Patent Application
20190326459
This invention relates to photovoltaic cell, module and mounting hardware manufacturing techniques that increase the robustness, throughput, performance and flexibility of cells and modules to overall reduce the cost of producing electricity from solar panels.
As mankind continues to develop around the world, the demand for energy rises. Most energy used to power machines and generate electricity is derived from fossil fuels, such as coal, natural gas or oil. These supplies are limited and their combustion causes atmospheric pollution and the production of Carbon Dioxide, which is suspected to accelerate the greenhouse effect and lead to global climate change. Some alternative approaches to produce energy include the harnessing of nuclear energy, wind, moving water (hydropower), geothermal energy or solar energy. Each of these alternative approaches has drawbacks. Nuclear power requires large capital investments and safety and waste disposal are concerns. Wind power is effective, but wind turbines require a windy site, often far away from grid connections and take up large footprints of land. Hydropower requires the construction of large, potentially environmentally harmful dams and the displacement of large volumes of flowing water. Geothermal power requires a source of energy that is relatively near the surface—a characteristic not common to a large portion of the Earth—and has the potential to disrupt the balance of forces that exist inside the Earth's crust. Solar is one of the cleanest and most available forms of renewable energy and it can be harnessed by direct conversion into electricity (solar photovoltaic) or by heating a working fluid (solar thermal).
Solar photovoltaic (PV) technology relies on the direct conversion of solar power into electricity through the photoelectric effect: solar radiation's quantized particles, or photons, impinging on semiconductor junctions may excite pairs of conduction electrons and valence holes. These charged particles travel through the junction and may be collected at electrically conductive electrodes to form an electric current in an external circuit.
Photovoltaic is one of the most promising technologies for producing electricity from renewable resources, for a number of reasons: 1. The photovoltaic effect in Si and other solid-state semiconductors is well understood and the technology fully validated; 2. PV power plants convert directly solar power into electrical power, have no moving parts and require low maintenance; 3. Solar radiation is quite predictable and is maximum during hours of peak electricity consumptions; and 4. The industry has been aggressively pursuing a performance improvement and cost reduction path similar to the Moore's law in semiconductor electronics, approaching the condition of market competitiveness with traditional energy resources in many parts of the world. In 2015, over 60 GW of solar photovoltaic will be installed globally, continuing strong year over year growth from about 50 GW of global installations in 2014.
However, a number of significant issues remain to be solved for photovoltaic to become a mainstream source of electricity in unsubsidized market conditions: 1. PV is still more expensive than traditional energy resources in most parts of the world: while economy of scale and low cost manufacturing will contribute to further reduce cost, technological innovation is needed to achieve market competitiveness more rapidly and on an economically sound and sustainable basis; 2. Manufacturing throughput is still largely inadequate for the potential market need; 3. Mainstream PV performs poorly in a number of real-world conditions, such as low-light, diffused light, partial shading, temperature excursions, etc.; and 4. As PV cell performance continues to increase and the costs of PV modules continue to drop, installation costs consisting of hardware and labor are proportionally increasing their contribution to the total installed costs of PV power plants.
Therefore, a technology would be desirable which can decrease the cost of photovoltaic energy, increase the throughput and flexibility of PV module manufacturing, reduce the cost of installation and resolve a number of the performance issues, while being compatible with the industry value chain. It is also desirable to provide technology, devices and techniques that provide durable and long-lasting PV cells and modules.
This invention overcomes disadvantage of prior art by providing a system and method that alleviates, for example, the breakage and degradation of PV cells in manufacturing lines; the lack of flexibility in module format and characteristics; and the performance limitations of current PV module architectures. Illustratively, a photovoltaic (PV) device is provided. The device is constructed using Single Cell Encapsulation (SCE), according to various embodiments and the assembly of the individually encapsulated cells into a module. Illustratively, by encapsulating individual PV cells of various dimensions in a multilayer structure comprising a bottom layer, a layer of encapsulant, the PV cell, another layer of encapsulant and the top layer, many benefits including flexible architecture, automated manufacturing, low cell breakage, cell and structure decoupling, etc., can be realized.
The bottom layer can consist of various materials (e.g. metals, plastic, glass, etc.), which are chosen in order to optimize mechanical, electrical and thermal transfer properties.
The top layer can consist of various transparent materials (e.g. glass, plastic, Teflon, etc.), which are chosen in order to optimize optical, mechanical, electrical and thermal transfer properties.
Electric contacts on the front and back of the cell can be already present on the cell or may be applied during single cell encapsulation. In each alternative, the contacts are illustratively extended to reach outside of the sealed structure and can be connected to an external connector, another cell's electrodes, circuitry or any conductor. The electric contacts can be of standard PV interconnect ribbon constructed, by way of non-limiting example, from tin or silver coated copper, bare copper, surface textured copper for advanced light capturing, thin silver nano-wire mesh or any other type of electric contact that can remove charge from the cell.
According to an illustrative embodiment, individual cells are plugged into (operatively connected to) a Flexible-format Module Architecture (FMA). FMA consists of a supporting sub-structure (also termed a “frame” or “framework”) that can be made from various materials formed with associated manufacturing process and dimensions. The FMA can incorporate slots or mounting pads for the insertion and support of the cells, electrical connections among the cells, power conditioning or other electronics and provision for the integration of mounting solutions. Illustratively, the FMA can allow cells to be replaced when worn or non-functional, or otherwise electrically bypassed without compromising the function of the remaining cells in the FMA.
