Reference: Photovoltaic Systems, p

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1 PV systems are comprised of building blocks of cells, modules and arrays to form a DC power generating unit with specified electrical output. Reference: Photovoltaic Systems, p Reference: Photovoltaic Systems, Chap

2 A solar cell is the basic element of a PV module. A PV module consists of many individual solar cells encapsulated in a glass or polymer laminate to provide environmental protection and electrical insulation for the cell circuits. A PV module is the smallest field-installable unit that produces DC power. A PV array consists of multiple individual modules that are mechanically and electrically configured to provide a desired output and is the complete DC power generating unit. Reference: Photovoltaic Systems, p. 116, A solar cell converts solar radiation to DC electricity, and is the basic building block of PV modules and arrays. Modern solar cells are created by junctions between different semiconductor materials. A typical crystalline silicon solar cell is a junction between boron-doped silicon (P-type) and phosphorus-doped silicon (N-type) semiconductors. N-type semiconductors are materials having excess electron charge carriers. P-type semiconductors are materials having a deficiency of electron charge carriers, or excess electron voids (holes). Reference: Photovoltaic Systems, p

3 The photovoltaic effect is the process of creating a voltage across charged materials that are exposed to electromagnetic radiation. Photons in sunlight have certain energy levels that are associated with their wavelength, and impart this energy to the solar cell materials. Photons with sufficient energy levels free the charge carriers from the valence band, jump the band gap and elevate their energy state to the conduction band, where they can move freely about the material. Charge opposition between the two materials creates an electrical field that provides momentum and direction to the charge carriers, resulting in current flow when the cell is connected to an electrical load. Individual silicon solar cells are manufactured in sizes up to and over 200 in 2 in area. The electrical current output of a solar cell is directly related to cell area, the cell efficiency, and the amount of solar radiation incident on the cell surface. A common crystalline silicon solar cell produces about 0.5 to 0.6 volt independent of cell area, but decreases with increasing temperature. This temperature affect on voltage has important ramifications for designing PV arrays to meet the voltage requirements of inverters in different climates. Reference: Photovoltaic Systems, p References: Photovoltaic Systems, p & CD-ROM

4 There are two basic types of crystalline silicon solar cells. Both types are fabricated beginning with the production of a P-type silicon ingot, from which individual wafers are sawn, and are subsequently processed to produce the actual solar cell. Both single and polycrystalline silicon solar cells are comparable in terms of efficiency, costs, reliability and performance. Reference: Photovoltaic Systems, p Single crystal or monocrystalline silicon wafers are grown in the form of a cylindrical ingot, creating a perfect tetrahedron crystal. A seed crystal is inserted into molten polysilicon doped with boron, rotated and drawn upward allowing the P-type silicon material to cool into a cylindrical ingot. The finished ingot is then divided and cropped on four sides to create a more rectangular shape, and individual wafers are then sawn from the cropped ingot with diamond wire saws. The cropping allows cells to be more densely packed in a given module area, and the slightly rounded edges result in visible diamond-shaped patterns between these cells in a module. Reference: Photovoltaic Systems, p

