Basics

How many solar panels do I need?

The right number of solar panels isn't the most your roof can fit — it's the amount that covers your usage at the best return. Without the federal tax credit softening the cost of extra panels, right-sizing matters more in 2026 than it used to.

6 min read · Updated June 20, 2026

Start with your usage, not your roof

Find your annual electricity use in kilowatt-hours — it's on your utility bill, or add up 12 months. A typical U.S. home uses somewhere around 10,000–11,000 kWh a year, but yours could be far higher or lower.

Decide what share of that you want to offset. Covering 90–100% is common, but in states with poor export credit, sizing closer to your daytime usage (say 70–80%) can give a better return per dollar because you avoid dumping cheap exports onto the grid.

Convert usage into system size

The core sizing formula is:

System size (kW) = annual kWh to offset ÷ your local yield (kWh per kW per year).
Number of panels = system size (kW) × 1,000 ÷ panel wattage.

Example: to offset 9,000 kWh in a region producing 1,400 kWh/kW, you need about 6.4 kW. With 400-watt panels, that's roughly 16 panels. In a sunnier region producing 1,700 kWh/kW, the same offset needs only about 5.3 kW — around 13 panels.

Then check your roof

Only now does the roof enter the picture. Each panel needs roughly 18 square feet. South-facing, unshaded roof planes produce the most; east and west work but yield less; heavy shading from trees or chimneys can rule out sections entirely.

If your roof can't fit the ideal system, you size to what fits and accept a smaller offset. If it can fit far more than you need, resist the urge to fill it just because there's space — every extra panel is money you now finance without a federal credit.

Why bigger isn't automatically better

Worth knowing

With the 30% federal credit gone for new systems, oversizing means paying full price for panels whose output you mostly export at a discount. Match the system to your usage first, then expand only if the export economics justify it.

All figures on this site are estimates, not tax or financial advice. Verify current incentives and confirm tax questions with a qualified professional before making a decision.

Frequently asked

How many solar panels does a typical house need?

Most homes land somewhere around 13–22 panels, but it depends entirely on your electricity usage, your local sun, and your panel wattage. Start from your annual kWh, divide by local yield to get system size, then divide by panel wattage for the count.

Should I fill my whole roof with panels?

Usually no. Size the system to offset your usage at the best return. Since the federal tax credit no longer applies to new systems, extra panels are paid in full and their output is often exported at below-retail rates — which can lower your overall return.