The solar panel is the main component in any solar power system. Therefore, its functioning should be smooth and efficiency has to be maintained to get the desired output. The blocking diode and By-pass diode plays very important role in maintaining the performance of your solar roof (Please read "How to measure the efficiency of your solar roof?"). They help in restoring the charge in the battery, protect solar panel from the reverse current and by-pass the current for the smooth functioning of your solar roof.
(1) What is a diode?
(2) Understanding the function of the Blocking diode
The following diagram shows two panels are charging the battery through blocking diode, connected in series with the panels and the battery.
When the sunlight falls on the panels, they generate electricity which passes through the blocking diode and charges the battery (Please read "How to size the battery of your solar power system?"). This process goes on until there is sunlight. During night, when there is no sunlight the solar panels stop generating electricity and there develops zero voltage across the terminals of solar panels. The voltage of battery becomes higher than that of panels and it causes the current to flow from battery to the panels. It means that the battery will get discharged if current keeps on flowing from battery to the panels. Here, the role of blocking diode is highlighted; it stops the reverse flow of current from battery to the panels. It prevents the battery from discharging during night and also protects the panels from heating through the reverse current.
(3) Understanding the importance of By-pass diode
The following diagram shows the flow of current when both the panels are working correctly:
In this diagram two additional diodes are present, each are in parallel with their respective panels (Please read "How to size the panels of your solar power system?"). These two diodes are By-pass diodes. These are called so because of their ability to bypass the current which is finding difficult to pass through the panel. Sometimes, the solar panels do not work properly because of snow, debris or shading on their surface. These things causes panel to produce very low power and increases its resistance. Its high resistance blocks the flow of current and becomes hindrance for other panels which are unshaded and are producing desired power.
Case 1: Solar panel 1 is not working properly because of debris or shade on it:
In this case the current produced by the un-shaded panel-2 will pass through the by-pass diode-1 and avoid the high resistance of shaded solar panel-1.
Case 2: When the solar panel-2 is not working properly due to debris, snow or shading
In this case the current from the un-shaded solar panel -1 will pass through the by-pass diode-2 and avoid the high resistance shaded solar panel-2.
So, you can see that how effectively the by-pass diodes are working and maintaining the flow of the current in the circuit.
These are very small devices but their function of blocking the reverse current from battery to panel and by-passing the current through diodes are very important in maintaining the performance of the complete solar power system.