Determine how many solar panels your home needs. Enter your monthly electricity usage, local sun hours, and preferred panel wattage to get a system size recommendation.
Check your utility bill
Avg 3–6 hours in the US
Panels Needed
21 panels
System Size
8.4 kW
Est. Daily Production
30.2 kWh
Est. Annual Production
11,038 kWh
Each block represents one 400W panel
10,800 kWh
11,038 kWh
426
sq ft needed
6 x 4
array layout
21 ft
min roof width
System Configuration
21 panels at 400W each
Total capacity: 8.4 kW
Monthly Balance
Production: 920 kWh
Usage: 900 kWh
+20 kWh surplus
Estimated Cost
Before incentives: $23,268
30% Federal ITC: -$6,980
At avg $2.77/watt installed
Environmental Impact
CO2 offset: 10.2 tons/year
Equivalent to: 23 trees planted
Sizing a solar system starts with your electricity usage. The calculator takes your monthly kWh consumption, converts it to annual demand, and divides by the energy each panel can produce given your local sun hours and an efficiency derate factor. The result tells you how many panels and total system wattage you need to cover your electricity bill.
The average US home uses about 900 kWh per month and typically needs 20 to 25 solar panels (each 350-400W) to offset 100% of electricity usage. Your actual number depends on your energy consumption, local sun hours, and panel efficiency.
Peak sun hours represent the number of hours per day when sunlight intensity averages 1,000 watts per square meter. Most US locations get between 3 and 6 peak sun hours per day. This is different from total daylight hours.
Solar panels lose some output due to temperature, shading, inverter conversion, wiring losses, and panel degradation. An 80% efficiency factor (also called a derate factor) accounts for these real-world losses to give you a more accurate system size.
Solar Panel Payback Calculator
Calculate how long it takes for solar panels to pay for themselves. Estimate your solar ROI based on system cost, energy production, and local electricity rates.
Electricity Cost Calculator
Calculate how much it costs to run any appliance or device. Enter wattage, usage hours, and your electricity rate to see daily, monthly, and yearly costs.