allows the generation of
hydrogen gas (H.sub.2) and oxygen gas (O.sub.2) from water using
solar energy. Conventional PV electrolysis arrays generate
electricity with PV elements that is then used by conventional
high-current density electrolyzers to drive the electrolysis of
water.
[0005] These conventional systems may include a number of
drawbacks. For example, conventional systems do not utilize all of
the energy received by the PV elements. Conventional systems may
have high balance of system (BOS) cost associated with all of the
auxiliary equipment that is needed to coordinate both PV and
electrolyzer operation. Conventional systems may have significant
decreases in efficiency due to operation requirements of the
aforementioned auxiliary components. Accordingly, improved devices
and methods for PV electrolysis are desired.
SUMMARY OF THE INVENTION
[0006] Aspects of the present invention are directed to devices and
methods for photovoltaic electrolysis.
[0007] In accordance with one aspect of the present invention, a
device for photovoltaic electrolysis is disclosed. The device
comprises a photovoltaic cell element and an electrolysis
compartment. The photovoltaic cell element is configured to convert
a portion of solar energy received into electrical energy. The
photovoltaic cell element is further configured to pass another
portion of the solar energy. The electrolysis compartment includes
an aqueous electrolyte positioned to receive the other portion of
the solar energy passing through the photovoltaic cell element. The
electrolysis compartment further includes electrodes electrically
connected to receive the electrical energy produced by the
photovoltaic cell element.
[0008] In accordance with another aspect of the present invention,
a method for photovoltaic electrolysis is disclosed. The method
comprises receiving solar energy with a photovoltaic cell element,
converting a portion of the received solar energy into electrical
energy with the photovoltaic cell element, passing another portion
of the received solar energy through the photovoltaic cell element,
receiving with an aqueous electrolyte the other portion of the
solar energy passing through the photovoltaic cell element,
transmitting the electrical energy generated by the photovoltaic
cell element to a pair of electrodes, and electrolyzing the aqueous
electrolyte with the pair of electrodes.
BRIEF DESCRIPTION OF THE DRAWINGS
[0009] The invention is best understood from the following detailed
description when read in connection with the accompanying drawings,
with like elements having the same reference numerals. When a
plurality of similar elements are present, a single reference
numeral may be assigned to the plurality of similar elements with a
small letter designation referring to specific elements. When
referring to the elements collectively or to a non-specific one or
more of the elements, the small letter designation may be dropped.
This emphasizes that according to common practice, the various
features of the drawings are not drawn to scale unless otherwise
indicated. On the contrary, the dimensions of the various features
may be expanded or reduced for clarity. Included in the drawings
are the following figures:
[0010] FIG. 1 is a diagram illustrating a side view of an exemplary
device for photovoltaic electrolysis in accordance with aspects of
the present invention;
[0011] FIG. 2 is a diagram illustrating a top view of the device of
FIG. 1;
[0012] FIG. 3 is a diagram illustrating a front view of the device
of FIG. 1;
[0013] FIG. 4 is a diagram illustrating the energy flow in the
device of FIG. 1;
[0014] FIG. 5 is a diagram illustrating a side view of another
exemplary device for photovoltaic electrolysis in accordance with
aspects of the present invention;
[0015] FIG. 6 is a diagram illustrating a top view of the device of
FIG. 5; and
[0016] FIG. 7 is a flowchart illustrating an exemplary method for
photovoltaic electrolysis in accordance with aspects of the present
invention.
DETAILED DESCRIPTION OF THE INVENTION
[0017] Aspects of the present invention relate to the production of
hydrogen from the electrolysis of water with a high
solar-to-hydrogen (STH) conversion efficiency using a single
device. As used herein, the terms "solar" and "solar energy" are
not limited to energy coming from the Sun. To the contrary, as used
herein, the terms "solar" and "solar energy" refer to any energy
suitable for use by the present invention to (a) produce the
photovoltaic (PV) effect and/or (b) heat the aqueous electrolyte,
as will be explained in further detail below. Additionally, the
devices and methods described herein are not limited to use with
water as the aqueous electrolyte. As used herein, the term "aqueous
electrolyte" is intended to encompass all suitable electrolytes
known to one of ordinary skill in the art from the description
herein. Still further, as used herein, references to the directions
"front" and "back" refer respectively to the sides of the device
closest to and farthest from the incident solar energy.
