Interactive battery tool

Panel Estimator

Estimate solar system size, panel count, and roof area needs from monthly usage, sun hours, panel wattage, and losses to inform solar-battery pairing decisions.

Methodology

How this calculator works

Panel count is estimated from monthly usage, average sun hours, panel wattage, roof area, and system loss assumptions.
Loss assumptions include inverter losses, wiring losses, soiling, temperature effects, and shading entered by the user.
Final layouts can change after a roof survey, fire setbacks, equipment selection, and local permitting checks.

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.

Pair solar size with battery storage

Now that you know the estimated solar system size, estimate the battery storage capacity needed to back up your critical loads.

Size a battery

Understand solar-battery pairing

Use the buying guide to understand how solar panel size affects battery sizing and backup capacity decisions.

Read battery buying guide

How this calculator works

Panel count is estimated from monthly usage, average sun hours, panel wattage, roof area, and system loss assumptions.
Loss assumptions include inverter losses, wiring losses, soiling, temperature effects, and shading entered by the user.
Final layouts can change after a roof survey, fire setbacks, equipment selection, and local permitting checks.

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.

Pair solar size with battery storage

Now that you know the estimated solar system size, estimate the battery storage capacity needed to back up your critical loads.

Size a battery

Understand solar-battery pairing

Use the buying guide to understand how solar panel size affects battery sizing and backup capacity decisions.

Read battery buying guide

Panel Estimator

How this calculator works

Formula used

Key inputs defined

Pair solar size with battery storage

Understand solar-battery pairing

Panel Estimator

System sizing assumptions

How this calculator works

Formula used

Key inputs defined

Pair solar size with battery storage

Understand solar-battery pairing

System sizing assumptions