Cells, Modules and Arrays - Solar Power Financing Iowa - … · 2012 Jim Dunlop Solar Cells, Modules and Arrays: 5 - 5 . The Photovoltaic Effect The photovoltaic effect is the process
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2012 Jim Dunlop Solar Chapter 5 Cells, Modules and Arrays Principles of Operation ● I-V Characteristics ● Response to Irradiance and Temperature ● Series/Parallel Connections ● Specifications and Ratings
Principles of Operation ● I-V Characteristics ● Response to Irradiance and Temperature ● Series/Parallel
Connections ● Specifications and Ratings
Presenter
Presentation Notes
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, Chap. 5
2012 Jim Dunlop Solar Cells, Modules and Arrays: 5 - 2
Overview
Describing the photovoltaic (PV) effect and comparing the fabrication of solar cells from various manufacturing processes.
Defining the current-voltage (I-V) characteristic for a PV device and the key operating parameters.
Understanding how sunlight, temperature and electrical load affect the output of a PV device.
Determining the electrical output of similar and dissimilar PV devices connected in series and parallel.
Explaining the purpose and operation of bypass diodes.
Describing the performance rating conditions and labeling requirements for PV modules.
Presenter
Presentation Notes
Reference: Photovoltaic Systems, p. 115-118
2012 Jim Dunlop Solar Cells, Modules and Arrays: 5 - 3
Cells, Modules and Arrays
Cell
Module
Array
Presenter
Presentation Notes
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, 134-136
2012 Jim Dunlop Solar Cells, Modules and Arrays: 5 - 4
Solar Cells
Solar cells are semiconductor devices that convert sunlight to DC electricity.
Photovoltaic cell
Phosphorous-doped silicon (N-type) layer ~ 0.3 μm
Electrical Load
(-)
(+) Boron-doped silicon (P-type) wafer < 250 μm
DC current flow
Presenter
Presentation Notes
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. 115-118
2012 Jim Dunlop Solar Cells, Modules and Arrays: 5 - 5
The Photovoltaic Effect
The photovoltaic effect is the process of creating a voltage
across charged materials that are exposed to electromagnetic radiation.
Photons in sunlight impart their energy to excess charge carriers (electrons and holes) allowing them to freely move about the material.
Charge opposition between the two materials creates an electrical field that provides momentum and direction to the free charge carriers, resulting in the flow of electrical current flow when the cell is connected to a load.
Presenter
Presentation Notes
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. References: Photovoltaic Systems, p. 115-118 & CD-ROM
2012 Jim Dunlop Solar Cells, Modules and Arrays: 5 - 6
Silicon Solar Cells
Silicon solar cells produce about 0.5 to 0.6 volt independent of cell area, depending on temperature.
The current output of a solar cell depends primarily on the cell area, its efficiency, and the incident solar radiation.
Modern silicon solar cells are up to 8 inches in diameter and produce up to 4 watts and 8 amps under full sunlight.
Monocrystalline cell Polycrystalline cell
Presenter
Presentation Notes
Individual silicon solar cells are manufactured in sizes up to and over 200 in2 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. 118-122
2012 Jim Dunlop Solar Cells, Modules and Arrays: 5 - 7
Crystalline Silicon Wafer Production
The following processes are commonly used to create P-type
silicon wafers:
The Czochralski method produces a single or monocrystalline wafer.
The cast ingot method produces a multigrain or polycrystalline wafer.
The ribbon method produces polycrystalline wafers by drawing molten silicon between dies in a continuous process.
Wafer are additionally processed to produce a complete solar cell.
Presenter
Presentation Notes
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. 118-122
2012 Jim Dunlop Solar Cells, Modules and Arrays: 5 - 8
silicon wafers are grown in the form of a cylindrical ingot, creating a perfect 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.
Czochralski Method
Presenter
Presentation Notes
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. 118-122
2012 Jim Dunlop Solar Cells, Modules and Arrays: 5 - 9
Polycrystalline Silicon Wafer Production
Polycrystalline or multi-
crystalline silicon wafers are cast, forming a block-shaped ingot that has many crystals.
Molten polysilicon doped with boron is poured into a rectangular crucible, and slowly cooled at controlled rate.
Polycrystalline wafers are also made using the ribbon method.
