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.