Solar Panel Calculator
Size a rooftop solar array from consumption, sun hours and panel rating.
About Solar Panel Calculator
Peak sun hours already fold in latitude and climate, so annual yield per installed kilowatt is a single multiplication. System losses of around 18 per cent are typical and cover inverter, temperature and soiling effects. Offsetting much beyond annual consumption rarely pays unless export rates are favourable, because the surplus is sold at far less than the retail price avoided.
Formula
Solar Panel
Annual yield per kW = peak sun hours × 365 × performance ratio
- peak sun hours
- Equivalent hours of full 1 kW/m² irradiance per day
- performance ratio
- Output after inverter, temperature, soiling and wiring losses
Worked example
With the default values below, Solar Panel Calculator returns Panels Required of 9. Change any input above and every figure here is recalculated in your browser.
Inputs used
- Annual electricity useminimum 0 kWh
- 4,200 kWh
- Average peak sun hoursminimum 0.1 h
- 3.4 h
- Panel ratingminimum 50 W
- 420 W
- System lossesaccepts 0–60 %
- 18 %
- Share of use to offsetaccepts 1–200 %
- 90 %
Results
- Panels Required
- 9
- System Size
- 3.780 kW
- Annual Production
- 3,847 kWh
- Roof Area Required
- 18.00 m2
- Consumption Offset Achieved
- 91.59%
Step by step
- 1Values used
- 2Solar Panel
- 3Panels Required= 9
- 4System Size= 3.780 kW
- 5Annual Production= 3,847 kWh
- 6Roof Area Required= 18.00 m2
- 7Consumption Offset Achieved= 91.59
Assumptions and limits
- The result is derived only from the 5 inputs listed above. Anything not among them is not part of the calculation.
- In particular, this calculator does not take inflation, tax or fees or charges into account.
- Figures are rounded for display to 3 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.
How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.
Frequently Asked Questions
How is Solar Panel calculated?
Annual yield per kW = peak sun hours × 365 × performance ratio Peak sun hours already fold in latitude and climate, so annual yield per installed kilowatt is a single multiplication. System losses of around 18 per cent are typical and cover inverter, temperature and soiling effects.
Why does Solar Panel matter?
Offsetting much beyond annual consumption rarely pays unless export rates are favourable, because the surplus is sold at far less than the retail price avoided.
What values do I need to enter?
This calculator takes 5 inputs: Annual electricity use, Average peak sun hours, Panel rating, System losses, Share of use to offset. The pre-filled defaults are a realistic starting point — replace them with figures from your own environment for a result you can act on.