How Many Solar Panels Do I Need for My House?

You are thinking about solar. The first question on your mind is probably: how many panels do I need?

The answer depends on several factors. Here is how to figure it out without calling a salesperson.

The short answer

The average American home needs between 20 and 35 solar panels to go 100% solar. This covers most households with monthly electric bills between $150 and $300.

But your specific number depends on your energy usage, your location, and your roof.

Step 1: Check your energy usage

Look at your last 12 electric bills. Add up the kilowatt-hours (kWh) used each month. Divide by 12 to get your average monthly usage.

For example:

• Average bill shows 900 kWh per month
• Annual usage = 10,800 kWh
• This is a typical single-family home

Step 2: Know your location

Solar panels produce more energy in sunny locations. A panel in Phoenix produces roughly 50% more energy than the same panel in Seattle.

Key metric: peak sun hours per day

• Southern US (Arizona, California, Florida): 5-6 peak sun hours
• Northeast US: 3.5-4.5 peak sun hours
• Pacific Northwest: 3-4 peak sun hours

Step 3: Calculate system size

Divide your annual kWh usage by your location peak sun hours, then by 365 days.

Example for a home using 10,800 kWh/year in Los Angeles (5.5 peak sun hours):

• 10,800 kWh / (5.5 hours x 365 days) = 5.4 kW system needed

Step 4: Convert to panel count

Most residential solar panels today produce between 350 and 400 watts each.

Using 400W panels:

• 5,400 watts / 400 watts per panel = 13.5 panels
• Round up to 14 panels

Using 350W panels:

• 5,400 watts / 350 watts per panel = 15.4 panels
• Round up to 16 panels

Step 5: Check your roof space

Each solar panel takes up about 17 to 20 square feet. You also need spacing between rows for maintenance access.

Rule of thumb: plan for 25 to 30 square feet per panel.

For 16 panels: 400 to 480 square feet of unshaded roof space.

This is where most people get stuck. They calculate they need 16 panels but only have room for 10 on their roof. Or they have room for 20 but their roof faces the wrong direction.

Why you need a roof analysis first

Before you calculate panel count, you need to know:

1. How much unshaded roof space do you actually have? Trees, chimneys, and HVAC units reduce usable area.
2. Which direction does your roof face? South-facing roofs need fewer panels to produce the same energy.
3. How old is your roof? If it is over 15 years old, you may need to replace it before installing solar.
4. Can your roof support the weight? Solar panels add 2 to 4 pounds per square foot.

SolrScan checks all of this from satellite imagery. You enter your address and get a report showing:

• Available roof space
• Estimated panel count
• Orientation and shading analysis
• Roof age estimate

Cost: $19. Time: 60 seconds. No account needed.

What if my roof cannot fit enough panels?

If your roof space is limited, you have options:

1. Partial offset — Install as many panels as fit. This reduces your bill even if it does not eliminate it.
2. Community solar — Subscribe to a local solar farm. You get credit on your bill without panels on your roof.
3. Ground mount — If you have yard space, ground-mounted systems can be larger than roof-mounted ones.
4. Higher efficiency panels — Premium panels produce more energy in less space but cost more upfront.

The bottom line

You cannot know how many panels you need without analyzing your roof first. Skipping this step means you are guessing. And guessing with a $20,000 investment is not smart.

Get your SolrScan report at solrscan.com. $19 tells you exactly how many panels fit on your roof and how much energy they will produce.