How the solar panel calculator works
Enter your monthly electricity use, your local peak sun hours, an installed cost per watt, and your electricity rate, and the tool estimates the system size you would need, how many panels that is, the rough cost, and how long it would take to pay back through bill savings.
Sizing a system
The tool sizes the system to roughly cover your annual usage. It divides your yearly kilowatt hours by your peak sun hours over a year to find the kilowatts of panels needed, then divides by 400 watts to estimate panel count. Peak sun hours, the daily equivalent of full strength sunlight, vary by location and season.
Cost and payback
Estimated cost is the system size in watts times your cost per watt. Annual savings are your yearly usage times your electricity rate, assuming the system offsets most of your bill. Payback is cost divided by annual savings. Real payback is affected by incentives, financing, rate increases, and how much energy you actually self consume.
What this estimate leaves out
This is a planning starting point, not a quote. It does not model tax credits or rebates, system efficiency losses, panel degradation over time, roof orientation and shading, or your utility net metering and time of use rules, all of which can change the result significantly. Always get detailed quotes from local installers.
Frequently asked questions
How big a solar system do I need? Roughly your annual kWh divided by peak sun hours over a year; the tool estimates this.
What are peak sun hours? The daily equivalent hours of full strength sunlight for your location, often around 4 to 6.
Is the payback exact? No, it ignores incentives, losses, and rate changes; treat it as a rough guide.
Related calculators: Electricity Cost, Carbon Footprint, Tree Offset.