Solar Panel Calculator
System size, panel count and payback period.
Enter your values
Results update instantly as you type — no submit needed.
Results
- System size needed
- 8.21 kW
- Number of panels
- 21
- Estimated installed cost
- $22996
- Annual bill offset
- $1728
- Simple payback
- 13.3 years
Quick answer
System size in kW equals daily kWh use divided by peak sun hours divided by system efficiency, usually around 0.8.
kW = daily kWh ÷ sun hours ÷ 0.8
How to use the Solar Panel Calculator
- 1Take monthly kWh from your utility bill.
- 2Look up peak sun hours for your area.
- 3Read the system size and payback period.
Frequently asked questions
What are peak sun hours?
The equivalent hours of full 1,000 W/m² sunlight per day — typically 3.5 in the northern US and 5.5–6 in the southwest.
Does payback include incentives?
No. The 30% US federal tax credit and state rebates typically cut the payback period by around a third.