Cast Ingot Method
Presenter
Presentation Notes
Polycrystalline or multi-crystalline silicon wafers are cast, forming a block-shaped 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. Reference: Photovoltaic Systems, p. 118-122
2012 Jim Dunlop Solar Cells, Modules and Arrays: 5 - 10
Solar Cell Manufacturing
Once a P-type silicon ingot is produced, a number of additional steps are required to create an actual solar cell.
SolarWorld USA
Cropping
Phosphorous diffusion
Screen printing Electrical testing
Sawing
Presenter
Presentation Notes
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 anti-reflective 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. 118-122 & CD-ROM
2012 Jim Dunlop Solar Cells, Modules and Arrays: 5 - 11
Flat-Plate PV Modules
Flat-plate PV modules respond to both direct and diffuse solar radiation, and are the smallest field installable generating unit.
Single (mono) crystalline Polycrystalline SolarWorld
Presenter
Presentation Notes
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 ft2 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. Reference: Photovoltaic Systems, p. 134-144
2012 Jim Dunlop Solar Cells, Modules and Arrays: 5 - 12
Flat-Plate PV Modules
Single (mono) crystalline Polycrystalline
36 cell modules
60 cell polycrystalline module
Presenter
Presentation Notes
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 series-connected 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. 134-144
2012 Jim Dunlop Solar Cells, Modules and Arrays: 5 - 13
Typical PV Module Construction
Continuous silicone seal
Tempered glass EVA embedding
Solar cells Tough polymer back sheet
High strength frame
SolarWorld USA
Presenter
Presentation Notes
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. 134-135 & CD-ROM
2012 Jim Dunlop Solar Cells, Modules and Arrays: 5 - 14
Emerging PV Module Technologies
Thick wafer silicon P-N junction solar cells are considered first
generation PV devices.
Second generation devices are thin-film devices including: Amorphous silicon (a-Si) Cadmium Telluride (CdTe) Copper indium gallium selenide (CIS or CIGS)
Other advanced PV module designs include:
Concentrating PV modules AC modules Polymer and organic solar cells
Presenter
Presentation Notes
Reference: Photovoltaic Systems, p. 118-119
2012 Jim Dunlop Solar Cells, Modules and Arrays: 5 - 15
Thin-Film PV Modules
Thin-film PV modules are
produced by depositing ultra-thin layers of semiconductor materials on a flexible or rigid substrate.
Thin-film modules have significant potential for cost and weight reductions.
Disadvantages include lower efficiencies and higher degradation rates than crystalline silicon modules.
Presenter
Presentation Notes
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. Reference: Photovoltaic Systems, p. 118-119
2012 Jim Dunlop Solar Cells, Modules and Arrays: 5 - 16
Concentrating PV Modules
Use optics to focus sunlight on
solar cells up to 200-500 X.
Employ advanced multijunction solar cells approaching efficiencies of up to 40%.
Utilize only direct component of total global solar radiation, and employ two-axis sun tracking.
Design challenges include
managing high temperatures and high DC currents.
NREL, Bill Timmerman
Presenter
Presentation Notes
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
2012 Jim Dunlop Solar Cells, Modules and Arrays: 5 - 17
AC Modules and Micro-Inverters
Alternating-current (AC) modules
are an integrated PV module and inverter product intended for installation as a single unit.
AC modules do not have any field-installed DC wiring.
Micro-inverters are separate module level inverters intended for field installation.
Presenter
Presentation Notes
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. 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, 690.6
2012 Jim Dunlop Solar Cells, Modules and Arrays: 5 - 18
Photovoltaic Arrays
PV arrays are constructed from building blocks of individual PV modules, panels and subarrays that form a mechanically and electrically integrated DC power generation unit.
Presenter
Presentation Notes
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
2012 Jim Dunlop Solar Cells, Modules and Arrays: 5 - 19
Photovoltaic Arrays
Ground-mounted rack array
Pole-mounted tracking array
Standoff roof-mounted array
Building-integrated array
Presenter
Presentation Notes
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
2012 Jim Dunlop Solar Cells, Modules and Arrays: 5 - 20
Photovoltaic Arrays
Roof-mounted rack array
Roof-mounted standoff array
Presenter
Presentation Notes
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, 49
2012 Jim Dunlop Solar Cells, Modules and Arrays: 5 - 21
Leading Manufacturers of PV Cells and Modules
BP Solar
First Solar
JA Solar
Kyocera
Mitsubishi
Motech
Q-Cells
Sanyo
Schott Solar
Sharp Solar
SolarWorld
SunPower
Suntech
Trina
Yingli
Presenter
Presentation Notes
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.
