Budget, roof dimensions and other site-specific factors often call for custom system design. If you are planning to mount your array on a roof, decide which module best fits into the available roof space, taking into consideration obstructions such as chimneys, plumbing vents and skylights.
The worksheet below will help you decide what size PV array would be required to eliminate your electric bill. This would be the largest system that would be cost-effective to install. A smaller system can reduce your electric bill.
PV ARRAY DESIGN WORKSHEET
Step 1 - Find your monthly average electricity usage from your electric bill. (This will be in KWH): ______________
Step 2 - Find your daily average electricity use ________
Step 3 - Find your locations PEAK SUN-HOURS per day _____
Step 4 - Divide your daily average by Peak hours ________
Step 5 - Divide Step 4 number by the Power rating of the PV modules you'd like to use. The resulting number is the number of modules you will use _________________
After Step 5 round up to the nearest even number. This will be number of modules (you choose the power rating of the module in Step 4), and together will give you an energy production of your daily consumption.
This strategy is for net-metering systems, of course, you can choose to do a smaller system, if so use a smaller daily KWH consumption.