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Although a PV cell is the basic device that converts sunlight into electricity, it’s not practically useful in this form. Individual cells produce very small amounts of power, so many must be connected together to create appreciable amounts of power. Also, PV cells are delicate and degrade rapidly if exposed to dirt or moisture. Individual cells must be protected from the environment, electrically insulated to protect installers and operators against electrical shock, and packaged in a manner that allows them to be mechanically installed to a support structure and connected to the rest of the electrical system. A module is a PV device consisting of a number of individual cells connected electrically, laminated, encapsulated, and packaged into a frame. The PV cells are laminated within a polymer (plastic) substrate to hold them in place and to protect the electrical connections between cells. The cell laminates are then encapsulated (sealed) between a rigid backing material and a glass cover. Some thin-film laminates use flexible materials such as aluminum or stainless steel substrate and polymer encapsulation instead of a glass cover. Module Construction POLYMER SHEETS BACKING MATERIAL --21. Modules are constructed from PV cells that are encapsulated by several layers of protective materials. An array is a complete PV power- generating unit consisting of a number of individual electrically and mechanically integrated modules with structural supports, trackers, or other components. The term "panel" is also used in relation to modules and arrays. Sometimes panel is used as an alternate term for a module. More commonly, the term panel refers to an assembly of two or more modules that are mechanically and electrically integrated into a unit for ease of installation in the field. FRAME--GLASS COVER --22. An array is a group of PV modules integrated as a single power-generating unit. --23. Several modules may be connected together to form a panel, which is installed as a preassembled unit. Module Assembly Once crystalline silicon cells are fabricated, tested, and sorted, they are ready for assembly into complete modules. First, the cells are laid out in the specified physical and electrical configuration and soldered together with tin- or silver-coated copper strips. The strips are flexible enough to allow slight movement due to thermal expansion and minor stresses. The conductors for circuit connections are routed to one area on the back of the cell circuit where connections can be made to other modules or system components with external conductors. Next, the completed cell circuit is placed between thin, clear polymer sheets, with a sheet of tempered glass on top and the back surface material beneath, and these layers are laminated in a press at high temperatures. The intermodule connectors are attached to the back of the module, and the entire laminate is framed with aluminum channel. The frame provides mechanical support, structural mounting features, and electrical grounding for the modules. A final visual inspection and electrical test are performed on all modules before packaging for shipment. All modules include some means for making intermodule electrical connections, through the use of either pre-wired connectors or a junction box. The junction box may also include bypass diodes and the ability to change the series or parallel configuration of the module cells with certain jumper arrangements. For example, a module might be changed from 36 series-connected cells to two parallel strings of 18 series-connected cells. This doubles the current and halves the voltage, but the power output remains the same. Electrical Connections Junction Box: A junction box on the back of a module provides a protected location for electrical connections and bypass diodes. PV devices are generally first connected in series to achieve a desired voltage, forming a string. These series strings are then connected in parallel to build current and power. Cells are connected to form modules and modules are connected to form arrays. The same principles are used to build successively larger systems. Series Connections. Individual cells are connected in series by soldering thin metal strips from the top surface (negative terminal) of one cell to the back surface (positive terminal) of the next. Modules are connected in series with other modules by connecting conductors between the negative terminal of one module to the positive terminal of another module. When individual devices are electrically connected in series, the positive connection of the whole circuit is made at the device on one end of the string and the negative connection is made at the device on the opposite end. Only PV devices having the same current output should be connected in series. When similar devices are connected in series, the voltage output of the entire string is the sum of the voltages of the individual devices, while the current output for the entire string remains the same as for a single device. Correspondingly, the I-V curve for a string of similar PV devices is the sum of the I-V curves of the individual devices. When PV devices with dissimilar current outputs are connected in series, the devices with lower current output absorb current from the devices with higher current output. This results in a loss of power, and potential overheating and damage to the lower-current output devices. The current output for a circuit of dissimilar devices in series is limited to the current of the lowest- current output device in the entire string. However, PV devices