2012 Jim Dunlop Solar Cells, Modules and Arrays: 5 - 22
Current-Voltage (I-V) Characteristic
The electrical performance of a
PV device is given by it current-voltage (I-V) curve.
Represents an infinite number of I-V operating points.
Varies with solar radiation and device temperature.
Voltage (V)
Presenter
Presentation Notes
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. 123-130
2012 Jim Dunlop Solar Cells, Modules and Arrays: 5 - 23
Key I-V Parameters
PV device performance is
specified by the following I-V parameters at a given temperature and solar irradiance condition:
Open-circuit voltage (Voc) Short-circuit current (Isc) Maximum power point (Pmp) Maximum power voltage (Vmp) Maximum power current (Imp)
Voltage (V)
Isc
Voc
Imp
Vmp
Pmp
Area = Pmp
Presenter
Presentation Notes
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. 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. 124-127
2012 Jim Dunlop Solar Cells, Modules and Arrays: 5 - 24
Power vs. Voltage Curve
Voltage (V)
Isc
Imp
Vmp Voc
Pmp = Imp x Vmp
Pmp
Current vs. Voltage Power vs. Voltage
Presenter
Presentation Notes
Current-voltage curves can also expressed as power-voltage curves where the maximum power point (Pmp) is clearly shown. Reference: Photovoltaic Systems, p. 126-127
2012 Jim Dunlop Solar Cells, Modules and Arrays: 5 - 25
PV Module Rating Conditions
The electrical performance of PV modules is rated at Standard Test Conditions (STC): Irradiance: 1,000 W/m2 , AM 1.5 Cell temperature: 25°C
Source: SolarWorld USA
Presenter
Presentation Notes
Standard Test Conditions (STC) is the universal rating condition for PV modules and arrays, and specifies a solar irradiance level of 1000 W/m2 at air mass 1.5 spectral distribution, operating at 25°C cell temperature. Reference: Photovoltaic Systems, p. 141-143
2012 Jim Dunlop Solar Cells, Modules and Arrays: 5 - 26
Fill Factor
Fill factor (FF) is an indicator of the quality of a solar cell.
FF = (Vmp x Imp) / (Voc x Isc) = Pmp / (Voc x Isc)
Voltage (V)
Isc
Imp
Vmp Voc
Pmp = Imp x Vmp
Isc x Voc
Presenter
Presentation Notes
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. 127
2012 Jim Dunlop Solar Cells, Modules and Arrays: 5 - 27
Efficiency
Efficiency of a PV device is the
ratio of the electrical power output and the solar irradiance input over the device area, expressed as a percentage:
Example: What is the efficiency for a PV
module that has a surface area of 1.4 m2, and produces 200 W maximum power when exposed to 1000 W/m2 solar irradiance?
2
2
efficiency maximum power rating (W)
solar iradiance (W/m ) surface area (m )
mp
mp
PE A
where
P
EA
η
η
=×
==
=
=
2 2
200 W(1000 W/m 1.4 m )
0.143 14.3%
mpPE A
η
η
η
=×
=×
= =
Presenter
Presentation Notes
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 m2 x 1000 W/m2 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/m2). Suggested Exercise: Use example PV module specifications to calculate the module efficiency. Reference: Photovoltaic Systems, p. 127-128
2012 Jim Dunlop Solar Cells, Modules and Arrays: 5 - 28
Response to Electrical Load
The electrical load connected to a PV device determines its operating point. If a battery is connected to a PV device, the battery voltage sets the
operating voltage for that PV device. In a grid-connected PV system, the inverter loads the PV array at its
maximum power point.
From Ohm’s Law, the electrical load resistance that operates a PV device at its maximum power point is equal to Vmp/Imp (ohms).
PV Device
+
-
Electrical Load
Presenter
Presentation Notes
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.
