Bypass Diode
Protective component in a solar module that routes current around shaded cells to prevent power loss and hot spots.
Also known as: Bypass Diodes, Freewheeling Diode
What Is a Bypass Diode?
A bypass diode is an electronic protective component installed in the junction box of a solar module. It routes current around shaded or defective cells, preventing power losses and heat damage (hot spots).
How It Works
In a solar module, cells are connected in series. When a cell is shaded, it limits the current of the entire string. Without a bypass diode, the shaded cell would:
- Drastically reduce the current of the entire string
- Heat up as a hot spot (the cell becomes a load)
- Potentially suffer permanent damage
The bypass diode bridges the shaded cell group and allows current to flow through the remaining cells.
Typical Configuration
| Property | Value |
|---|---|
| Number per module | 3 (for 60/120-cell modules) |
| Bypassed cells | 20 cells each (or 40 half-cells) |
| Active voltage drop | approx. 0.5—0.7 V per diode |
| Location | Junction box |
Effect During Shading
When one third of the module is shaded, one bypass diode activates and the module loses about one third of its power — without the bypass diode, the loss would be significantly higher.
Practical Tip
Bypass diodes are passive and maintenance-free. If they malfunction, hot spots can develop, which are visible in thermographic images. Regular visual inspections and occasional thermography help detect problems early.
Related Terms
Solar Module
Assembly of multiple solar cells in a weatherproof housing for generating electricity from sunlight.
Shading
Partial or complete shading of solar modules by trees, buildings, or other obstacles.
String Inverter
Central inverter that converts the direct current from one or more series-connected module strings into alternating current.