Mo’ current, mo’ problems as higher wattage solar modules increase risk of thermal runaway

Due to increases in efficiency and size, higher wattage solar panels are generating higher electrical currents – and thus an increased probability of heat events. LONGi Solar has taken note of this as they develop solar modules, and they have released a brief analysis of their modules and junction boxes..

Junction boxes are placed on the back of solar panels, and are the interface that connects the panels to the outside world. LONGi was the world’s largest seller of solar panels in 2021, so naturally they sold more junction boxes than any other manufacturer. (They also predict that global solar installations will reach 1 TW each year by 2030.)

The company notes that the ‘hot spot durability and diode thermal performance testing’ logic is designed in accordance with the IEC 61215 & 62790 standards.

LONGi compares their bifacial Hi-MO5 solar modules series, which has a lower front side short circuit current value of 13.9A, to a unit with a current of 18.5A. The company said lower currents produce long term product stability by lowering module temperatures, and associated temperature swings. LONGi asserts that higher currents increase the chance of a fire.

Glass-glass bifacial solar panels do have an opportunity to reach 50 year useful lifetimes.

LONGi’s analysis states that a competing 18.5A module can simply upgrade its junction box to 30A protection and meet a safety margin of 1.25 (accounting for bifacial gains). However, reducing current can limit the number of modules that can be wired on a string, due to lower voltage allowances.

Additionally, the temperature range of this higher current module would place it outside of LONGi’s suggested potential thermal runaway zone. Higher temperatures carry higher risks.

LONGi explains that hot spots and thermal runaway can occur when modules are shaded while operating outdoors (as opposed to highly controlled lab conditions). This shading can be caused by fallen leaves, an accumulation of dust, or anything that blocks enough light to stop and reverse current, leading to thermal runaway. These hot spots can occur under fairly normal conditions, meaning these conditions must be accounted for as a design standard.

Since higher current panels tend to produce higher temperature hot spots and increased heat build up, LONGi concludes that heat dissipation gear must be improved, particularly in equipment that doesn’t meet certain standards.

When these local current leaks occur regularly over decades of expected electricity generation, they silently, and permanently, reduce system output. While manufacturers could potentially mitigate the challenges of high currents with fuses and thicker copper wiring, LONGi believes that starting with lower currents is the better solution, for now.

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