The role of diodes in solar panelling

Diodes may not be much to look at. But these simple semiconductor components perform many critical functions in electrical circuits – including controlling the direction of current flow. 

Modern diodes are constructed primarily from doped silicon, with a ‘p-side’ and ‘n-side’ that are doped differently to provide positive and negative charges. The area where they meet is known as the ‘n-p-junction’. If you apply a negative charge to the n-side and a positive charge to the p-side, electrons transfer over this junction to create current flow in one direction.

Diodes can also function as rectifiers, signal limiters, voltage regulators, switches and more. They come in a variety of types and are used widely in modern technology, including in LED lights and when converting AC power to DC power. Diodes also protect electronic devices from dangerous voltage surges.   

Another increasingly common application of diodes is in solar panels. Two key types are bypass diodes and rectifier or Schottky diodes, which we explore in more detail below.

How diodes are used in solar panels

Solar power generation has increased dramatically in the U.S. in the past decade. It reached a high point of nearly 91,000 kilowatt hours of solar thermal and photovoltaic (PV) power in 2020. And all this eco-friendly power generation is made more efficient with diodes! 

While not essential, it’s recommended to fit PV solar panels with a diode to prevent reverse current flow occurring at night-time. When fitted between the fuse and battery, low-loss Schottky diodes reduce the amount of power lost through voltage drop in 12-volt or higher systems.

Bypass diodes meanwhile are fitted across each solar panel in multi-panel setups to reduce the risk of overheating damage in shaded or damaged panels. As the name suggests, they allow current to bypass these panels when such conditions are present. Their use is essential in systems over 36 volts.  

PV characteristics of diodes and usage in PV arrays

Choosing the right diodes for your solar application depends on factors including the maximum deliverable current of your PV cells, as well as their surface area and the amount of sunlight present. 

In PV arrays of multiple solar panels connected in a series, blocking diodes only allow current to flow from the solar cells to the output. In their absence, the circuit may suffer voltage loss and overheating.

Both bypass and blocking diodes are usually internally connected by the manufacturer, though they can also be retrofitted to benefit your DIY application. Did you realise how critical these components are? 

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