[0018] The devices and methods described herein exhibit a novel
method of collection and use of the infrared (IR) portion and other
low wavelength portions of solar energy in an integrated thin film
PV device configuration. In other words, the disclosed devices and
methods embody a new way to achieve "spectral resolution" of the
solar spectrum into high and low energy photons, which can be used
for producing electricity and heat, respectively.
[0019] Generally, an exemplary device of the present invention uses
solar energy to drive the electrolysis of water to produce hydrogen
gas. This device contains one or more photovoltaic (PV) cells that
create electricity usable to electrochemically split water at the
anode and cathode in an electrolyte-containing compartment (an
"electrolysis compartment") of the device. By definition, hydrogen
is evolved at the cathode of the device via a hydrogen evolution
reaction (HER), while oxygen is evolved at the anode of the device
via a oxygen evolution reaction (OER). The exemplary device uses
transparent, thin film PV components that allow for the infrared
(IR) portion and other low wavelength portions of solar energy to
pass through to the interior of the electrolysis compartment, where
they heat up the aqueous electrolysis solution (the "aqueous
electrolyte"). At elevated temperatures, the electrolysis of
aqueous solutions requires lower electrical energy inputs, because
the reaction is thermodynamically more favorable and because of
improved kinetics at the electrocatalyst surfaces. This decrease in
over-potential losses may enable overall solar-to-hydrogen (STH)
conversion efficiencies that substantially exceed those of
conventional PV electrolysis cells. This exemplary electrolysis
device may also be manufactured at lower cost than conventional PV
electrolysis devices that include separate PV and electrolyzer
components.
[0020] The disclosed devices may be modular in nature, such that
they may be linked together depending on the amount of gas (e.g.,
H.sub.2) needed for a given application. The modularity of the
exemplary devices described herein makes them well-suited for
manufacturing and easily scalable for use in both large and small
applications.
[0021] Referring now to the drawings, FIGS. 1-4 illustrate an
exemplary device 100 for photovoltaic electrolysis in accordance
with aspects of the present invention. Device 100 may be used to
produce hydrogen (H.sub.2) from the electrolysis of water. As a
general overview, device 100 includes a photovoltaic (PV) cell
element 120 and an electrolysis compartment 140. Additional details
of device 100 are described below.
[0022] PV cell element 120 converts solar energy to electrical
energy. Preferably, PV cell element 120 is semi-transparent to the
solar energy, i.e., PV cell element 120 is configured to absorb a
portion of received solar energy (e.g. the visible light portion),
and convert it into electrical energy, and is configured to pass
another portion of solar energy (e.g. the infrared portion and/or
another low wavelength portion) therethrough.
[0023] PV cell element 120 includes a PV cell substrate 122, as
shown in FIGS. 1 and 2. PV cell substrate 122 is desirably
transparent to the solar energy. In an exemplary embodiment, PV
cell substrate 122 comprises glass.
[0024] PV cell element 120 further includes one or more
photovoltaic (PV) cells 124 mounted on PV cell substrate 122, as
shown in FIGS. 1 and 2. Where PV cell element 120 includes multiple
PV cells 124, as shown in FIG. 3, they may be connected in series,
in order to obtain the desired electrical energy for device 100. PV
cells 124 are mounted to the back surface of PV cell substrate 122.
PV cells 124 are components that undergo the photovoltaic effect
upon receipt of photons of solar energy through PV cell substrate
122. The photovoltaic effect causes PV cells 124 to generate the
electrical energy that is produced by PV cell element 120. The
generation of electrical energy using PV cells 124 will be
understood by one of ordinary skill in the art from the description
herein.
[0025] In an exemplary embodiment, PV cell 124 comprises a thin
film photovoltaic (PV) layer. This thin film PV layer comprises a
p-n junction semiconducting cell that converts parts of the visible
and ultraviolet (UV) portions of the solar spectrum into
electricity through the photovoltaic effect. The thin film PV layer
is semi-transparent, allowing the visible and infrared portions of
the solar spectra having energy less than the semiconductor band
gap to pass through to electrolysis compartment 140.
[0026] The thin film PV layer can be formed, for example, from
cadmium telluride or silicon. Other suitable materials for use as
PV cell 124 will be known to one of ordinary skill in the art from
the description herein. PV cell 124 may be positioned in either a
substrate or superstrate configuration (with respect to the
direction of incoming light and PV cell substrate 122). The
selection of PV material for use as PV cell 124 may be selected
based on the configuration used. As discussed above, it is
desirable that PV cell 124 be transparent over a wide range of the
solar spectrum. This is especially important when PV cell 124 is in
a superstrate configuration, since any light absorbed or reflected
by the substrate will likely be rejected as lost energy to the
surroundings.