The sub-structure, frame or framework of the FMA can incorporate features that ease the installation of PV modules in the field, on a roof or on any structure. The sub-structure can also allow for factory pre-assembly of modules, integrating a large number of cells, cells oriented in preferred direction or orientation or any other customized form for specified functions.
In various illustrative embodiments, a platform or assembly seat for fabrication of a solar PV module is provided. This platform includes a sub-structure and one or more solar cells. The solar cells are illustratively interconnected to provide electrical power and the sub-structure is constructed and arranged to provide physical protection and support to individual ones of the solar cells. Illustratively, the solar cells are each individually encapsulated and the sub-structure includes an integral joint assembly to join a mounting structure or to adjacent sub-structures. The sub-structure can include a composite material. The composite material can comprise a thermoplastic, and thermoplastic can include PET and/or glass fibers. The glass fibers can be continuous and/or can be chopped, with an aspect ratio of length-to-diameter greater than approximately 10. The materials of the sub-structure can be constructed and arranged to be resistant to ultraviolet light and/or flame retardant. Illustratively, the sub-structure can be constructed by a low-cost thermoplastic process, and can be positioned at a location corresponding to a back sheet of a conventional PV module. The joint assembly can be constructed and arranged for direct mounting to roof integrated hardware. The joint assembly can be constructed and arranged to provide a direct connection to pylons of a ground mounted system. The sub-structure can also be constructed and arranged to allow factory pre-assembly of multiple modules into larger systems that contain predetermined structural support and to allow for assembly of a multi-module onto field-installed footings. Illustratively, the solar cells can be individually, optimally inclined for a specified location and connected so that a center of gravity of the module enables mounting thereof onto a single axis tracker. Between 2 and 2,000 solar cells (per-module, by way of non-limiting example) can be assembled and interconnected. Note, further, that the number of cells-per-module and overall number of modules is highly variable and not limited by a specific parameter. The sub-structure can be constructed and arranged to enclose or attach wiring and/or to allow for integration of electrical storage devices. The sub-structure can include an integrated junction box, an integrated micro inverter, cell-level electronics and/or integrated busbars and tabs, constructed and arranged to interconnect to the solar cells. The sub-structure is also illustratively constructed and arranged to be optimized so as to reduce weight thereof while maintaining structural integrity thereof. The arrangement can be free of exposed metallic components. In embodiments, the sub-structure is ungrounded and constructed and arranged to reduce potential induced degradation of PV modules in the ungrounded state. Also, the sub-structure can be constructed and arranged to optimize packing density of modules for shipping cost reduction.
A method for encapsulating solar cells is provided in illustrative embodiments. This method includes the step of providing a source of silicone encapsulant, applying silicone to the solar cells in an amount that efficiently generates a layer of encapsulant on each of the solar cells. In this manner, an amount of silicone utilized for the encapsulant provides an economically viable production process. The step of applying the silicone reduces glass bowing during encapsulation of each of the solar cells, and can include encapsulating individual ones of the solar cells. Illustratively, a thickness of silicone between an edge of each of the solar cells and an outer edge of the encapsulant layer is no more than approximately 1.5 mm so as to allow cells to be packaged within 3 mm of each other in a module. A plurality of electrically interconnected solar cells can be constructed according to the above method for encapsulating. The solar cells can include an edge exclusion that is no more than 5 mm. Illustratively, the silicone provides a high transparency so as to optimize light transmission to the solar cells. The solar cells and connections between solar cells can be constructed and arranged to withstand string voltages of at least (e.g.) 1500 V. The photovoltaic module can be constructed and arranged to reduce degradation of the module electricity generation potential over time.
In illustrative embodiments, a method for continuous encapsulation of solar cells is also provided. This method includes the steps of arranging solar cells so as to provide for the inspection and qualification (steps of inspecting and qualifying) of each individual one of the solar cells, and encapsulating the arranged solar cells so that, after encapsulation, and before integration of encapsulated solar cells into a PV module, each of the encapsulated solar cells can be inspected and qualified. The inspection and qualification can include performing an electroluminescence test and/or a solar simulation (IV) test. Results of the inspection and qualification can provide a decision on Maximum Open Circuit Voltage, Closed Circuit Current, Fill Factor and efficiency of the encapsulated cell. The results of the inspection and qualification can also provide a decision on utility of the encapsulated cell and/or enable sorting of the encapsulated solar cells based upon performance thereof. The continuous encapsulation can comprise a lean manufacturing process in illustrative embodiments. The method can further include constructing the PV module to contain the encapsulated solar cells, so as to exhibit similar response to light to enable a manufacturing yield with a statistically higher performing module with a tighter distribution. The encapsulant can comprise silicone. Additionally, the method can include connecting tabs of the solar cells to cell busbars using a solderless process. The illustrative solderless process can utilize advanced light capturing ribbons. The method can also include utilizing conductive adhesive to electrically connect the ribbons to the solar cells. In various embodiments, the method can include electrically connecting the ribbons to the solar cells using direct connections. The method can include the use of solar cells with substantially reduced silver content or the elimination of busbars on the cells. The method is generally adapted to reduce manufacturing-induced defects in the solar cells. The arrangement can include a Non-Fluorinated back sheet and the solar cells can include individual glass having chamfers on edges thereof constructed and arranged to optimally refract light falling between the solar cells.
