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How Much Power Do I Need?
Appliances run on amps. Amps, the amp-hour (abbreviated as “Ah“), refers to the number of amps an appliance uses when it is run for an hour.

These amp-hours will be drawn from the batteries, and the batteries, in turn, will look to the solar panels to recharge the amp-hours they have used to power the appliance.

It is for this reason that you need to know how many amp-hours you will use in a typical day. Ultimately those amp-hours must be replaced by the solar panels, so the size and number of panels you purchase will be determined by how many amp-hours you use in a day.

To estimate how many amp-hours you might use in a day, estimate how many hours each appliance will run and multiply that by the number of amps the appliance uses.
Good Rule of Thumb
So as a rule of thumb, here is the number of amp-hours you might consume per day:

• 6 Ah = living ultra-conservatively
• 35 Ah = living very modestly
• 120 Ah = living much the way you do in your house

The amp-hour capacity of your battery bank should be three (to four) times your typical daily amp-hour usage.

A popular rule of thumb is to match (roughly) the amp-hour capacity of the batteries to the watts capacity of the solar panels. So, 140 Ah of battery capacity “goes with” 140 watts of solar power. 440 Ah of batteries “goes with” 440 watts of solar power.