You need to estimate the DC amp-hours you will drain from the batteries every day. That's interior lights, circuit boards for fridge and water heater, water pump demand, furnace fan if that will be in use, and any inverter usage you may have (tvs, satellite, microwave, etc). Get the amp draw for each item and estimate how many hours per day it is typically used and multiply each to get amp-hours. Some of it is going to be a SWAG, of course, but you need to come up with some idea of the amount of battery load, then figure the solar capacity that will replace it. Or perhaps just partially replace it and plan on using a generator for an hour or so a day. This effort also tells you how much battery capacity you need - you need to have about 2x as many amp hours in the battery rating as the amount you will use every day. That's because you should only draw a battery down to about 50% capacity. Any more will shorten its life.

Solar panels are measured in watts, so the basic formula is watts = amps x volts. The panel charges at around 15v, so divide the wattage rating by 15 to get the amps it can load into the battery. That's only in full sum, so estimate less for off-peak hours when the sun is at a lower angle.