[0027] Depending on the voltage generated by each PV cell 124, one,
two, or three PV cells might be used in each device 100 (as shown
in FIG. 3). As shown in FIG. 3, the total output voltage equals the
sum of that from each individual PV cell 124, but the effective
current density of the total area is reduced to 1/3 of an
individual PV cell. For all configurations, the voltage generated
by the PV cell desirably exceeds the sum of the thermodynamic
voltage requirement to perform the electrolysis in electrolysis
compartment 140.
[0028] Electrolysis compartment 140 is configured to perform
electrolysis on an aqueous electrolyte 142. Aqueous electrolyte 142
may desirably be configured to flow within electrolysis compartment
140, as shown by block arrows in FIG. 1. Electrolysis compartment
140 performs electrolysis on aqueous electrolyte 142 using anode
electrodes 144 and cathode electrodes 146, as shown in FIG. 2. Each
of anode electrode 144 and cathode electrode 146 comprise a
catalyst layer to promote the desired electrolysis reaction.
Aqueous electrolyte 142 may flow between electrodes 144 and 146,
where electrolysis can be performed. In an exemplary embodiment,
the aqueous electrolyte 142 comprises water (H.sub.2O), in which
are dissolved suitable conducting ions.
[0029] The flow of aqueous electrolyte 142 may be generated, for
example, by gravity. Aqueous electrolyte 142 is desirably fed to
electrodes 144 and 146 from the bottom of electrolysis compartment
140, in order for the buoyant product gasses to escape through
membrane 150 at the top of electrolysis compartment 140. It is
preferable that the aqueous electrolyte be gravity fed in order to
eliminate the need for a separate pumping unit to force aqueous
electrolyte 142 through electrolysis compartment 140. However,
conventional pumping components may be incorporated into device
100, as would be understood by one of ordinary skill in the art
from the description herein. Such components may desirably provide
higher pressures, which may aid in the collection and compression
of the product gasses at the outlet side of membrane 150.
[0030] Electrodes 144 and 146 may be formed on both the front and
back sides of electrolysis compartment 140, as shown in FIGS. 1 and
2, in order to allow for a catalyst/PV area ratio of 2:1. This may
desirably drive down kinetic over-potential losses compared to
conventional PV electrolysis devices. If the front electrode is a
continuous thin film, it may absorb a significant portion of the
solar energy that is transmitted through the transparent front
portion of the electrolysis compartment 140, converting it to heat
that will primarily be transferred to the aqueous electrolyte 142
in the electrolysis compartment 140. Accordingly, it may be
desirable to use a photoactive catalyst in conjunction with this
front electrode to further increase photovoltage and/or enhance
catalytic activity.
[0031] As shown in FIG. 2, electrolysis compartment 140 may include
a divider 148 positioned to partition the flow of aqueous
electrolyte 142 into one flow between anode electrodes 144 and
another flow between cathode electrodes 146. Divider 148 may
comprise, for example, an ionic bridge such as a membrane that
allows for ion transfer between the sections and to separate the
different product gasses (e.g. O.sub.2 and H.sub.2). As illustrated
in FIG. 2, one section may be made larger than the other, allowing
for the incorporation of a larger total catalyst area for one of
the reactions.
[0032] Additionally, as discussed above, electrolysis compartment
140 includes a membrane 150 positioned adjacent electrodes 144 and
146. Membrane 150 is configured to enable the removal of gas
produced during electrolysis from electrolysis compartment 140,
while sealing in aqueous electrolyte 142. Membrane 150 may
comprise, for example, a standard gas-liquid separation membrane,
which will be known to one of ordinary skill in the art from the
description herein.
[0033] In accordance with aspects of the present invention,
electrolysis compartment 140 is integrated to form a single unit
with PV cell element 120, as described below.
