How do I determine what solar system size is right for my electricity usage?
If you need a quick estimate of what system size you need based on your monthly usage or monthly electricity bill, you can use a free tool called Google Project Sunroof. All you need to input is your home address and your monthly electricity bill amount, and the tool will give you the recommended solar system size needed to offset your usage. This system size estimate is based on typical solar panel production for your area, your local electricity rates and the sunlight your roof gets throughout the year.
Please note that this tool will cap the solar system size based on how much space you have on your roof, and you may not be able to fit a large enough system to offset your full electricity bill if it is too high. Although this is not completely accurate (you may have unusable areas on your roof, such as areas that have skylights, vents, chimneys etc), it is a good starting point in determining how big a system you need.
If you have more time on your hands and are interested in getting a better system size estimate, you can use a more accurate tool such as the PV Watts calculator. This tool allows you to input a lot more details about your planned solar system, such as the type of panel you are using, inverter efficiency, roof tilt angle and much more. This tool also works for a variety of solar panel installation types including roof-mounts, ground-mounts and even trackers.You can check out this video made by Ian Farneth, where he goes over a quick example using the PV Watts calculator.