• Sonny Rivers

Sizing a Solar Power System

In many cases, sizing a solar power system comes down to the available space to install solar panels, but systems are also sized based on energy usage.

Spacial capacity

Roof mounted systems are often sized to fit within the roof space, while systems on the ground are typically chosen to allow for more than the roof can accommodate.

Sizing for a roof begins with a look at the roof either by satellite image, contractors drawings, and/or seeing the roof in person. We generally start by measuring the width of the roof and how many panels will fit in one row across. Additional rows may be added, else another layout favorable to the size and shape of the roof.

Sizing for a ground mount is in part dependent on the type of mounting system, usually in multiples of three or four. Since ground mount systems are usually larger in size, they are mostly sized with energy capacity in mind.

Energy capacity

To design based on energy use, details can be obtained from individual power bills or a by requesting a 12-month usage and billing summary from the utility. Some bills also display a monthly bar chart, which works well to quickly estimate. Our sizing tools allow us to closely approximate an optimal system size depending on the energy needs.

For new construction or off-grid homes, the energy capacity is estimated according to the total loads expected (especially major appliances), the size of the home, and the number of occupants.


System sizing can be based on a combination of options and not necessarily to find one specific, best system size. Options depend on the usable space, a preferred layout (appearance), a percentage of total energy use, annual savings/ROI, economy-of-scale, or to fit a budget. It is also optional to add additional solar panels and/or batteries over time.

From an investment perspective, smaller systems offer a faster return-on-investment, while larger systems have a larger return in the long-term.