Cold Weather Operation

Cold Weather Operation

Solar power systems in cold climates face challenges that warm-climate systems do not. This page consolidates solar-specific cold weather guidance. See also the DIY Build Guide > Cold Weather & Winter Operation page for enclosure and battery chemistry details.

Solar Panel Performance in Cold

Cold temperatures actually improve solar panel efficiency slightly. A standard silicon solar panel produces about 0.4% more power per degree Celsius below 25°C. At - 20°C (45° below the standard test condition), a 6W panel produces approximately 6.1W - a small but measurable benefit.

The main cold-weather solar challenge is reduced daylight hours and lower sun angle, not panel efficiency. A December day in North Dakota has only about 8.5 hours of daylight with the sun reaching a maximum elevation of ~21° above the horizon, far less than the 70+° of midsummer.

Snow Accumulation on Panels

Snow covering the panel can reduce output to zero. Mitigation strategies:

• Steep mounting angle: 55 - 65° from horizontal allows most wet snow to slide off. Dry powder snow may still accumulate.
• Dark-coloured back-sheet: Panels with a black or dark back sheet absorb more heat and melt snow faster.
• Panel heating: Some high-end installations use resistive heating elements on the panel back, powered by the battery during overnight cold snaps. Rarely justified for community mesh nodes due to the added power consumption.
• Size for zero-solar periods: The most practical approach - size the battery for 5 - 7 days of operation with no solar input.

Battery Temperature Management

Batteries lose capacity in cold. Key thresholds for Li-ion 18650 cells:

A charge controller that monitors battery temperature and reduces or stops charging below 0°C is ideal. The CN3791 does not have temperature sensing - for extreme cold deployments, consider using a temperature-sensing charge controller or a LiFePO4 cell with a BMS that includes low-temperature charge protection.

Enclosure Thermal Behaviour

An enclosed node generates a small amount of heat (~75 - 150 mW from the node and charge controller). In a sealed IP67 enclosure, this self-heating can keep the interior several degrees above ambient, which helps battery performance marginally. A black enclosure absorbs more solar heat during daylight, which can add a few more degrees of warmth. A white enclosure stays cooler in summer (preventing overheating) but provides less passive warming in winter.

For very cold deployments, a small Nichrome heating resistor (1 - 2W) inside the enclosure, powered from the battery via a thermostat relay when temperature drops below - 10°C, can prevent the battery from reaching critically low temperatures. This adds complexity and power consumption but can be worthwhile for nodes at critical infrastructure sites.

Annual Maintenance Schedule

Cold-climate solar nodes require more frequent inspection than warm-climate nodes:

• Pre-winter (October): Inspect gaskets, cable glands, replace desiccant; verify battery capacity is adequate; clean solar panel; verify mounting is secure
• Mid-winter (January): Remote check - verify node is online and battery voltage is above 3.5V; investigate any offline nodes promptly
• Post-winter (April): Inspect for frost/condensation damage inside enclosure; replace desiccant; clean solar panel; verify all connections