2012 Jim Dunlop Solar Cells, Modules and Arrays: 5 - 29
Operating Point
Voltage (V)
Isc Imp
Vmp Voc
Pmp = Imp x Vmp
Presenter
Presentation Notes
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. Reference: Photovoltaic Systems, p. 128-129
2012 Jim Dunlop Solar Cells, Modules and Arrays: 5 - 30
PV Modules for Battery Charging
PV module maximum power voltage must be higher than battery voltage at highest operating temperature
Voltage (V)
Cur
rent
(A)
Module with 36 series-connected cells operating at temperature of 50°C (optimal)
10 20
Operating voltage range for 12-volt lead-acid battery: 11.5 to 14.5 volts.
Maximum power points
Module with 30 series-connected cells at 50°C (voltage too low to deliver maximum current to battery)
Module with 42 series-connected cells at 50°C (voltage is more than adequate for charging, but power is wasted)
Presenter
Presentation Notes
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.
2012 Jim Dunlop Solar Cells, Modules and Arrays: 5 - 31
Effect of Electrical Load on Operating Point
Voltage
Decreasing
resistance
Constant Temperature
Increasing
resistance
R = 0
R = ∞
Load lines of constant resistance
Presenter
Presentation Notes
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. 123-130
2012 Jim Dunlop Solar Cells, Modules and Arrays: 5 - 32
I-V Measurement Methods
PV Device
Variable resistor
Electrolytic capacitor
Variable battery
V
A
Presenter
Presentation Notes
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. 123-130
2012 Jim Dunlop Solar Cells, Modules and Arrays: 5 - 33
2012 Jim Dunlop Solar Cells, Modules and Arrays: 5 - 34
Raydec DS-100 IV Curve Tracer
2012 Jim Dunlop Solar Cells, Modules and Arrays: 5 - 35
Spire 4600 SLP Flash Simulator
2012 Jim Dunlop Solar Cells, Modules and Arrays: 5 - 36
Response to Electrical Load: Example
The maximum power voltage (Vmp) and maximum power current (Imp) for a PV module are 35.8 volts and 4.89 amps, respectively. What is the maximum power and load resistance required to operate at maximum power?
The maximum power is calculated by the product of the maximum power voltage and maximum power current:
35.8 volts x 4.89 amps = 175 watts From Ohm’s Law, resistance is equal to the voltage divided by
the current: 35.8 volts / 4.89 amps = 7.32 ohms
Presenter
Presentation Notes
Reference: Photovoltaic Systems, p. 128-129
2012 Jim Dunlop Solar Cells, Modules and Arrays: 5 - 37
Solar Cell Equivalent Circuit
A solar cell equivalent circuit consists of a current source in parallel with a diode and shunt resistance, connected to a series resistance.
Shunt resistance Load resistance
Series resistance
Diode Current source
Presenter
Presentation Notes
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
2012 Jim Dunlop Solar Cells, Modules and Arrays: 5 - 38
Series Resistance
Voltage
Moderate Rs
Low Rs Increasing Rs decreases Pmp, Vmp and Imp, and also reduces FF and efficiency.
Rs = - ∆V / ∆ I
High Rs
∆V
∆I
Presenter
Presentation Notes
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. Reference: Photovoltaic Systems, p. 129-130
2012 Jim Dunlop Solar Cells, Modules and Arrays: 5 - 39
Shunt Resistance
Voltage
Moderate Rsh
High Rsh
Decreasing Rsh decreases Pmp, Vmp and Imp.
