Circuit breaker sizing for solar system

Circuit breaker sizing for a solar system is a critical aspect of ensuring the safe and efficient operation of the system. Here are some guidelines to help you size the circuit breakers for your solar system:

General Guidelines

  1. Current Rating: The circuit breaker should be rated for the maximum current expected to flow through the circuit. For a solar system, this is typically the maximum current output of the solar panels.
  2. Voltage Rating: The circuit breaker should be rated for the maximum voltage of the solar system. For a grid-tied solar system, this is typically 240V or 208V.
  3. Inrush Current: Solar panels can produce a high inrush current when they are first connected to the grid. The circuit breaker should be able to handle this inrush current without tripping.
  4. Arc Fault Protection: The circuit breaker should be equipped with arc fault protection to detect and interrupt arcing faults in the system.

Sizing Formulas

  1. Maximum Current Rating: The maximum current rating of the circuit breaker (I) can be calculated using the following formula:

I = (Number of Panels x Panel Current Rating) / (Number of Strings x String Current Rating)

Where:

  1. Inrush Current Rating: The inrush current rating of the circuit breaker (I_inrush) can be calculated using the following formula:

I_inrush = (Number of Panels x Panel Inrush Current Rating) / (Number of Strings x String Inrush Current Rating)

Where:

Example Calculation

Let's say you have a 10 kW solar system with 20 solar panels, each with a maximum current rating of 7.5A and an inrush current rating of 15A. The system has 4 strings of 5 panels each.

To calculate the maximum current rating of the circuit breaker:

I = (20 panels x 7.5A) / (4 strings x 15A) = 37.5A

To calculate the inrush current rating of the circuit breaker:

I_inrush = (20 panels x 15A) / (4 strings x 15A) = 75A

Based on these calculations, you would need a circuit breaker with a maximum current rating of at least 40A (to account for the 10% margin) and an inrush current rating of at least 80A (to account for the 10% margin).

Additional Considerations

  1. System Voltage: The circuit breaker should be rated for the maximum voltage of the solar system.
  2. Grounding: The circuit breaker should be equipped with grounding to ensure safe operation of the system.
  3. Arc Fault Protection: The circuit breaker should be equipped with arc fault protection to detect and interrupt arcing faults in the system.
  4. Certifications: The circuit breaker should be certified by a reputable testing laboratory, such as UL or ETL.

By following these guidelines and formulas, you can ensure that your circuit breaker is properly sized for your solar system and provides safe and efficient operation.