5 Polycrystalline or multi-crystalline silicon wafers are cast, forming a blockshaped ingot that has many crystals. Often these crystalline structures and grain boundaries appear as patterns of darker and lighter blue colors across the cell surface, although this appearance is sometimes masked by anti-reflective coatings. Polycrystalline wafers are commonly made by pouring molten polysilicon doped with boron into a rectangular crucible, and slowly cooled at controlled rate. Square or rectangular-shaped polycrystalline wafers are then sawn from the ingot and processed in a manner similar to monocrystalline cells. The ribbon method is another method to manufacture polycrystalline wafers, where molten silicon is drawn between dies, relying on surface tension to create a film between the dies, and the silicon solidifies as it passes through the dies and cools. A continuous strip or ribbon of polycrystalline wafers are formed, and individual wafer are cut from the ribbon. Once a P-type silicon ingot is produced, a number of additional steps are required to create an actual solar cell. The ingot is first cropped and blocked, then individual wafers are sawn from the ingot. Next, the wafers are etched in a sodium-hydroxide solution to create an irregular surface that absorbs more solar radiation and allows better adhesion for the N-type layer and anti-reflective coatings. The N-type silicon layer is created by passing the wafers through a furnace and diffusing phosphorous gas into the outer surfaces of the wafer. The edge layer is removed and a antireflective coating of titanium-oxide is applied to the top surface. Metallic grid patterns are screen printed on the front and back surfaces of the cells to conduct current. The back aluminum contact alloys with silicon and neutralizes the N-type layer on the back of the cell. Each cell is electrically tested and sorted based on its current output prior to assembly into cell strings and PV modules. Reference: Photovoltaic Systems, p & CD-ROM Reference: Photovoltaic Systems, p

6 A PV module is the basic building block for PV arrays, and the smallest integrated field-installable unit that produces DC power. Flat-plate PV modules respond to the total global solar radiation incident on their surface, utilizing both direct and diffuse components. Flat-plate PV modules are not intended for use under concentrated sunlight. Flat-plate PV modules are by far the most common type used in the industry today, ranging in size up to and over 24 ft 2 in area and weighing up to and over 50 pounds each - why PV installers must be able to carry bulky, heavy loads. Module rated peak power output can be up to and above 300 watts DC, with most manufacturers offering standard products in the 175 to 250 watt range to permit easier handling and installation by one person. First generation PV modules typically used 36 series-connected solar cells, which produce a high enough voltage at higher operating temperatures to adeqautely charge nominal 12-volt batteries. Newer, larger modules have 60, 72 or more seriesconnected cells designed for higher voltage applications with interactive inverters. Most listed modules can be connected in series up to a maximum limit of 600 volts DC, and some allow configurations up to 1000 volts DC where permitted. Reference: Photovoltaic Systems, p Reference: Photovoltaic Systems, p

7 Flat-plate modules typically have the solar cell circuits encapsulated in a polymer laminate for electrical insulation and environmental protection, and are covered with tempered glass for hail resistance and strength. The perimeter of the laminate is framed with extruded aluminum channels for additional strength, to provide a means to mechanically attach the module to a support structure, and to provide a conductive surface for equipment grounding connections. Reference: Photovoltaic Systems, p Reference: Photovoltaic Systems, p & CD-ROM

8 Thin-film PV modules use a module-based continuous manufacturing process involving the deposition of ultra-thin layers of semiconductor materials on a flexible or rigid substrate. Thin-film PV materials include amorphous silicon (a-si), cadmium telluride (CdTe), copper indium gallium selenide (CIS or CIGS) and others. The primary advantage of thin-film PV modules is their potential for significant cost and weight reductions through use of fewer raw materials. However, they are generally less efficient than mono or polycrystalline silicon cells and modules, and hence require larger surface areas to generate the same amount of power. This also increases costs for balance of system components, such as racking and support structures for the array, and more wiring and connections are required per unit array size. Many thin-film modules have low current output and voltages as high as 100 volts dc, and may use parallel connections of modules before they are connected in series in array source circuits. Flat-plate thin-film PV modules are currently 10 to 15% of the market mostly used for larger utility-scale applications, but are expected to increase market share in years to come with cost reductions and increasing performance. Concentrating PV (CPV) modules are special designs that use plastic lenses, mirrors or other optical means to focus solar radiation through a larger aperture area onto a smaller area of highly efficient solar cells. Concentrator designs use less solar cell material per unit collector area, and take advantage of increasing solar cell efficiencies at higher levels of solar irradiance. Since concentrating PV modules only utilize the direct component of solar radiation (about 60-70% of total global), they are installed on two-axis sun-tracking structures. Depending on the design, concentrating PV modules can have concentration ratios up to 500 times normal non-concentrated sunlight, and achieve cell efficiencies up to 40%. Major design challenges include thermal management of the module and conducting very high DC currents. Projects using concentrating PV arrays are generally custom designs and require special product installation training. References: Photovoltaic Systems, p. 20, 49 Reference: Photovoltaic Systems, p

