Free energy calculator
Solar Panel Daily Output Calculator
Estimate a solar array’s daily energy output. Weather and shading make day-to-day production variable.
Calculate your estimate
Change the example values to match your system.
Estimated result
Ideal—
Typical—
Conservative—
These are estimates, not guaranteed performance.
Formula and method
Ideal Wh/day = panel watts × peak sun hours. Typical output multiplies this by system efficiency.
Percent fields are entered as percentages; the calculation converts them to decimal fractions. Displayed results are rounded to two decimal places.
What the inputs mean
- Array rating (W)
- Enter array rating in W.
- Peak sun hours (hours/day)
- Enter peak sun hours in hours/day.
- System efficiency after losses (%)
- Enter system efficiency after losses in %.
- Conservative retained fraction (%)
- Enter conservative retained fraction in %.
Worked example
A 400 W array with 5 peak sun hours has 2,000 ideal Wh/day and 1,600 typical Wh/day at 80% system efficiency.
Why the real result may differ
- Temperature, battery age, wiring resistance, and changing loads can move actual results away from the estimate.
- Manufacturer ratings may be measured under different test conditions. Measure the load when practical.
Common mistakes
- Do not confuse watts (power) with watt-hours (energy).
- Do not enter a percentage as a whole number: 90% is entered as 90 in this form and converted internally.
Frequently asked questions
Is this result guaranteed?
No. It is an engineering estimate; equipment, temperature, age, and duty cycle affect real performance.
Why are three estimates shown?
The ideal case ignores practical losses, while typical and conservative cases apply the efficiency and margin entered above.
Related tools
References
Last reviewed: August 6, 2026