Plan your system according to meet your estimated emergency power needs. The number of batteries will depend on how many panels you use and maintain sufficient amp-hours to run the inverter at the level required to power your appliances. Two types of batteries that work best for solar power storage are golf cart types and deep cycle industrial batteries. Golf cart batteries will work for smaller power systems while the deep cycle type will last longer through many discharge cycles but cost more. Whichever type you decided on keep spare batteries on hand. Do not use car batteries as they were not designed for this type of use.
The panels, themselves, need to produce enough power to replenish the batteries, which will be at least 5 hours per day in sunny climates — more for cloudy days. The average solar panel on today’s market produces about 200 watts. More efficient monocrystalline panels will have a somewhat higher output.
The average household in the US uses approximately 903 kilowatt-hours each month which is about 30kWh per day. This, of course, varies depending on the seasons, air-conditioning use, efficiency of appliances and how many are used. You can gauge your household’s energy use by checking with your energy company for usage history. This is the easiest way, otherwise, you would need to calculate the electrical use of each appliance in your home individually. The household usage history can then be used in consultation with your solar power dealer to determine the size of array needed for your home.