Solar Panel

 Individual solar cell devices are often the electrical building blocks of photovoltaic modules, known colloquially as "solar panels". A PV module consists of several interconnected solar cells encapsulated into a single, long-lasting, stable unit. The key purpose of encapsulating a set of electrically connected solar cells is to protect them and their interconnecting wires from the typically harsh environment in which they are used. For example, solar cells, since they are relatively thin, are prone to mechanical damage (break) unless protected. In addition, the metal grid on the top surface of the solar cell and the wires interconnecting the individual solar cells may be corroded by water or water vapour. The two key functions of encapsulation are to prevent mechanical damage to the solar cells and to prevent water or water vapour from corroding the electrical contacts.

Many different types of PV modules exist and the module structure is often different for different types of solar cells or for different applications. For example, amorphous silicon solar cells are often encapsulated into a flexible array, while bulk silicon solar cells for remote power applications are usually rigid with glass front surfaces.

A Solar Panel has multiple layers from top to bottom they are -

Front Glass:
The front glass protects the Solar Cells from the weather and impact from hail or dust. The glass is typically low Iron high-strength tempered glass which is 3.0 to 4.0mm thick and is designed to resist mechanical loads and extreme temperature changes. The IEC minimum standard impact test requires solar panels to withstand an impact of hail stones of 1 inch (25 mm) diameter travelling up to 60 mph (27 m/s). In the event of an impact tempered glass is also much safer than standard glass as it shatters into tiny fragments rather than sharp jagged sections.

Upper EVA Layer:
EVA stands for ‘ethylene vinyl acetate’ which is a specially designed polymer highly transparent (plastic) layer used to encapsulate the cells and hold them in position during manufacture. It is extremely durable and tolerant of extreme temperatures and humidity, it plays an important part in long-term performance by preventing moisture and dirt ingress.

Solar Cell:
Solar Cell is mainly the optoelectronic device that converts the light to electricity.

Lower EVA Layer:
The lamination on either side of the PV cells provides some shock absorption and helps protect the cells and interconnecting wires from vibrations and sudden impact from hail stones and other objects. During manufacture the cells are first encapsulated with the EVA before being assembled within the glass and back sheet.

Backsheet:
The backsheet is the rearmost layer of standard solar panels which acts as a moisture barrier and final external skin to provide both mechanical protection and electrical insulation. The backsheet material is made of various polymers or plastics including PP, PET and PVF which offer different levels of protection, thermal stability and long-term UV resistance. The backsheet layer is typically white in colour but is also available as clear or black, depending on the manufacturer and module.

The most common modules have 36 cells, 60 cells or 72 cells with bypass diodes. A 36-cell produces a maximum open circuit voltage of 17-18 Volts while a 60-cell module produces around 36-38 Volts. A 72-cell panel produces 46-47 Volts. With the Wp (Watt-Peak) of the module increase number of cells increases. Example 10 Wp, 20 Wp, and 40 Wp module comes with 36 cells in series. On the other hand, 325 Wp, 330 Wp, and 335 Wp modules come with 72 cells in series.

Module lifetimes and warranties on bulk silicon PV modules are over 20 years, indicating the robustness of an encapsulated PV module.

Every module comes with some technical specifications written on its back, and also in the Test Report.
The main electrical specifications are:

Peak Power Pmax (Wp): The maximum power that can be drawn from a solar panel while tested with some standards. The Standard Test Condition (STC) is 1000 W/m2 irradiance, 25°C cell temperature, and AM1.5g spectrum.

Maximum Voltage Vmpp (V): This is the voltage available when the panel is connected to a load and is operating at its maximum capacity under standard test conditions.

Maximum Current Impp (A): This current is obtained when the solar panels are producing their maximum power under standard test conditions.

Open Circuit Voltage Voc (V): It is the maximum voltage a solar panel can produce under Standard Test Conditions without any load connected.

Short Circuit Current Isc (A): This is the highest current the solar panel cell can deliver without any damage at Full Load condition or Short Circuit Condition while it is in Standard Test Conditions.
 
Module Efficiency (%): It is defined as the ratio of energy produced by a solar cell to the energy it receives from the sun. The efficiency of solar panels depends on the efficiency of the solar cell. Most solar cells available in the market offer an efficiency of 17-19% and the highest efficiency of a commercial solar panel is about 23%.

The mechanical specifications are:
Length × Width × Height

Weight
Number of Cells

Reference

[1] https://www.pveducation.org/pvcdrom/modules-and-arrays/module-structure
[2] https://en.wikipedia.org/wiki/Solar_panel

[3] https://www.sovasolar.com/upload/media/23102019/Datasheet-23102019.pdf
[4] https://www.vikramsolar.de/download-category/data-sheets/
[5] https://www.renewsysworld.com/post/understanding-open-circuit-voltage-voc-and-short-circuit-current-isc-in-solar-panels
[6] https://www.electronicsforu.com/market-verticals/solar/difference-nominal-voltage-voc-vmp-isc-imp-solar-panels
[7] https://www.cleanenergyreviews.info/blog/solar-panel-components-construction