The Impact of Cracked Solar Cells on Solar Panel Energy Delivery

Solar panel degradation is usually assessed by the change in power at standard testing conditions (STC). However, some degradation mechanisms have shunting or recombination characteristics which have the potential to reduce performance at low irradiances significantly more than at 1-Sun conditions. We present data at both the single cell coupon level and at the module level that demonstrate this effect with cracked cells, where the effect scales with the total length of the cracks. The effect is present even for modules with tightly closed cells where the metallization is continuous across the cracks and no dark areas are seen in the electroluminescence (EL) images. Depending on the system geographic location, mounting angles, the time of year, and the clipping characteristics, the daily energy delivery of a system can depend quite strongly on the module performance at low irradiances. We show through simulations that energy delivery may degrade significantly more than $\mathrm{P}_{\max}$ with damage from cracked cells. Since electricity generated at lower irradiances often has more value than electricity generated at high irradiances, the impact on system revenue may be even larger. We conclude that the degradation from accelerated testing and field exposure should be assessed not just at an irradiance of 1-Sun but also at lower values as well.