Does the Panel Estimator replace a roof survey?

No. It gives a planning estimate. A final design still needs roof measurements, setbacks, shade review, and permitting checks.

Should I size for 100 percent offset?

Not always. Utility export rules, roof limits, and future usage can make a smaller or larger system more reasonable.

How do system losses affect panel count?

Higher loss assumptions mean more panels may be needed to reach the same annual production target.

Interactive solar tool

Panel Estimator

Estimate solar system size, panel count, and roof area needs from monthly usage, sun hours, panel wattage, and losses.

Inputs

System sizing assumptions

Turn consumption and local production assumptions into a practical panel estimate.

Methodology

How this calculator works

The Panel Estimator turns electricity use, sun hours, panel wattage, roof area, and system losses into a first-pass solar system size. It is useful before quote calls because it gives you a baseline for panel count and roof-fit discussions.

What the calculator estimates

Approximate system size needed to offset the entered electricity use.

Estimated panel count based on panel wattage and production assumptions.

Roof-space fit based on the available square footage entered in the form.

Inputs to verify before comparing proposals

Use annual or monthly kWh from actual bills instead of guessing from home size.

Adjust loss assumptions when shade, heat, dirt, roof direction, or inverter clipping may be meaningful.

Remember that fire setbacks, vents, roof shape, and local code can reduce usable roof space.

After estimating panel count, use the Solar Planning Guide to connect system size with roof checks and proposal review.

Formula used

Annual usage = monthly kWh x 12.
Annual production per kW = peak sun hours x 365 x system performance factor.
System size kW = annual usage / annual production per kW; panel count = system size watts / panel wattage, rounded up.

Key inputs defined

Peak sun hours: The average usable solar intensity at your location, expressed as full-sun equivalent hours rather than daylight duration.
System losses: Expected production reductions from inverter conversion, wiring, temperature, soiling, panel mismatch, and normal operation.
Shade losses: Production loss from trees, dormers, chimneys, nearby buildings, or roof sections that block sunlight.
Panel wattage: The rated output of one solar panel under standard test conditions. Higher-watt panels can reduce panel count.
Roof area: The usable roof space available after setbacks, obstructions, vents, skylights, and unsafe layout areas are excluded.

Convert panel count into payback

Now that you know the estimated system size and panel count, compare the project cost, incentives, and payback period.

Calculate total savings

Connect system size to roof reality

Use the planning guide to connect panel count estimates with roof space, shading, and proposal review.

Read solar planning guide