Temperature of photovoltaic combiner box in winter

PV combiner boxes are designed to operate safely in ambient temperatures as low as −20°C, but winter conditions can still stress components and affect performance. Winter Operating TemperaturePV combiner boxes, both DC and AC types, are typically rated to withstand ambient temperatures from −20°C up to +50°C according to IEC 61439-2 standards. This means that in winter, even in very cold climates, the box itself can function without immediate risk of thermal failure.

However, the internal temperature of components such as busbars, terminals, fuses, and disconnect switches will be slightly higher than ambient due to I²R losses, though these losses are generally lower in winter because solar current is often reduced by shorter daylight hours and lower irradiance.

Thermal Effects in Cold Weather

Cold temperatures can introduce specific challenges: Material brittleness: Plastic housings and gaskets may become brittle, increasing the risk of cracking or seal failure. Thermal contraction: Repeated expansion and contraction of internal components can loosen electrical connections over time, potentially increasing resistance and localized heating. Moisture condensation: Cold weather can lead to condensation inside the box, which may cause corrosion or short circuits if seals are compromised.

Safe Component Temperatures

Even in winter, the maximum allowable temperature rise for terminals and busbars is defined by standards: IEC 60947-1: Terminal temperature rise up to 70°C above ambient.

IE

C 61439-1: Copper busbars can tolerate up to 140°C, with a typical rise limit of 70°C above ambient.

U

L 489: Standard-rated terminations allow a 50°C rise above 40°C ambient, giving a maximum of 90°C. In winter, the ambient is much lower, so the absolute temperature of components is reduced, which generally improves safety margins and reduces the risk of overheating.

Practical Considerations

Ensure proper sealing and insulation to prevent moisture ingress and maintain thermal stability. Inspect for loose connections caused by thermal contraction. Consider low-temperature-rated materials for enclosures and internal components in extremely cold climates.

Monitor string currents and box loading, as higher currents can still generate heat even in cold ambient conditions. In summary, PV combiner boxes are engineered to operate safely in winter temperatures down to −20°C, but attention to material properties, moisture management, and connection integrity is essential to maintain long-term reliability and prevent cold-weather-related failures.