Solar Panel Output Calculator
Estimate the electricity a solar array makes by multiplying its size in kW by your local peak sun hours and a performance ratio that accounts for real losses. Enter a system size directly, or switch to By panels and give the panel wattage and count. A 5 kW array at 5 sun hours and a 0.75 ratio produces 18.75 kWh a day, which projects to about 570.31 kWh a month and 6,843.75 kWh a year.
How to estimate solar panel output
- Pick a tab: System size to enter kW directly, or By panels to enter Panel watts and Panel count.
- Fill in the chosen fields (the tool multiplies watts by count and divides by 1000 for kW).
- Enter your local average in the Sun hours/day field.
- Set Performance ratio to your losses factor, from 0 to 1, with 0.75 as a typical default.
- Read the daily kWh headline plus the Per month and Per year cards, then Copy result.
Examples
5 kW system at 5 peak sun hours
System size 5 kW, Sun hours/day 5, Performance ratio 0.75
18.75 kWh/day, 570.31 kWh/month, 6,843.75 kWh/year
Twelve 400 watt panels (By panels tab)
Panel watts 400, Panel count 12, Sun hours/day 5, Performance ratio 0.75
4.8 kW system, 18 kWh/day, 547.5 kWh/month, 6,570 kWh/year
8 kW array in a sunnier spot
System size 8 kW, Sun hours/day 4.5, Performance ratio 0.8
28.8 kWh/day, 876 kWh/month, 10,512 kWh/year
Frequently asked questions
What are peak sun hours?
A peak sun hour is one hour during which sunlight averages 1000 watts per square meter, the standard test condition for panels. It bundles a whole day of varying sunshine into an equivalent count of full-strength hours. Most locations average about 3 to 6, and a solar irradiance map for your area gives a good figure to enter.
What is the performance ratio and why is it below one?
The performance ratio captures real-world losses that panel nameplates ignore: heat, wiring resistance, inverter conversion, dust and shading. A ratio of 0.75 means the array delivers about 75 percent of its ideal output. The tool accepts any value above 0 and up to 1, and rejects anything larger.
Should I enter system size or use the By panels tab?
Use whichever you know. If your quote lists a kW figure, enter it on the System size tab. If you only have the panel spec, switch to By panels and enter the wattage and count; the tool multiplies them and divides by 1000, so twelve 400 watt panels resolve to a 4.8 kW system.
How are the monthly and yearly numbers derived?
Daily kWh is size times sun hours times the ratio. Yearly is that daily figure times 365, and monthly is the yearly total divided by 12. Every month is treated as an equal twelfth, so the monthly value is an average rather than a real calendar month.
Why are results shown to two decimals?
The engine computes to four decimal places, and the display rounds to two for readability. A number like 570.3125 kWh per month appears as 570.31. The extra precision stays in the underlying value if you use the API.
Will my system really produce this every day?
No. Actual output swings with weather, season, panel tilt, orientation and shading, so a clear summer day beats the estimate and an overcast winter day falls short. Treat the result as a long-run average for planning, not a daily guarantee.
Does this estimate savings or payback?
No. It reports energy in kWh only. To estimate bill savings, multiply the kWh by your electricity rate, and remember net metering, time of use pricing and self-consumption all change the real value of each kWh.
Should I still get a professional quote?
Yes. This is a planning estimate, not a design. A local installer will run a shading study, confirm roof orientation and structure, and model losses specific to your site, which can move the numbers up or down.
Is my data kept private?
Yes. The calculation runs entirely in your browser and nothing is uploaded, so your system details never leave your device.
Learn more
- Peak sun hours and performance ratio explained
The two inputs that decide a solar estimate, where to find real numbers for your roof, and how each one moves your kWh.
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