Nowadays, PV modules usually have bypass diodes. These ensure a higher level of efficiency in the event of shading and dirt. They are also important for the efficiency and longevity of PV modules. You can find out everything about bypass diodes here.
First things first
What is that?
A bypass diode protects solar cells from damage caused by partial shading by redirecting current flow.
Disadvantages of bypass diodes
Bypass diodes are not a solution for permanent and regular shading.
How many bypass diodes?
A solar module typically has three bypass diodes. However, some models also have two, four or six diodes.
What alternatives?
If there is permanent shading, you should use power optimizers or module inverters.
What is a bypass diode?
The bypass diode is an important component in PV modules and serves as protective measureIt redirects the flow of electricity around areas of lower power, ensuring that defective or unexposed solar cells do not affect the module's overall power production.
Do all PV modules have bypass diodes?
Nowadays, most solar modules have bypass diodes as standard. In the past, Schottky diodes were used for this task. However, these are not as efficient for use in PV modules.
Can bypass diodes retrofitting?
In principle, you can retrofit bypass diodes, but this may invalidate the warranty on the PV modules. If you insist, hire an experienced solar installer to do it.
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What are the functions of a bypass diode?
The bypass diode bridges areas in the PV module that do not generate electricity due to shading or dirt. This prevents overheating and defects in the solar module as well as performance losses.
reduction of shading losses
Typically, three bypass diodes are used per PV module, dividing it into three areas. If part of the solar module is shaded or dirty, the current flow is diverted. This reduces the shading losses significantly, as the following figure shows.
How exactly does this process work?
At all solar cells a positive voltage is applied to minimize shading losses. If a cell is shaded, a negative voltage is created. This causes the bypass diode to redirect the current flow. This allows the remaining cells to conduct their full current. As soon as the current drawn from the PV module is low enough, the bypass diode switches off.
Avoiding hotspots
By redirecting the current flow, no overvoltages occur on the solar cells. The blocking diodes thus prevent the formation of so-called hotspotsThese occur when the affected cells experience an increase in internal resistance. This leads to a concentration of current in a few cells, resulting in overheating and possible melting.
How does a bypass diode work?
In trouble-free operation, the blocking diodes are polarized in the opposite direction. This means that the bypass diodes remain inactive if there are no problems in the module string. It is important that the individual solar cells are not bridged during normal operation. Otherwise, yield reductions occur. Bypass diodes are only activated if a problem occurs. This activation occurs automatically due to the high voltage levels.
When a solar cell is shaded or its performance decreases, the electrons cannot flow through it efficiently. This creates an "electron jam" and the Tension increases. As soon as the voltage or current becomes too high, the bypass diode switches on. The current is then diverted through the blocking diode instead of through the solar cell.
How many bypass diodes does a solar module have?
Most solar modules have three bypass diodes, in rare cases two, four or six. These cannot bridge individual solar cells, but combine several cells. Although they increase the power output when cells fail, they cannot completely compensate for operational disruptions.
What happens if a bypass diode is defective?
If a bypass diode in a PV module is defective, one of the three strings of the module switches off. This reduces the performance of the module by a third. This decline in earnings can be observed in the yield curve of a string with good irradiation conditions if several modules are affected. However, it is difficult to detect a defect in the entire PV system.
For this reason, a regular maintenance important for solar systems. In this test, current is fed backwards to test the PV system. A current is applied in the dark and it is checked whether individual solar cells heat up. If this is the case, the bypass diode is not working. This indicates a defect that requires the diode to be replaced.
Can a broken bypass diode be replaced?
Defective bypass diodes can be replaced. Replacing or repairing a bypass diode in a PV system requires technical expertise, skills and the use of special tools. For insurance and safety reasons, you should leave this task to a professional solar installer
What are the limitations of bypass diodes and what are the alternatives?
Bypass diodes are only intended for temporary shading, for example due to cloud cover. For permanent shading, you need either a power optimizer, a multi-string inverter or a module inverter. The inverters should have an MPP tracker.
- Power optimizers use a DC/DC converter to adjust the operating points of solar panels and maximize their energy production. This is achieved by continuously varying the power in relation to the input power.
- With a multi-string inverters you can divide the PV system into two (or more, depending on the number of inputs) areas. This way, the shaded part of the system does not affect the performance of the non-shaded area.
- If only individual modules are shaded, you can use a module inverter. This encapsulates the shaded module from the PV system so that it does not affect the performance of the system.
