Surge capacity vs continuous load — what’s the difference?

Understanding Surge Capacity

Surge capacity is a critical parameter in solar inverter sizing, particularly for systems with high power surges, such as those with large battery banks or high-power loads like water pumps or electric vehicle charging stations. A good surge capacity should be at least 200-300% of the continuous load, depending on the specific application. For example, if a system has a continuous load of 5 kW, the surge capacity should be at least 10-15 kW.

Calculating Continuous Load

To determine the continuous load, calculate the maximum power required by all loads connected to the inverter, taking into account the voltage and current ratings of each load. For example, a 2 kW water pump at 230V AC requires 8.7 A of current, while a 1 kW electric vehicle charging station at 230V AC requires 4.4 A of current. Add up the power requirements of all loads to determine the total continuous load.

Sizing Solar Inverters

When sizing solar inverters, consider both the surge capacity and continuous load. A general rule of thumb is to choose an inverter with a continuous load rating of 80-90% of the maximum power output of the solar array. This ensures that the inverter can handle the maximum power output of the solar array, while also allowing for some buffer to account for system losses and fluctuations in solar array performance. For example, if a solar array has a maximum power output of 10 kW, choose an inverter with a continuous load rating of 8-9 kW.