WO2012170726A2 - Solar panel systems having solar panels arranged in parallel, and associated methods - Google Patents

Solar panel systems having solar panels arranged in parallel, and associated methods Download PDF

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Publication number
WO2012170726A2
WO2012170726A2 PCT/US2012/041408 US2012041408W WO2012170726A2 WO 2012170726 A2 WO2012170726 A2 WO 2012170726A2 US 2012041408 W US2012041408 W US 2012041408W WO 2012170726 A2 WO2012170726 A2 WO 2012170726A2
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WIPO (PCT)
Prior art keywords
solar panels
plurality
inverter
solar
panels
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PCT/US2012/041408
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French (fr)
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WO2012170726A3 (en
Inventor
Matthew J. STOCKS
Jonathan Ashley NORMAN
Jacob E. Steele
Mark John Kerr
James E. Seymour
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Transform Solar Pty Ltd.
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Priority to US201161494379P priority Critical
Priority to US61/494,379 priority
Application filed by Transform Solar Pty Ltd. filed Critical Transform Solar Pty Ltd.
Publication of WO2012170726A2 publication Critical patent/WO2012170726A2/en
Publication of WO2012170726A3 publication Critical patent/WO2012170726A3/en

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    • HELECTRICITY
    • H01BASIC ELECTRIC ELEMENTS
    • H01LSEMICONDUCTOR DEVICES; ELECTRIC SOLID STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H01L31/00Semiconductor devices sensitive to infra-red radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus peculiar to the manufacture or treatment thereof or of parts thereof; Details thereof
    • H01L31/02Details
    • H01L31/02016Circuit arrangements of general character for the devices
    • H01L31/02019Circuit arrangements of general character for the devices for devices characterised by at least one potential jump barrier or surface barrier
    • H01L31/02021Circuit arrangements of general character for the devices for devices characterised by at least one potential jump barrier or surface barrier for solar cells
    • HELECTRICITY
    • H02GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02JCIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J3/00Circuit arrangements for ac mains or ac distribution networks
    • H02J3/38Arrangements for parallely feeding a single network by two or more generators, converters or transformers
    • H02J3/381Dispersed generators
    • H02J3/382Dispersed generators the generators exploiting renewable energy
    • H02J3/383Solar energy, e.g. photovoltaic energy
    • YGENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02EREDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E10/00Energy generation through renewable energy sources
    • Y02E10/50Photovoltaic [PV] energy
    • Y02E10/56Power conversion electric or electronic aspects
    • Y02E10/563Power conversion electric or electronic aspects for grid-connected applications

Abstract

Solar panel systems having solar panels arranged in parallel, and associated methods are disclosed. Systems in accordance with particular embodiments include an inverter (e.g., a DC/AC inverter), and a plurality of solar panels electrically connected to the inverter. The plurality of solar panels can be connected in parallel, with individual solar panels not connected to an intermediate transformer between the panels and the inverter.

Description

SOLAR PANEL SYSTEMS HAVING SOLAR PANELS ARRANGED IN

PARALLEL, AND ASSOCIATED METHODS

CROSS-REFERENCE TO RELATED APPLICATION

[0001] The present application claims priority to U.S. Provisional Patent Application No. 61/494,379, filed on June 7, 2011 , entitled SOLAR PANEL SYSTEMS HAVING SOLAR PANELS ARRANGED IN PARALLEL, AND ASSOCIATED METHODS, which is incorporated herein by reference.

TECHNICAL FIELD

[0002] The present disclosure relates generally to solar panel systems having solar panels arranged in parallel, and associated methods.

BACKGROUND

[0003] In recent years, environmental issues have become an increasing concern for governments and for citizens. A particular concern is the world economy's heavy reliance on polluting energy sources, such as fossil fuels and nuclear power. As a result, there has been significant interest in improving the effectiveness and utility of alternative power sources. Solar power is particularly popular because it makes use of sunlight that is already striking the Earth's surface and that has relatively little environmental impact, even compared to other alternative energy sources such as wind power. However, solar power has generally remained too expensive to be an effective replacement for power generated from fossil fuels and other traditional sources. The costs of solar power include the cost of manufacturing panels, as well as the costs for deploying panels onto buildings or other structures and configuring the associated components.

