Solar Traffic Light Battery & Panel Sizing Guide

Introduction

If you are buying solar traffic lights for a school zone, a work zone, a rural crossing, or a temporary intersection, the two questions that decide whether the unit actually works are: what size battery and what size solar panel does it need?

The short answer: battery capacity should cover the load for at least 3 to 5 days without sun (autonomy), and the solar panel should recharge that battery in one good sunny day with about 25-30% margin. This guide walks through the sizing math with real examples so you can compare supplier quotes with confidence.

Step 1: Calculate the Daily Energy Use

Every solar traffic light has three loads that consume power: the LED signal modules, the controller, and (for wireless units) the radio receiver. LED power depends on the signal size and aspect count:

• 100mm (4-inch) module: approximately 3-5W per aspect
• 200mm (8-inch) module: approximately 8-12W per aspect
• 300mm (12-inch) module: approximately 12-18W per aspect

A flashing warning light typically runs at 40-60% of the duty cycle of a solid signal, which reduces average consumption. For example, a 200mm two-aspect flasher that alternates red/yellow at 60 flashes per minute uses roughly 8-10W average.

Daily energy (Wh) = average load (W) × operating hours per day. A 24-hour school-zone flasher running at 9W average needs about 216 Wh/day; an 8-hour work-zone signal at 12W needs only 96 Wh/day.

Step 2: Size the Battery

Battery capacity is calculated so the light keeps working through consecutive cloudy or rainy days. The formula is:

Battery Ah = (daily Wh × autonomy days) ÷ (system voltage × depth of discharge × efficiency)

Use a depth of discharge of 0.8 for LiFePO4 (lithium iron phosphate) batteries and 0.5 for lead-acid, plus an efficiency factor of about 0.85 for the charge/discharge path.

Example: A 216 Wh/day flasher on a 12V LiFePO4 system with 4 days of autonomy:

(216 × 4) ÷ (12 × 0.8 × 0.85) ≈ 106 Ah. Round up to a 110-120 Ah LiFePO4 battery (or a 150-200 Ah lead-acid equivalent).

Step 3: Size the Solar Panel

The panel must put back the energy the battery used, normally in one day. The formula is:

Panel watts = daily Wh ÷ (effective sun hours × system efficiency)

Use 3.5-4.5 effective sun hours for most Asian, Middle Eastern and southern US locations, 2.5-3.5 hours for northern Europe and Canada, and a system efficiency of about 0.75 (panel degradation, dust, wiring and charge controller losses).

Continuing the example: 216 Wh/day ÷ (4 sun hours × 0.75) ≈ 72W. A 75-80W monocrystalline panel gives the needed margin; in lower-irradiance climates, size it at 100W.

Practical Sizing Table

Application	Typical load	Battery (LiFePO4)	Solar panel
100mm solar flasher, 24h	4-6W	20-30Ah	15-20W
200mm solar flasher, 24h	8-12W	40-60Ah	30-40W
300mm solar signal, 24h	15-25W	80-120Ah	60-100W
Solar traffic light with controller, 8-12h/day	20-40W	100-160Ah	100-160W

These figures assume 3-4 autonomy days and average sun hours. Always ask the supplier for the exact load table and the autonomy days used in their quote — this is the fastest way to spot undersized systems.

Environmental Factors That Change the Sizing

Temperature

LiFePO4 batteries keep capacity down to about -20°C and are the best choice for cold regions. Lead-acid batteries lose 30-50% of capacity below 0°C. In hot climates, ventilation and the battery's thermal management matter more.

Dust and Pollution

Dust can cut panel output by 20-40% in construction and desert areas. Panel tilt, self-cleaning coating, and scheduled cleaning (see our signal maintenance checklist) should be part of the plan.

Site Conditions

Shading from trees, signs, or buildings is the most common cause of "solar" systems that fail in winter. A proper solar site survey measures daily irradiance and shade before you commit to a configuration.

Choosing a Solar Traffic Light That Is Sized Correctly

GAOQIAO offers solar warning lights, solar wireless lights and mobile solar traffic lights with matched panel and battery combinations for each application. Instead of guessing, tell us the duty cycle (24h, 12h, or flashing), your region, and the required autonomy days — our engineers will size the system for you.

Why Choose GAOQIAO

Nanjing Gaoqiao Traffic Technology Co., Ltd. has designed solar traffic devices since 2006. Every solar unit is tested for charging performance and autonomy before shipment, and we provide the load table and sizing assumptions in writing with every quotation.

Conclusion

Correct solar sizing is simple math: know the load, choose the autonomy days, then size battery and panel with margin. A properly sized system runs for years with no grid connection; an undersized one fails on the second cloudy day. Use the formulas above to check every quote, and ask suppliers for their load tables in writing.

Contact Us:

• 🌐 Website: www.led-trafficlight.com
• 📧 Email: info@led-trafficlight.com
• 📱 WhatsApp: +86-18805173545
• ☎️ Tel: +86-25-84471080

With 17 years of experience in traffic signal manufacturing, we are committed to providing high-quality products that meet international standards for customers worldwide.