Solar Cells and Modules

Solar Cells

A solar cell or photovoltaic cell is a semiconductor device that converts light directly into electricity by the photovoltaic effect.

There are different types of photovoltaic cells:

Single crystal silicon PV cells are manufactured using a single-crystal growth method and have commercial efficiencies between 15 % and 18 %.

Multicrystalline silicon cells, usually manufactured from a melting and solidification process, are less expensive to produce but are marginally less efficient, with conversion efficiencies around 14 %.

PV cells made from silicon ribbons demonstrate an average efficiency around 14 %.

Thin film cells, constructed by depositing extremely thin layers of photovoltaic semi-conductor materials onto a backing material such as glass, stainless steel or plastic, show stable efficiencies in the range of 7 % to 13 %. Thin film materials commercially used are amorphous silicon (a-Si), cadmium telluride (CdTe), and copper-indium-gallium-diselenide (CIGS).

Commercially available thin film modules:

• Are potentially cheaper to manufacture than crystalline cells
• Have a wider customer appeal as design elements due to their homogeneous appearance
• Present disadvantages, such as low-conversion efficiencies and requiring larger areas of PV arrays and more material (cables, support structures) to produce the same amount of electricity

Source: IEA PVPS

Solar Modules

A solar or photovoltaic module or panel is a packaged interconnected assembly of solar cells.

In order to use solar cells in practical applications they must be:

• connected electrically to one another and to the rest of the system,
• protected from mechanical damage during manufacture, transport and installation and use (in particular against hail impact, wind, sand and snow loads). This is especially important for wafer-based silicon cells which are brittle.
• protected from moisture, which corrodes metal contacts and interconnects, (and for thin-film cells the transparent conductive oxide layer) thus decreasing performance and lifetime.

The peak power output of a solar module depends on the number of cells connected and their size. Module performance is generally rated under Standard Test Conditions (STC) : irradiance of 1,000 W/m², solar spectrum of AM 1.5 and module temperature at 25°C. Solar modules are rated in peak watts [Wp] according to their output under STC. Thus, a 50 Wp module can be expected to supply 50 W of power in full sunshine. The performance is reduced by high temperatures.

Modules can be connected in series and/or in parallel depending on the system requirements. A serial connection increases the voltage, a parallel connection increases the current.

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