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Solar Array Size and Panel Count Estimator

Reviewed for 2026, updated September 8, 2026.

Estimates the solar system size, panel count and roof area a home needs to offset its annual electricity use, for homeowners comparing premium solar quotes.

Your numbers

Results update as you type.

Your estimate

Recommended array size...
Panels required...
Roof area required...
Estimated first-year production...

Estimates only. Assumptions are listed below, and you can change every input.

Every solar quote leads with a system size in kilowatts, and most homeowners have no independent way to tell whether that number matches their actual consumption. Oversized arrays cost more up front and can push production into export rates that pay far less than retail. Undersized arrays leave the bill you were trying to eliminate mostly intact. This estimator gives you a reference figure to hold each proposal against before anyone starts talking about panels.

The math is the same first-principles approach installers use. Your annual usage, multiplied by the share you want to offset, is the energy target. Dividing that target by the useful sun hours your location receives each year, after system losses for wiring, inverter conversion, soiling and heat, gives the DC array size. Panel count and roof area follow from the wattage and footprint of the module you are considering. It is an estimate, not a production guarantee, and it will not replace a shade analysis on your actual roof.

How to use this tool

  1. Enter your annual electricity use from the last 12 utility bills and the percentage of it you want solar to cover.
  2. Set the peak sun hours for your location and roof, then adjust the loss percentage if your installer report suggests something different from the default.
  3. Enter the wattage and physical size of the panel in the quote and compare the resulting array size and panel count with the proposal.

What the math assumes

  • Peak sun hours are treated as an annual daily average that already reflects your roof orientation and tilt; shading must be reflected in that number or in the loss percentage.
  • Losses are applied as a single flat percentage across the year rather than modeled hour by hour.
  • Panel count is rounded up to the next whole module, so the estimated production is for the rounded array, not the exact target.
  • Roof area is panel footprint only and does not include the setbacks, walkways and spacing that fire codes and installers require.
  • The estimate does not account for panel degradation, snow cover or future changes in consumption such as an electric vehicle or heat pump.

Frequently asked questions

Why does my quote show a larger system than this estimator recommends?

Installers sometimes size for expected future loads, for a utility program cap, or simply to sell more capacity. Ask which of those applies and whether the extra production would be paid at retail or at a lower export rate.

Where do I find peak sun hours for my address?

Solar irradiance maps published by government energy labs give annual averages by region, and a professional shade report converts that to a figure for your specific roof. If the two disagree, trust the roof-specific number.

Should I offset more than 100 percent of my usage?

Only when you expect consumption to rise, for example with an electric vehicle or heat pump, or when your utility credits exports at close to retail. Otherwise the extra panels earn less per kilowatt-hour than the ones covering your own load.

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