About the Solar Panel Output Calculator
How much electricity will a set of solar panels produce? This calculator gives a good first estimate. Enter the power of one panel, how many you have, the number of peak sun hours at your location and the efficiency of the whole system, and it returns the energy per day, month and year. With the price of electricity it also gives the yearly value. Type the panel power, the number of panels, the peak sun hours, the system efficiency and, optionally, the electricity price and the solar panel output appears at once, with a few related figures underneath, and you can copy the result with one tap. The sums run in your browser, so nothing you enter is uploaded.
Updated October 2026
How to use the Solar Panel Output Calculator
- 1Enter the panel power, the number of panels, the peak sun hours, the system efficiency and, optionally, the electricity price.
- 2Pick the units or options from the menus if the solar panel output tool offers them.
- 3Read the solar panel output in the large result box.
- 4Look at the extra rows for related figures.
- 5Press Copy result to keep the answer.
When you need the solar panel output
People use the estimate to size a roof system, compare it with their yearly use, and see how long it would take to repay the cost. Caravan and cabin owners use it for off-grid systems to decide how many panels will fill a battery bank.
A peak sun hour is one hour of sunlight at 1,000 watts per square metre, the strength the panel rating is based on. A day with 8 hours of daylight might have only 4 to 6 peak sun hours. Local maps give typical values for each month.
How the solar panel output is worked out
Daily energy = panel watts × number of panels × peak sun hours × system efficiency ÷ 1,000. Ten 400 W panels make a 4 kW system. With 5 peak sun hours a day and 75 percent system efficiency, they produce 15 kWh a day, about 457 kWh a month and 5,479 kWh a year. At 0.20 per kWh that is worth 1,095.75 a year.
Every answer on this page comes from that one rule, so you can check any result by hand with a calculator. The figures shown underneath, such as other units, are conversions of the same answer.
- Day, month and year
- Optional yearly value
- Adjustable efficiency
Mistakes to avoid with solar panel output
System efficiency covers the losses from heat, dirt, shading, cable resistance and the inverter. 75 to 85 percent is typical. Panel output also falls slowly with age, about half a percent a year. Use the lowest month if you need power all year round.
On phone and computer
On a phone, type into the boxes one after another and read the solar panel output underneath; Copy result puts it on the clipboard for a message or a note. On a computer the inputs sit on the left and the answer on the right, so you can change one figure and watch the solar panel output move. The solar panel output calculator works the same on both. Output matters most with the money side beside it. Work out the cost of the power with the Electricity Cost Calculator, how long a battery lasts with the Battery Runtime Calculator, and the payback with the ROI Calculator.
Features
- Use peak sun hours, not daylight hours
- 75 to 85% system efficiency
- Check the worst month
- Clear messages when the solar panel output inputs make no sense
- Copy the result with one tap
- Private: nothing is uploaded
Frequently asked questions
How do I calculate solar panel output?
Daily energy = panel watts × number of panels × peak sun hours × system efficiency ÷ 1,000. Ten 400 W panels make a 4 kW system. With 5 peak sun hours a day and 75 percent system efficiency, they produce 15 kWh a day, about 457 kWh a month and 5,479 kWh a year. At 0.20 per kWh that is worth 1,095.75 a year.
What is the formula for solar panel output?
Daily energy = panel watts × number of panels × peak sun hours × system efficiency ÷ 1,000. The solar panel output calculator applies it exactly and rounds only the displayed answer to six significant figures.
What are peak sun hours?
The number of hours per day with the equivalent of full 1,000 W per square metre sunshine. It depends on place and season.
Why is the output lower than the panel rating?
Panels reach their rated power only in ideal test conditions. Heat, haze, angle and wiring all reduce it.
Does the estimate include batteries?
No. It gives the energy from the panels. Battery losses come on top.
Is this solar panel output calculator free and private?
Yes. It is free, needs no account and runs in your browser, so the numbers you type are not uploaded or stored.