☀️ Solar Panel Calculator
To fully cover your daily electricity use with solar panels, you need enough panels to produce sufficient energy on an average day. Enter your daily use in kWh, the power per panel in Wp and the number of peak sun hours, and this calculator instantly works out how many panels and what system size you need. That gives you a realistic first estimate before requesting quotes.
Formula
Number of panels = (daily use in Wh) ÷ (power per panel × peak sun hours)
Peak sun hours are not the number of hours the sun shines, but the number of hours at full-intensity sunlight (1000 W/m²) that would deliver the same total energy as a real day. In the Netherlands this averages around 3 to 3.5 hours per day over the year. You multiply the power per panel by the peak sun hours to get the daily output per panel, then divide your total daily use by that figure.
Steps
- 1Enter your average daily electricity use in kWh.
- 2Enter the power per panel (Wp) and the number of peak sun hours for your location.
- 3See the number of panels needed and the total system size in kWp instantly.
Panels and system size for 400 Wp panels
| Daily use (kWh) | Panels (400 Wp, 3.5 h) | System size (kWp) |
|---|---|---|
| 5 | 4 | 1,6 |
| 8 | 6 | 2,4 |
| 10 | 8 | 3,2 |
| 12 | 9 | 3,6 |
| 15 | 11 | 4,4 |
| 20 | 15 | 6,0 |
Assumes 400 Wp panels and 3.5 peak sun hours per day; use the calculator above for your own values.
limitations
- This calculation does not account for roof orientation, shading or system losses; an installer will calculate this more precisely.
commonMistakes
- Confusing peak sun hours with the number of daylight hours, leading to a far too low panel count.
- Not accounting for system losses (cabling, inverter, temperature), which typically cost 10 to 15% of the yield in practice.
- Forgetting that you always round up: a result of 7.1 panels means you need to buy 8 whole panels.
useCases
- Making an initial estimate before getting a quote from an installer.
- Sizing an off-grid or battery system based on your energy needs.
- Comparing different panels and wattages before choosing a supplier.