Quick Answer
Increase your inverter's surge capacity when you're connecting high-power loads like electric water heaters or large air conditioning units, or when you're adding new high-voltage DC sources like multiple solar panels in series.
Sizing Surge Capacity for High-Power Loads
When installing high-power loads like electric water heaters or large air conditioning units, it’s essential to size your inverter’s surge capacity correctly. A general rule of thumb is to calculate the inrush current of the load and add 10-20% to the nominal load current. For example, if a 4 kW electric water heater has a 40 A inrush current, you should size the inverter to handle at least 44-48 A of surge current.
Determining Surge Capacity for Multi-Source Systems
When connecting multiple solar panels in series, the total DC voltage increases, but the current remains the same as the smallest panel. However, when connecting panels in parallel, the total current increases, and the voltage remains the same. To size the surge capacity correctly, calculate the total DC current from all the panels and add 10-20% to the nominal current. For example, if you have 5 x 300 W panels in parallel, the total DC current is 10 A, and you should size the inverter to handle at least 11-12 A of surge current.
Choosing the Right Surge Capacity Rating
Inverters come with different surge capacity ratings, typically measured in kVA or kW. When selecting an inverter, choose one with a surge capacity rating equal to or greater than the calculated surge current. For example, a 5 kW inverter with a surge capacity rating of 8 kW would be suitable for a 4 kW electric water heater or a 5 kW solar array with panels in parallel. Always consult the inverter manufacturer’s documentation for specific surge capacity ratings and guidelines.
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