If you don’t have a bill but you know approximately what you pay, you can divide your monthly charge by 31 and then divide by $.29 (utility kWh rate as of April, 2010) then enter the number of daily kWh consumed in one of the months in the table above.
Example: $200/month bill ÷ 31 ÷ $.29 = 22 kWh/day.

Choose your zip code. This is important because each area has an estimated number of sun hours. It should be noted that zip codes don’t always yield accurate sun hours and your system could produce more or less energy once installed.