Calculators
Solar Panel Calculator
Estimate how many solar panels you need, the system size, monthly production, and bill savings from your electricity use locally in your browser.
Enter your average monthly electricity use in kWh, the nameplate output of one panel in watts, the peak sun hours for your location, the system loss percentage, the share of your usage you want to cover, and your electricity rate per kWh. Add your system cost if you want a simple payback estimate. The calculation runs locally in your browser; your values are not uploaded or stored.
Size a solar array without sending any data anywhere.
Enter your average monthly electricity use, the panel output in watts, the peak sun hours for your location, system losses, the share of usage you want to cover, and your electricity rate per kWh. The calculator estimates panel count, array size in kW, monthly and annual production, the share of your usage covered, and monthly and annual bill savings, plus a simple payback estimate when you add a system cost. This private browser estimate uses a constant production average and does not account for seasonal weather, roof orientation and shading, degradation, financing, incentives, export rates, or taxes; it is not financial, investment, or tax advice. Your values are not uploaded or stored.
Frequently Asked Questions
Everything you need to know about this tool, how it works, and privacy.
How does the solar panel calculator work?
Enter your average monthly electricity use in kWh, the nameplate output of one panel in watts, the peak sun hours per day for your location, the system loss percentage, and the share of usage you want to cover. Each panel is sized as panel kW multiplied by peak sun hours, reduced by losses, and multiplied by 30 days. The required number of panels is that per-panel monthly output divided into your target usage, rounded up to the next whole panel.
What peak sun hours and system losses should I use?
Peak sun hours per day is the average daily sunlight energy for your location, typically between 2 and 6 hours depending on climate and latitude. System losses cover inverter, wiring, soiling, shading, and temperature effects; 10% to 20% is a common planning range, and 14% is a reasonable default for a well-oriented roof.
Which inputs are accepted?
Monthly use greater than zero through 10,000,000 kWh, panel output greater than zero through 2,000 watts, peak sun hours between 0.5 and 24, losses between 0% and 99%, a coverage target between 1% and 100%, an electricity rate from $0 to $100 per kWh, and an optional system cost up to $100,000,000. Missing or non-numeric entries show a clear error instead of a result.
What does this estimate not include?
The estimate assumes constant daily production and no seasonal variation, and it does not account for roof orientation and tilt, shading, panel degradation, financing, incentives or tax credits, export rates for surplus power, or maintenance. It is a planning estimate, not financial, investment, or tax advice.
Do my values stay private?
Yes. The calculation and copy action run locally in your browser. CodeASystem does not upload or store the values you enter.