BRIEF DESCRIPTION OF THE DRAWINGS

[0004] Figure 1 illustrates a representative environment in which a solar panel system in accordance with an embodiment of the present technology may be deployed. [0005] Figure 2 illustrates an example of a circuit including a solar panel in accordance with an embodiment of the present technology.

[0006] Figure 3 illustrates a representative circuit for connecting an array of solar panels for use with standard electrical systems in accordance with an embodiment of the present technology.

[0007] Figure 4A illustrates a representative conventional circuit including a string of solar panels connected in series.

[0008] Figure 4B illustrates a representative conventional circuit for use in a commercial deployment using solar panels connected in series strings with the strings connected in parallel.

[0009] Figure 5A illustrates a representative conventional circuit in which individual solar panels are connected to an inverter in parallel using DC-to-DC converters.

[0010] Figure 5B illustrates the voltages and currents associated with a portion of the circuit of Figure 5A.

[0011] Figure 6 illustrates a representative circuit configured in accordance with an embodiment of the present technology in which solar panels are connected in parallel without the use of DC-to-DC converters.

[0012] Figure 7A shows a graph of power as a function of voltage for a single solar panel operating at maximum efficiency.

[0013] Figure 7B illustrates a graph of power as a function of voltage for a series- connected string of solar panels operating at less than full efficiency.

[0014] Figure 7C illustrates a comparison of current/voltage curves for a string of panels connected in series and a current/voltage curve for parallel-connected panels.

[0015] Figure 8A illustrates a representative solar cell bank suitable for implementing the circuit of Figure 6 in accordance with an embodiment of the present technology.

[0016] Figure 8B illustrates a representative solar panel suitable for implementing the circuit of Figure 6 in accordance with an embodiment of the present technology. [0017] Figure 9 illustrates a representative embodiment of the system deployed on a house with an irregularly shaped roof.

DETAILED DESCRIPTION

[0018] The presently disclosed technology is directed generally to solar panel systems in which the panels are electrically connected in parallel. In particular embodiments, the panels are configured so as to avoid the need for DC-to-DC converters (e.g. , step-up transformers) between the panels and an associated DC/AC inverter, thus simplifying the system and reducing system cost. The parallel connection of module enables increased flexibility in system design and installation while producing superior system efficiency. The following description provides specific details for a thorough understanding and enabling description of representative examples of the disclosed technology. One skilled in the relevant art will understand, however, that the present technology may be practiced without at least some of these details. Likewise, one skilled in the relevant art will also understand that the present technology can include other features not described in detail herein. Additionally, some well-known structures or functions may not be shown or described in detail below, so as to avoid unnecessarily obscuring the relevant description.

[0019] Figure 1 illustrates a representative environment 100 in which a solar panel system may be deployed. The environment 100 includes the sun 102, which irradiates a building 104 or other support structure. In Figure 1 , the building 104 is depicted as a house, but the building 104 can also be an office building, factory, or any other type of building or structure with surfaces or other features (e.g., racks) suitable for deploying solar panels. Solar panels 106, 108 and 1 10 have been deployed on the roof of the building 104. As discussed below, the solar panels 106, 108, and 1 10 are connected to various other electrical components and/or systems to collect and convert the power generated by the panels; however, for simplicity these components are not shown in Figure 1. The panels 106, 108, and 110 may be connected to provide power to the building 104 for powering devices such as home appliances, computers, etc. The solar panels 106, 108, and 1 10 may also be connected to the electrical power grid 114 via a transmission line 1 12. In this case, the connection between the building 104 and the grid 114 may include an electrical meter or other device for measuring power being provided to the grid 1 14. [0020] Figure 2 illustrates an example of a circuit 200 including a solar panel 204. Conventionally sized panels typically range in size from 1 m2 to 6 m2. Larger panels are generally not used because of the difficulty in deploying them and because they generally have a lower yield during manufacturing. The solar panel 204 receives sunlight 202 incident on the surface of the panel. The solar panel 204 includes a first terminal 206 and second terminal 208 and is designed to produce a pre-determined voltage between the terminals during operation. The solar panel 204 generates current (indicated as lp in Figure 2) between the terminals 206 and 208 in response to the incident sunlight 202, based on any of a variety of techniques generally known to those of ordinary skill in the relevant art. The amount of current varies depending on the amount and distribution of incident light and the efficiency with which the panel 204 converts the incident light. Because the voltage of the panel 204 typically varies much less strongly with light intensity changes during operation, the power generated by the panel is generally directly proportional to the generated current. The current flows to a load 210, which may be any component that can be powered by or make use of the generated power, such as appliances, light bulbs, etc.