with different voltage outputs can be connected in series without loss of power as long as each device has the same current output. As with similar devices, the current output remains the same and the voltage output of the circuit equals the sum of the voltages of the individual devices. --25. PV cells or modules are connected in series strings to build voltage. Series Connections NEGATIVE SURFACE -\ INDIVIDUAL CELLS LMETAL STRIPS CELLS POSITIVE SURFACE (UNDERNEATH) MODULES --26. The overall I-V characteristics of a series string are dependent on the similarity of the current outputs of the individual PV devices. PV Devices in Series: PV DEVICE 1; PV DEVICES 1 2 IN SERIES VOLTAGE (V) SIMILAR PV DEVICES -- VOLTAGE (V) -- DISSIMILAR PV DEVICES Connecting devices with different voltages may be done when the load requires a nonstandard voltage. For example, a circuit with signal lamps designed to operate from a nominal 30 V battery may include two standard 36-cell (12 V) modules connected in series with a third module having only 18 cells (6 V), as long as they have similar current outputs. The maximum number of modules that may be connected in a series string is limited by the maximum system voltage rating of the modules and other components. Most modules are rated for a maximum system voltage of 600 V. Parallel Connections. Parallel connections are not generally used for individual PV devices, especially cells, but for series strings of cells and modules. Parallel connections involve connecting the positive terminals of each string together and all the negative terminals together at common terminals or busbars. When similar devices are connected in parallel. the overall circuit current is the sum of the currents of individual devices or strings. The overall voltage is the same as the average voltage of all the devices connected in parallel. 8. As opposed to series connections, PV devices with dissimilar current output may be connected in parallel. This commonly occurs when an existing array is expanded. New module strings are connected in parallel with existing strings having similar voltage but different current output. --28. The overall l-V curve of PV devices in parallel depends on the similarity of the current outputs of the individual devices. PV Devices in Parallel; TWO PV DEVICES OR ( STRINGS OF DEVICES IN PARALLEL PV DEVICE OR STRING OF DEVICES VOLTAGE (V) SIMILAR PV DEVICES --27. Strings of PV cells or modules are connected in parallel to build current. DEVICE 1; PV DEVICES 1 and 2 IN PARALLEL PV DEVICE 2 VOLTAGE (V) DISSIMILAR PV DEVICES Parallel Connections: COMMON BUSBAR; CONNECTION __ COMMON BUSBAR CONNECTION; SERIES STRINGS; CELLS Module Character PV modules are available in a range of sizes and designed for a variety of applications. 9. Smaller modules of less than 50 W are typically used individually for low-power battery charging applications, such as navigational aids, accent lighting, motorist- aid call boxes, and small circulation pumps. Smaller modules are often more expensive per unit watt output than larger ones, and are not typically used to build large arrays due to the large number of intermodule connections and mechanical attachments that would be required. Larger modules with peak output of 50 W and greater are often referred to as power modules, and are connected in groups to configure arrays with higher voltage and power output. A typical 120 W crystalline silicon module that is 12% efficient has a surface area of about 1 m and weighs approximately 20 lbs to 30 lbs. Production costs and systems integration time are significantly less with larger modules, so the typical power module size is steadily increasing. Modules of about 200W peak power are now common, with some modules at more than 300W and 100 lbs each. The factors currently limiting module size include the module's packaging and weight, structural integrity and resistance to high wind loads, and the ability to easily ship and handle the modules in the field. Flat-plate modules are used in the majority of residential and commercial applications. Flat-plate modules are generally rectangular in shape and about 1" to 2" thick (including the frame and laminate). Some manufacturers offer other shapes, such as triangles, to better utilize space on hipped or angled roof surfaces and for aesthetic appeal. Bypass Diodes Reverse bias is the condition of a PV device operating at negative (reverse) voltage. A reverse- biased device will continue to pass current, but since the voltage is negative, the device will consume power instead of producing power. Modules -- Modules are available in several sizes and shapes, including squares, rectangles, triangles, flexible units, and shingles. Made by: Solar World Industries America; Sharp Electronics Corp Robots arrange cells in various configurations and build complete modules with little or no intervention from human workers. Reverse-bias conditions can occur when a PV cell is open-circuited or shaded, or when other conditions result in unequal current output from devices in a series string. Bypass diodes, sometimes called shunt diodes, are used in parallel with groups of cells or modules to prevent a reverse-bias condition. A bypass diode is a diode used to pass cur rent around, rather than through, a group of PV cells. The current is allowed to pass around groups of cells that are shaded or develop an open-circuit or other high resistance condition, preventing an interruption of the continuity of the string. This allows the functional cells or modules in the string to continue delivering power. The consequence, however, is that the string will operate at a lower voltage. 