Photovoltaic panels are made up of cells. There are usually 60, or 72, or sometimes more, depending on the power you intend to get from a single panel. It should be clear that the efficiency of commercial photovoltaic cells is currently at \( ~25\% \) and for a panel to have more power it must occupy a larger area. The power output of a standard cell (with dimensions of 156 mm * 156 mm) is about 5 Wp. Therefore, in order for the panel to generate 800 Wp of power, it must consist of 200 cells, which translates into the size of its surface. A standard panel installed in popular photovoltaic installations has dimensions 165 cm * 100 cm. Sometimes these dimensions vary slightly, depending on the manufacturer. A panel made of monocrystalline silicon with such dimensions has power from 310 Wp to 340 Wp.
Depending on the type of cell used to build the panel, its name is adopted, e.g. monocrystalline panel - c-Si, polycrystalline panel - mc-Si, or amorphous panel - a-Si. In addition to typical silicon panels, thin-film panels are also produced. In this case the names are given according to the type of active layer in the cell. And so, for example, photovoltaic panel CIGS/CIS is built on one side from a mixture of copper, indium, gallium and selenium (CIGS), and on the other from copper, indium and selenium (CIS).
Among photovoltaic panels, due to the structure of the cell and the whole panel, we can distinguish groups such as: thin-film panels, panels with contacts at the back, HIT type panels, PERC type panels, double-sided panels, panels made with SmartWire technology. Of course, in each group you can specify additional types, which will be distinguished by some element, such as thin-film cells connected together in SmartWire technology.

HIT technology - photovoltaic panels with HIT cells

An inner thin layer based on n-type crystalline silicon is sandwiched between two thin amorphous layers. The technology of monocrystalline panels was developed by the Sanyo company. The advantage of this type of panels is the conversion of low energy radiation (infrared) into electricity, and low temperature power drop factor which is at \( 0.29\% \)/ \( _{}^{o}\textrm{C} \). The silicon wafer processing is done at a lower temperature of about \( 200_{}^{o}\textrm{C} \). The panels are also produced in a hexagonal shape (bee slice, honeycomb), which results in better utilization of the crystalline silicon.

Technology based on p-type monocrystalline silicon

A typical photovoltaic cell based on p-type Si semiconductor is shown in Fig. 1. Figure (a) presents a schematic cell, while figure (b) depicts an actual cell made with 2 busbar technologies, that is, 110 common points with charge-collecting fingers. Finally in figure (c) one can see a photovoltaic panel made with 2 busbar technologies.

Nowadays you can find technology with 2, 3, 5 busbars, but also with 12 wires acting as busbars ( Fig. 2 ).

Panels fabricated with 12-wire busbar technology are still spot soldered at \( 250_{}^{o}\textrm{C} \), which stresses the cell. Polycrystalline or amorphous silicon panels are produced in a similar manner.

Panels with both electrodes at the back

'All back contact' technology with both electrodes at the back has relatively high efficiencies up to \( 24\% \). The front of the panel is homogeneous, with no electrodes visible. The location of the electrodes at the back contributes to greater corrosion resistance of the electrical connections. The disadvantage of this solution is the so-called PID degradation effect, i.e. degradation related to the occurrence of high voltages (~600V) between the panel frame and the semiconductor. This causes charges to flow to the ground and the panel power decreases. Therefore, it is necessary to ground the positive pole and appropriate selection of the inverter to adapt to the problem.

SmartWire technology - photovoltaic panels with microwires

This consists of replacing the classical soldering by lamination with a film containing 18 to 32 microwires, which from 990 to 1760 contact points with charge-collecting fingers. This reduces the temperature at which the photovoltaic panel is generated to \( 150_{}^{o}\textrm{C} \) across the surface, rather than point-wise, as in the case of soldering at \( 250_{}^{o}\textrm{C} \). The wire wrap is applied to the front and back of the panel. This allows manufacturers to save silver paste and solder material. This large number of contact points allows the cell to work even with microcracks.

Shingled technology - shingle photovoltaic panels

The photovoltaic cell in a shingled panel [1] is cut into 3 to 6 strips, which are then assembled into strings that connect the front of each strip to the back of the next strip using a suitable electrically conductive adhesive (ECA) that can be printed or dispensed onto the surface of the strip. The individual cells are assembled "overlapping", i.e., each thin strip slightly overlaps the next, and their joints are hidden under individual "busbars" ( Fig. 3 ) [2]. To obtain the required panel layout, the cell needs to be divided into a sufficient number of parts. Typically, strip strings up to 2 m long are assembled, which corresponds to the longer side of a traditional 72-cell panel. The strips are then connected to each other by conductive ribbons, assembled according to the traditional photovoltaic panel manufacturing procedure.

This design makes optimal use of the surface area of the entire panel, which increases the active area of the panel and thus allows for higher efficiency from 1 \( m^{2} \) area by up to \( 15\% \).

In summary, in panels made with Shingled technology, the panel area is better utilized, there are lower ohmic losses and increased reliability. Lower ohmic losses also mean lower operating temperature of the cell.