In illustrative embodiments a mounting structure for a solar PV module is provided. The mounting structure includes a mounting assembly constructed and arranged to be attached to a rooftop, free of (without or avoiding) penetration of the rooftop weatherization layer. The mounting structure can further include a sheet-shaped foot with one or more locking members configured to lock into a solar module. The mounting structure can be constructed and arranged to replace conventional rooftop weatherization structures, and/or is constructed and arranged to be located under an existing composite shingle and physically attached to a supporting structure of the rooftop. The mounting structure can also be constructed and arranged to be attached to the rooftop by adhesively bonding to the weatherization layer, and/or to be attached to the rooftop by fastening through the sheet-shaped foot, into an underlying structure of the roof and beneath the rooftop weatherization layer. Illustratively, the sheet-shaped foot is constructed and arranged to conform to a profile of a clay tile roof for mounting thereto. The locking members can respectively define differing heights to allow the module to be mounted with a tilt in a favorable position with respect to a position of the sun. Illustratively the mounting structure includes a composite material. The composite material can include a thermoplastic, such as, but not limited to, PET. The composite material can include glass fibers that are continuous and/or chopped with an aspect ratio of length-to-diameter greater than approximately 10. The composite material can be resistant to ultraviolet (UV) light and/or is flame-retardant. Illustratively the arrangement can include solar cells that are individually encapsulated before integration into a sub-structure, the sub-structure being operatively connected to the mounting structure.
The invention description below refers to the accompanying drawings, of which:
Single cell encapsulation (SCE) technology according to the illustrative embodiments described below can be a plug-in solution for existing cell and/or module manufacturing lines, which enables the production of lower-cost and higher-performance PV modules, while incorporating a number of desirable features.
Standard cell manufacturing lines produce photovoltaic cells, which consist of a thin (typically approximately 180 μm) silicon wafer with front and back electrodes. The cells are very fragile and need to be handled with extreme care, and therefore breakage of the cells poses limits on the minimum practical thickness of the cell in a conventional module assembly line. On the other hand, thinner cells require less silicon material and therefore enable lower material cost. Encapsulating the cells as they leave the cell manufacturing line provides strength and protection to the fragile silicon and will enable the handling of ultra-thin (<120 μm) cells without the need for specialized equipment, reducing breakage rates without incurring additional capital equipment expenses.
During manufacturing of an integrated solar module, interconnect ribbons are soldered to the top and bottom of busbars of adjacent cells to form strings which are then laid out in a multilayer structure comprising: a bottom layer or “backsheet”, such as TPE (Tedlar, Polyster, Ethyl Vinyl Acetate (EVA)), TPT (Tedlar, Polyster, Tedlar), glass, etc.; a layer of encapsulant, such as ethylene vinyl acetate (EVA), polyvinyl butyral (PVB), silicone, polyolefin resins, polydimethylsiloxane (PDMS), polyepoxide resins, etc.; the PV cells; a second layer of encapsulant; and a transparent top layer of glass, which also provides structural integrity. The multilayer structure is then laminated in machines, which combine the layers by pressing them together for approximately 1 to 30 minutes. The lamination time depends on the type of encapsulant and on the encapsulation process, which may include application of heat, force and/or vacuum. Finally, an aluminum (or other metal, polymer, composite, etc.) frame is typically adhered to the edges multilayer structure and the electric junction box with bypass diodes is connected to the electric contacts from the strings, on the back of the module. The whole process can take up to 1 hour per module with manual assembly. Module line automation is a desirable option for manufacturers in countries with high cost of labor, however automated production lines are quite complex and expensive.
In its generalized implementation, SCE plus FMA technology includes laminating individual cells in standalone elements with mechanical, thermal and electronic properties. There are numerous advantages to this approach over current techniques as described in prior art, including for example:
Note, as used herein the term “standalone” or “stand-alone” in the context of the illustrative embodiments of SCEs refers to the fact SCEs are each essentially discrete, stand-alone, weatherized components and that the frame used to hold such SCEs is only (illustratively) a supporting structure with interconnections and other features. This arrangement is novel distinct from various prior art implementations, which integrate the frame as a portion of the overall system in terms of weatherization and/or other functions.