[0021] Figure 3 illustrates a representative circuit 300 for connecting an array of solar panels for use with standard electrical systems. The circuit 300 includes an array 302 of solar panels, which is connected to an inverter 304. The array 302 includes individual solar panels 306, 308, and 310. As discussed below, the solar panels 306, 308, and 310 may be arranged in various electrical configurations within the array 302 (e.g., series, parallel, or a combination). Regardless of how the solar panels 306, 308 and 310 are arranged, the array 302 provides a direct current (DC) output to the inverter 304. The inverter 304 converts the received DC current to alternating current (AC) for output to the grid or to be used within the building. Inverters are well known in the art and are accordingly not described in detail here.

[0022] Conventional solar panels typically operate at less than 100 volts and most operate at 30 to 40 volts. By contrast, typical inverters operate at significantly higher voltages, for example with a maximum of 600 volts and peak efficiency at about 470 volts. These inverters generally do not operate when the input voltage is below a threshold operating voltage. [0023] In conventional arrangements, the voltage mismatch between panels and inverters is addressed by connecting multiple panels in series, so that the voltages across each panel are additive. This series connection of a grouping of solar panels is commonly referred to as a "string". Figure 4A illustrates a representative circuit 400 including a string 402 of solar panels. As shown in Figure 4A, the string 402 consists of a group of solar panels 404a-404n connected in series where the total number "n" of panels in a string is selected by the designer and may vary from one installation to another. The output of the final solar panel in the string, solar panel 404n, is connected to the input of the inverter 304 to provide current generated by the panels 404a-404n. The inverter 304 converts the DC current from the panels 404a-404n to AC current as described above. The string of solar panels is configured so that the total voltage across the entire string is within the specified operating range of the inverter 304.

[0024] Although the string 402 of Figure 4A includes four solar panels, the actual number of panels in a string will vary depending on the operating voltages of the solar panels and the input voltage characteristics of the inverter 304. Furthermore, because the panels 402a-402n are connected in series, the same amount of current must flow through each panel. That is, the current in the entire string 402 is limited to the smallest current that can be produced by an individual solar panel 404a-404n.

[0025] Figure 4B illustrates a representative circuit 450 for use in a commercial deployment using solar panels connected in series. The circuit 450 includes first and second strings 452, 456, each of which includes multiple solar panels connected in series. In particular, the first string 452 includes solar panels 454a-454n. The second string 456 includes solar panels 458a-458n. Each of these strings is connected in parallel to the inverter 304. As with the circuit 400 shown in Figure 4A, the number and type of panels in the strings 452, 456 are selected to produce a total voltage suitable for use with the inverter 304. As discussed above, each string generates current based on the amount of incident light it receives and is limited by the lowest current generated by any panel in the string. Designers increase the total power generated by the circuit 450 by adding additional strings. The currents from each string are added together at the inverter 304.

[0026] The series-connected configuration has a number of limitations. In particular, each of the strings connected to the inverter 304 must operate at the same string output voltage, because the inverter 304 must itself be operating at a single voltage for converting the input DC current into AC current. This characteristic imposes a significant constraint on system design. For example, each string in an array constructed according to this configuration must produce exactly or nearly exactly the same voltage. Similarly, each string must have the same number of panels to ensure that each string produces the same output voltage to the inverter 304. These design constraints can result in significant efficiency losses when the solar array is deployed in practical installations. For example, an optimal solar deployment on a building generally uses all available surface area on the roof to carry solar panels. However, the foregoing design limitations mean that the deployed system might not be able to use all the available area because strings of equal length cannot easily cover an irregularly shaped roof.

