How to calculate dc breaker size in pv installation
Calculating the correct DC breaker size for a PV installation is crucial to ensure safe and reliable operation. Here's a step-by-step guide to help you calculate the DC breaker size:
Step 1: Determine the Maximum Power Output (MPO)
- Calculate the maximum power output of the PV array in watts (W) by multiplying the total number of panels by their maximum power output per panel (Wp).
- For example, if you have 10 panels with a maximum power output of 300W each, the MPO would be: 10 panels * 300W = 3000W
Step 2: Determine the Maximum Current (IMAX)
- Calculate the maximum current (IMAX) in amperes (A) by dividing the MPO by the system voltage (Vdc) and multiplying by 1.25 (a safety factor).
- For example, if the system voltage is 500Vdc and the MPO is 3000W, the IMAX would be: 3000W / 500Vdc * 1.25 = 7.5A
Step 3: Determine the DC Breaker Size
- Choose a DC breaker with a rating that exceeds the IMAX calculated in Step 2. A common practice is to select a breaker with a rating that is 1.5 to 2 times the IMAX.
- For example, if the IMAX is 7.5A, you would choose a DC breaker with a rating of 11.25A (7.5A * 1.5) or 15A (7.5A * 2).
Additional Considerations
- System voltage: The DC breaker size may also depend on the system voltage. For example, a 500Vdc system may require a larger breaker than a 400Vdc system.
- Inverter efficiency: The inverter efficiency can affect the maximum current drawn from the PV array. A lower inverter efficiency can result in a higher maximum current, which may require a larger DC breaker.
- System design: The system design, including the number of strings, parallel connections, and grounding, can also impact the DC breaker size.
Example Calculation
Let's say you have a 10 kW PV array with a system voltage of 500Vdc, and you want to calculate the DC breaker size.
- MPO = 10 kW = 10,000W
- IMAX = 10,000W / 500Vdc * 1.25 = 20A
- Choose a DC breaker with a rating of 1.5 to 2 times the IMAX: 30A (20A * 1.5) or 40A (20A * 2)
In this example, you would choose a DC breaker with a rating of 30A or 40A to ensure safe and reliable operation of the PV installation.
Remember to always follow the manufacturer's recommendations and local electrical codes when selecting a DC breaker for your PV installation.