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Solar Panel System Sizing Calculator

Calculate exactly how many solar panels your home needs based on your electricity bill, local sun exposure, panel wattage, and desired offset. Ideal for homeowners planning a rooftop PV installation.

Average monthly electricity use (kWh)

Peak sun hours (daily average) (h/day)

Share of usage to offset (%)

System losses (inverter, wiring, soiling, heat) (%)

Panel power rating (W)

Solar panels needed

21 panels

Lean sizingStandard full offsetLow-sun sizingOversized or low-sun

9.33: 7-10 W per monthly kWh is the normal range for a 100% offset at 4.5-5.5 sun hours. The example (9.3 W/kWh: 21x400W panels for 900 kWh) sits here.

This is installed watts per kWh of monthly usage; the formula's own math ties panel count to your offset target, sun hours, and losses, with ~7-13 W per monthly kWh being typical.

Solar Energy

Solar Payback Period Calculator

Calculate how many years a solar PV system takes to pay back its net upfront cost through annual electricity bill savings. Use it as the primary financial test when evaluating whether to install solar.

Total System Cost ($)

Annual Savings ($/year)

Tax Incentives ($)

Fill in the required fields to see your result.

Key differences

	Solar Panel System Sizing Calculator	Solar Payback Period Calculator
Category	Solar Energy	Solar Energy
Inputs required	5	3
Result	Solar panels needed (panels)	Payback Period (years)
What it does	Calculate exactly how many solar panels your home needs based on your electricity bill, local sun exposure, panel wattage, and desired offset. Ideal for homeowners planning a rooftop PV installation.	Calculate how many years a solar PV system takes to pay back its net upfront cost through annual electricity bill savings. Use it as the primary financial test when evaluating whether to install solar.