[0027] The series configuration of solar panels produces additional problems during operation. For example, if any connection in a series string stops working during operation, the entire string will stop working, because it breaks the series connection. This is generally similar to the effect commonly seen with series-connected strings of Christmas tree lights - when a single light bulb in a string of such Christmas lights burns out, the entire string is rendered unusable. Finding the correct connection to repair is similar to finding the correct light bulb to replace; that is, a technician must examine each panel to verify whether it is working or not. The expense of repairing or replacing the solar panel, including lost revenue is, of course, significantly greater than that associated with a Christmas tree light bulb.

[0028] An additional problem occurs when some of the panels in a string are shaded, e.g., blocked by soiling, nearby building structures, and/or other obstructions. As discussed above, the current in an individual string is limited by the lowest current produced by any panel in the string. When a solar panel is shaded, its output current drops. If the modules do not have bypass diodes, there is a resulting drop in current for every panel in the string and a corresponding reduction in the power produced by the string. This occurs even when only one of the panels is shaded.

[0029] If the shaded panel has bypass diodes, the module can pass sufficient current to enable operation of the remaining panels in the string. However, this comes at the sacrifice of some of the string voltage. If the overall voltage produced by a string falls below a threshold level required by the inverter 304, the power produced by the entire string is lost. Further, if the string is connected in parallel to other strings, the lower output voltage of the string with shading may not match the voltage of the other strings, leading to non-optimal power generation in one or more strings..

[0030] Similarly, these characteristics of series-connected solar panels restrict the types of replacement panels that can be used when swapping out panels. Because each string is designed to produce a specified output voltage, each replacement panel must operate at the same voltage as the panel it is replacing. Similarly, because the current in a string is limited to the lowest current produced by any of its panels, substituting a higher-power panel for a lower-power panel will have no effect on the output current for the string as a whole. As a result, the building owner loses the benefit of technology improvements that boost the power of the replacement panel when compared with the original panel. Finally, a designer must take care during deployment to ensure that every panel will have approximately equal characteristics and, thus, must make sure that no panel in an array loses efficiency or is partially blocked from light due to surrounding structures (including trees that grow over time) and/or other design factors.

[0031] Figure 7A shows a power/voltage curve 702 for a single solar panel operating at maximum efficiency. As shown in Figure 7A, the power curve 702 slopes upward until it reaches the maximum power voltage VMP at which the solar panel produces maximum power (the area under the curve). At voltages beyond VMP, the power produced by the solar panel falls rapidly. The power is zero at the open circuit voltage, Voc- In general, systems discussed herein are designed to have a maximum power point tracker (e.g., via internally programmed logic) to find and operate at the voltage VMP in order to produce the maximum possible power for the string.

[0032] However, the characteristics of the curve may change during operation when multiple panels are interconnected. Figure 7B illustrates a power/voltage curve 710 where an array of solar panels is operating at less than full efficiency. This may occur, for example, when one or more of the solar panels in the string are shaded or otherwise receiving less illumination. In this case, the current/voltage curve 710 has two distinct local maxima at points 712 and 714. In this situation, the maximum power point tracker may select the incorrect maximum and, as a result, operate at a lower power than desired. The current/voltage curve shown in Figure 7C relates to configurations that will be discussed in detail below.

[0033] Figure 5A illustrates a representative conventional circuit 500 in which individual solar panels are connected to the inverter in parallel using DC-to-DC converters. The circuit 500 includes solar panels 502, 504, 506, and 508. Because the solar panels 502, 504, 506, and 508 are connected in parallel, the voltages for each panel are equal, rather than additive (as in the series configuration). As discussed previously, conventional panels generally produce an output voltage of 30-50 V, which is well below the required operating voltage for the inverter. To solve this problem, the circuit 500 includes DC-to-DC converters 510, 512, 514, and 516, each connected to one of the solar panels 502, 504, 506, and 508. Each of the DC-to-DC converters 510, 512, 514, and 516 is designed to raise the output voltage from the 30-50 V produced by the solar panel to the higher input voltage required by the inverter 304 (e.g., 470 V). In one embodiment, the DC-to-DC converters 510, 512, 514, and 516 are step-up transformers

[0034] As shown in Figure 5A, the DC-to-DC converters 510, 512, 514, and 516 are connected in parallel to the inverter 304. This is shown in more detail in Figure 5B, which illustrates the voltages and currents associated with a portion of the circuit 500 of Figure 5A. As shown in Figure 5B, each of the solar panels 506 and 508 has a voltage of approximately 45 V between its two terminals. This voltage is provided to the corresponding DC-to-DC converters 514, 516. The DC-to-DC converters 514, 516 then produce an output voltage based on the requirements of the inverter 304. In the example shown in Figure 5B, this output voltage is approximately 470 volts.

