Three core factors affect the sizing of your system: your electricity usage, space availability on your property, and your budget.
YOUR ELECTRICITY USAGE
Do you want to try to produce 100% of your power or some smaller percentage?
While any excess production from month to month will carry over as a credit on your utility bill (net metering), you will not want to install a system that produces more than 100% of your power as the utility will not reimburse you for excess power produced at the end of the year. You may also not want to size the system too large if you are planning more energy conservation measures for the future.
To determine how much power you use right now, look for the kilowatt-hour (kWh) consumption on your utility bill. Sum the kWh for the past year to get your annual electricity usage.
Space Availability
The amount of unshaded, easy-to-access, space available for mounting panels will limit the size of the system. You can use In My Back Yard (IMBY), an online tool created by the National Renewable Energy Laboratory to estimate the area on your property available for mounting a system. IMBY allows you to draw a system on a map of your property and then estimates the specifications of the array given the size and orientation of your drawing.
PV panels vary in their dimensions. While a vast number of PV panels are undergoing research and development, a limited number are available on the retail market. Each year Home Power publishes evaluations of different panels. Local contractors will have particular brands they install regularly. When talking with them, find out which panels they use, why they like them, if the panels are UL Listed (required for electrical inspection and utility interconnection) and the panel’s warranty length. A standard industry PV panel warranty is 20–25 years, and manufacturers expect the panel will produce 80% of its rated capacity at the end of the warranty period.
YOUR BUDGET
It is a good idea to evaluate your budget and goals before choosing your system. Some questions to consider include: What is my budget for this project? Will I finance or pay for it out of my savings? Keep your budget in mind.
