How to calculate the inverter size for a 5kw system?

I would have more questions than ansewers Rajesh Kumar.
If your battery banks is at 48 volts nominal and the PV array experiences up to 4 hours of equivalent full rated charge per day on aveage for the year, then your looking at the potential of somewhere in the vicinity of 400 amphours. If your battery bank is sized to stay in the top 20 % of full charge per 24 hour day/night cycle then you would have a 2000 amphours battery bank at 48 volts nominal.

Using the figure of 400 amphours daily though and assuming all loads are to be vac from the inverter then you should have somewhere in the vicinity of 20 kWh's total. If you utilize a 5,500 watt inverter at maximum potential it might run for about 3 hours. Or any variation of this. Such as 2,750 watts for about 6 hours and so on and so fourth,

As with most renewable energies that rely on the weather, your "mileage" may vary. Know what I mean?