Choosing the right system size

Before making a decision about what size solar panel system to install, it’s important to understand how installers size solar panel systems in the first place.

There are three key factors that go into an initial solar panel system design:

• Your annual electricity consumption: how much electricity you use–or plan to use–in a year, expressed in kilowatt-hours (kWh).
• Solar insolation (i.e. the amount of solar radiation that will hit your solar panels): this will vary depending on where you live, as well as the tilt and angle of your future solar array.
• The amount of space available for your installation: of course, if you’re placing panels on your roof, you’ll be limited by the size of it!

Installers commonly propose a system size that will cover as close to 100% of your electricity needs as possible – that’s how you’ll save the most money! That said, it’s not uncommon for solar shoppers to receive quotes with slightly different system sizes, even if every company that provides a quote has access to all the same information. 

What to do when you receive quotes with different system sizes

Here are a few steps you can take to make sure installers size your future solar panel system as accurately as possible:

• Provide up-to-date electric bill information, with any additional context. If you plan to use more or less electricity in the future, make sure the installers know this. It’s also important to communicate why you’re expecting a change in electricity consumption, as it can influence their system size recommendation.
• Ask installers to update quotes according to your preferences (e.g. specific solar panels, layout for the array). Remember, number of panels ≠ system size; even if installers are maxing out your available roof space, the system size will be different if the solar panels they propose have different wattages. If you have a strong preference for one type of equipment, let installers know so you can better compare competing offers in an apples-to-apples format.

• Invite installers out for a site visit to fine-tune their system design. Remote design tools are extremely accurate these days, but it’s never a bad idea to invite an installer to see your property in person. Not only will it give them the chance to take measurements and inspect your roof and electrical panel, but also give you the opportunity to ask questions and learn more about their company.

Learn more about system sizing or how installers calculate production estimates