How to read and understand the basic characteristics of solar panels (PV modules)
Each solar panel has mechanical and electrical characteristics. Let’s see what it looks like.
Solar cells dimensions
The cell is usually squares like shapes 161.7 x 161.7 mm / 6 inches x 6 inches. It could vary depending on the technology being produced. A solar panel, or PV module, is a set of solar cells. Typically, the solar panels used in residential solar installations include 60 or 72 cells. Although 60-cell solar panels are more affordable, 72-cell solar panels are more powerful and larger.
Solar panel dimensions and number of cells
Panel dimensions are not strictly standardized and vary depending on the manufacturer. This dimension depends on the number of cells and their arrangement. Foe example, panel with 60 cell typically has measure 1.65 m (65 inches) in length and 1m or 40 inches width. A 72-cell solar panel typically measures 2m 79 inches (2 meters) long, 40 inches (1 meter) wide. All PV modules are 1.5 inches (37–40 mm) thick. Depending on the efficiency coefficient, we can roughly calculate that about 200 W is obtained per square meter of panel. solar panel typically measures 2m 79 inches (2 meters) long, 40 inches (1 meter) wide. Almost all PV modules are 1.5 inches (37–40 mm) thick. Depending on the efficiency coefficient, we can roughly calculate that about 200 W is obtained per square meter of panel.
Picture above : Some of the dimensions of solar panels With the increase in surface area, the obtained energy also increases
Half cut solar cells
There are also other varieties of solar panels. This relatively new technology has been promoted as a mitigating method for solar panel shading. Half-cut solar panels employ the same cells as conventional solar panels. Approximately equal in size to 60-cell solar panels are 120 half-cut solar panels, and 72-cell solar panels are 144 half-cut solar panels. Some solar panels used in residential installations have different numbers of cells. For example: 66 or 96.
Cell types: monocristaline and polycristaline
The main difference between the two technologies is in the crystal purity of the panel cells. Monocrystalline solar panels have solar cells made from a single crystal of silicon, while polycrystalline solar cells are made from several fragments of silicon melted together. The crystalline purity of the cells of monocrystalline solar panels is therefore much higher than that of polycrystalline solar panels. Efficiency is greater on monocristaline and varies from 16% to 24%, and with polycristaline, it varies from 14 % upto 200%, but price is lower on polycristalin. The efficiency warranty at both is usually up to 25 years.
Cell types: N and P-type
P-type cells are doped with atoms that have one fewer electron than silicon, such as boron, resulting in a positive (P) charge. N-type cells, on the other hand, are doped with atoms that have one more electron than silicon, making them negative (N). While N-type cells offer higher efficiency potential than P-type cells, they are more costly.
All types of solar panels have two warranties: a physical warranty and an efficiency warranty.
The physical warranty is generally 15 to 30 years and covers any physical damage.
The efficiency warranty means that cells will produce X nominal power after N years. Every year PV module loses 0.5% from declared power. For example, 80% after 25 years means the panels will produce 80% of the electricity they produced in their first year. Although they produce less energy, the panels still work very well.
The weight of the panel depends on the dimensions more precisely than the surface of the panel and ranges from 19 to 35 kg. Bifacial panels are heavier than regular ones.
Front and rear load
anels must withstand static loads such as snow and dynamic loads such as wind. The panels have declared front and rear loads. Each panel has a declared durability per square meter, which is usually expressed as pressure in measurement units called Pascals. 1Pa = 102g/m2. For example, 5400 Pa Front Load means that the panel can withstand 540 kg per m2.
The panel must be coated with anti-reflective glass. Anti-reflective glass reduces surface glare and increases substrate transmission and brightness. It produces single- or multi-layer dielectric AR coatings. Anti-reflective coatings can be designed from: acrylic, poly carbonate, heat tempered glass.
Number of Bussbar
The busbar is the number of metalized strips a single solar cell has printed on the front and rear sides. Usualy we have is the 3 main types of busbars: 3BB, 4BB, and 5BB.
Common electrical properties
The solar PV industry uses several types of connectors or standard non-connector junction boxes. The most frequently used ones are: MC4 (most popular) , MC3 (slovly going to pension), T4 (Canadian Solar standard) , Amphenol, Tyco and Radox. The only purpose of the positive and negative labels is to assist the installation. A cable couple is required for each connector. One of the most crucial steps in connecting the modules in a solar PV system is crimping the cable couple. Resistance might greatly lower efficiency if improperly made. Amphenol connectors and MC4 connectors can be interchanged. The connectors must be connected and disconnected using a tightening or unlocking tool. The cable must be attached to the connector using a crimping tool. Special dies for the Rennsteig crimping tool can be switched out. Each connector can be installed using a different set of crimping tools.