[0034] Electrolysis compartment 140 and PV cell element 120 may be
integrated such that the aqueous electrolyte 142 in electrolysis
compartment 140 is positioned to receive the portion of solar
energy passing through PV cell element 120. In an exemplary
embodiment, PV cell element 120 is substantially transparent or
transmissive to the infrared (IR) portion and other low wavelength
portions of incident solar energy (referred to hereinafter
collectively as the "IR portion"). Accordingly, PV cell element 120
passes IR radiation through to aqueous electrolyte 142. The IR
radiation heats the aqueous electrolyte 142, thereby lowering the
electrical current that is required to perform electrolysis of the
aqueous electrolyte 142. In a preferred embodiment, the aqueous
electrolyte 142 is heated by the IR radiation before flowing
between electrodes 144 and 146 (e.g., before electrolysis takes
place). After heating, all or a portion of the heated aqueous
electrolyte 142 may flow between electrodes 144 and 146. If only a
portion of the heated aqueous electrolyte 142 is desired to be
electrolyzed, another portion may be diverted through a side panel
of electrolysis compartment 140, as shown in FIG. 1. The diverted
aqueous electrolyte may be directed, for example, toward a hot
water storage chamber or a heat exchanger. If electrolyte is
diverted to a heat exchanger, the cooled electrolyte may be
circulated back through electrolysis compartment 140, in order to
maintain a steady flow of aqueous electrolyte 142 through
electrolysis compartment 140. A suitable storage chamber or heat
exchanger will be known to one of ordinary skill in the art from
the description herein.
[0035] Electrolysis compartment 140 and PV cell element 120 may
also be integrated such that there is an electrical connection
between the two. In an exemplary embodiment, electrodes 144 and 146
are electrically connected to PV cell element 120 via electrical
connections 128 in order to receive the electrical energy produced
by PV cell element 120. Electrical connections 128 are shown
diagrammatically in FIG. 1, and their illustrated position and
structure is not intended to be limiting. The energy received by
electrodes 144 and 146 may be used to perform the electrolysis of
the aqueous electrolyte 142. The integrated nature of electrolysis
compartment with the PV cell element 120 is desirable to minimize
the ohmic losses associated with this transfer of electricity, and
may further obviate the need for a DC-DC converter that may be
found in conventional PV electrolysis devices.
[0036] Electrolysis compartment 140 includes at least one
transparent substrate 152. Transparent substrate 152 is configured
to pass (i.e. be transparent to) substantially the same portion of
solar energy passed by PV cell substrate 122. The front surface of
the transparent substrate 152 may be textured as a means to balance
the amount of heat and electricity generated by device 100. For
example, if it is desirable to produce more electricity, the
surface may be made more reflective/textured so that light is
reflected back to the PV cell element 120. If it is desirable to
produce more heat, the surface may be made less reflective/textured
so that all light transmitted through the PV cell element 120 is
also passed through transparent substrate 152 to electrolysis
compartment 140.
[0037] Depending on how PV cell element 120 is integrated with
electrolysis compartment 140, transparent substrate 152 may be the
same or a different substrate from PV cell substrate 122. As shown
in FIG. 1, the front-most transparent substrate 152 is the same as
the PV cell substrate 122, while the back-most transparent
substrate 152 is separate from PV cell element 120.
[0038] The operation of device 100 will now be described with
respect to FIGS. 1-3. In FIGS. 1-3, PV cell element 120 is
integrated with the front panel of electrolysis compartment 140. In
this embodiment, PV cell element 120 includes an encapsulant layer
126. Encapsulant layer is formed on PV cells 124 to protect PV
cells 124 from aqueous electrolyte 142, which may corrode PV cells
124. Encapsulant layer 126 is desirably transparent so that solar
energy not absorbed by PV cells 124 is transmitted to electrolysis
compartment 140 to heat up aqueous electrolyte 142. Encapsulant
layer 126 may be formed, for example, from an epoxy coating.
[0039] Aqueous electrolyte 142 in electrolysis compartment 140
contacts the encapsulant layer 126. Providing aqueous electrolyte
142 in contact with PV cell element 120 may assist in cooling PV
cell element 120 (which can become hot during production of
electrical energy). In may be desirable to cool PV cell element 120
in order to ensure proper and efficient conversion of solar energy
to electrical energy by PV cells 124.
[0040] As described above and illustrated in FIG. 1, aqueous
electrolyte 142 may flow through electrolysis compartment 140. In
this embodiment, the encapsulant layer 126 defines at least a
portion of a channel 154 through which aqueous electrolyte 142
flows. As shown in FIG. 1, aqueous electrolyte 142 travels in a
first flow through channel 154 (in contact with encapsulant layer
126 of PV cell element 120) before traveling in a second flow
through channel 156 (between electrodes 144 and 146). Channel 154
may desirably be positioned between PV cell element 120 and channel
156, in order to enable heating of aqueous electrolyte 142 prior to
electrolysis. Channels 154 and 156 may provide for flows of aqueous
electrolyte 142 that are in substantially opposite in
direction.
