What is a solar bypass diode?

Most solar panel systems consist of individual solar panels being connected in a series to produce higher watts at a steady amperage. For example, a 180 watt, 3.6 amp solar panel system may consist of three 60 watt, 3.6 amp solar panels connected together in a series. The overall productivity - 180 watts - of the solar panel system depends on all three of the 60 watt panels working efficiently. However, if one solar panel connected in a series string fails, due to shade, dirt, destruction or other factors, it will produce electrical resistance (called a hot spot) and now the weakest panel in the solar panel system determines the total current. The covered or damaged solar panel now acts like a resistor and it can actually damage the entire solar panel. A bypass diode creates a path or least resistance around the disabled solar panel and can help to protect your solar panels from damage.

Many panels are set up as actually two strings in one frame. So one 60 watt panel is actually made up of two 30 watt panels. Each half of the panel has a bypass diode, usually inside the junction box, or built into the frame to allow for electricity flow should one of the panels begin acting like a resistor.

It is recommended that a bypass diode be placed in between each solar panel in a multi-panel system to help keep the system working effeciently. I have read that bypass diodes are not needed in all systems, and usually not at all in 12 volt systems, but I feel that it is best to use them to prevent any long-term damage to your system.

What is a solar blocking diode?

If you think of the flow of electricity like the flow of water, then a diode can most closely be related to a one-way valve in a sewage pipe. It lets electricity flow one-way only and blocks it from coming back in - just like a one-way valve operates in a sewage pipe - letting sewage out, but not back into your house.

A solar blocking diode (or low voltage drop diode) is a diode that is used in the electrical schematic of a solar panel to restrict or block the electrical current coming out of the solar panels to reverse or flow backward through the solar panels. If the current were allowed to flow back into the solar panel, the solar panel could get damaged by the current and suffer from thermal destruction. So you do not want the power coming out of a solar panel to ever flow back into it.

It is claimed that if you have a charge controller and a single panel or single string of panels, that you do not need a blocking diode - but I still recommend that you put a blocking diode on every solar panel you create or that you purchase solar panels with blocking diodes to prevent any possibly damage to your solar panels.


It is important to note that the rating on a blocking diode - for example; 8 amps, 45volts - is rated on a free-air system. The effeciency of a blocking diode decreases as the temparature around the diode increases (as is the case when blocking diodes are installed inside solar panels and solar panel junction boxes, so make sure that you purchase blocking diodes from manufacturers that allow a safety factor when selling diodes to you. A diode I like to use is a Schottky blocking diode. The amps and volts depend on the application. Some sellers advertise an 8amp 45 volt blocking diode for sale, but the diode is actually rated at 16 amps. The company is good about selling this diode with a safety factor so that you can use it correctly in your application. Always check for the full rating of a diode and how temparature affects its performance if that information is available.