Bypass Diodes

You may have read about bypass diodes and solar panels. But what are they, and what do they do? Well there are 2 main types commonly used in solar panels. Bypass and Blocking. In this article I will explain about Bypass Diodes.

In almost all crystalline photovoltaic solar panels there are bypass diodes. Panels are made up of silicon cells that each produces approximately half a volt. Linking these together in series allows the voltage to increase to the desired output. For example 36 cells will produce 18v. Once a load is attached this will reduce to around 12-14v making a perfect 12v Solar panel.So we’ve learnt that connecting 36 cells in a row makes a good 12v panel. But 36 cells in a row can make for a strange and awkward shape panel. The answer is to lay the cells in shorter rows and make the panel more compact. The string is then made into 4 shorter strips and connected at the ends making effectively a “W” shape.

Now the panel is compact and pretty. But there is another reason for this “W” shape. And on larger panels this is done even more to make more points/ends. The reason is this. If at any time you cover over one of the cells the voltage will drop hugely. You may think that by covering one of the 36 cells would reduce the voltage from 18v to 17.5v. After all each cell is 0.5v and only one have been covered. The reality is that it will drop to more like 5v rendering the panel almost useless.
With the “W” shape layout this allows for a bypass to be made and effectively removing the covered cell from the circuit. Between the points at the top of the “W” 2 diodes are inserted to span the gap. The diode allows the energy to take the easiest route. If there is no energy or significantly less energy being generated by one of the sections it finds an easier route through the diode. The voltage is now 9v and not the stunted 5v.
You may be saying “9 volt is still useless”. And in this example you are right. It may not be enough to charge a 12v battery successfully. But in home systems particularly as well as 24v and higher voltage systems 2 or more panels are linked up to make a “WWWWWW”shape. Now if one of the sections is covered the voltage drop is low as a percentage of the total.
Covered cells can occur in instances like the dreaded bird mess , a bird, leaves, heavy levels of dust and dirt, snow and on very large installations even small clouds.
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