0. If a series string of cells is thought of as a highway for current, bypass diodes can be considered a detour route. Under normal conditions, highway traffic flows smoothly and the detour is not needed. However, if an accident slows or stops highway traffic, traffic can continue flowing by taking the detour route. In a similar way, bypass diodes allow current to flow around obstructed paths. Without a bypass diode, reverse voltage may decrease until the breakdown voltage is reached. Breakdown voltage is the minimum reverse-bias voltage that results in a rapid increase in current through an electronic device. The high currents can result in potentially damaging levels of power dissipation within the module, and under extreme cases, the resulting high temperatures can melt the module laminate and pose a fire hazard. A bypass diode allows a reverse bias of only 0.7 V, which limits the reverse voltage to a level where only a small amount of power may be dissipated. Bypass diodes are either embedded in the module laminate, and therefore are non-serviceable, or are located in the module junction box, where they can be inspected and replaced as required. Bypass diodes are typically installed around groups of 12 to 18 series-connected cells, with most modules of 36 cells or more incorporating two or more bypass diodes. Bypass diodes must be able to handle the maximum operating voltage for the number of cells or modules bypassed, and must be rated in excess of the maximum circuit current. === -- Bypass diodes allow current to flow around devices that develop an open-circuit or high-resistance condition. Bypass Diodes --- CURRENT FLOW , CELL ACTS/ AS RESISTANCE SHADED CELL OPERATION === --A bypass diode limits reverse current through PV devices, preventing excessive power loss and overheating. Breakdown Voltage: VOLTAGE (V); PV DEVICE IN BIAS REVERSE BIAS; WITHOUT WITH BYPASS; BYPASS DIODE DEVICE BREAKDOWN; REGION OPERATING; BREAKDOWN VOLTAGE Module Standards A number of standards have been developed to address the safety, reliability, and performance of modules, arrays, and other equipment, as well as complete PV systems. Safety. PV modules are classified as electrical equipment, so they must conform to accepted product safety standards, and must be listed or approved by an OSHA Nationally Recognized Testing Laboratory (NTRL). In the United States, Underwriters Laboratories, Inc. (UL) tests and certifies modules for electrical safety according to UL 1703 Safely Standard for Flat-Plate Photovoltaic Modules and Panels. The requirements cover flat-plate modules intended for roof-mounted, ground-mounted, or building-integrated systems with a maximum system voltage of 1000 V or less. The standard also covers components intended to provide electrical system connections or structural mounting for modules. Installation requirements for modules and arrays is covered primarily by the NEC. In addition, all PV installers should be familiar with construction standards established by OSHA, which are covered in Chapter 29 of the U.S. Code of Federal Regulations, Part 1926, Safely and Health Regulations for Construction. Reliability. The reliability of modules is a critical factor affecting the performance, life time, and costs for PV systems. To promote a high standard for quality, modules produced by leading manufacturers are often tested according to International Electrotechnical Commission (IEC) standards, including the standards IEC 61215 Crystalline Silicon Terrestrial Photovoltaic (PV) Modules -Design Qualification and Type Approval and IEC 61646 Thin-Film Terrestrial Photovoltaic (PV) Modules -Design Qualification and Type Approval. These standards are commonly used as guidelines for module procurement. Design qualification tests include thermal cycling, humidity and freezing, impact and shock, immersion, cyclic pressure, twisting, vibration and other mechanical tests, and excessive and reverse current electrical tests. These tests are similar to, but more extreme than, the product listing tests. Design qualification has important implications for product warranties offered by manufacturers. As a result, most major module manufacturers offer warranties of 20 years or more, guaranteeing module peak power output of at least 80% of initial nameplate ratings. This equates to a degradation rate of no more than 1% per year. These exceptionally long warranty periods are not typical among other electrical equipment and appliance warranties but are offered to assure buyers of the long- term performance of PV systems. Performance Ratings Modules are rated for electrical performance as part of product testing. Financial incentives for PV installations are in many cases based on an array's electrical performance rating. Module manufacturers develop performance ratings for their products based on the I-V curves of sample modules under simulated sunlight. Since modules are most often marketed based on their peak power rating, accurate representation of this information is critical to the consumer. ASTM International and the IEC produce standards used by manufacturers and independent laboratories in testing and rating the performance of modules. These standards include test methods, test equipment, calibration, specifications, terminology, and translation of the results. Standard performance ratings for modules are referred to as nameplate ratings, and they are required by the NEC to be clearly labeled on every module. At a minimum, each module must be marked with polarity identification, maximum overcurrent device rating, and ratings at specified conditions for key I-V curve parameters, including open-circuit voltage, maximum permissible system voltage, maxi mum power current, short-circuit current, and maximum power. Additional information may include applicable certifications such as design qualification, fire class rating, ratings at other temperatures, and allowable wire sizes. In addition, all modules must have an installation guide that covers additional requirements for wiring, mounting, and other installation and operation considerations. 