9 An alternating-current (AC) module is an integral PV module and inverter unit that is designed to produce AC power for interactive operations with the utility grid. The inverter for AC modules is physically attached to the DC terminals at the back of the PV module at time of manufacture, forming a single integrated unit. Consequently, AC modules do not have accessible, field-installed DC wiring, and the requirements for the PV array DC source circuits and output circuits do not apply. The output from up to a dozen or more AC modules may be connected in parallel through a common cable to dedicated branch circuits. The mechanical and electrical layout and installation of PV arrays involves many interrelated considerations and tradeoffs that are affected by the system design, the equipment used and the site conditions. References: Photovoltaic Systems, p. 20, 49 Micro-inverters are module-level inverters installed on support structures immediately behind PV modules in an array. Similar to AC modules in their function, capabilities and benefits, micro-inverters are separate from the PV module and may be serviced independently. Reference: NEC 690.2,

10 Types of PV arrays can be broadly classified according to their electrical characteristics, the types of PV modules used, or by the way that PV arrays are mechanically integrated with buildings and other structures. PV arrays are also characterized by their surface orientation towards the sun, and whether they are installed on fixed or movable structures. References: Photovoltaic Systems, p. 20, 49 The size of PV arrays is often described by their peak rated DC power output at a standard condition, or sum of the individual PV module DC power ratings. PV array sizes can range from individual modules of a few watts to large fielded arrays of several megawatts using thousands of individual PV modules. The array electrical parameters dictate the system design and installation requirements, and must be appropriately matched to and compatible with the input ratings of inverters, charge controllers or any other DC power processing hardware that PV arrays are interfaced with. References: Photovoltaic Systems, p. 20,

11 Leading manufacturers of PV cells and modules represent diverse and well-known international companies, many from China and Japan. Suggested Exercise: Visit PV module manufacturer s websites and review product specifications. The current-voltage (I-V) characteristic or I-V curve is the basic descriptor of photovoltaic cell, module or array electrical performance. An I-V curve represents an infinite number of current and voltage operating points at which a PV device can operate, depending on its electrical load. A single I-V curve represents only one operating condition for a PV device at a specified level of solar radiation and device temperature. Reference: Photovoltaic Systems, p

12 Open-circuit voltage (Voc) is the maximum voltage on an I-V curve, and is the operating point for a PV device with no connected load. Voc corresponds to an infinite resistance or open-circuit condition, and zero current and power output. Open-circuit voltage is independent of cell area, decreases with increasing cell temperature and used to determine maximum circuit voltages for PV modules and arrays. For crystalline silicon solar cells, the open-circuit voltage is typically on the order of 0.6 volts at 25 C. Current-voltage curves can also expressed as power-voltage curves where the maximum power point (Pmp) is clearly shown. Reference: Photovoltaic Systems, p Short-circuit current (Isc) is the maximum current on an I-V curve. Isc corresponds to a zero resistance and short-circuit condition, and zero voltage and power output. Short-circuit current is directly proportional to solar irradiance, and used to determine maximum circuit design currents for PV modules and arrays. The maximum power point (Pmp) of a PV device is the operating point where the product of current and voltage (power) is at its maximum. The maximum power voltage (Vmp) is the corresponding operating voltage at Pmp, and is typically 70 to 80% of the open-circuit voltage. The maximum power current (Imp) is the operating current at Pmp, and typically 90% of the short-circuit current. The maximum power point is located on the knee of the I-V curve, and represents the highest efficiency operating point for a PV device under the given conditions of solar irradiance and cell temperature. Maximum power point tracking (MPPT) refers to the process or electronic equipment used to operate PV devices at their maximum power point under varying conditions, and is integral to interactive inverters and some battery charge controllers to maximize PV array efficiency and energy production. Reference: Photovoltaic Systems, p