These are only some of the immediate advantages in accordance with the teachings herein; SCE is an enabling technology in a number of ways over the current architectures described in prior art:
An illustrative embodiment of an integrated encapsulated solar cell (SCE) is shown in
As will be known to those skilled in the art, solar cell 3 is equipped with front and back electrodes, which are employed to extract the photocurrent generated by the incoming solar radiation. The cell front electrode usually comprises a large number of fingers, approximately 10 to 20 micrometers high and 50 to 200 micrometers wide, and several bus bars, approximately 10 to 20 micrometers high and 1.5 to 3-millimeter wide. The main function of the bus bars is to collect the electric current from all the fingers and to offer a soldering pad for the strips of metal, known as tabs or ribbon, which interconnect solar cells in a module. Cell top layer 8, on which the cell front electrode is formed, is usually a Silicon Nitride layer added for optical efficiency and electrical passivation. Cell top layer 8 is non-conductive and a manufacturing process is employed to make electric contact to solar cell 3 through cell top layer 8. An example of such a process is where the cell front electrode is screen-printed using a conductive paste, usually containing Silver particles. The cell is then baked at high temperature, which allows some of the paste to diffuse though the Silicon Nitride in order to make electric contact with solar cell 3. The cell back electrode usually comprises an Aluminum-based layer covering the full extent of the back of solar cell 3 and several bus bars, approximately 10 to 20 micrometers high and 3 to 5 millimeter wide. Akin to cell front electrode, the cell back electrode is usually screen-printed and baked at high temperature into solar cell 3. Alternatively, both the cell front electrode and the cell back electrode can reside on the bottom face of solar cell 3. Several methods are available for creating such a configuration, including Metal-Wrap-Through (MWT), Emitter-Wrap-Through (EWT) and Interdigitated-Back-Contact (IBC), as it is known to those skilled in the art. In an embodiment, the cell front and back electrodes are assumed to be an integral part of solar cell 3. However, it is contemplated that such electrodes can also be created during the SCE process described herein.
SCE top electrode 6 is connected with the cell front electrode and SCE bottom electrode 7 is connected with the cell back electrode, therefore guaranteeing electrical access to the cell from outside the SCE package. In one illustrative embodiment, the cell front electrode is located on the top face of solar cell 3; however, it should be clear and apparent to those skilled in the art that the scope of the various embodiments extends to other cell electrode configurations, including, but not limited to, MWT, EWT and IBC configurations, in which cases SCE top electrode 6 is relocated to the back of solar cell 3.
In one illustrative embodiment of a lamination process, SCE 9 consists of a sandwich of multiple layers that, in order, include a transparent SCE top layer 1 such as glass, acrylic, Teflon or other transparent materials as known to those skilled in the art. SCE top electrode 6, made from appropriate conducting materials such as copper, aluminum, other conductive metals and conductive non-metals whether they are transparent or non-transparent, is placed between SCE top layer 1 and cell top layer 8 of solar cell 3. SCE top electrode 6 can be integrated into SCE top layer 1 in multiple ways as known to those skilled in the art or can be a standalone layer. Top encapsulant layer 2, consisting of a thermo-set or non-thermo-set materials characterized by low Equilibrium Moisture Content (EMC) of less than 0.2% at 85 C and 85% relative humidity and by low surface tension of less than 30 mN/m, such as polydimethylsiloxanes (PDMS), is placed between SCE top layer 1 and solar cell 3. It is recognized that certain types of encapsulants can be desirable for use in the illustrative SCE architecture—for example those that are characterized by (a) very low EMC and (b) very high wetting properties. Illustratively, acceptable thresholds for these two physical parameters (a and b) can be provided. For example, the EMC was found to be 0.28% for EVA and only 0.035% for PDMS at 85 C/85% RH in a recent study by Dow Corning (See: http://onlinelibrary.wiley.com/doi/10.1002/pip.1025/abstract). Additionally, silicones have a surface tension of 20.4 mN/m, while that of EVA is in the range 30-36). See: http://www4.dowcorning.com/content/publishedlit/silicones_in_industrial_applications_i nternet_version_080325.pdf and www.vtcoatings.com/plastics.htm. The bottom encapsulant layer 4, consisting of thermo- or non-thermo-set materials of similar properties as top encapsulant layer 2, is placed between the back of solar cell 3 and SCE bottom layer 5. SCE Bottom layer 5 can be a multitude of materials chosen for a specific additional feature of SCE 9. By way of example, SCE bottom layer 5 provides weather, impact and electrical insulation to solar cell 3. In another embodiment, SCE bottom layer 5 can incorporate additional functions and processes, such as electronics, micro fluidics for cooling and purification, advanced cooling and other chemical, mechanical and electrical functions that are powered by the solar electricity generated by solar cell 3. SCE bottom electrode 7 is placed between SCE bottom layer 5 and the back of solar cell 3. SCE bottom electrode 7 can be integrated into SCE bottom layer 5 in multiple ways as known to those skilled in the art or can be a standalone layer. The lateral dimensions of the SCE can be 100-200 mm. Illustratively, the thickness of the layers can be as follows: SCE top layer 1 1-4 mm for glass, 0.13-1.3 mm for Teflon; top encapsulant layer 2 0.001-1.5 mm; solar cell 3 0.001-0.2 mm; bottom encapsulant layer 4 0.001-1.5 mm and SCE bottom layer 5 0.2-0.5 mm. The aforementioned materials and thickness values are illustrative of a wide range of possible materials and dimensions.
