Solar (PV) Cell Module, Array

The basic element of a PV System is the photovoltaic (PV) cell, also called a Solar Cell. An example of a PV / Solar Cell made of Mono-crystalline Silicon is shown in Fig. 3 below. This single PV / Solar Cell is like a square but with its four corners missing (it is made this way!).
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Fig.3. PV / Solar Cell

Theory of Operation of PV / Solar Cell

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Fig.4. Construction and Working of PV / Solar Cell

A PV / Solar Cell is a semiconductor device that can convert solar energy into DC electricity through the “Photovoltaic Effect” (Conversion of solar light energy into electrical energy). When light shines on a PV / Solar Cell, it may be reflected, absorbed, or passes right through. But only the absorbed light generates electricity.

PV Module / Panel and PV Array

To increase their utility, a number of individual PV cells are interconnected together in a sealed, weatherproof package called a Panel (Module). For example, a 12 V Panel (Module) will have 36 cells connected in series and a 24 V Panel (Module) will have 72 PV Cells connected in series

To achieve the desired voltage and current, Modules are wired in series and parallel into what is called a PV Array. The flexibility of the modular PV system allows designers to create solar power systems that can meet a wide variety of electrical needs. Fig. 5 shows PV cell, Panel (Module) and Array.

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Fig.5. PV cell, Module and Array

The cells are very thin and fragile so they are sandwiched between a transparent front sheet, usually glass, and a backing sheet, usually glass or a type of tough plastic. This protects them from breakage and from the weather. An aluminum frame is fitted around the module to enable easy fixing to a support structure. The picture in Fig. 6 below shows a small part of a Module with cells in it. It has a glass front, a backing plate and a frame around it.
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Fig.6. Construction of a typical Mono-crystalline PV / Solar Panel

Bypass Diodes

As mentioned, PV / Solar cells are wired in series and in parallel to form a PV / Solar Panel (Module). The number of series cells indicates the voltage of the Panel (Module), whereas the number of parallel cells indicates the current. If many cells are connected in series, shading of individual cells can lead to the destruction of the shaded cell or of the lamination material, so the Panel (Module) may blister and burst. To avoid such an operational condition, Bypass Diodes are connected anti-parallel to the solar cells as in Fig.7 As a consequence, larger voltage differences cannot arise in the reverse-current direction of the solar cells. In practice, it is sufficient to connect one bypass diode for every 15-20 cells. Bypass diodes also allow current to flow through the PV module when it is partially shaded, even if at a reduced voltage and power. Bypass diodes do not cause any losses, because under normal operation, current does not flow through them.
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Fig.7. Parallel PV cell with bypass diodes