Quick answer
Daily energy = panel watts × number of panels × peak sun hours × (1 − losses) ÷ 1,000. Ten 400 W panels with 4.5 peak sun hours and 20% losses produce 14.4 kWh a day, 438.3 kWh a month and 5,256 kWh a year.
Enter the panel rating, number of panels, peak sun hours and system losses. The calculator returns daily, monthly and yearly energy. Use this solar panel output calculator to check your own figures.
Related tools: Solar Payback Calculator: Simple payback period of an installation after incentives. Potential Energy Calculator: Gravitational potential energy from mass, height and gravity. Power Calculator: Mechanical power from work and time, or force and velocity.
How to use the Solar Panel Output Calculator
- Enter panel rating (W) (above 0).
- Enter number of panels (a whole number, 1 or more).
- Enter peak sun hours per day (h) (above 0).
- Enter system losses (%) (between 0 and 99). It starts at 14.
- Press Calculate to see the result, and use Reset to start again.
| Input | What to enter | Allowed values |
|---|---|---|
| Panel rating | A number, in W | > 0 |
| Number of panels | A whole number | ≥ 1 |
| Peak sun hours per day | A number, in h | > 0 |
| System losses | A number, in % | ≥ 0, ≤ 99, starts at 14 |
Formula and method
Formula
kWh/day = panel watts × panels × sun hours × (1 − losses) ÷ 1000
IEEE-754 double precision; shown to the decimals indicated.
Peak sun hours for your location come from a solar resource map; losses cover wiring, inverter, soiling and temperature.
Worked examples
These examples are verified: each one is an automated test case that the live calculator must reproduce exactly.
Example 1
Inputs: Panel rating = 400; Number of panels = 10; Peak sun hours per day = 4.5; System losses = 20.
| Result | Value |
|---|---|
| Energy | 14.4 kWh/day |
| Per month (average) | 438.3 kWh |
| Per year | 5,256 kWh |
Example 2
Inputs: Panel rating = 300; Number of panels = 6; Peak sun hours per day = 5; System losses = 14.
| Result | Value |
|---|---|
| Energy | 7.74 kWh/day |
| Per month (average) | 235.6 kWh |
| Per year | 2,825 kWh |
Example 3
Inputs: Panel rating = 550; Number of panels = 4; Peak sun hours per day = 3.2; System losses = 25.
| Result | Value |
|---|---|
| Energy | 5.28 kWh/day |
| Per month (average) | 160.7 kWh |
| Per year | 1,927 kWh |
The first line is the headline result (energy). Below it the solar Panel Output Calculator lists per month (average) and per year, which describe the same case from other angles. IEEE-754 double precision; shown to the decimals indicated.
Peak sun hours
A peak sun hour is 1 kW/m² of irradiance for an hour. 4.5 hours is typical in many parts of the US; desert sites exceed 6 and northern sites can be under 3. Seasonal variation is large.
Losses
20% covers inverter efficiency, wiring, dust, temperature and shading. 4 kW of panels × 4.5 × 0.8 = 14.4 kWh, enough for a typical household's daily use of about 29 kWh only in part. Check local data from a tool such as PVWatts.
How the result changes with panel rating
Holding every other input at the first worked example, this table changes only panel rating. It shows how sensitive the answer is to that one value; each row was produced by running this calculator.
| Panel rating | Energy | Per month (average) | Per year |
|---|---|---|---|
| 200 | 7.2 kWh/day | 219.2 kWh | 2,628 kWh |
| 400 | 14.4 kWh/day | 438.3 kWh | 5,256 kWh |
| 800 | 28.8 kWh/day | 876.6 kWh | 10,512 kWh |
| 1600 | 57.6 kWh/day | 1,753.2 kWh | 21,024 kWh |
What happens with invalid input
These messages are produced by the calculator itself, so you know what to fix.
- Panel rating: entering "0" shows "Panel rating must be greater than 0." beside that field and no result.
- System losses: entering "100" shows "System losses must be at most 99." beside that field and no result.
Choosing between the Solar Panel Output Calculator and similar calculators
Each row shows what a related calculator on this site asks for and what it returns, so you can pick the one that matches your question.
| Calculator | You enter | It returns |
|---|---|---|
| [Solar Payback Calculator](/science/solar-payback-calculator/) | system cost and annual savings | Payback period |
| [Potential Energy Calculator](/science/potential-energy-calculator/) | mass, height and gravitational acceleration | Potential energy |
| [Power Calculator](/science/power-calculator/) | use | Power |
| [Wind Power Estimate Calculator](/science/wind-power-estimate-calculator/) | rotor diameter, wind speed and power coefficient | Power |
| [Work Calculator](/science/work-calculator/) | force, distance and angle between force and motion | Work |
Background: motion and mechanics
For constant acceleration the standard relations are v = u + at, s = ut + ½at², v² = u² + 2as and s = ½(u + v)t. Pick the equation that contains your three known quantities and the one you want. Use SI units (metres, seconds, kilograms, newtons, joules) throughout or the answer will be off by a factor.
These equations stop applying when acceleration changes during the motion, as with a rocket burning fuel; that needs calculus or numerical methods.
Assumptions and limitations
- Seasonal variation is large
If a required value is empty, not a number, or outside its allowed range, the form marks that field with a message and shows no result instead of a misleading number. The automated checks deliberately try invalid entries for panel rating and system losses to confirm this.
Frequently asked questions
How many panels do I need?
Divide your daily use by the output per panel.
Do panels work in winter?
Yes, at a reduced output.
What is a good loss figure?
System losses of about 14 to 25% are typical; this calculator uses 20% by default in the example.
What does the Solar Panel Output Calculator calculate?
Daily, monthly and yearly energy from a solar array. It returns Energy, Per month (average) and Per year.
What formula does the Solar Panel Output Calculator use?
kWh/day = panel watts × panels × sun hours × (1 − losses) ÷ 1000. Peak sun hours for your location come from a solar resource map; losses cover wiring, inverter, soiling and temperature.
What do I need to enter in the solar Panel Output Calculator?
You enter Panel rating (W), Number of panels, Peak sun hours per day (h) and System losses (%).
How is the result rounded or limited?
IEEE-754 double precision; shown to the decimals indicated. Seasonal variation is large.
What is an example of a solar Panel Output result?
With panel rating 400, number of panels 10, peak sun hours per day 4.5 and system losses 20, the energy is 14.4 kWh/day.
Where does the method come from?
The method follows: Standard PV energy estimate (e.g. NREL PVWatts documentation).
Related calculators
- Solar Payback Calculator — Simple payback period of an installation after incentives.
- Potential Energy Calculator — Gravitational potential energy from mass, height and gravity.
- Power Calculator — Mechanical power from work and time, or force and velocity.
- Wind Power Estimate Calculator — Power from a wind turbine rotor at a wind speed.
- Work Calculator — Work done by a force over a distance at an angle.
- Energy Converter — Convert joules, calories, kWh, BTU and more.
Sources
- Standard PV energy estimate (e.g. NREL PVWatts documentation)
Content last reviewed 2026-11-04. Formulas and worked examples are checked by automated tests against independently computed values.