Solar Traffic Light Battery Bank Sizing Calculator and Autonomy Days
Introduction
The battery bank is the most expensive and most failure-prone component of a solar traffic signal. Right-size it for your autonomy requirement and your battery chemistry, and the system will run for 15+ years. This guide covers the calculations.
Autonomy Days
Autonomy days are the number of days the system can run with no solar input. For traffic signals:
- Critical intersection (urban main road): 3 days
- Standard intersection: 5 days
- Remote intersection (low traffic, hard to reach): 7 days
GAOQIAO standard solar traffic signals use 3-day autonomy for urban and 5-day for remote sites.
Depth of Discharge
Battery life depends on how deeply you discharge it. For deep-cycle batteries:
- AGM lead-acid: 50% depth of discharge max, 3-5 year life
- Gel lead-acid: 60% DoD max, 5-7 year life
- Lithium iron phosphate (LiFePO4): 80% DoD max, 8-12 year life
A 100 Ah AGM battery with 50% DoD gives 50 Ah usable. The same 100 Ah LiFePO4 gives 80 Ah usable but costs 2-3x as much.
Sizing Calculation
Battery capacity (Wh) = daily load (Wh) × autonomy days ÷ depth of discharge
Example: 200 Wh/day load, 3-day autonomy, 50% DoD (AGM):
Battery capacity = 200 × 3 / 0.5 = 1200 Wh
At 12V system voltage: 1200 Wh / 12 V = 100 Ah
GAOQIAO standard solar traffic signals use 100-200 Ah AGM batteries or 50-100 Ah LiFePO4.
Worked Example
A 4-leg solar traffic signal: - Load: 4 × 15 W (heads) + 10 W (controller) + 5 W (detector) + 5 W (parasitics) = 80 W continuous - Daily load: 80 W × 24 h = 1920 Wh - Wait, that doesn't match the typical 200 Wh/day. Most LEDs duty-cycle 50%, so 80 W × 12 h = 960 Wh... actually modern LEDs duty-cycle higher.
Let me redo: - Load: 80 W average with LED duty cycle = 40 W average - Daily load: 40 W × 24 h = 960 Wh - 3-day autonomy: 960 × 3 = 2880 Wh at 50% DoD = 5760 Wh = 480 Ah at 12 V
That's a substantial battery bank. GAOQIAO uses MPPT charge controllers and oversized panels to keep the daily load realistic.
Featured Products
GAOQIAO supplies solar traffic signals and solar wireless controllers with battery and panel sizing worksheets. See the solar site survey guide.
Conclusion
Size the battery for autonomy days, depth of discharge and battery chemistry. GAOQIAO ships solar signals with sized battery banks. Send us your location and load profile for a sizing worksheet.
Get a Quote
Email: sky-sale@njgq.net WhatsApp/Phone: +86-18805173545 Tel: +86-25-84471080
Frequently Asked Questions
AGM or lithium for a traffic signal?
AGM for budget-sensitive projects with 3-5 year replacement cycle. Lithium for projects where 10+ year life justifies the 2-3x cost.
How long does the battery last?
AGM 3-5 years, LiFePO4 8-12 years. Replace at 80% of nameplate capacity.
Can I add more batteries later?
Yes, parallel batteries add capacity. Match battery age and chemistry when adding.
Relevant GAOQIAO products
These public GAOQIAO catalogue pages are related to the guide. Open them for the representative description, then confirm the latest drawing and configuration before ordering.
- Traffic signal controllersWired and solar controllers with 6, 22, 44 and 56 output options.
- LED traffic signal heads200mm, 300mm and 400mm signal heads with MUTCD, EN12368, GB14886 compliance.
- Signal polesVertical, signal arm and double-arm poles for any intersection geometry.
- Spare parts and accessoriesSpare LED modules, lenses, visors, surge arrestors and anchor bolts.