Rsh = - ∆V / I
Low Rsh
∆V
∆I
Presenter
Presentation Notes
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 ground-faults 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. 129-130
2012 Jim Dunlop Solar Cells, Modules and Arrays: 5 - 40
Response to Solar Irradiance
Voltage
1000 W/m2
750 W/m2
500 W/m2
250 W/m2
Current increases with increasing irradiance
Voc changes little with irradiance
Maximum power increases with increasing irradiance
Maximum power voltage changes little with irradiance
Constant Temperature
Presenter
Presentation Notes
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. 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/m2 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/m2, assuming constant temperature. Reference: Photovoltaic Systems, p. 130-131
2012 Jim Dunlop Solar Cells, Modules and Arrays: 5 - 41
Response to Solar Irradiance
Irradiance (W/m2)
1000
Isc increases with increasing irradiance
Voc changes little with irradiance above 200 W/m2
Constant Temperature
800 600 400 200 0
Presenter
Presentation Notes
Reference: Photovoltaic Systems, p. 130-131
2012 Jim Dunlop Solar Cells, Modules and Arrays: 5 - 42
Response to Solar Irradiance
The power and current output of a PV device are proportional to the solar irradiance:
Example: A PV module produces 200 watts maximum power at 1000 W/m2. Assuming constant temperature, the maximum power output at an irradiance level of 600 W/m2 would be:
2 2 2
1 1 1
E I PE I P
= =
22 1
1
600 200 120 W1000
EP PE
= × = × =
Presenter
Presentation Notes
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: Isc2 = Isc1 x (E2/E1) Pmp2 = Pmp1 x (E2/E1) Imp2 = Imp1 x (E2/E1) where Isc1 = rated short-circuit current at irradiance E1 (A) Isc2 = short-circuit current at new irradiance E2 (A) E1 = rated solar irradiance (W/m2) E2 = new solar irradiance (W/m2). Pmp1 = rated maximum power at irradiance E1 (W) Pmp2 = new maximum power at new irradiance E2 (W). Imp1 = original maximum power current at irradiance E1 (A) Imp2 = new maximum power current at new irradiance E2 (A). Reference: Photovoltaic Systems, p. 130-131
2012 Jim Dunlop Solar Cells, Modules and Arrays: 5 - 43
Response to Temperature
For crystalline silicon PV devices, increasing cell temperature results in a decrease in voltage and power, and a small increase in current.
Voltage
T = 25°C
T = 50°C
T = 0°C
Increasing temperature reduces voltage
Increasing temperature reduces power output
Increasing temperature increases current
Presenter
Presentation Notes
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. 131-134
2012 Jim Dunlop Solar Cells, Modules and Arrays: 5 - 44
Temperature-Rise Coefficient
The temperature-rise coefficient relates the temperature of a given PV array to the ambient air temperature and solar irradiance:
At peak sun, the difference between PV array and ambient air temperature can vary from 20 to 40°C, depending on the array mounting system design.
2
( )
cell temperature ( C)
ambient air temperature ( C)
temperature-rise coefficient ( C/kW/m )
cell amb T rise
cell
amb
T rise
T T C EwhereT
T
C
−
−
= + ×
=
=
=
Presenter
Presentation Notes
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/m2, while standoff roof-mounted arrays may have T-rise coefficients as high as 30 to 40°C/kW/m2. Reference: Photovoltaic Systems, p. 131-134
2012 Jim Dunlop Solar Cells, Modules and Arrays: 5 - 45
Temperature Coefficients
Temperature coefficients relate the effects of changing PV cell temperature on voltage, current and power.
Percentage change coefficients are commonly used to translate voltage, current and power from one temperature condition to another temperature.
For crystalline silicon PV, percentage change temperature coefficients are approximately: CV = -0.4%/°C (voltage decreases 1% for 2.5°C increase in temperature) CI = +0.04%/°C (current increases 1% for 25°C increase in temperature) CP = -0.45%/°C (power decreases 1% for 2.2°C increase in temperature)
Since the temperature coefficient for current is an order of magnitude
less than for voltage or power, the effects of temperature on current are not usually considered in systems design.
Presenter
Presentation Notes
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 short-circuit current is approximately +0.04 %/°C, and the temperature coefficient for maximum power is approximately -0.45 %/°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. 131-134
2012 Jim Dunlop Solar Cells, Modules and Arrays: 5 - 46
Temperature Translation Equations
cell
ref
cell
[ ( )]
[ ( )]
translated voltage at T (V) reference voltage at T (V)
translated power at T (W) reference
trans ref ref V cell ref
trans ref ref P cell ref
trans
ref
trans
ref
V V V C T TP P P C T T
whereVVPP
= + × × −
= + × × −
=
=
=
= refpower at T (W)
voltage-temperature coefficient (% per C)
power-temperature coefficient (% per C)
cell temperature ( C)
reference temperature ( C)
V
P
cell
ref
C
CT
T
=
=
=
=
Presenter
Presentation Notes
Reference: Photovoltaic Systems, p. 131-134
2012 Jim Dunlop Solar Cells, Modules and Arrays: 5 - 47
Response to Temperature: Example 1
A 72-cell crystalline silicon PV module has a rated open-circuit voltage of 44.4 V at 25°C, and a voltage-temperature coefficient of -0.33 %/°C. What would the open-circuit voltage be at a cell temperature of 60°C?