In the example of using thermoset materials as encapsulant, the aforementioned sandwich of multiple layers is then placed under pressure while exposing it to heat in a ubiquitous lamination process. The heat of the process initially softens and allows encapsulant layers 2 and 4 to melt and flow. By way of a non-limited example (and for which further alternate processes are described below), pressure applied to the sandwich while encapsulant layers 2 and 4 are melted, squeezes encapsulant material out between SCE top electrode 6 and cell top layer 8, allowing SCE top electrode 6 to make electric contact with the cell front electrode. Similarly flow of bottom encapsulant layer 4 under pressure allows for SCE bottom electrode 7 to make electric contact with the cell back electrode. The temperatures employed in the process are illustratively in the range of 25° C. to 1,000° C.
After sustained exposure to heat, the polymer material of encapsulant layers 2 and 4 will cross link, bonding to all material that is in contact with it. Hence, SCE top layer 1 and cell top layer 8 is illustratively bonded in a similar manner as the back of solar cell 3 and SCE bottom layer 5. However, since all encapsulant has flowed under pressure from between SCE electrodes 6 and 7, a suitable electric connection between the cell electrodes and the SCE electrodes is ensured. Because such interconnection process is solder-less, the bus bars on the front and the back of solar cell 3 can be made free of bus bars. Therefore, the width of such bus bars can be substantially reduced or the bus bars can be entirely omitted from the structure, with significant savings in conductive paste usage. The lamination bond secures solar cell 3 between SCE top layer 1 and SCE bottom layer 5, giving it the mechanical properties of the respective layers and forming SCE 9. This lamination is durable and reduces the risk that the inner layer will crack.
In one possible variation of the lamination process, SCE top electrode 6 can be placed between top encapsulant layer (also termed “encapsulant top layer”) 2 and cell top layer 8. Likewise, SCE bottom electrode 7 can be placed between bottom encapsulant layer (also termed “encapsulant bottom layer”) 4 and the back of solar cell 3.
As yet another alternative, SCE top electrode 6 can be directly attached to the cell front electrode by soldering, ultrasonic welding, conductive glue or other suitable technique, as it will appear to those skilled in the art. Likewise, SCE bottom electrode 7 can be directly attached to the cell back electrode by similar process or technique.
As will be appreciated by those skilled in the art, thermosetting is one of many processes available to bond the sandwiched layers of the SCE 9 according to an embodiment. For example in another variation of the lamination process, a PDMS (silicone) encapsulant can be used. Silicone can be tailored to cure with the addition of heat, ultra-violet light (UV) or a catalyst or a combination of the aforementioned in just a few minutes. Furthermore, silicone can be tailored to have a specific hardness and Young's modulus of choice. Commercial silicone encapsulants feature a number of properties that make them ideal for SCE, for example: High transparency; Stability to ultra-violet light; High breakdown voltage; Superior volume resistivity; Higher resistance to potential induced degradation (PID); Excellent adhesion to glass and other SCE relevant materials. By virtue of the low equilibrium moisture content and excellent weather resistance of silicone encapsulants, SCEs can be made with very small clearance between the edge of solar cell 3 and the edge of integrated SCE 9, thereby enabling a high packaging density of PV cells in PV modules. For example, current cell package density for ubiquitous modules requires 3 mm between cells. An SCE encapsulated with silicone can have an edge distance from cell to air from 0.1 mm to 1.5 mm, the latter allowing for the same packing density and module efficiency as common modules, the former increasing said efficiency. The weatherization of PV cells can be further improved by an additional layer of suitable sealant applied around the edges of SCE 9, which should be clear to those skilled in the art.
During lamination, it can be desirable to employ a physical structure to prevent layers from slipping and misaligning with respect to each other as bonding layers cure.
As an alternative, SCE bottom electrode 7 can consist of several conductive strips of metal independent of SCE bottom layer 5, also known as tabs, of the type conventionally used to interconnect solar cells in PV modules. The tabs can be located either between SCE bottom layer 5 and bottom encapsulant layer 4 or between bottom encapsulant layer 4 and the back of solar cell 3.
The viscosity of the silicone encapsulant can be tailored to improve the ability to align the layers to be laminated. In some cases, the viscosity can be adjusted within the silicone encapsulant formulation. In other illustrative embodiments, the silicone can be partially cured to increase viscosity. Partial curing can be accomplished by the application of a moderate amount of UV light, moderate heat for a short time, or a minimal amount of time exposure to controlled humidity, depending on the type of curing required for the specific encapsulant formulation.
SCE top electrode 6 serve to conduct electricity generated from the solar cell 3. However, when made from non-transparent material, they also reduce the amount of light that penetrates cell top layer 8, thereby effectively reducing the efficiency of solar cell 3. In
In one embodiment as illustrated in the cross section of
As an alternative, SCE top electrode 6 can consist of a plurality of conductive strips of metal independent of SCE top layer 1, also known as tabs, of the type conventionally used to interconnect c-Si cells in PV modules. The tabs can be located either between SCE top layer 1 and top encapsulant layer 2 or between top encapsulant layer 2 and cell top layer 8.
In a further alternate embodiment/example, to minimize front surface shading, SCE top electrode 6 can consist of a single strip of interconnect material, including without limitation a light capturing ribbon, a fine metal or nanowire mesh or a conventional interconnect ribbon situated at the edge of the cell connecting perpendicular to and connection all of the conductive silver fingers. This arrangement may be facilitated by the addition of one or more fine conductive silver fingers spaced across the solar cell perpendicular to the primary conductive silver fingers and connecting them electrically.
