Using 12V panels/batteries and just for explanation assuming 100% overall.
Thats 252w/12v = 21Amps
At a rough calculation for a 24hr worst case period thats a 24hr * 21A =504AHr battery.!
Allowing for a invertor conversion efficiency of say, 75% gives 504/0.75 =672AHr Battery.
Allowing for a battery recharge efficiency of 60% at a charge rate 21Amps,
just to keep the batteries topped up, 21/0.6 = 36Amps
Allowing for 12hrs of sunshine per day,,, 36A * 2 =72A
Although these calculations are very rough, it would suggest to me that the project is going to be VERY expensive.
You have explained that you need to keep the system running 24/7, can I ask why.?