[0035] In addition, each of the DC-to-DC converters 514, 516 produces current based on the current produced by the corresponding panel 506, 508. In particular, the first DC-to-DC converter 514 produces output current la, and the second DC-to-DC converter 516 produces output current lb. These currents, along with the current produced by the other solar panels connected to this set of lines, add to produce the total output current lc, which is received by the inverter 304.

[0036] One drawback with the configuration disclosed in Figures 5A and 5B is that the DC-to-DC converters 510-516 are expensive relative to the total cost of the panel. This expense arises because the converters must be designed to handle variations in input voltage resulting from changing light conditions on the corresponding panel. The DC-to-DC converters must take the variable input and convert it into the same output voltage regardless of input conditions. In addition, simply adding the converter component to the system reduces the overall reliability of the system, because it provides an additional part that can fail during operation. Still further, adding the converters requires additional wiring to connect the various components in the system. This can also add significantly to the overall cost of the system. The DC-to-DC converters also need to have a reliable operational lifetime greater than that of the solar array (i.e. >25 years); otherwise, the converters will need to be replaced or will cause the array to lose efficiency during its operational lifetime. This requires additional monitoring and maintenance costs. An additional disadvantage of using DC- to-DC converters is the inherent efficiency losses. Altering a module's output voltage to match an inverter's input voltage costs some energy during regular operation. A module with a sufficiently high output voltage can avoid these losses in efficiency..

[0037] Figure 6 illustrates a representative circuit 600 in which solar panels are connected in parallel without the use of DC-to-DC converters. The circuit 600 includes solar panels 604, 606, and 608. The circuit 600 also includes an inverter 602 for converting DC current from the solar panels 604, 606, and 608 to AC current. Each of the solar panels 604, 606, and 608 is connected in parallel to the inverter 602. The solar panels 604, 606, and 608 are configured so that each produces a voltage V|. In particular embodiments of the circuit 600, each panel is designed to operate within the acceptable voltage range for the inverter and at at least as high a voltage as the AC output voltage of the inverter 602. As discussed above, this voltage may be on the order of 400 to 500 volts, but can be higher depending on the selected inverter. Constructing the circuit 600 without DC-to-DC converters requires that solar panels 604, 606, and 608 be able to operate higher voltages than are available with conventional solar panels.

[0038] As noted above, in particular embodiments, the circuit 600 is designed so that the input voltage to the inverter 602 is at least as high as the inverter's AC output voltage. This allows the panels 604, 606, and 608 to be connected in parallel to the inverter without requiring any type of voltage up-conversion, including voltage converters within the inverter. For example, the output voltage of an inverter intended for use in the United States would generally be 120 V, while the output voltage of an inverter intended for use in France or the United Kingdom would generally be 230 V. Thus, in a circuit according to these embodiments, the panels 604, 606, and 608 would be designed to operate at a higher voltage, such as 175 V, 200 V, 300 V, 400 V, 500 V, 600 V, 1000 V, or 1500 V, depending on the selected embodiment. In at least some embodiments, the particular value that is selected for the inverter input voltage will generally be as high as allowed by government regulations in order to achieve maximum efficiency for the DC to AC conversion.

[0039] Higher photovoltaic system DC output voltage provides an additional advantage in that the current of the photovoltaic array is proportionally reduced for a given system power. This reduces the resistance losses in the wiring as the power loss is proportional to l2R where I is the system current and R is the wiring resistance. Consequently, higher voltage systems require less expensive wiring than low voltage systems. For example, a 100V system would require 4 times as much copper as a 200V system for equivalent power losses which increases the cost of wire in the system.

[0040] The circuit 600 addresses the problems discussed above with the parallel configuration of Figures 5A and 5B. In particular, it reduces or eliminates costs and reliability risks that arise from using the DC-to-DC converters. The circuit 600 also eliminates the additional wiring and connections required to connect the panels through the step up transformer to the inverter. In some embodiments, the panels 604, 606, and 608 are conventionally sized panels, such as the sizes discussed above (i.e., 1-6 m2).