If the same PV module operates at -10°C (35°C lower than the reference temperature), the translated voltage is:
[ ( )]
44.4 V + [44.4 V × -0.0033/ C × (60-25) C]44.4 V - 5.19 V = 39.2 V
trans ref ref V cell ref
trans
trans
V V V C T T
VV
= + × × −
=
=
44.4 V + [44.4 V × -0.0033/ C × (-10 - 25) C]44.4 V + 5.19 V = 49.6 V
trans
trans
VV
=
=
Presenter
Presentation Notes
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/m2 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. 132-134
2012 Jim Dunlop Solar Cells, Modules and Arrays: 5 - 48
Response to Temperature: Example 2
A crystalline silicon PV array has a power-temperature coefficient of -0.45 %/°C and rated maximum power output of 50 kW at 25°C and solar irradiance of 1000 W/m2. What would the array maximum power be at a cell temperature of 50°C?
If the same PV module operates at 0°C (25°C lower than the reference temperature of 25°C), the translated power is:
2012 Jim Dunlop Solar Cells, Modules and Arrays: 5 - 49
Building PV Arrays
PV modules are connected
electrically in series to build voltage output.
Series strings of PV modules are connected in parallel to build current and power output.
Voltage (V) C
urre
nt (A
)
Presenter
Presentation Notes
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. 136-138
2012 Jim Dunlop Solar Cells, Modules and Arrays: 5 - 50
Monopole and Bipolar PV Arrays
Monopole PV arrays consist of two output circuit conductors.
Bipolar PV arrays combine two monopole arrays with a center tap.
Bipolar Array Monopole Array
PV Array
Positive (+) Negative (-) Center Tap
PV Array
Positive (+) Negative (-)
PV Array
Presenter
Presentation Notes
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.
2012 Jim Dunlop Solar Cells, Modules and Arrays: 5 - 51
Connecting Similar PV Devices in Series
(-)
Pos (+) Neg (-)
1 2 (+) (-) (+) n (-) (+)
Vseries string = V1 + V2 ….. + Vn Vseries string = V1 x n
Iseries string = I1 = I2 ….. = In (for similar devices)
Presenter
Presentation Notes
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. 136-138
2012 Jim Dunlop Solar Cells, Modules and Arrays: 5 - 52
I-V Curves for Similar PV Devices in Series For similar PV devices in series:
Vseries = V1 + V2 ….. + Vn
Vseries = V1 x n
Iseries = I1 = I2 ….. = In
Voltage (V)
Cur
rent
(A)
1 device 2 devices in series
“n” devices in series
Presenter
Presentation Notes
Reference: Photovoltaic Systems, p. 136-138
2012 Jim Dunlop Solar Cells, Modules and Arrays: 5 - 53
Dissimilar PV Devices in Series
When dissimilar PV devices are connected in series, the voltages still add, but the current is limited by the lowest current output device in series.
Not acceptable.
Vseries = VA + VB
Iseries = IA < IB
Pos (+) (-) (+) Neg (-)
Pos (+) Neg (-)
A B
Presenter
Presentation Notes
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. 136-138
2012 Jim Dunlop Solar Cells, Modules and Arrays: 5 - 54
2012 Jim Dunlop Solar Cells, Modules and Arrays: 5 - 56
Connecting Dissimilar PV Devices in Parallel
When PV devices with the same voltage but with different current output are connected in parallel, the individual currents add, and the voltage is the average of devices.
Vparallel = (VA + VB) / 2
Iparallel = IA + IB
B
A
Pos (+) Neg (-)
Presenter
Presentation Notes
Reference: Photovoltaic Systems, p. 136-138
2012 Jim Dunlop Solar Cells, Modules and Arrays: 5 - 57
Series strings of PV modules with similar voltage but having different current output may be connected in parallel.