[0041] When the aqueous electrolyte 142 flows between electrodes
144 and 146, electrolysis is performed using the electrical energy
received from PV cell element 120. Gas created during electrolysis
may flow outward from electrolysis compartment 140 through membrane
150.
[0042] FIG. 4 illustrates the solar energy flow in device 100 in
accordance with aspects of the present invention. As shown in FIG.
4, solar energy incident upon device 100 may be reflected by PV
cell substrate 122 (arrow 182), absorbed by PV cell substrate 122
(arrow 183), or passed through PV cell substrate 122 (arrows
184-191). Energy absorbed by PV cell substrate 122 may be radiated
outward away from device 100 (arrow 181). Energy passing through PV
cell substrate 122 may be converted to electricity by PV cell 124
(arrow 184), absorbed by PV cell 124 (arrow 185), or passed through
PV cell 124 (arrows 186-191). Energy passing through PV cell 124
may be absorbed by encapsulant layer 126 (arrow 186) or passed
through encapsulant layer 126 (arrows 187-191). Energy passing
through encapsulant layer 126 may be absorbed by, and thereby heat,
aqueous electrolyte 142 in channel 154 (arrow 187), reflected by
the back surface of channel 154 (arrow 188), or passed through
channel 154 (arrows 189-191). Energy passing through channel 154
may be absorbed by transparent substrate 152 (arrow 189), or
absorbed by electrodes 144 and 146, or by the back panel of
electrolysis compartment 140 (arrows 190 and 191). Any energy
absorbed by the back panel may be radiated outward away from device
100 (arrow 192). The absorption of solar energy and conversion of
solar energy to electrical energy with a single device, as
illustrated in FIG. 4, enables overall conversion efficiencies
(e.g. solar-to-hydrogen conversion efficiency, for water) that
substantially exceed those of conventional PV electrolysis
cells.
[0043] FIGS. 5 and 6 illustrate another exemplary device 200 for
photovoltaic electrolysis in accordance with aspects of the present
invention. Device 200 may also be used to produce hydrogen
(H.sub.2) from the electrolysis of water. As a general overview,
device 200 includes a photovoltaic (PV) cell element 220 and an
electrolysis compartment 240. Device 200 is substantially the same
as device 100, except as described below.
[0044] PV cell element 220 converts solar energy to electrical
energy, substantially as described above with respect to PV cell
element 120. PV cell element 220 includes a PV cell substrate 222
and one or more PV cells 224.
[0045] Electrolysis compartment 240 is configured to perform
electrolysis on an aqueous electrolyte 242, substantially as
described above with respect to electrolysis compartment 140.
Electrolysis compartment 240 performs electrolysis on aqueous
electrolyte 242 using anode electrodes 244 and cathode electrodes
246, as shown in FIG. 6. Electrolysis compartment 240 may include a
divider 248 positioned to partition the flow of aqueous electrolyte
242. Additionally, electrolysis compartment 240 may include a
membrane 250 configured to enable the removal of gas produced
during electrolysis from electrolysis compartment 240, while
sealing in aqueous electrolyte 242.
[0046] In accordance with aspects of the present invention,
electrolysis compartment 240 is integrated to form a single unit
with PV cell element 220, as described below.
[0047] Electrolysis compartment 240 and PV cell element 220 may be
integrated such that the aqueous electrolyte 242 in electrolysis
compartment 240 is positioned to receive the portion of solar
energy passing through PV cell element 220. Further, PV cell
element 220 may be sized to allow solar energy to reach aqueous
electrolyte 242 without having to first pass through PV cell
element 220 (shown in the lower portion of FIG. 5). In a preferred
embodiment, the aqueous electrolyte 242 is heated by infrared
radiation from the solar energy before and while flowing between
electrodes 244 and 246 (e.g., before and during electrolysis).
[0048] Electrolysis compartment 240 and PV cell element 220 may
also be integrated such that there is an electrical connection
between the two, substantially as described above. Electrical
connections 228 are shown diagrammatically in FIG. 5, and their
illustrated position and structure is not intended to be
limiting.
[0049] Electrolysis compartment 240 includes at least one
transparent substrate 252. Transparent substrate 252 is configured
to pass (i.e. be transparent to) substantially the same portion of
solar energy passed by PV cell substrate 222. As shown in FIG. 5,
the front transparent substrate 252 is different from the PV cell
substrate 222.
