[flybouy]

To piggyback on John's comment, you also must calculate how many hrs a day it's actually charging and how much. A panel rated at 150 watts is in full DIRECT sun so if your on the equator or somewhere that has not only full exposure to the sun but also has a sun angle perpendicular to the solar panel then you MAY get that 150 watts. At least until the sun moves across the sky.

If the panel is charging say at a rate of 60 % for 3 hrs, then 20% for 4 hrs. then the math should tell you what the actual charge rate is. So if you Know your load on the battery and it's constant then multiply by 24 for the AH load. Or multiply by the number of hours the device is used. Subtract the amount being used from the amount going back in and iof the charge rate exceeds the load then you're good.