2. Manufacturers typically guarantee the peak power ratings for a given product model to within ±10% of the nameplate rating, though actual performance is typically on the lower side of the rating. Module performance on the higher side of the rating is uncommon, but has important implications on module and system safety and for the adequate sizing of conductors and overcurrent protection for array source circuits. Measuring performance in the field can be complicated and expensive and requires special equipment, so performance verification is difficult. However, verification is usually not necessary because most modules perform to within an acceptable level of their nameplate ratings. Module Labels. Module labels must include performance ratings for the module and may include other information used to design a PV system. Test Conditions --33. Various test conditions can be used to evaluate module performance and may produce different results. STANDARD OPERATING CONDITIONS –PV USA TEST CONDITIONS Test Conditions Due to the dynamic nature of module performance and constantly changing operating conditions, the performance specifications of a module or array have meaning only when the rating conditions are given. These reference conditions are the basis for module performance ratings. Output at other conditions can be determined by translating the data using formulas for temperature and irradiance, the two principal factors affecting PV device performance. Standard Test Conditions (STC). Standard test conditions (STC) is the most common and internationally accepted set of reference conditions, and rates module performance at a solar irradiance of 1000 W/m spectral conditions of AM 1.5, and a cell temperature of 25°C (77°F). SIC is the basis for module electrical ratings required on module labels by the NEC. However, with the exception of clear days in extremely cold climates, modules and arrays seldom operate at STC in the field. Cell temperatures are often 15°C to 30°C (27°F to 54°F) above ambient temperature. Furthermore, peak irradiance levels are only experienced within an hour or so of solar noon on clear days, so modules usually operate under irradiance levels of less than 1000 W/m^2. For these reasons, other rating conditions are sometimes used. Standard Operating Conditions (SOC). Standard operating conditions (SOC) is a set of reference conditions that rates module performance at a solar irradiance of 1000 W/m^2 spectral conditions of AM 1.5, and at nominal operating cell temperature. Nominal operating cell temperature (NOCT) is a reference temperature of an open-circuited module based on an irradiance level of 800 W/m^2 ambient temperature of 20°C (68°F), and wind speed of 1 m/s. NOCT is product-dependent because it largely depends on a module's construction and heat transfer characteristics. SOC uses more realistic temperature conditions than STC, and results in lower peak power and voltage ratings than at STC. Manufacturers sometimes list I-V parameters for SOC on module labels or specification sheets. Nominal Operating Conditions (NOC). Nominal operating conditions (NO C) is a set of reference conditions that rates module performance at a solar irradiance of 800 W/m spectral conditions of AM 1.5, and at nominal operating cell temperature. NOC indicates a more typical peak module performance be cause solar irradiance is closer to 800 W/m for most of the day. As with SOC, manufacturers may provide NOC ratings in addition to other module specifications. PV USA Test Conditions (PTC). PV USA test conditions (PTC) is a set of reference conditions that rates module performance at a solar irradiance of 1000 W/m ambient temperature of 20°C (68°F), and wind speed of 1 m/s. PTC are nearly identical to SOC. except that the resulting cell temperatures are higher. The SOC rating uses NOCT, which is based on 800 W/m irradiance, while the cell temperature for PTC is based on 1000 W/m irradiance. This higher cell temperature makes the PTC peak power ratings a little lower than ratings at SOC for a given module. Other rating conditions have also been developed in efforts to more realistically estimate actual module performance in the field. Some financial incentive programs may also have means to estimate the AC energy performance for complete PV systems, using specific performance ratings from a given array and inter active inverter, and factoring in the orientation of the array and expected solar energy received on that surface at a given location. Due to slight variations in performance between batches of PV cells, manufacturers may offer two or more modules that appear the same in terms of the number and physical size of individual cells used, but that have slightly different performance ratings. Module Selection A number of factors may be considered when selecting modules for an array. including price, availability, and warranty, as well as the physical and electrical characteristics. These factors present numerous options and tradeoffs for integrators, installers, and buyers of PV systems. Electrically, the voltage, current, and power output values are the most