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. The most common material in solar cell production is silicon that can be applied in different ways.
Monocrystalline Silicon PV Cells
Monocrystalline silicon PV cells are manufactured using a single-crystal growth method and have commercial efficiencies between 15 % and 18 %.
PV cells made from silicon ribbons demonstrate an average efficiency around 14 %.
Polycrystalline Silicon PV Cells
Polycrystalline or multicrystalline silicon PV cells are usually manufactured from a melting and solidification process, are less expensive to produce but are marginally less efficient, with conversion efficiencies around 14 %.
Thin Film PV Cells
Thin film PV cells are 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 under optimal conditions. 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.
Comparison of Different Types of PV Modules
|
Cell material |
Module efficiency |
Surface area needed for 1 kWp |
|
Monocrystalline silicon |
15-18 % |
7-9 m² |
|
Polycrystalline silicon |
13-16 % |
8-9 m² |
|
Micromorphe tandem (aµ-Si) |
6-9 % |
9-12 m² |
|
Thin film: Copper-indium-diselenide (CIS) |
10-12 % |
9-11 m² |
|
Thin film: Cadmium-telluride (CdTe), |
9-11 % |
11-13 m² |
|
Amorphus silicon (a-Si) |
6-8 % |
13-20 m² |
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