As previously mentioned in our solar charge controller article, shading can be a major problem for system performance. Some of the older type solar panels can suffer significant performance drop with partial shading and even complete interruption if cells are blocked by leaves or other debris.
Solar panels or modules are comprised of many cells arranged in series as shown in the diagrams below;
As with any series connection, an interruption to cells, as in the example shown above right, will disable the entire string and therefore output from the solar panel/module will be interrupted. To counter this problem solar panel manufacturers added Bypass Diodes.
Without going too much into the science a Bypass Diode does exactly what it's name suggests, it allows current to bypass the affected section of the module and pass current, albeit at a reduced output. In standard panels this would significantly reduce panel performance as in the example on the left, a drop of 33% would occur. This would severely affect the performance of the series array of a solar system, as the output would drop to the level of the lowest performing module. The impact would however be much lower on a parallel connected array (a separate article on series, parallel and series/parallel connections will be available shortly).
Manufacturers are constantly finding ways to improve solar module performance, enter the Half-Cut module. These are essentially two smaller modules incorporated into a single panel, drastically improving the performance of the panel under shading conditions. To illustrate this take a look at the diagram below and compare the full module vs the half-cut module;
As you can see the Half-Cut module bypass diodes are arranged at the junction of the integrated modules and this reduces the number of cells in each series loop, and therefore reduces the number of cells affected by shading or total blockage.
The illustration left clearly shows the reduced shading impact on the module through the loss of fewer cells and the resulting performance loss being reduced to only 10% of the potential total panel output. This is a far better outcome for panels exposed to shading and minimises the impact on the overall series array.
The reality is that many modern motorhomes or caravans have a plethora of gadgets or devices mounted on the roof and at some part of the day shading may be unavoidable. For those of us totally off-grid, it becomes crucial to minimize the impact of shading so we can harvest as much of the sun's energy as possible. Some would argue that you just add more or bigger capacity modules to the roof . This is not always possible due to limited roof space or undesirable due to cost constraints. More panels generally means more of everything else in your system (larger/additional solar controllers, bigger wires, fusing, etc...). The advances in solar module technology can certainly help if you wish to minimise the impact of shading on your system and replacing older panels with more efficient modern panels may be all that's needed.
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