How many solar panels for 20 kWh a day?
For 20 kWh a day with 4.5 peak sun hours (typical of the Philippines and much of the tropics): about 5,930 W of panels, 11 × 550 W modules, and for a night off-grid a 25,000 Wh LiFePO4 bank.
| Peak sun hours | Panel array | 450 W modules | 550 W modules |
|---|---|---|---|
| 3 h | 8,890 W | 20 × 450 W | 17 × 550 W |
| 4 h | 6,670 W | 15 × 450 W | 13 × 550 W |
| 4.5 h | 5,930 W | 14 × 450 W | 11 × 550 W |
| 5 h | 5,340 W | 12 × 450 W | 10 × 550 W |
| 6 h | 4,450 W | 10 × 450 W | 9 × 550 W |
Peak sun hours: about 4–5.5 in the Philippines (lower in the rainy season), 4–6 across most of the US, 2.5–4 in northern Europe. Use the worst month you need to cover.
How it is worked out
- Panel watts = daily energy ÷ (sun hours × 0.75): 25 % goes in heat, dust, wiring, the controller and the battery's charge losses.
- A grid-tie system (no battery) needs the same array; an off-grid one adds a battery: one day of use ÷ 80 % usable = 25,000 Wh of LiFePO4.
- Round up to whole modules, and check that the string voltage fits the inverter's window: the lab's safety check does that for you.
Check it in the solar calculator · Open it on the benchMy house designs the system for 600 kWh a month, builds it and runs the safety check.
For planning and learning. Use the appliance's nameplate (amps, MCA and MOCP) when you have it, follow your local electrical code, and have a licensed electrician do work on a building's wiring.