important considerations because they define the total number of modules needed to meet the desired energy production requirement. Fewer higher-voltage modules will be required in series, and fewer higher-current modules will be required in parallel, to achieve a desired array configuration. The provisions for electrical connections may also be considered. While the efficiency of modules does not necessarily affect module costs, it does affect the area required for a given power output desired, and consequently may affect balance of system costs, such as space or land area, as well as structural support requirements. On the physical side, among factors that may be considered for module selection are the overall weight, size, and dimensions of the module, the type of frame and laminate construction, the means for structural attachments, the ability to withstand high mechanical loads, and perhaps even the color and appearance. Larger modules generally require less array field assembly, but may require special handling for lifting and installation. Some types of modules, particularly those intended for building-integrated applications, may use unique means or materials for structural attachments. Building-integrated modules replace conventional building materials such as roofing, glazing, or awnings. Certain sizes and shapes of modules may also be chosen to best utilize the available space for mounting the array. Arrays The construction of arrays from modules is similar to the construction of modules from cells. Groups of modules are combined electrically and mechanically, typically first into strings, to achieve the desired array voltage. Strings of series-connected modules may be called panels or sub-arrays. Connecting modules into series strings before making parallel connections makes it easier to expand the array in the future, replace individual modules, and troubleshoot and diagnose module problems within the array. The U S Coast Guard has special design specifications for modules used in marine navigational aids These specifications and associated tests require more durable and weatherproof modules for use in harsh marine environments The modules or groups of modules are then integrated to form a complete array, using additional series or parallel connections. The result is a complete array that integrates all the modules into a single power-generating unit, with one positive terminal and one negative terminal for connection to other components. In stand-alone systems, the array must be sized to produce enough energy to meet a specific load during the period with the greatest load and lowest insolation, plus some excess energy to account for inefficiencies in battery charging, voltage drop, and other system losses. For interactive PV systems used to supplement normal electrical service, the array is designed to produce a desired amount of peak power or energy over a given period. More typically, the array size is dictated by available financing or the area available for the array, or because interconnection rules or financial incentives otherwise limit the size of the array. Building an Array INDIVIDUAL STRING MODULES; ARRAY--C BUS BAR--VOLTAGE (V) RESULTING I-V CURVE -- Modules are added in series to form strings or panels, which are then combined in parallel to form arrays. SUMMARY: • Photons striking a PV cell give electrons the energy to move freely, which induces the flow of electrical current. • Many materials can be made into PV cells, but crystalline silicon is currently the most common and economical material. • Silicon wafers can be made with mono-crystalline, polycrystalline, or ribbon silicon methods. • The I-V curve illustrates the basic electrical parameters and characteristics of PV devices. • The maximum power point is the operating point at which the PV device produces the most power and is the most efficient. • The inherent properties of the PV material and the resistances in the PV system affect the shape of the I-V curve. • Solar irradiance and cell temperature affect the magnitude and position of the I-V curve. • Any single I-V curve represents only one set of conditions for solar irradiance and cell temperature. • Cell temperature is influenced by ambient temperature, wind speed, solar irradiance, thermal characteristics of the device's packaging, and the way the cell or module is installed or mounted. • I-V curve parameters can be translated from reference irradiance and temperature conditions to other conditions through the use of equations. • PV cells are integrated electrically and mechanically to build modules. Modules are integrated electrically and mechanically to build arrays. • The electrical concepts used to build voltage and current through series and parallel connections are scalable from cells to arrays. • Bypass diodes protect PV devices from damage and excessive loss of power by directing current around shaded or damaged devices. • Standard test conditions are used with performance --s so that modules can be compared. • Various standard test conditions have been developed in efforts to more realistically estimate module performance in real-world situations. TERMS: • A photovoltaic cell is a semiconductor device that converts solar radiation into direct current electricity. • A semiconductor is a material that can exhibit properties of both an insulator and a conductor. • Doping is the process of adding small amounts of impurity elements to semiconductors to alter their electrical properties. • A p-type semiconductor is a semiconductor that has electron voids. • An n-type semiconductor is a semiconductor that has free