[0041] Figures 8A and 8B illustrate a design for solar panels capable of operating at the higher voltage required. Similar designs are also described in U.S. Patent Application No. 1 1/883,083, U.S. Patent Application No. 10/432,936, U.S. Patent Application No. 10/562,316, U.S. Patent Application No. 11/660,006, and "65-micron Thin Monocrystalline Silicon Solar Cell Technology Allowing 12-fold Reduction in Silicon Use" by M.J. Stocks et al., which are included in Appendix A.

[0042] Figure 8A illustrates an example of a solar cell bank 800 suitable for implementing the circuit of Figure 6. The bank 800 consists of a group of small solar cells 802i-802n (e.g., strip-shaped cells), that are connected in series. In one embodiment, the solar cells 802 802n are each 55 mm by 2 mm and are connected in groups of 144, such that the total length of the bank (including connections between cells) is approximately 300 mm. In another embodiment, the solar cells 802r802n are each 55 mm by 1.5 mm and are spaced apart by a 2 mm gap. Each solar cell 802r 802n operates at a pre-determined voltage; therefore, the operating voltage for the bank 800 can be set by selecting the number of individual cells to connect in series.

[0043] Figure 8B illustrates an example of a solar panel 810 suitable for implementing the circuit of Figure 6. The solar panel 810 consists of multiple rows 812, 814, 816, 818, and 820. Each row contains multiple banks 822, 824, and 826, which may be implemented using the design shown in Figure 8A. The banks (e.g., banks 822, 824, and 826) are connected in parallel within each row, which increases the current generated while keeping the voltage constant. The rows 812, 814, 816, 818, and 820 are then connected in series, which increases the total voltage of the panel. In some embodiments, individual banks operate at 95 V and are arranged into 5 separate rows of 14 banks, resulting in a total panel voltage of 475 V. However, one skilled in the art will appreciate that panels with different operating voltages can be made by changing the number of rows in the panel or by changing the design of the individual banks to increase or decrease the number of cells in a bank.

[0044] The foregoing approach of connecting the solar panels in parallel has significant technical advantages over conventional systems. For example, systems constructed using this approach are much more tolerant of shading and/or other conditions at which part of the solar array is subject to reduced light conditions. As discussed above in association with series-connected solar panels, shading of individual panels reduces the current output from the affected panels. However, in the parallel-connected configuration, the current through a particular solar panel does not limit the current that can flow through any other solar panel. Thus, shading merely reduces the affected panel's contribution to the total current provided to the inverter. Un-shaded panels continue producing current regardless of the reduced contribution from the shaded panel. Because current varies more significantly than voltage due to changes in illumination from differences in orientation and/or shading, systems connected in parallel can be more freely designed than systems using series connections. [0045] This behavior is shown in the voltage to current curves of Figure 7C. Figure 7C illustrates a comparison of the current/voltage curves for a string of panels and the current to voltage curve of a collection of parallel-connected panels. The power/voltage curve for the series-connected string is shown by the combination of curves 720, 722, 724, 726, 728. Each of these curves represents the curve for an individual solar panel in the string. During operation, the string as a whole exhibits the behavior shown by the combination of these curves. When the current produced by a panel drops, for example due to shading or different orientation, there is a corresponding dip in the combined current/voltage current curve. This produces the power to voltage curve shown in Figure 7B.

[0046] In contrast, curve 730 is the current/voltage curve for a group of high voltage solar panels connected in parallel. If the current for one panel drops, the curve as a whole will drop due to the reduction in current, but will generally retain the same overall shape as shown in Figure 7A. As a result, the parallel-connected panels avoid the problem of multiple local maxima discussed above.

[0047] Another advantage of the parallel configuration is that a designer has significantly more flexibility in selecting and configuring a solar array. This flexibility includes the ability to use solar panels of different sizes in a single string. For example, a representative system can include a 200 W panel and a 100 W panel in parallel, as long as the output voltages of the two panels are at least approximately the same. This might occur when a manufacturer sells solar panels that have different sized cells (e.g., 125 mm and 156 mm). In a series connected string, the lower current of the panels with 125 mm cells would affect the performance of panels with 156mm cells. In an all- parallel configuration, these modules can operate in the same system without compromising the performance of the other.

