About the Solar Panels Needed Calculator
How many solar panels you need for a daily energy target, and the roof space they take.
Also known as: how many solar panels do i need, number of solar panels, panel count calculator.
How to use this calculator
- Enter daily energy use, panel rating, peak sun hours per day, system efficiency and the other fields.
- The result updates instantly as you type — press Calculate (or Enter) at any time.
- Review the breakdown shown under the main result.
- Use Copy result or Share to save the answer or send a link with your inputs.
Formula
panels = daily need ÷ (panel kW × sun hours × derate)
Worked example
Using the values pre-filled in the calculator above:
- Daily energy use = 12 kWh
- Panel rating = 450 W
- Peak sun hours per day = 4
- System efficiency = 80 %
- Area per panel = 2.1 m²
the calculator returns:
- Panels required: 9
- Energy per panel per day: 1.44 kWh
- Array size: 4.05 kWp
- Roof area needed: 18.9 m²