electrons. • The photovoltaic effect is the movement of electrons within a material when it absorbs photons with energy above a certain level. • A photon is a unit of electromagnetic radiation. • A p-n junction is the boundary of adjacent layers of p-type and n-type semiconductor materials in contact with one another. • A multi-junction cell is a cell that maximizes efficiency by using layers of individual cells that each respond to different wavelengths of solar energy. • A thin-film module is a module-like PV device with its entire substrate coated in thin layers of semi-conductor material using chemical vapor deposition techniques, and then laser-scribed to delineate individual cells and make electrical connections between cells. • A photo-electrochemical cell is a cell that relies on chemical processes to produce electricity from light, rather than using semiconductors. • A wafer is a thin, flat disk or rectangle of base semiconductor material. • A mono-crystalline wafer is a silicon wafer made from a single silicon crystal grown in the form of a cylindrical ingot. • A polycrystalline wafer is a silicon wafer made from a cast silicon ingot that is composed of many silicon crystals. • A ribbon wafer is a silicon wafer made by drawing a thin strip from a molten silicon mixture. • The current-voltage (I-V) characteristic is the basic electrical output profile of a PV device. • An I-V curve is the graphic representation of all possible voltage and current operating points for a PV device at a specific operating condition. • The open-circuit voltage is the maximum voltage on an I-V curve and is the operating point for a PV device under infinite load or open-circuit condition, and no current output. • The short-circuit current (I) is the maximum current on an I-V curve and is the operating point for a PV device under no load or short-circuit condition, and no voltage output. • The maximum power point (em) is the operating point on an I-V curve where the product of current and voltage is at maximum. • The maximum power voltage (V_m) is the operating voltage on an I-V curve where the power output is at maximum. • The maximum power current Urn) is the operating current on an I-V curve where the power output is at maximum. • Fill factor (FF) is the ratio of maximum power to the product of the open-circuit voltage and short-circuit current. • Efficiency is the ratio of power output to power input. • A family of I-V curves is a group of I-V curves at various irradiance levels. • The temperature-rise coefficient is the coefficient for estimating the rise in cell temperature above ambient temperature due to solar irradiance. • A temperature coefficient is the rate of change in voltage, current, or power output from a PV device due to changing cell temperature. • A module is a PV device consisting of a number of individual cells connected electrically, laminated, en capsulated, and packaged into a frame. • An array is a complete PV power-generating unit consisting of a number of individual electrically and mechanically integrated modules with structural supports, trackers, or other components. • Reverse bias is the condition of a PV device operating at negative (reverse) voltage. • A bypass diode is a diode used to pass current around, rather than through, a group of PV cells. • Breakdown voltage is the minimum reverse-bias voltage that results in a rapid increase in current through an electronic device. • Standard test conditions (STC) is the most common and internationally accepted set of reference conditions, and rates module performance at a solar irradiance of 1000 W/m spectral conditions of AM 1.5, and a cell temperature of 25°C (77°F). • Standard operating conditions (SOC) is a set of reference conditions that rates module performance at a solar irradiance of 1000 W/m^2 spectral conditions of AM1.5, and at nominal operating cell temperature. • Nominal operating cell temperature (NOCT) is a reference temperature of an open-circuited module based on an irradiance level of 800 W/m^2 ambient temperature of 20°C (68°F), and wind speed of 1 m/s. • Nominal operating conditions (NOC) is a set of reference conditions that rates module performance at a solar irradiance of 800 W/m^2 spectral conditions of AM 1.5, and at nominal operating cell temperature. • PV USA test conditions (FTC) is a set of reference conditions that rates module performance at a solar irradiance of 1000 W/m^2 ambient temperature of 20°C (68°F), and wind speed of 1 m/s. QUIZ: 1. Describe the basic process of manufacturing PV cells. 2. Explain the relationships between PV cells, modules, panels, and arrays. 3. How does the photovoltaic effect limit the short-circuit current in PV devices? 4. Which methods can be used to estimate or calculate the maximum power point on an I-V curve? 5. How does PV device efficiency affect required device area? 6. What effects do series and shunt resistance have in PV systems? 7. Describe how varying solar irradiance affects the I-V characteristics of a PV device. 8. Describe how varying temperature affects the I-V characteristics of a PV device. 9. Describe how key I-V curve parameters are compensated for varying cell temperature. 10. How are cells electrically connected to produce a module with desired voltage and current parameters? 11. What is the voltage and current resulting from series or parallel connections of dissimilar PV devices? 12. How do bypass diodes protect modules from damage and preserve power performance? 13. Why is it important to understand the test conditions used in a module performance evaluation? Next: PV Battery Principles Prev: Device Response |