Energy, battery, and panel in three steps.
Learning Track · Module 5: Solar street lights · Step 35 of 101
1. Daily energy = LED watts × burn hours × average level
30 W × 12 h × 60% = 216 Wh per night
2. Battery = daily energy × days of autonomy ÷ usable depth of discharge
216 Wh × 3 days ÷ 0.8 = 810 Wh (≈ 63 Ah at 12.8 V)
3. Panel = daily energy ÷ (peak sun hours × system efficiency)
216 Wh ÷ (4.5 h × 0.75) = 64 Wp → choose 70 Wp or more
30 W × 12 h × 60% = 216 Wh per night
2. Battery = daily energy × days of autonomy ÷ usable depth of discharge
216 Wh × 3 days ÷ 0.8 = 810 Wh (≈ 63 Ah at 12.8 V)
3. Panel = daily energy ÷ (peak sun hours × system efficiency)
216 Wh ÷ (4.5 h × 0.75) = 64 Wp → choose 70 Wp or more
- Peak sun hours: use the value for the worst month, not the yearly average.
- Autonomy: the number of nights with no charge. 2 to 3 days is common; more in monsoon or northern climates.
- System efficiency: includes controller, battery, wiring, dust, and heat losses. 0.7 to 0.8 is typical.
- Dimming: a deep late-night profile reduces battery and panel size a lot.
Try your own values in the solar sizing tool.
Sources
- IEC 62124
- IEC 62509
- NREL PVWatts / national solar resource data for peak sun hours
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