Did you know?
Once installed, modules should last for well over 20 years and achieve a high output day after day?- Price and efficiency alone are not sufficient decision criteria when choosing a solar panel?
- Further characteristics of the module quality affect yield and durability – and thereby investment security
When assessing the total yield of a solar energy system, today the focus is often on the time it takes to break even or the length of time the state will fund the project. A basic assumption is that the system will operate without errors, although this is not always true. Often, users base their solar module choice solely on the nominal degree of efficiency and peak price per watt. From a long-term perspective, however, other criteria should be taken into consideration during the assessment. A good module should be able to achieve a reliably high yield for well over two decades.
Module Components
CELLS |
| At the heart of the solar module is the solar cell. A careful combination of efficient cells with uniform properties is the prerequisite for a high degree of module efficiency, a long service life and high yields. |
| The most commonly used cells throughout the word are made from polycrystalline silicon. These cells are always square and can easily be identified by their uneven markings. Cells made from monocrystalline silicon usually feature a somewhat higher degree of efficiency. The typical ‘cropped’ corners, however, reduce the size of the active cell surface and the higher cell efficiency is not fully converted into a higher overall module efficiency. In terms of the output generated and durability, there is no difference between the two types. |
| Practical Tip #1: Note the number of busbars. |
| To be able to conduct the electricity generated by the cell to a load, this must have an electrical contact. This is formed by the metallic contact grid mounted on the cell surface that consists of thing fingers and wide strips – to so-called busbar.
A number of module manufacturers use cells with two busbars, as these cells can be obtained from various sources and ofter posses a high degree of cell efficiency. To be able to conduct the electricity generated particularly reliably, cells are being fitterd with three busbars, as this allos the load to be better distributed and contact resistances between the cells to be reduced. This enables cells with three busbars to achieve a higher degree of module efficiency and at the same time improved reliability. |
GLASS |
| The glass is a stabilising, translucent support material on the module. In contrast to window glass, highly transparent, thermally pre-stressed toughened glass (solar glass) is usually used for modules. |
| Practical Tip #2: Check the glass surface. |
| A wide range of different solar glasses are available on the market: flat, unstructured, microstructured, heavily structured glasses or even specially coated glasses. The task of these glass types is to channel as much sunlight as possible into the module. Heavily structured glasses, however, tend to be prone to contamination, which can have a negative impact on the module output over time. Better suited to European latitudes is the use of microstructured glass, which features a self-cleaning effect when subjected to occasional rainfall and is far less likely to result in the build-up of moss.
Modules with anti-reflective-coated glass are also available on the market. Here, it is important to ensure that the durability of the coating is guaranteed for the extended service life of the module (at least 20 years). As with spectacle lenses, the anti-reflective coating can age or even flake off, which in extreme cases can lead to the deterioration of the module output. |
FRAME |
| The module frame protects the delicate outer edges of the glass film laminate and, together with the special glass, guarantees stability and torsional rigidity.
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| Practical Tip #3: Check the condition and quality of the frame.
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| The most robust and stable frames are those made from anodised aluminium, which in contrast to coated frames are less prone to scratches. Frames should not feature any closed cavities as these can collect water, which can corrode the frame and lead to bends or to break completely. A flat runoff edge along the cells can also ensure that contamination such as pollen or dust cannot collect on the edges, which means that moss is unable to grow. Such contamination is particularly critical when it covers parts of the cells, as this can considerably reduce the output of the module.
A good frame is screwed together. Special screw connect all parts of the frame in such a way that they are mechanically and electrically conductive and thereby enable the module to be earthed throughout. Frame parts that are not screwed together but rather interlocked, and non-metallic corner connections are not recommended. The frame should of course feature good, clean workmanship without sharp edges or protruding screws. Also ensure that the frame parts are properly attached to the laminate. On the rear of the frame, on the inside edges, special frame hinges ensure a clean and consistent seal. Ensure the parallel and straight alignment of the hinge. Silicon can also provide adhesion when applied evenly and flush and not sprayed onto the frame. Silicon is, however, more susceptible to climatic conditions and should therefore be avoided. |
JUNCTION BOX |
| The primary task of a junction box is to channel the direct current generated by the module to the outside. If incorrectly designed or manufactured it can represent a risk of fire for the photovaltaic system in certain circumstances.
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| Practical Tip #4: Check for soldered and encapsulated junction boxes.
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| Soldered or welded connections created in automated processes are secure and stable. Proceed with caution with clamped, plug-in or screw connections. If these are improperly manufactured, they can become loose or rust and thus cause a short circuit. The resulting electric arc can cause fires in the junction box.
Junction boxes cast with flame-retardant plastic are protected against the ingress of moisture and air. This provides additional safety. |
| Practical Tip #5: Bypass diodes protect cells from damage.
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| Bypass diodes support optimised operation, even under unfavourable operating conditions. If cells are covered temporarily, eg by leaves, the bypass diodes channel the electricity from the cells that are not covered across the covered cells and thereby protect them against damage. When the cells are no longer covered, the bypass diodes switch back to their original state and the module is again able to achieve its full output. Good modules have several bypass diodes, each of which should be connected to a maximum of 16-20 cells. A special diode cooling system dissipates the heat generated by the diodes.
It is also important to ensure that in the box, the connection area of the cells is electrically and thermally isolated from teh diode area. Also avoid plugged-in diodes here. This guarantees maintenance-free operation of the module throughout its entire service life. It is not necessary to replace the diodes. |