How to Figure How Many Solar Panels You Need

Review your electric bills over the last year. Many electric companies show a break down of the amount of power used during each billing cycle.

Add up the kilowatt-hours used for the entire year by adding up the amounts for each month. For example, you may find that you use 4,850 kWh per year in your home.

Divide the yearly amount by the number of months in a year. From the example above, divide 4,850 by 12. You use 404 kWh per month on average.

Find your daily average. Solar panels collect energy on a daily basis, so it's important to know how much power they can supply each day. Divide 404 by 30, and you have 13.5 kWh per day.

Find the average daily usable hours of sunlight for your area. This is important information because it is a big factor in finding out how many panels you will need. For example, you may have 4.5 hours of usable sunlight on an average daily basis. Divide 13.5 by 4.5 in this example, and you have 3 kWh or 3,000 watts per usable sunshine day that you need to supply.

Determine how many watts each solar panel will create. If, for example, each one creates 220 watts of power every hour, you will need 3,000 divided by 220, or 17 solar panels to meet your energy needs on a daily basis.