Solar Panel Output Calculator
Enter the rating of your panels, how many you have and how much sun you get. The calculator estimates the energy they produce each day, month and year and what it is worth.
How to use this Solar Panel Output Calculator
- Enter the rating of one panel in watts.
- Enter how many panels are in the array.
- Enter the peak sun hours per day for your location.
- Keep or change the system losses.
- Enter your electricity price to see the value of the energy, then press Calculate.
How to calculate solar panel output
Output is the array size times the sun hours, reduced by losses.
- System size (kW) = panel watts x panels / 1,000
- Energy per day = system size x sun hours x (1 – losses)
- Energy per year = energy per day x 365
- Value = energy x price per kWh
Worked example
Ten 400 W panels make a 4.00 kW system. With 5 peak sun hours and 14% losses the array produces 4 x 5 x 0.86 = 17.2 kWh a day. Over a 30 day month that is 516 kWh, and over a year it is 6,278 kWh. At $0.16 per kWh the energy is worth $82.56 a month and $1,004.48 a year.
Output changes a lot by season. Summer days give far more than winter days, so a single average hides the swings. Shade on even one panel can lower the output of a whole string unless the system uses optimizers or micro-inverters. If your utility pays less for exported power than it charges for imported power, the value of the energy depends on when you use it, so treat the dollar figure as a rough guide.
Assumptions & limits
- Peak sun hours and losses are editable inputs. Check a solar resource map and ask your installer for the values they use.
- The result is a yearly average. Real output varies by day and by season.
- Shade, direction, tilt and panel ageing are not modelled.
- The dollar value assumes every kWh offsets the price you enter. Export rates and net metering rules differ.
- It is a planning estimate and not a guarantee of production.
Frequently asked questions
How do I calculate how much power a solar panel produces?
Multiply the panel watts by the peak sun hours and by one minus the losses, then divide by 1,000 to get kWh per day.
How much does a 400 watt panel produce a day?
With 5 sun hours and 14 percent losses it makes about 1.7 kWh a day.
What are peak sun hours?
The hours per day with sunlight strong enough to give the rated power. It depends on location and season.
Why does my real output differ?
Shade, weather, direction, tilt and the age of the panels all change output.
How do I find the value of the energy?
Multiply the energy by your price per kWh, or by the rate your utility pays for exports.
Does the output drop over time?
Yes. Panels slowly lose output as they age, so check the warranty.
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Last updated: November 2026