[0048] As a corollary to this, the parallel-connected configuration is better able to take advantage of improvements in panel technology. For example, in the series- connected configuration, if a panel fails it must be replaced with a substantially identical panel operating at the same power output. This is the case even if technology has improved so that the same-sized panel is capable of producing a higher output power. By contrast, in the parallel configuration, if one panel fails it can be replaced with a new, improved (e.g., higher power) panel without any changes to the rest of the system, and can produce the additional power the new panel is designed to produce. For example, consider a system consisting entirely of 180 W panels arranged in series strings. At the time one of the panels fails, 195 W panels that otherwise have identical physical characteristics have become available due to improvements in cell current. If a panel differs significantly in current (e.g. , by more than 10%) from the other panels in the string, the string may perform well below the optimum performance of its individual panels. Because panels in a string in the series-connected configuration are limited by the lowest current that can be passed through any of the panels, the building owner would see no improvements by adding in the new 195 W panel. In contrast, if a 180 W panel in the parallel configuration fails, the initial 180 W panel can be replaced with a 195 W panel and the system overall will contribute the extra current generated by the 195 W panel over the 180 W panel, because the currents from each panel are additive, as long as all panels operate at approximately the same voltage.

[0049] Similarly, the parallel-connected configuration allows additional flexibility to expand an existing system after it has been deployed. In the series-connected configuration, a designer must spend significant time and effort to ensure that strings of panels are properly selected and properly arranged to work together. Strings must be of identical length (e.g., number of panels) and cannot easily be extended. By contrast, a parallel-connected configuration allows the building owner/operator to easily expand an existing system by simply adding additional panels in parallel, as long as the inverter for the system has the capacity to handle the increased current.

[0050] As discussed above, the design for these solar arrays becomes significantly simpler by virtue of using the parallel configuration. Similarly, maintenance becomes simpler because the operator no longer has to manage each string as a whole unit. Rather, the operator can simply test individual panels to ensure continued functionality. When a panel fails, it alone can be replaced without having any effect on the other panels in the system. Similarly, the parallel-connected configuration no longer imposes limits on where panels can be placed. Because an underperforming panel no longer drags down the performance of the whole string, a building owner can place panels over the entire roof of the building, regardless of differences in incident light to particular areas of the roof. For example, consider a system installed on a building in the northern hemisphere with roofs facing southeast and southwest. Modules on each roof orientation receive different illumination in the morning and afternoon. Currently, each string has to be positioned on a single roof to ensure that the modules receive similar illumination to avoid lower current modules (e.g. southwest in the morning) restricting the performance of the higher current modules (e.g. southeast in the morning). This requires a designer to restrict panels from each string to only a single roof orientation. In contrast, an all-parallel connection allows modules to be positioned across multiple roof sections while maintaining good performance.

[0051] For example, Figure 9 illustrates a representative embodiment of the system deployed on a house with an irregularly shaped roof. As shown in Figure 9, the solar cells have been incorporated into residential rooftiles. This was difficult with conventional technologies because these tiles need to be relatively small to enable efficient installation and meet aesthetic requirements. Arrays in accordance with conventional techniques typically require a large number of rooftiles connected in series to build up to the inverter input voltage range. By using the system with tiles measuring 909x443 mm and having an open circuit voltage of ~270V, each tile can be connected in parallel to an ideal inverter input. This has the advantage of maximizing the number of tiles that can be fit to the roof because the system can be built in units of 1 tile rather than, for example, strings of 50 tiles in series. Furthermore, the array can have the tiles aligned on different surfaces of the roof without string losses impacting performance. In addition, system of Figure 9 can be deployed rapidly because there is no need to design complex strings to meet voltage requirements, which lowers installation costs.

[0052] Any or all of the foregoing advantages can be realized at a lower initial cost and a lower overall lifetime cost by eliminating the DC-to-DC converters, as described above. Accordingly, embodiments of the present technology that eliminate or at least reduce the number of DC-to-DC converters further enhance the efficiency and utility of solar panels. In addition, embodiments of the technology that include higher voltage inverters realize increased power transmission efficiency when compared with inverters that operate at low input voltages.

