Solar panel efficiency matters less than system design and shading analysis

The difference between a 20% and 22% efficient panel is about 10 watts per panel — maybe $200 over 25 years. But a single chimney shadow crossing one panel can reduce entire string output by 30-50% if microinverters or optimizers are not used. Per NABCEP guidelines, a proper shading analysis (Solmetric SunEye or similar) is worth more than premium panels. System design beats panel specs every time.