What do the blocking and bypass diodes do for solar cells?

There are two types of diodes that can be quite smart to have mounted on your PV panels. It’s different what type is needed and we will try to explain it here and try not to be too nerdy.
The diagram shows 2 solar panels mounted in series connection, which charges a battery. We have simplified the chart and omitted the charge controller, so you should not do that.

What makes Blocking and ByPass diodes for solar cells?

Blocking diode:

Blocking diodes are needed in Off-Grid battery installations and not in On Grid installations on villa roofs that transmit the surplus power to the grid.

When the sun is shining and the voltage across the solar panels is higher than the battery voltage, the battery will be charged. When it gets dark and the solar cells stop producing, then the power will begin to leak back to the panels and thereby discharge your battery.
This will be prevented by a Blocking Diode.
Therefore, a blocking diode is important in all Off-Grid systems where a battery is being charged (On Grid hybrid systems on rooftops with battery, is typically handled in the inverter).
Blocking Diode is mounted or included for our SunWare and SpectraLite solar panels. All other photovoltaic panels must have them purchased … or they shouldn’t, anyway, because the Blocking diodes are built into all our solar cell controllers, with the exception of HRDi and HRSi.

HRDi and HRSi are combined wind turbines and solar cell chargers. They use the same electronics for both solar cell and wind turbine input. Therefore, the wind turbine at night can stand and produce electricity that ends up in the solar cells rather than the battery. Therefore, a blocking diode must be mounted on HRDi and HRSi.
Parallel connected solar panels must each have their own Blocking Diode mounted.
The Rutland 1200 charging regulator has separate electronics with a built-in diode for the solar cells and therefore there is no need for an external Blocking Diode.

ByPass Diodes:

ByPass Diodes have a completely different function. They have to make sure that if a solar panel is shaded in your series of connected solar panels, then only the one panel/cell of connected solar cells are affected by this. This applies to access for both On Grid and Off Grid solar cells. ByPass diodes are almost always built into the solar panels from the factory (and at least in all ours).
The reason for ByPass Diodes is that if you have 2 solar panels in series connection (see diagram above) and you get shade on panel no. 1, then panel no. 1’s resistance rises sharply and thus the current from panel no. 2 is “eaten” by panel no. 1. The ByPass diode ensures that the current produced on Panel no. 2 can “bypass” thus flow outside panel no. 1 instead of disappearing in panel no 1.
It is very normal that there are several ByPass Diodes in each solar panel, so for example. If a solar panel of 300 watts has 3 ByPass Diodes and the panel is shaded 1/3, then only 100 watts are lost and not the entire panel.
CIGS panel does often have many bypass diodes, which is one of the reasons that they are superior in shaded environments.

When you connect solar panels in parallel, you do get anything from the ByPass diodes. There is nothing to bypass, except the ones built in the panel and they are normally always there.

Conclusion:

Blocking Diode and ByPass Diodes are really important to have in your solar cell system, but it is usually taken care of by the manufacturers. At Energig it is only when you use an HRDi or HRSi let the regulator for a combined solar and wind generator setup that you need a diode that can block backflow to the solar cells at night. The rest is provided for.