13 Standard Test Conditions (STC) is the universal rating condition for PV modules and arrays, and specifies a solar irradiance level of 1000 W/m 2 at air mass 1.5 spectral distribution, operating at 25 C cell temperature. Reference: Photovoltaic Systems, p Fill factor (FF) is the ratio of maximum power to the product of the short-circuit current and open-circuit voltage, and an indicator of the quality of a solar cell. FF is represented graphically by the area of a rectangle bounded by Imp and Vmp, divided by the area of a rectangle defined by Isc and Voc. Most crystalline silicon PV solar cells have fill factor greater than 70%. Suggested Exercise: Use example PV module specifications to calculate the fill factor. Reference: Photovoltaic Systems, p

14 The efficiency of a PV device defines the area required to generate a given amount of power under a specified level of solar radiation. As rule of thumb, it takes 10 square meters for a 10% efficient PV array to produce 1000 watts maximum power at peak sun: 10 m 2 x 1000 W/m 2 x 0.10 = 1000 W = 1 kw PV modules with higher efficiencies require less surface area to produce a given amount of power, saving on costs for raw materials, mounting structures and balance of system equipment. However, higher efficiency modules are generally more expensive than less efficient modules per rated power output. Efficiency depends on temperature and the operating point on an I-V curve, and increases with increasing irradiance. Rated efficiency is typically expressed for PV modules at Standard Test Conditions (25 C, 1000 W/m 2 ). In application, the operating point is determined by the specific equipment connected to the output of the PV array. If the load is a battery, the battery voltage sets the operating point on the I-V curve, and thus sets the operating current. If the PV array is connected to an interactive inverter, internal inverter circuitry operates the PV array at its maximum power point under over a range of operating conditions, as long as the array voltage operates within the inverter specifications. Array maximum power point tracking (MPPT) function is integral to all listed utility-interactive inverters that directly interface with PV arrays, including microinverters and inverters integral to ac modules. Some battery charge controllers also include an MPPT function and dictate the allowable maximum array voltage. Suggested Exercise: Use example PV module specifications to calculate the module efficiency. Reference: Photovoltaic Systems, p

15 The efficiency and power output of a PV device depend on the operating point on its I-V curve, and the operating point depends on the electrical load connected to the device. The area of a rectangle bounded by the current-voltage operating pair defines the power output at any given operating point. Early PV modules were designed for battery charging applications. For higher PV cell operating temperatures, generally 36 series-connected silicon solar cells are needed to provide adequate maximum power voltage to fully charge a lead acid-battery. Reference: Photovoltaic Systems, p

16 The specific operating point on an I-V curve is determined by the electrical load resistance according to Ohm s Law. Consequently, the load resistance to operate a PV module or array at its maximum power point is equal to the voltage at maximum power divided by the current at maximum power (Vmp/Imp). The DC power produced is simply the product of the applicable current-voltage operating pair on the I-V curve. Reference: Photovoltaic Systems, p The I-V curve for a PV device can be measured by connecting an electrical load to operate the device over its range of operating points. A variable resistor or power supply may be used for PV cells and smaller modules, while capacitors are used in special test equipment to measure the I-V curves for larger arrays. A voltmeter in parallel and an ammeter is series with the PV device are used to measure voltage and current, respectively. Suggested Exercise: Measure the I-V curves for small PV devices or modules, and examine the effects of changing electrical load. Reference: Photovoltaic Systems, p

