Solar street light sizing: panel, battery and autonomy for India

The sizing chain

A solar street light is an energy budget: the LED load decides battery size, the battery and the sunlight available decide the panel.

1. Nightly energy

Choose the LED wattage from road width (see our street-light wattage guide), then multiply by operating hours. Most installations run 12 hours with dimming after midnight, so a 30 W fixture at full power for 5 hours and 50% for 7 hours uses 30 × 5 + 15 × 7 = 255 Wh per night.

2. Battery

Divide the nightly energy by the depth of discharge (80% for LiFePO4) and multiply by autonomy days. For 255 Wh, 2.5 days of autonomy: 255 × 2.5 ÷ 0.8 ≈ 800 Wh, so a 12.8 V 60 Ah or 25.6 V 30 Ah LiFePO4 pack.

3. Panel

Divide nightly energy by peak sun hours and system efficiency. Kerala averages 4–4.5 peak sun hours; allow 0.7 for charge controller, temperature and dust losses. 255 ÷ (4 × 0.7) ≈ 90 W, so specify a 100–120 W monocrystalline panel to recharge after cloudy days.

Quick reference

LED wattage	Nightly energy (with dimming)	Battery (LiFePO4)	Panel
15 W	130 Wh	12.8 V 30 Ah	60 W
30 W	255 Wh	12.8 V 60 Ah	100–120 W
50 W	425 Wh	25.6 V 50 Ah	180–200 W
80 W	680 Wh	25.6 V 80 Ah	300 W

Installation notes

• Face the panel south at 10–15° tilt in Kerala, with no shade between 9 am and 3 pm.
• Use MPPT charge controllers; PWM controllers lose 15–25% of panel output.
• Choose IP66 fixtures with an IP65 or better battery enclosure.
• Ask for motion or time-based dimming; it halves the battery and panel size for residential streets.

Select "Solar standalone" in the bulk portal and the calculator sizes panel and battery for the fixture you choose, using the autonomy and sun-hour figures above.