Traditional PV modules incorporate a multiplicity of cells in one final assembly step. A large transparent layer, typically glass (but alternatively a durable, weather-resistant and UV-stable polymer), resides on top of the cells. Traditionally, this transparent layer has been of rectangular cross section. This cross section is an optimization of structural and cost features. Since the transparent layer of SCE is a single piece of material for each encapsulated cell, and is generally free of system-wide structural requirements, it can define a wide variety of shapes to optimize the optical efficiency of the device. In one embodiment as shown in the cross section of
To increase design flexibility of the SCE, it can be desirable to incorporate mechanical arrangements for structurally and electrically coupling the SCE to other SCEs in a module. In
In one possible embodiment, FMA 91 incorporates slots 92 for mechanical connection 72 and electrical connection 73 of SCE 9. In another illustrative embodiment, adjacent SCEs are directly connected to one another, as shown and described above in
SCEs 9 can be inserted in the FMA 91 by a ubiquitous pick-and-place robot, widely used in the automation industry, and implemented in accordance with ordinary skill. These robots are able to move and insert SCEs 9 rapidly and precisely, without causing breakage due to the mechanical resistance of individually encapsulated cells. Alternatively, SCEs 9 can be directly connected to one another to form strings and strings can be subsequently mounted and interconnected on FMA 91.
FMA 91 can also incorporate electrical interconnections between cells, electrical interconnections between strings of cells and power conditioning electronics, both at the cell level and at the module level. As an illustrative example, electrical by-pass diodes can be co-molded at each SCE in order to isolate individual SCEs in case of partial shading or failure. More generally, the FMA can include electrical connections that interconnect predetermined of the cells together, the electrical connections including bypass diodes constructed and arranged to enable inoperative cells and cells that are functioning poorly (e.g. shaded cells or degraded cells) to be bypassed in an overall electrical connection of the cells. As another illustrative example, the junction box containing string-level electrical by-pass diodes can be incorporated in FMA 91 by co-molding it into the structure. Alternatively, each cell's positive and negative electrode can be wired to the junction box where sophisticated cell level power optimization electronics can regulate the power generated by each cell. These are just some of a wide variety of implementations of FMA-integrated power conditioning electronics according to various non-limiting examples and embodiments.
Furthermore, FMA 91 can include a plurality of mounting solutions (not shown), which allow seamless and low-cost integration of the module in a photovoltaic power plant. Such mounting solutions can be posts, pedestals, holes, screws, interlocking mechanisms, ballasts, and many others, as it will be apparent to those skilled in the art.
One of the advantages of SCE 9 and FMA 91 is the flexibility of electrical configurations attainable for PV cells. Electrical interconnections built into FMA 91 can have a larger cross section and lower resistance than those of conventional PV modules, because they do not fall in the light path and can avoid being routed in the tight spaces between neighboring cells. In one embodiment, electric connections departing from SCE electrodes 6 and 7 of all SCEs 9 in FMA 91 converge into a central electronic board where they are interconnected in series, parallel or hybrid configuration, with or without power conditioning electronics, as it will be clear to those skilled in the art. In an alternate embodiment, each SCE 9 is connected directly to its immediate neighboring cells and the power conditioning electronics is located on or near SCE 9.
In one embodiment of the circuitry of FMA 91, SCEs 9 are connected in series (
In another embodiment, FMA 91 circuitry connects SCEs 9 in parallel as shown in
It should be clear that SCE, FMA and methods for constructing the same, according to the illustrative embodiments described herein, provide a flexible-format module architecture to be implemented at the cell level. This enables cost reduction and improved performance of photovoltaic power generation.
External electric connector 73 can be optionally applied (step 240) and the cell is finished into SCE 9 (step 230). A final outgoing quality control inspection (step 250) can be applied to sort SCE's by measured properties such as: total conversion efficiency, spectrally resolved conversion efficiency, light reflectance, micro-crack analysis (e.g. electroluminescence), mechanical properties, thermal characteristics, lumped electric parameter characteristics (resistance, capacitance and inductance), DC and AC electric characteristics of the junction, current-voltage response (IV curves) at different irradiances and temperatures, and other measurements known to those skilled in the art. By performing outgoing quality control after encapsulation (and generally before mounting into a PV module), an accurate estimate is obtained of the real performance of the cell in the field. As a consequence, modules built with SCEs can achieve tight output power distribution at their nominal power rating.
In an illustrative embodiment using silicone encapsulants, the silicone can be dispensed between the front surface tabs and the front transparent layer and the back surface tabs and the back sheet. Due to the small area of the SCE, the silicone can be dispensed in multiple macroscopic parallel lines, in a radial pattern or even as a single application near the center of the application surface, rather than requiring a uniform coating of less than 450 microns, making encapsulant dispense a more robust process. The silicone can be dispensed in the amounts necessary to form a layer that is thinner than a 400-500 micron state of the art EVA encapsulant. With the use of a low viscosity silicone material, the laminate stack can be pressed to final thickness by uniform axial compression or by passing the assembled stack through a set of rollers or by application of vacuum compression or other processes known to those skilled in the art. The application of pressure to the stack will disperse the applied silicone encapsulant to the desired final thickness. The laminate stack can then be cured to ensure adhesion and cross linking of the silicone encapsulant without the continuous application of pressure. In the case of a low viscosity silicone encapsulant, the applied encapsulant will flow easily to the desired final thickness, so it may be desirable to partially cure the encapsulant to decrease the viscosity or to complete the cure of the encapsulant with the continued application of pressure.