Connecting Dissimilar PV Devices in Parallel
Voltage (V)
Cur
rent
(A)
Device 1
Devices 1+2 in parallel
For dissimilar current PV devices in parallel:
Vparallel = (V1 + V2 … + Vn) / n
Iparallel = I1 + I2 ….. + In
Device 2
Presenter
Presentation Notes
Reference: Photovoltaic Systems, p. 136-138
2012 Jim Dunlop Solar Cells, Modules and Arrays: 5 - 58
Bypass Diodes
Bypass diodes are connected in parallel with series strings of cells to prevent cell overheating when cells or parts of an array are shaded.
When cells are not shaded, the bypass diode is reverse biased and does not conduct current
Shaded cell
When a cells is shaded, the bypass diode is forward biased and conducts current
Pos (+) Neg (-)
Presenter
Presentation Notes
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. Reference: Photovoltaic Systems, p. 139-140
2012 Jim Dunlop Solar Cells, Modules and Arrays: 5 - 59
Without Bypass Diodes
Voltage (V)
Cur
rent
(A)
Module 1
Module 2
0
operating current
Power produced by module with higher current (healthy module)
Large power dissipation in module with lower current (failing module)
<< Negative voltage (reverse bias) Positive voltage (forward bias) >>
Presenter
Presentation Notes
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. 139-140
2012 Jim Dunlop Solar Cells, Modules and Arrays: 5 - 60
With Bypass Diodes
Voltage (V)
Cur
rent
(A)
Module 1
Module 2
0
operating current
Power produced by module with higher current (healthy module)
Low power dissipation in module with lower current (failing module)
<< Negative voltage (reverse bias) Positive voltage (forward bias) >>
Presenter
Presentation Notes
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. 139-140
2012 Jim Dunlop Solar Cells, Modules and Arrays: 5 - 61
Module Junction Box with Bypass Diodes
Presenter
Presentation Notes
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. 139-140
2012 Jim Dunlop Solar Cells, Modules and Arrays: 5 - 62
PV Module Rating Conditions
The electrical performance of PV modules is rated at Standard Test Conditions (STC): Irradiance: 1,000 W/m2 , AM 1.5 Cell temperature: 25°C
Source: SolarWorld USA
Presenter
Presentation Notes
Standard Test Conditions (STC) is the universal rating condition for PV modules and arrays, and specifies a solar irradiance level of 1000 W/m2 at air mass 1.5 spectral distribution, operating at 25°C cell temperature. Reference: Photovoltaic Systems, p. 141-143
2012 Jim Dunlop Solar Cells, Modules and Arrays: 5 - 63
Other PV Module Ratings
Standard Operating Conditions (SOC) Irradiance: 1,000 W/m2
Nominal Operating Cell Temperature (NOCT) Irradiance: 800 W/m2
Ambient Temp: 20°C PV Array: open-circuit Wind Speed: 1.0 m/s
PVUSA Test Conditions (PTC):
1000 W/m², 45°C, 1 m/s
Presenter
Presentation Notes
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. 141-143
2012 Jim Dunlop Solar Cells, Modules and Arrays: 5 - 64
PV Module Rating Conditions
Voltage
STC SOC
PTC NOC
Presenter
Presentation Notes
The differences between rating conditions can be clearly shown by the I-V curves. Reference: Photovoltaic Systems, p. 141-143
2012 Jim Dunlop Solar Cells, Modules and Arrays: 5 - 65
Approved Modules
Certain listed PV modules have been approved as “eligible
equipment” for California incentive programs. See: www.gosolarcalifornia.org
These modules have had additional independent performance
tests for PTC ratings.
Many other states refer to this list for eligible equipment for their incentive programs.
Qualification and Type Approval IEC 61646: Thin-Film Terrestrial Photovoltaic (PV) Modules - Design Qualification
and Type Approval
Performance Measurement ASTM E1036: Standard Test Methods for Electrical Performance of Non-
concentrator Terrestrial Photovoltaic Modules and Arrays Using Reference Cells
Presenter
Presentation Notes
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 61730 is published by the International Electrotechnical Commission (IEC), and harmonized with the UL 1703 standard. Reference: Photovoltaic Systems, p. 141-143
2012 Jim Dunlop Solar Cells, Modules and Arrays: 5 - 67
PV Module Markings
All PV modules must be marked
with the following information [NEC 690.51]:
Open-circuit voltage Short-circuit current Operating voltage Operating current Maximum power Polarity of terminals Maximum overcurrent device
rating Maximum permissible system
voltage
Presenter
Presentation Notes
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. 142-143 NEC 690.51
2012 Jim Dunlop Solar Cells, Modules and Arrays: 5 - 68
Fire Classification
PV modules may be evaluated for external fire exposure for
building roof covering materials.