[0053] From the foregoing, it will be appreciated that specific embodiments of the disclosure have been described herein for purposes of illustration, but that various modifications may be made without deviating from the disclosure. For example, the parallel arrangement discussed above may also be formed using any solar panel technology capable of operating at a sufficient voltage and is not limited to the solar panel technology discussed above. Furthermore, the panels and the inverter may be designed to operate in different voltage ranges than those discussed above. In some embodiments, functionality described above with reference to a single component may be split up over multiple components. For example, a solar array as discussed above may use multiple inverters to achieve the effect of a single inverter as described above. The array may use any type of inverter and is not limited to any specific inverter design.

[0054] Certain aspects of the disclosure described in the context of particular embodiments may be combined or eliminated in other embodiments. For example, solar panels may be deployed on any type of structure and are not limited to deployment on buildings. Panels may also be deployed as free-standing components (e.g., in a desert or other unpopulated area) without connection to any structure. Further, while advantages associated with certain embodiments have been described in the context of those embodiments, other embodiments may also exhibit such advantages, and not all embodiments need necessarily exhibit such advantages to fall within the scope of the present disclosure. Accordingly, the present disclosure and associated technology can encompass other embodiments not expressly shown or described herein.

Claims

1. A solar energy system, comprising:
an inverter having an input terminal, an output terminal, and circuitry coupled between the input terminal and the output terminal that directs an output alternating current (AC) signal to the output terminal based on an input direct current (DC) signal received from the input terminal, wherein an output voltage produced by the circuitry is at or below a corresponding input voltage provided to the circuitry; and
a plurality of solar panels electrically coupled to the inverter, wherein the plurality of solar panels are connected in parallel and wherein individual solar panels of the plurality of solar panels are not coupled to an intermediate converter between the individual solar panels and the inverter.
2. The solar energy system of claim 1 , wherein the inverter is configured to operate over a voltage range of from about 175 volts to about 1500 volts.
3. The solar energy system of claim 1 , wherein individual solar panels of the plurality of solar panels have a size of from about 1 square meter to about 6 square meters.
4. The solar energy system of claim 1 , wherein individual solar panels of the plurality of solar panels have different power generation or current generation characteristics.
5. A method for generating solar energy, comprising:
electrically coupling a plurality of solar panels in parallel without coupling individual solar panels of the plurality of solar panels to an intermediate converter; and
electrically coupling the plurality of solar panels to an inverter configured such that an input voltage provided to the inverter is at least as high as an output voltage produced by the inverter.
6. The method of claim 5, wherein the inverter is configured to operate over a voltage range of from about 175 volts to about 1500 volts.
7. The method of claim 5, wherein individual solar panels of the plurality of solar panels have a size of from about 1 square meter to about 6 square meters.
8. The method of claim 5, wherein individual solar panels of the plurality of solar panels have different power generation or current generation characteristics.
9. A solar energy system, comprising:
a building;
a first plurality of solar panels electrically coupled in parallel, the first plurality of solar panels comprising a first string, wherein individual solar panels of the first plurality of solar panels are not connected to an intermediate converter;
a second plurality of solar panels electrically coupled in parallel, the second plurality of solar panels comprising a second string, wherein individual solar panels of the second plurality of solar panels are not connected to an intermediate converter; and
an inverter, wherein the inverter is electrically coupled to: (a) receive input currents from the first string and the second string at input voltages and (b) output electrical current at an output voltage to a power system associated with the building, the output voltage being equal to or less than the input voltage.
10. The solar energy system of claim 9, wherein the inverter is configured to operate over a voltage range of from about 175 volts to about 1500 volts.
11. The solar energy system of claim 9, wherein individual solar panels of the first plurality of solar panels and the second plurality of solar panels have a size of from about 1 square meter to about 6 square meters.
12. The solar energy system of claim 9, wherein individual solar panels of the first plurality of solar panels have different power generation or current generation characteristics.
13. The solar energy system of claim 9, wherein the first string has a different number of solar panels than the second string.
PCT/US2012/041408 2011-06-07 2012-06-07 Solar panel systems having solar panels arranged in parallel, and associated methods WO2012170726A2 (en)

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