It should be noted that
PV module weight influences the cost of a PV power plant in many ways. For one, structures need to be suitably large and strong to accommodate the modules. In the case of roof mounted systems, pre-installed roofs often need additional bracing to support a PV system. Secondly larger equipment, more labor and increased power is required to move, lift and install heavier modules. Thirdly, it is more costly to ship heavier items. It is therefore desired to make lower weight PV modules. PV module weight is largely driven by the glass (front and back when applicable) and sub-structure materials. One of the advantages of making a FMA 91 sub-structure 93 from composite materials is that the composite sub-structure can be designed and optimized to bear substantially the required load of the PV system, a function shared between the glass and sub-structure of current module designs. Since sub-structure 93 can be optimized for minimum weight with required strength it is possible to remove the burden of structural integrity from the glass. Therefore the SCE can implement thinner glass since the glass sheet is smaller and since it does not need to be part of the structural backbone of the module. By utilizing the sub-structure in this manner weight savings of (e.g. approximately 20% and more is achievable. Even higher weight reduction is possible when the front protection of the PV cell is made from a transparent material other than glass that has a lower density. These materials such as PTFE and PCB are utilized today in specialty modules and should be known to those skilled in the art.
Modules built with SCE's and incorporating an FMA sub-structure can reduce input material costs. Cell busbars fabricated from silver paste act mainly as soldering pads to connect tabs. When utilizing conductive adhesive, substantial cost savings is enabled by reducing the amount of silver paste used in the busbars, both in the front and the back of the cell. Since the FMA sub-structure is designed to bear all the required loads of the module, the glass of the SCEs can be thinner, saving on material cost. Since the price of glass drops as thickness decreases from today's module standard of approximately 3.2 mm down to approximately 1.9 mm and then becomes more expensive as the thickness reduces further, the currently most cost effective glass thickness is approximately 2 mm. Sub-structures formed from engineering materials with new processes are generally less expensive than aluminum frameworks. The smaller area of the SCE requires less encapsulant to fill up voids due to misalignment of the back sheet/glass and front glass, saving between 15% and 60% on encapsulant volume. Lastly, when silicone is used as the encapsulant, the module edge area can be 1 mm instead of the current 20-25 mm. This allows an average 1.0 m by 1.6 m module to be reduced in size by (e.g.) approximately 6%, saving proportionally on glass, back sheet and encapsulant.
A number of examples are provided herein to illustrate the design flexibility and the number of useful features that are obtained by using a specifically manufactured sub-structure. These examples are illustrative of but not limiting to the possibilities that exist in utilizing a custom sub-structure versus the traditional aluminum sub-structure utilized in PV modules today.
As a first example of useful features, consider the components illustrated in
As another illustrative example of the utility of the FMA, refer to
The previous examples serves as illustrate examples of how FMA 91 can be designed and manufactured as to meet specific customer requirements and needs. These examples are far from exhaustive and only serve to illustrate how the flexibility of the architecture achieved by combining SCE 9 and FMA 91 can be customized to solve a number of real life issues and cost drivers for the industry. A few further examples are listed for illustration. These include: very large modules with hundreds of cells can be made because cells that are defective can be found during the OQC process and replaced before the large module leaves the factory; Non-conventional module shapes are possible. For instance triangular or smaller rectangular shapes that can fill the space left empty by the restrictive conventional module size on a rooftop; Modules integrated into structural and/or decorative elements of a building that enable cost effective BIPV; Optimally inclined rooftop systems where the angle of the cells will be optimal regardless of the angle of the roof; Various mounting hardware solutions that can reduce the logistical, labor and part count burden currently imposed onto installers by conventional architecture; Lightweight car ports, building facades, awnings and other building features can be designed with SCE 9 incorporated into the sub-structures; and/or specialty systems for cars, boats, RV's and other mobile vehicles can be designed to incorporate SEC 9.
A significant feature of FMA 91 is that sub-structure 93 can be made from non-electrically-conductive materials. The use of non-conductive materials for the sub-structure reduces the need for grounding modules, removing the significant expense of both the copper wire and ground penetrating hardware as well as the labor associated with grounding modules. Another driver for installation cost is the maximum voltage that the string can operate on. Maximizing the voltage of the system reduces the current that conductors need to carry and therefore reduce their cross sectional area, size and cost. The industry is currently moving toward 1,000V systems with a strong desire to extend that to (e.g. approximately) 1,500V. The use of silicone as encapsulant in combination with non-electrically conductive sub-structure 93 increases both the di-electric strength as well as the electric resistivity of the module. These attributes are currently lacking in conventional modules and are considered to be enabling for the drive to 1,500V strings as will be known to those skilled in the art. Volume resistivity is also a contributing factor to a degradation mechanism that is becoming more important for the longevity of solar PV plants: Potential Induced Degradation or PID. Higher voltages, grounded modules and the use of lower di-electric strength and volume resistivity EVA has contributed significantly to PID degradation as will be known to those skilled in the art. Thus the use of advanced materials with its superior electric qualities has the potential to reduce PID and extend PV power plant life as well increased energy output over time.
