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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 Load Calculator

Calculate the total daily energy demand of your home's lighting, appliances, and HVAC to correctly size a solar system. Use this before getting solar quotes to know exactly how many kilowatt-hours per day you need to generate.

Lighting Load (watts)

Appliances Load (watts)

HVAC Load (watts)

Average Daily Usage (hours)

System Efficiency Factor

Fill in the required fields to see your result.

Key differences

	Solar Panel System Sizing Calculator	Solar Load Calculator
Category	Solar Energy	Solar Energy
Inputs required	5	5
Result	Solar panels needed (panels)	Required Solar Capacity (kW)
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 the total daily energy demand of your home's lighting, appliances, and HVAC to correctly size a solar system. Use this before getting solar quotes to know exactly how many kilowatt-hours per day you need to generate.