WO2012044891A2

WO2012044891A2 - Devices and methods for increasing solar hydrogen conversion efficiency in photovoltaic electrolysis

Info

Publication number: WO2012044891A2
Application number: PCT/US2011/054138
Authority: WO
Inventors: Daniel Esposito; Robert W. Birkmire; Jingguang G. Chen
Original assignee: University Of Delaware
Priority date: 2010-09-30
Filing date: 2011-09-30
Publication date: 2012-04-05
Also published as: US20130175180A1; WO2012044891A3

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.

Description

DEVICES AND METHODS FOR INCREASING SOLAR HYDROGEN CONVERSION EFFICIENCY IN

PHOTOVOLTAIC ELECTROLYSIS

CROSS-REFERENCE TO RELATED APPLICATIONS

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 September 30, 2010, the contents of which are incorporated herein by reference in their entirety.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH

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.

FIELD OF THE INVENTION

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

Photovoltaic (PV) electrolysis allows the generation of hydrogen gas (H₂) and oxygen gas (0₂) 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.

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

Aspects of the present invention are directed to devices and methods for photovoltaic electrolysis. 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.

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

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 nonspecific 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:

FIG. 1 is a diagram illustrating a side view of an exemplary device for photovoltaic electrolysis in accordance with aspects of the present invention;

FIG. 2 is a diagram illustrating a top view of the device of FIG. 1;

FIG. 3 is a diagram illustrating a front view of the device of FIG. 1 ; FIG. 4 is a diagram illustrating the energy flow in the device of FIG. 1;

FIG. 5 is a diagram illustrating a side view of another exemplary device for photovoltaic electrolysis in accordance with aspects of the present invention;

FIG. 6 is a diagram illustrating a top view of the device of FIG. 5; and

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

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.

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.

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.

The disclosed devices may be modular in nature, such that they may be linked together depending on the amount of gas (e.g., H₂) 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.

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 (H₂) 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.

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.

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.

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.

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.

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.

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.

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 (H₂0), in which are dissolved suitable conducting ions. 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.

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.

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. 0₂ and H₂). 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.

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.

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. 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.

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.

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.

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.

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.

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.

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. 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.

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.

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 (H₂) 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.

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.

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.

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.

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).

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 .

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.

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.

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.

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.

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 (H₂) 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.

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.

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. 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.

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.

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.

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.

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.

Claims

What is Claimed :

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.