Junction box and IP protection
Most PV junction boxes have diodes. The function of the diodes is to keep the power flow going in one direction and prevent hot spots from forming when the resistance increases in parts of the panels when there’s no sunshine. IP68 type is widely used. Protection is marked with the initials IP. “Ingress Protection” is an international standard used to determine the protection of junction box panels and lamps from some solid objects and elements, such as water and dust. The IP rating consists of two numerical numbers; the first determines the level of protection against the penetration of solid objects, such as dust. IP with initial numbers 5 and 6 is more suitable for areas that will be exposed to severe weather conditions. Initial number 5 means “dust protection,” preventing the ingress of dust sufficient to cause harm. Initial number 6 means “total protection.” No ingress or dust. The usual protections for the junction box are: IP 65: water jet protection, such as water from a hose at any angle. IP 66: protection against a strong jet of water on any surface of the panel; IP 67: protection against submersion for a limited time. IP 68: Protection during permanent submersion, at a depth defined by the manufacturer. The panels have a lower level of protection, usually IP 56, which requires protection against a strong jet of water on any surface of the panel to obtain full functionality.
I - V curve
The panel manufacturer provides a functional characteristic of voltage and current depending on the radiation. From the curve, it is easy to read the maximum power for each option. The diagram shows the short-circuit current and the open-circuit voltage, as well as the maximum power point.
I -V curve for half and maximum load
I -V curve with Power points
Nominal (NOCT) and Standard (STC) properties
All PV panels have this confusing terms for common users.
STC (Standard Test Condition)
Is an industry-wide standard to indicate the performance of PV modules and specifies Irradiance 1000 W/m², Cell Temperature 25 °C, Air mass AM 1.5 * T discretion. The Typical change in module efficiency as 200W/m² in relation to irradiance 1000W/m² is: +-2.0%
NOCT (Nominal Operating Cell Temperature)
PV modules often does not work in ideal conditons. NOCT is defined as the temperature reached by open circuited cells in a module under the conditions : solar iradiance 800 W/m2, ambient temperature 20 °C, wind speed 1 m/s.
Maximum power Pmax with NOCT
The Pmax is the sweet spot of the solar panel power output, located as the arc of the curves in the I-V graph. It is point where the combination of the volts and amps results in the highest wattage P=V*I. If we use a Maximum Power Point Tracking MPPT charge controller or inverter, this is the point that the MPPT electronics tries to keep the volts and amps as to maximize the power output.
Electrical properties similear for STC and NOCT
- * Maximum Power Point Voltage – Mpp Voltage (Vmpp)
*Maximum Power Point Circuit- MPPC or (Impp)
* Open Circuit Voltage (Voc)
* Short Circuit Current (Isc)
Maximum Power point Voltage (Vmpp)
The Vmpp is the voltage as which the power output is greatest. It is the actual voltage we want to see when it is connected to the MPPT solar equipment.
Open Circuit Voltage (Voc)
Open circuit voltage is measure volts the solar panel outputs with no load on it. If we measure with a voltmeter across the plus and minus leads, we will read Voc. Since the solar panel isn’t connected to anything, there is no load on it, and it is producing no current. This is a very important number, as it is the maximum voltage that the solar panel can produce under standard test conditions, so this is the number to use when determining how many solar panels you can wire in series going into your inverter or charge controller.
Short Circuit Current (Isc)
When a PV cell’s terminals are connected in a short circuit, the cell can produce its maximum current, known as its short-circuit current (Isc). However, as this maximum current, the terminal voltage of the cell would be 0.
Maximum Power Point Circuit- MPPC or (Impp)
The Impp is the current (amps) when the power output is the greatest. It is the actual amperage you want to see when it is connected to the MPPT solar equipment under standard test conditions.
Module Efficiency (%)
In general, module efficiency is a term for all energy conversion machines. In PV refers to the portion of energy in the form of sunlight that can be converted to current (DC). The average value for polycrystals ranges from 20% to 21%, although some manufacturers claim that they reach as much as 24.5%.
Operating Temperature (°C)
represent external temperature as which PV will work. This range goes from -40 °C to 85 °C. Keep in mind that the ideal outside temperature is 25 °C. As the temperature increases, the characteristics of the panel decrease.
Maximum System Voltage (V)
is a measure that must not be exceeded. Typically, the maximum voltage of the residential system is 600 V or 1000 V. For some panels could be 1500V.
Maximum Series Fuse Rating
is amount of current that is permitted to be imposed on a PV module for any conditions. For residential this rating is 15 A., but could be 20 A and 25 A.
Power Tolerance (%)
Power Tolerance is the real range that a PV module can deviate in STC Max Power. Common values are: -10% / +10%