Increased module efficiency is a highly desired feature. Higher efficiency results in more electric energy production for the same input cost and therefore lower levelized cost of electricity (LCOE) as known to those skilled in the art. The combination of SCE and FMA provide a gain of, for example, approximately 1.4% absolute efficiency when compared with conventional modules utilizing the same cells. Efficiency is defined as the amount of power generated by the cells divided by the product of the module size and the sunlight delivered to the module per square meter. Thus to increase module efficiency, more power must be generated by the module, the module size must be reduced or the amount of sunlight captured and absorbed by the module should increase.
The drivers for the efficiency gain of the combined SCE and FMA system are the following: Silicone is transparent to lower wavelength, ultraviolet (UV), sunlight whereas EVA absorbs UV light. Therefore more sunlight is delivered a cell encapsulated by silicone; Thinner glass reflects less sunlight and thus also allows more sunlight to pass onto the cells; As discussed earlier, the smaller encapsulation edges possible with silicone allows the module area to be smaller, also increasing efficiency.
A standard module has cells laid up next to each other with a 3 mm spacing between the cells. This spacing is a function of the di-electric strength and volume resistivity of the encapsulant, EVA. However, in one embodiment of the SCE, it is encapsulated by silicone, with a 1 mm edge. In
In support of the industry effort to reduce the cost of photovoltaic energy and become competitive with fossil fuel generation, the flexible-format module architecture based on individually encapsulated cells enables significant savings by moving to thinner and cheaper SCE front layer materials; reducing the amount of encapsulant needed; eliminating the external sub-structure of the PV module; and substantially reducing the amount of conductive paste required for the cell front and back bus bars. Furthermore, fast-curing silicone encapsulants are especially suited for single cell encapsulation and enable high-throughput, compact machines with a level of complexity and cost substantially reduced with respect to standard manufacturing equipment. Finally, single cell encapsulation can be implemented in continuous processes, with obvious benefits in terms of process control, reproducibility and yield.
The foregoing has been a detailed description of illustrative embodiments of the invention. Various modifications and additions can be made without departing from the spirit and scope of this invention. Each of the various embodiments described above can be combined with other described embodiments in order to provide multiple features. Furthermore, while the foregoing describes a number of separate embodiments of the apparatus and method of the present invention, what has been described herein is merely illustrative of the application of the principles of the present invention. For example, the sizes, shapes and form factors of components described herein can be varied to suit a particular application. Likewise, additional layers, enclosures, housings and mounting assemblies can be employed in conjunction with SCEs and FMAs as appropriate. Also, while orientational terms such “top”, “bottom”, “left”, “right”, “upper”, “lower”, “upward”, “downward”, “forward”, “rearward”, “front”, “rear”, and “back” are employed, these should be taken as relative only and not in reference to a global coordinate system such as the acting direction of gravity. Additionally, where the term “substantially”, “about”, or “approximately” is employed with respect to a given measurement, value or characteristic, it refers to a quantity that is within a normal operating range to achieve desired results, but that includes some variability due to inherent inaccuracy and error within the allowed tolerances of the system. Moreover, materials used for encapsulant and other components are described by way of non-limiting example, and it is expressly contemplated that other materials that may be developed and/or are known to those of skill in the art having similar performance and properties can be substituted for the above-described materials. Accordingly, this description is meant to be taken only by way of example, and not to otherwise limit the scope of this invention.
This application is a divisional of copending U.S. patent application Ser. No. 15/579,192, filed Dec. 1, 2017, entitled SINGLE-CELL ENCAPSULATION AND FLEXIBLE-FORMAT MODULE ARCHITECTURE AND MOUNTING ASSEMBLY FOR PHOTOVOLTAIC POWER GENERATION AND METHOD FOR CONSTRUCTING, INSPECTING AND QUALIFYING THE SAME, which is a U.S. National Phase of International Patent Application Serial No. PCT/US2016/035462, entitled SINGLE-CELL ENCAPSULATION AND FLEXIBLE-FORMAT MODULE ARCHITECTURE AND MOUNTING ASSEMBLY FOR PHOTOVOLTAIC POWER GENERATION AND METHOD FOR CONSTRUCTING, INSPECTING AND QUALIFYING THE SAME, filed Jun. 2, 2016, which claims the benefit of U.S. Provisional Application Ser. No. 62/169,938, entitled SINGLE-CELL ENCAPSULATION AND FLEXIBLE-FORMAT MODULE ARCHITECTURE AND MOUNTING ASSEMBLY FOR PHOTOVOLTAIC POWER GENERATION AND METHOD FOR CONSTRUCTING, INSPECTING AND QUALIFYING THE SAME, filed Jun. 2, 2015, the entire disclosure of each of which applications are herein incorporated by reference.
| Number | Date | Country | |
|---|---|---|---|
| 62169938 | Jun 2015 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | 15579192 | Dec 2017 | US |
| Child | 16376157 | US |
