I have got a 3 kVA (2400 watt) solar hybrid inverter (pure sine wave) which is connected to a 1280 watt PV array and 2 x 12 volt 150 Ah batteries. It is supposed to switch to utility mode if the combined voltage of PV and batteries goes below 23 volts.

This afternoon (during plenty of sunlight), I tried to power my refrigerator using the system but as soon as the compressor started, I could hear some knocking sound from the fridge, and at the same time, the LED lights in the house (also powered by the inverter) started to flicker.

Next, I tried using a voltage stabilizer on the fridge to see if that made any difference but the result was the same (knocking sound from compressor, and flickering lights).

The display on the inverter showed that it was producing enough output at that time for the required load (sometime like 550 watts). To validate this, I connected a 1200 watt halogen heater and ran a 100 watt ceiling fan, and it was able to power this load without any issues. The display on the inverter showed a load of 1.1 kW.

My batteries are about 2 years old and normally don’t give a long backup. Even on a 150 watt load I might get about 10 to 15 minutes out of them. So, could the problem be that the refrigerator’s compressor produces a sudden spike in the required load and the batteries are not able to handle this?

Or, do I need more solar panels to be able to handle this spike? I’m planning to run my DC inverter air conditioner on this during summer and want to know before I replace the batteries or buy more solar panels.