[0050] The operation of device 200 will now be described with
respect to FIGS. 5 and 6. In FIGS. 5 and 6, PV cell element 220 is
mounted on the front transparent substrate 252 of electrolysis
compartment 240. PV cell element 220 is mounted on support posts
230 such that it is spaced from electrolysis compartment 240 by an
air gap 232. Providing air gap 232 between PV cell element 220 and
electrolysis compartment 240 may assist in cooling PV cell element
220 (which can become hot during production of electrical energy).
Additionally, a fan or other such component may be provided to
generate an air flow through air gap 232 to further promote cooling
of PV cell element 220.
[0051] As described above and illustrated in FIG. 5, aqueous
electrolyte 242 may flow through electrolysis compartment 240. In
this embodiment, aqueous electrolyte 242 flows through a first
channel portion 254 before flowing through a second channel portion
256 (between electrodes 244 and 246). First channel portion 254 may
desirably not be positioned behind PV cell element 220, in order to
promote heating of aqueous electrolyte 242 prior to
electrolysis.
[0052] When the aqueous electrolyte 242 flows between electrodes
244 and 246, electrolysis is performed using the electrical energy
received from PV cell element 220. Gas created during electrolysis
may flow outward from electrolysis compartment 240 through membrane
250.
[0053] FIG. 7 illustrates an exemplary method 300 for photovoltaic
electrolysis in accordance with aspects of the present invention.
Method 300 may be used to produce hydrogen (H.sub.2) from the
electrolysis of water. As a general overview, method 300 includes
receiving solar energy, converting a portion of the solar energy
into electrical energy, receiving another portion of the solar
energy with an aqueous electrolyte, and electrolyzing the aqueous
electrolyte. Additional details of method 300 are described below
with reference to the components of device 100.
[0054] In step 310, solar energy is received with a photovoltaic
(PV) cell element. In step 320, a portion of the received solar
energy is converted into electrical energy with the PV cell
element. In step 330, another portion of the received solar energy
is passed through the PV cell element. In an exemplary embodiment,
PV cell element 120 receives solar energy. As set forth above, PV
cell element 120 is semi-transparent to the solar energy, i.e., PV
cell element 120 is configured to absorb a portion of received
solar energy, and convert it into electrical energy, and is
configured to pass another portion of solar energy therethrough.
The other portion of solar energy passing through PV cell element
120 may further pass through a transparent substrate 152 in
electrolysis compartment 140.
[0055] In step 340, the other portion of the solar energy is
received by an aqueous electrolyte. In an exemplary embodiment, PV
cell element 120 passes infrared (IR) radiation through to aqueous
electrolyte 142. The IR radiation heats the aqueous electrolyte
142, thereby lowering the electrical current that is required to
perform electrolysis of the aqueous electrolyte 142. The heated
aqueous electrolyte 142 may then flow between electrodes 144 and
146, in order to be electrolyzed. Alternatively, the heated aqueous
electrolyte 142 may be diverted to a storage chamber or a heat
exchanger, as described above.
[0056] In step 350, the electrical energy generated by PV cell
element 120 is transmitted to a pair of electrodes. In an exemplary
embodiment, PV cell element 120 transmits the generated electrical
energy to electrodes 144 and 146 via electrical connections
128.
[0057] In step 360, the aqueous electrolyte is electrolyzed. In an
exemplary embodiment, the electrical energy received by electrodes
144 and 146 is used to electrolyze the aqueous electrolyte 142. The
resulting gas may flow outward from electrolysis compartment 140
through membrane 150.
[0058] The exemplary devices and methods for photovoltaic (PV)
electrolysis described herein may provide a number of advantages
over conventional devices, as described below. The device described
above will have lower balance-of-system costs and higher efficiency
compared to conventional PV electrolysis systems because all
components critical to device operation (e.g. both PV components
and electrolyzing components) are integrated into a single unit,
obviating the need for most of the ancillary equipment used in
conventional devices. In addition, integration of the components in
a single unit will likely achieve a significant cost benefit over
conventional devices. Further, the device uses the low-energy
portion of the solar spectrum, providing the opportunity to achieve
higher conversion efficiencies.
[0059] Additionally, conventional devices only recognize the
thermodynamic benefits of electrolyzing water at high temperature,
and thus proposes to use a large scale concentrated solar set-up to
take advantage of these benefits. These conventional devices do not
make use of the kinetic benefits that are very important at
intermediate temperatures (50-200 C), and from which aspects of
this invention are based.
[0060] Although the invention is illustrated and described herein
with reference to specific embodiments, the invention is not
intended to be limited to the details shown. Rather, various
modifications may be made in the details within the scope and range
of equivalents of the claims and without departing from the
invention.
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