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19 The electrical performance of solar cells can be modeled by evaluating an equivalent circuit, and developing a series of equations to solve for the circuit current and voltage unknowns as a function of sunlight, temperature and electrical load. This is an advanced problem suitable for electrical engineering students. Reference: Photovoltaic Systems, p. 129 Series resistance (Rs) represents circuit resistance in series with a PV device or array. Series resistance can include resistance internal to a cell, its electrical contacts, module interconnections, or source circuit wiring. Increasing Rs Series resistance has no effect on Voc because there is no current flow, however, other voltages along an I-V curve affected by Rs and the operating current according to Ohm s Law. Rs is approximately equal to the negative of the reciprocal of the slope of an I-V curve near open-circuit voltage: Rs = - V / I (evaluated near Voc) where Rs = series resistance (in ohms) V = change in voltage (in volts) I = change in current (in amps) Over time, increasing Rs can indicate problems with electrical connections internal to modules or within an array. If a PV device is operated at constant voltage (e.g. battery charging), increasing Rs results in decreasing operating current, and why it is so important to minimize PV array circuit resistance as much as possible, especially where long distances are involved between the array and DC utilization equipment

20 Reference: Photovoltaic Systems, p Shunt resistance (Rsh) represents circuit resistance in parallel with a PV device or array. Decreasing Rsh reduces fill factor and efficiency, and lowers maximum voltage, current and power, but does not affect Isc. Over time, decreasing Rsh can indicate leakage currents or short-circuits between cell circuits and module frames, or groundfaults within an array. Rsh is approximately equal to the negative of the reciprocal of the slope of an I-V curve near short-circuit current, and is ideally infinite: Rsh = - V / I (evaluated near Isc) Where Rsh = series resistance (in ohms) Reference: Photovoltaic Systems, p

21 Changes in solar radiation have a direct linear and proportional effect on the current and maximum power output of a PV module or array. Therefore, doubling the solar irradiance on the surface of an array doubles the current and maximum power output (assuming constant temperature). Changing irradiance has a smaller effect on voltage, mainly at lower irradiance levels. Because voltage varies little with changing irradiance levels, PV devices are well-suited for battery charging applications. Reference: Photovoltaic Systems, p PV installers may verify performance of PV systems in the field by measuring the solar irradiance incident on arrays with simple handheld meters, and correlating with the actual system power output. For example, if it has been established that the peak output rating for a PV array is 10 kw under incident radiation levels of 1000 W/m 2 at normal operating temperatures, then the output of the array should be expected to be around 7 kw if the solar irradiance is 700 W/m 2, assuming constant temperature. Reference: Photovoltaic Systems, p

22 The short-circuit current (Isc), maximum power current (Imp), and maximum power (Pmp) at one condition of solar irradiance may be translated to estimate the value of these parameters at another irradiance level: Isc 2 = Isc 1 x (E 2 /E 1 ) Pmp 2 = Pmp 1 x (E 2 /E 1 ) Imp 2 = Imp 1 x (E 2 /E 1 ) For crystalline silicon PV devices, increasing cell temperature results in a decrease in voltage and power, and a slight increase in current. Higher cell operating temperatures also reduce cell efficiency and lifetime. The temperature effects on current are an order of magnitude less than on voltage, and neglected as far as any installation or safety issues are concerned. Reference: Photovoltaic Systems, p where Isc 1 = rated short-circuit current at irradiance E 1 (A) Isc 2 = short-circuit current at new irradiance E 2 (A) E 1 = rated solar irradiance (W/m 2 ) E 2 = new solar irradiance (W/m 2 ). Pmp 1 = rated maximum power at irradiance E 1 (W) Pmp 2 = new maximum power at new irradiance E 2 (W). Imp 1 = original maximum power current at irradiance E 1 (A) Imp 2 = new maximum power current at new irradiance E 2 (A). Reference: Photovoltaic Systems, p

