Solar Panel Output Calculator

Estimate daily and yearly solar energy output.

System size

Peak sun hours / day

System efficiency(optional)

Accounts for losses; default 80%

Results update as you type.

Daily output

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Annual output—

How it works

This calculator estimates how much electricity a solar panel system will generate, using its size, your location's sunshine, and a real-world efficiency factor. You enter the system size in kilowatts, the average peak sun hours per day where you live, and an efficiency percentage, and it returns the estimated daily and annual output in kilowatt-hours. The core idea is simple: a system's rated kilowatts describe its output under ideal test conditions, so multiplying by peak sun hours, the equivalent number of hours of full-strength sun your site receives daily, gives raw energy, which is then scaled down by an efficiency factor to reflect real losses. Those losses come from inverter conversion, wiring, dust and soiling, heat, shading, and panel aging, and typically total around 15 to 25 percent, so an efficiency of about 80 percent is a reasonable default. Peak sun hours vary widely by region and season, from around three in cloudy northern climates to over six in sunny deserts. This estimate helps homeowners size a system, gauge how much of their electricity bill solar could offset, and evaluate payback before getting quotes. It is a planning approximation; a professional assessment accounts for roof orientation, tilt, and local shading. Enter your system size, sun hours, and efficiency to estimate solar output.

Formula

Daily kWh = system kW × peak sun hours × efficiency

The daily energy a solar array produces equals its rated size in kilowatts times the number of peak sun hours at the location, multiplied by a system efficiency factor that captures real-world losses. Annual output is the daily figure times 365. Peak sun hours represent the equivalent hours of full-strength sunlight per day for your location.

Source:Photovoltaic estimation

We review all our tools from time to time to ensure accuracy.

Worked example

System size:5Peak sun hours / day:4.5System efficiency:80

5 kW × 4.5 h × 0.80 = 18 kWh/day, about 6,570 kWh/year.

How to use this calculator

1
Enter your values
Enter system size and peak sun hours / day.
2
Adjust the options
Adjust system efficiency if they apply — sensible defaults are already set.
3
Read your result
Daily output updates instantly as you type — no button to press.

Frequently asked questions

How much energy will my solar panels produce?

Multiply your system size in kilowatts by your location's peak sun hours per day and by an efficiency factor for real-world losses. A 5 kW system with 4.5 peak sun hours at 80 percent efficiency makes about 18 kWh per day. The calculator estimates both daily and annual output when you enter these values.

What are peak sun hours?

Peak sun hours are the equivalent number of hours per day that sunlight hits at its full-strength intensity of 1,000 watts per square meter. A location might receive sunlight for twelve hours but only 4.5 peak sun hours' worth of usable energy. Peak sun hours vary by region, season, and weather, and are the key input for output estimates.

Why apply an efficiency factor?

A panel's rated wattage is measured under ideal lab conditions. In the real world, energy is lost to inverter conversion, wiring resistance, dust, heat, shading, and gradual panel aging. These losses usually total 15 to 25 percent, so applying an efficiency of around 80 percent gives a realistic estimate rather than the optimistic nameplate figure.

How many peak sun hours does my area get?

It depends on your latitude, climate, and season. Sunny desert regions may see six or more peak sun hours a day averaged over the year, while cloudy northern areas may get three or fewer. Solar maps and online databases provide local averages; use your area's annual average for a realistic yearly output estimate.

Is this estimate accurate enough to size a system?

It gives a solid planning estimate but not a final design. Actual output also depends on roof orientation and tilt, local shading from trees or buildings, temperature, and equipment quality. Use this calculator to gauge feasibility and rough payback, then get a professional assessment that models your specific roof for an accurate system size.