The fire class is identified in the individual Recognitions as class A, B or C in accordance with UL's Roofing Materials and Systems Directory.
Modules not evaluated for fire exposure are identified as NR (Not Rated), and not suitable for installation on buildings.
Presenter
Presentation Notes
Reference: Photovoltaic Systems, p. 141
2012 Jim Dunlop Solar Cells, Modules and Arrays: 5 - 69
additional reliability testing that validates long-term warranties.
The tests include: Thermal cycling tests Humidity - freezing tests Impact and shock tests Immersion tests Cyclic pressure, twisting, vibration and other mechanical loading tests Wet/dry hi-pot, excessive and reverse current electrical tests Other electrical and mechanical tests.
Presenter
Presentation Notes
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-61215 covers “Crystalline Silicon Terrestrial Photovoltaic (PV) Modules - Design Qualification and Type Approval”, and the second, IEC 61646 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. 141-143
2012 Jim Dunlop Solar Cells, Modules and Arrays: 5 - 70
Module Installation Instructions
Listed PV modules must be installed in accordance with
instructions provided (shipped) with product.
Includes safety information, working with PV modules during sun hours (energized electrical equipment), mounting configurations, and electrical wiring and grounding instructions.
Presenter
Presentation Notes
References: Photovoltaic Systems, p. 145-147 NEC 110.3
2012 Jim Dunlop Solar Cells, Modules and Arrays: 5 - 71
PV Module Safety
Most manufacturer’s literature states that module installation should be done by qualified, licensed electrical professionals.
Safety precautions for installing PV modules include: Do not insert electrically conducting parts into the plugs or sockets. Do not wear metallic jewelry while performing installation. Do not fit solar modules and wiring with wet plugs and sockets. Tools and
working conditions must be dry. Exercise extreme caution when carrying out work on wiring and use the
appropriate safety equipment (insulated tools/gloves, fall protection, etc.) Do not use damaged modules. Do not dismantle modules. Do not remove
any part or label fitted by the manufacturer. Do not treat the rear of the laminate with paint, adhesives or mark it using sharp objects.
Do not artificially concentrate sunlight on modules.
Presenter
Presentation Notes
Reference: Photovoltaic Systems, p.143-144
2012 Jim Dunlop Solar Cells, Modules and Arrays: 5 - 72
Handling PV Modules
Care in handling, transporting, storing and installing PV modules
includes the following: Leave modules in packaging until they are to be installed. Carry modules with both hands, do not use connectors as a handle Do not stand modules on hard ground or on their corners Do not place modules on top of each other or stand on them Do not mark or work on them with sharp objects Keep all electrical contacts clean and dry Do not install modules in high winds
2012 Jim Dunlop Solar Cells, Modules and Arrays: 5 - 73
Module Selection Criteria
The selection of PV modules for a given project may be based on
any number of factors, including: Module physical and electrical specifications Manufacturer certification to quality standards (ISO 9000) Module warranty and design qualification (IEC 61215/61216) Customer satisfaction and field results Company ownership and years in business Costs and availability
Presenter
Presentation Notes
Reference: Photovoltaic Systems, p. 143-144
2012 Jim Dunlop Solar Cells, Modules and Arrays: 5 - 74
Summary
Photovoltaic (PV) cells are semiconductor devices that produce electrical output when exposed to sunlight.
The current-voltage characteristic (I-V curve) is the basic descriptor of PV device performance.
The output of a PV device is dependent upon sunlight intensity, temperature and electrical load.
PV devices are connected in series to build voltage, and in parallel to build current and power output.
PV modules are installed in accordance with installation instructions and local building codes.
Presenter
Presentation Notes
Reference: Photovoltaic Systems, p.145-147
2012 Jim Dunlop Solar Cells, Modules and Arrays: 5 - 75
