How Many Solar Panels Do I Need?

The exact number of panels and rooftop square footage required for your solar PV system will vary depending on your specific household’s energy consumption level and solar goals. The table below, however, will give you a rough estimate of what to expect.

Utility Bill Offset Annually

= $510

Average Annual kWh

= 3315 kWh

Utility Bill Offset Annually

= $765

Average Annual kWh

= 4973 kWh

Utility Bill Offset Annually

= $1020

Average Annual kWh

= 6630 kWh

Utility Bill Offset Annually

= $1275

Average Annual kWh

= 8288  kWh

The Avg. San Antonio Household Uses 13200 kWh of Electricity per Year

How Much Energy Does Your Household Use?

Think of it as the first rule of residential solar PV: The more energy your household uses, the more energy that needs to be generated by your solar PV system. And the more energy required from your solar PV system, the more solar panels you are going to need. Note here that there is no mention of the total square footage of your home or the total number of rooms. That’s because it’s not about the size of the house, it’s about the amount of energy used inside it.

Average Solar Radiation

How Many Panels Can Fit?

Now that you know the number of kilowatts your solar array needs to generate, it’s time to figure out the number of solar panels it will take to meet that need. Here’s the next specific question that requires an answer: “How many panels can I actually fit on my roof?”

There are a couple factors to consider:

Direction of the Roof

For those living in the Northern Hemisphere (like all of us in the U.S.) the ideal roof direction for solar PV is south. The reason is that a south-facing roof is exposed to the maximum potential sunlight.



But, the total amount of roof space really isn’t the issue; it’s the total amount of shadeless roof space where panels can efficiently make use of the sunlight hitting them.

For the sake of this discussion, let’s make two assumptions. The first assumption is that the home has a nice south-facing section of roof that can be used for locating solar panels. The second assumption is the solar panel size. Currently, the average size of a solar panel is 3 feet by 5 feet, or 15 square feet. With these two assumptions in place, the calculation to determine the number of panels that can fit on the roof is pretty straightforward: total available roof space (in square feet) divided by 15 (the square footage of a single 3 ft. x 5 ft. panel) gives you the total number of panels. For example, if the total available roof space is 375 sq. ft., the calculation would be:

375 ÷ 15 = 25 (total number of panels)

Remember that this is only an estimate of the actual number of panels that will fit on a roof based on the assumptions given. Panel sizes do vary and an additional small amount of space around the entire solar panel arrangement will be required.