Failure Analysis of Accelerated Galvanic Corrosion in Hot-Dip Galvanized Roofing Supporting Aluminium-Framed Photovoltaic Systems

Aluminium-framed photovoltaic (PV) modules mounted on hot-dip Galvanized-Steel building envelopes are associated in this field cohort with severe, spatially localized corrosion of the galvanized cladding beneath panel runoff paths. This paper presents a field failure analysis drawn from 47 documented solar-on-galvanized installations across Southern Africa, supported by a comparative 56-installation dataset of Zincalume/Galvalume roofing and a forensic substrate investigation of a 19-structure commercial envelope. In the galvanized cohort, 44 of 47 installations had documented steel-substrate exposure (red rust), with documented onset no later than 36 months in those cases; because follow-up duration varied and some endpoints were censored, this value is reported as a descriptive cohort proportion rather than a 36 months cumulative-incidence estimate. Among installations in which perforation was documented, the descriptive median time to perforation was 36 months. By contrast, the Zincalume/Galvalume comparator dataset showed no corrosion attributed to the proposed Al–Zn galvanic mechanism over the observation period. A retrofit two-coat BA/MMA acrylate polymer barrier system, applied prior to solar installation, was field-observed across multiple sites exceeding six years of service with no galvanic attack detected at inspection. The observed spatial concentration of attack is consistent with galvanic coupling, concentrated wetting at panel drip zones, and an unfavorable effective cathode-to-anode geometry. Chemical modification of runoff by aluminium species is proposed as an additional contributory mechanism, but runoff chemistry was not directly characterized in this study. Mixed-potential theory and Faraday-based calculations are therefore used as mechanistic and order-of-magnitude consistency models rather than as precise predictors of field service life. The findings identify a practically important compatibility risk that can be mitigated by appropriate material selection, electrical/physical isolation strategies, runoff management, or suitably validated barrier coatings.