What is the certified operating temperature range for the solar outdoor wall lights and its battery

Solar outdoor wall lights are lighting products that rely on environmental conditions for operation, and their performance is closely tied to temperature. The operating temperature range is a key technical indicator for measuring their reliability and suitability. It defines the minimum and maximum ambient temperatures that the light fixture and its core component—the battery—can withstand without affecting normal function and lifespan. This certification range directly impacts the product's suitability in diverse climates around the world.

Solar Panel Performance at Different Temperatures
The core of a solar wall light is the photovoltaic module, or solar panel. The principle of the photovoltaic effect dictates that the efficiency of solar cells is affected by temperature. As temperature rises, the open-circuit voltage of the solar cell decreases, resulting in a decrease in output power, a phenomenon known as "thermal droop." Even in the heat of summer, with ample sunlight, a solar panel's efficiency can be lower than in a mild spring. Professional design considers heat dissipation, ensuring stable operation of the solar panel in high temperatures through material selection and structural design.

Core Component: Battery Operating Temperature Range
The battery is the energy storage center of a solar wall light, and its performance is much more sensitive to temperature than that of the solar panel. Currently, the battery types commonly used in solar wall lights are lithium-ion batteries (Li-ion) and lithium iron phosphate batteries (LiFePO4). The certified operating temperature ranges for these two types of batteries differ significantly.

Lithium-ion Batteries (Li-ion)

Charging Temperature Range: When charging at temperatures below 0°C, lithium ions may form metallic lithium on the negative electrode surface, causing irreversible lithium deposition. This not only severely reduces battery capacity but can also cause internal short circuits, increasing safety risks.

Discharging Temperature Range: At low temperatures, the electrolyte viscosity within the battery increases, slowing ion migration. This increases the battery's internal resistance, reduces output voltage, and significantly reduces available capacity.

Lithium Iron Phosphate Batteries (LiFePO4)

Charging Temperature Range: Similar to lithium-ion batteries, charging at low temperatures can also affect their performance. However, compared to lithium-ion batteries, lithium iron phosphate batteries are more stable at high temperatures and less prone to thermal runaway.

Discharge Temperature Range: Lithium iron phosphate batteries experience relatively minimal performance degradation when discharged at low temperatures, resulting in a longer lifespan and improved safety, making them a more suitable choice for cold regions.

Impacts of Extreme Temperatures and Countermeasures

Exceeding the certified operating temperature range can have a variety of negative effects on solar wall lights.

Impacts of High Temperature:

Accelerated Battery Aging: High temperatures accelerate chemical reactions within the battery, causing rapid capacity degradation and shortening its service life.

Increased Safety Risks: Excessively high temperatures can trigger thermal runaway, even leading to combustion or explosion.

Exacerbated LED Luminous Degradation: High temperatures accelerate the aging of LED chips, causing a rapid decrease in luminous flux and compromising lighting performance.

Impacts of Low Temperature:

Sudden Drop in Battery Capacity: Low temperatures increase the battery's internal resistance, significantly reducing its available capacity and making it impossible to provide sufficient lighting at night.

Unable to Charge: Below the charging temperature, the electricity generated by the solar panel cannot be safely stored in the battery, resulting in the light failing to effectively store energy during the day.

Embrittling Plastics: Extreme temperatures can weaken the plastic components of the light housing, making them susceptible to cracking.