Solar Panel Output Calculator
W
h
0.80
Daily Energy20.00 kWh
Monthly Energy608.8 kWh
Annual Energy7,300 kWh
The Solar Panel Output Calculator estimates how much energy a photovoltaic system actually delivers, not just its nameplate rating. By combining the array wattage with local peak sun hours and a real-world derate factor, it produces daily, monthly, and annual kWh figures you can compare against your electricity bill. This is an energy-yield tool, distinct from string-sizing tools that work out panel counts and voltages.
Formula
dailyKwh = (W × PSH × derate) / 1000; annual = dailyKwh × 365
- W
- Rated DC system size in watts
- PSH
- Peak sun hours per day (full-sun equivalent)
- derate
- Combined loss/efficiency factor, 0–1
How it works
- Enter the rated DC system size in watts and the average peak sun hours per day for your location.
- Set the derate factor (default 0.8) to account for inverter losses, temperature, wiring, soiling, and panel tolerance.
- Daily energy = (watts × peak sun hours × derate) ÷ 1000; monthly uses a 30.44-day average and annual multiplies the daily figure by 365.
Worked example
A 5 kW (5000 W) array with 5 peak sun hours and an 0.8 derate factor.
- Daily = (5000 × 5 × 0.8) ÷ 1000 = 20000 ÷ 1000 = 20 kWh.
- Monthly = 20 × 30.44 ≈ 608.8 kWh.
- Annual = 20 × 365 = 7300 kWh.
About 20 kWh per day, 608.8 kWh per month, and 7300 kWh per year.
Frequently asked questions
- What are peak sun hours?
- Peak sun hours are the number of hours per day when sunlight averages 1000 watts per square metre. A location with 5 peak sun hours can spread that energy across a longer but less intense day.
- Why apply a derate factor instead of using the nameplate rating?
- Real systems lose energy to inverter inefficiency, heat, wiring resistance, dust, and shading. A derate of about 0.75 to 0.85 turns the optimistic DC nameplate into a realistic AC output estimate.
- How is this different from a solar string sizing calculator?
- String sizing tools determine how many panels fit in series within an inverter voltage window. This calculator instead estimates energy yield in kWh once a system is sized, so the two are complementary.