Solar Panel Calculator
Calculate the number of solar panels, system size, and roof space needed to offset your energy bill.
System Details
Panel Configuration
Solar Estimate
For estimation purposes only. Actual savings depend on local rates, incentives, shading, and panel orientation. Consult a certified solar installer.
How This Calculator Works
The solar panel calculator estimates your energy needs by working backward from your monthly electric bill. By knowing how much you spend and your local rate, we determine your monthly Kilowatt-hour (kWh) consumption.
The formula for system size is: Required System Size (kW) = Daily kWh Consumption ÷ Peak Sun Hours. We then divide that system size by the wattage of the panels to find the total number of panels needed.
Example Calculation
If your average electric bill is $150/month, your rate is $0.15/kWh, you get 5 peak sun hours a day, and you are using 400W panels:
- Monthly Consumption: $150 ÷ $0.15 = 1,000 kWh per month
- Daily Consumption: 1,000 ÷ 30 days = 33.3 kWh per day
- System Size Needed: 33.3 kWh ÷ 5 sun hours = 6.66 kW system
- Number of Panels: 6,660 Watts ÷ 400W per panel = 16.65 panels (round up to 17)
- Roof Space: 17 panels × 17.5 sq ft = ~298 sq ft of roof area
Estimated System Sizes by Monthly Bill (at $0.15/kWh & 5 Sun Hours)
| Monthly Bill | System Size (kW) | Number of 400W Panels | Required Roof Area |
|---|---|---|---|
| $100 | 4.4 kW | 11 panels | 193 sq ft |
| $150 | 6.7 kW | 17 panels | 298 sq ft |
| $200 | 8.9 kW | 23 panels | 403 sq ft |
| $300 | 13.3 kW | 34 panels | 595 sq ft |