Hi premkumar9,
your total power demand is 40W for 24 hours which equals 960W/h. I assume that the sunlight duration at your location is similar to mine - 12 hours per day. Considering the rainy season with less sunlight (sky obscured, hence less power output from the panel(s)), I'd figure a safety factor of 25% which results in daily power rating of 1,200W/h.
The higher power solar panels start at about 170W. So using one of those your device is already overpowered. (2,040W/h)
If your panel manufacturer offers panels rated 100W they will suffice.