23 The temperature-rise coefficient relates the temperature of a PV array to the ambient temperature and solar irradiance incident on an array. When the solar irradiance on an array is nearly zero, the temperature of a PV array is very close to the ambient air temperature. As irradiance increases, the difference between the array and ambient air temperature increases in proportion to the irradiance level, and depends on the array mounting system and natural airflow. Rack-mounted arrays may T-rise coefficients of 20 to 25 C/kW/m 2, while standoff roof-mounted arrays may have T-rise coefficients as high as 30 to 40 C/kW/m 2. Reference: Photovoltaic Systems, p Temperature coefficients relate the effects of changing PV cell temperature on device performance, such as voltage, current and power. Temperature coefficients may be expressed as a unit, or a percentage change in a parameter. Unit temperature coefficients must be multiplied by the number of cells in series for the voltage, and by the number of cells in parallel and the cell area for current. Percentage change temperature coefficients are more commonly used. For crystalline silicon PV devices, the percentage change temperature coefficient for voltage is approximately -0.4%/ C (negative), the temperature coefficient for shortcircuit current is approximately %/ C, and the temperature coefficient for maximum power is approximately %/ C (negative). Note that the power and voltage temperature coefficients are negative, as these parameters decrease with increasing temperature. Other PV materials have varying temperature coefficients, and manufacturer s coefficients should be used for voltage calculations. Reference: Photovoltaic Systems, p

24 Reference: Photovoltaic Systems, p Suggested Exercise: Estimate the voltage-temperature coefficient for a typical PV module by measuring the open-circuit voltage at two different temperatures. Keep the module indoors at room temperature, and immediately measure the module temperature and Voc upon exposing to sunlight. As the module warms up, measure the temperature and voltage periodically until the module temperature stabilizes. Exposing the module to constant solar irradiance above 800 W/m 2 will yield more accurate results. Plot the module voltage versus temperature and the slope of the line is the temperature coefficient. Reference: Photovoltaic Systems, p

25 Reference: Photovoltaic Systems, p PV arrays consist of building blocks of individual PV modules connected electrically in series and parallel. PV modules are connected in series to build voltage suitable for connection to DC utilization equipment, such as interactive inverters, batteries, charge controllers or DC loads. Series strings of modules, or source-circuits, are connected in parallel at combiner boxes to build current and power output for the array. There are numerous ways PV arrays can be electrically and mechanically configured. The first objective is to create an array electrical configuration that meets the voltage, current and power requirements of the system. The electrical requirements establish the number of PV modules required, and the physical size of the PV array. The mechanical configuration then depends on the dimensions of the individual modules and the structure or foundation that the array attaches to. Reference: Photovoltaic Systems, p

26 Monopole PV arrays have a single pair of positive and negative output circuit conductors. Bipolar PV arrays are two monopole arrays connected together, and used for large inverter applications. A string is a series connection of PV devices. PV cells or modules are configured electrically in series by connecting the negative terminal of one device to the positive terminal of the next device, and so on. For the series connection of similar PV modules, the voltages add and the resulting string voltage is the sum of the individual module voltages. The resulting string current output remains the same as the current output of an individual module. Reference: Photovoltaic Systems, p

27 Reference: Photovoltaic Systems, p Connecting PV modules in series with dissimilar current ratings results in loss of power, similar in effect to partially shading an array, or having parts of a series source circuit located on surfaces facing different directions and receiving different solar irradiance. The resultant current output for a string of dissimilar current output devices is ultimately limited to the lowest current output device in the entire string, and should be avoided. However, it is perfectly acceptable to connect PV modules with different voltage output in series, as long as each module has the same rated current output. Reference: Photovoltaic Systems, p

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30 Bypass diodes are connected in parallel with series strings of cells to prevent cell overheating when cells or parts of an array are shaded. Bypass diodes are essentially electrical check valves, that permit the flow of current in only one direction. When modules in series strings are partially shaded, it may cause reverse voltage across the shaded cells or modules. The bypass diode shunts current around the shaded area and prevents cells overheating. Most listed PV modules are equipped with factory installed bypass diodes. Where sealed junction boxes are used, bypass diodes are not serviceable in the field. Connecting dissimilar current output PV devices in series without bypass diodes can lead to high power dissipation and overheating of the lower current device. Without bypass diodes, current from unshaded cells forces the shaded cells to operate in reverse bias, dumping excess power in the shaded cells. Reference: Photovoltaic Systems, p Reference: Photovoltaic Systems, p

31 Using blocking diodes limits power dissipation and prevents cell and modules from overheating when cells or modules with dissimilar current modules are connected in series. Reference: Photovoltaic Systems, p A junction box is an electrical enclosure on the back of PV modules which contains the module conductors, terminal blocks, and connectors to allow the module to be connected to a wiring system. Junction boxes may include bypass diodes and ability to change the series/parallel configuration of the cells in the module is accessible. Most PV modules today have a sealed junction boxes and come equipped with preinstalled external cables and connectors. Reference: Photovoltaic Systems, p

32 Standard Test Conditions (STC) is the universal rating condition for PV modules and arrays, and specifies a solar irradiance level of 1000 W/m 2 at air mass 1.5 spectral distribution, operating at 25 C cell temperature. Other conditions of solar irradiance and cell temperature are sometimes used for PV module and array ratings. Temperature and irradiance translations can be used to convert one rating condition to another. Reference: Photovoltaic Systems, p Reference: Photovoltaic Systems, p

33 The differences between rating conditions can be clearly shown by the I-V curves. Reference: Reference: Photovoltaic Systems, p

34 A number of standards have been developed to address the safety, reliability and performance of PV modules. PV modules are classified as electrical equipment, and must conform to accepted product safety standards. According to the NEC, they must be listed or approved by a recognized laboratory. In the U.S., PV modules are listed to for electrical safety to UL1703 Safety Standard for Flat-Plate Photovoltaic Modules and Panels. These requirements cover flat-plate photovoltaic modules intended for installation in accordance with the NEC, and for use in systems with a maximum system voltage of 1000 volts or less. The standard also covers components intended to provide electrical connections and for the structural mounting of PV modules. A similar international standard, IEC is published by the International Electrotechnical Commission (IEC), and harmonized with the UL 1703 standard. Reference: Photovoltaic Systems, p Certain key I-V parameters at Standard Test Conditions are required to be labeled on every listed PV module. These nameplate electrical ratings govern the circuit design and application limits for the module, and must include the following information and ratings: polarity of terminals maximum overcurrent device rating for module protection open-circuit voltage (Voc) short-circuit current (Isc) maximum permissible systems voltage operating or maximum power voltage (Vmp) operating or maximum power current (Imp) maximum power (Pmp) Other items found on PV modules labels include fire classification ratings, minimum conductor sizes and ratings, and additional design qualification and type testing certification (IEC 61215). Additional information related to PV module installation is found in the installation instructions included with listed PV modules. All installers should thoroughly read this information before working with or installing any PV modules or arrays [See NEC 110.2]. References: Photovoltaic Systems, p NEC

35 Reference: Photovoltaic Systems, p. 141 PV modules produced by leading Manufacturers may be type tested for design qualification according to IEC standards, which are becoming increasingly required for module procurements. The first, IEC covers Crystalline Silicon Terrestrial Photovoltaic (PV) Modules - Design Qualification and Type Approval, and the second, IEC covers Thin-film Terrestrial Photovoltaic (PV) Modules - Design Qualification and Type Approval. Among the tests modules are subjected to in design qualification include thermal cycling tests, humidity and freezing tests, impact and shock tests, immersion tests, cyclic pressure, twisting, vibration and other mechanical tests, wet/dry hi-pot tests and excessive and reverse current electrical tests. Design qualification has important implications on product warranties offered by manufacturers. As a result, today most major module manufacturers offer warranties of 20 years and greater that guarantee module peak power output to be within 80 percent of initial nameplate ratings, which equates to a degradation rate of no more than 1 percent per year. Reference: Photovoltaic Systems, p

36 References: Photovoltaic Systems, p NEC Reference: Photovoltaic Systems, p

37 Suggested Exercise: Review PV module manufacturer s installation instructions. Reference: Photovoltaic Systems, p Reference: NEC

38 Reference: Photovoltaic Systems, p Reference: Photovoltaic Systems, p