GALVANIZING – LIFE TIME
ELVAN S.A. manufactures its fixed photovoltaic support structures (piles and upper structure) using hot-dip galvanized steel post-production, according to EN ISO 1461. In contrast to pregalvanized materials, hot-dip galvanized steel offers very long service life with virtually no maintainance.
During the hot-dip galvanization process, steel is immersed in a bath of molten zinc at a temperature of 450 oC. Hot-dip galvanization forms an alloy rather than simply coating the steel with zinc. As a result, hot-dip galvanized steel is extremely resistant to oxidation, even in the most adverse environments.
Various zinc coating processes have been used in steel anti-corrosion protection for over 150 years. As such, information on hot-dip galvanized steel durability in various environments has been accumulated.
For each environment, the service life of a galvanized structure is affected by:
- Initial galvanization thickness and
- Annual depletion of the galvanized layer due to ground and atmospheric conditions.
In order to evaluate annual depletion for the thickness of the galvanized layer, the surrounding environment on the photovoltaic project’s site must be examined. EN 50929 (Corrosion likelihood of metallic materials when subject to corrosion from the outside – Classification of environmental conditions) defines six environmental categories: C1, C2, C3, C4, C5-I and C5-M. Most photovoltaic parks in Greece are installed in C3 areas (rural – medium burden – 2,1 μm annual galvanization layer depletion).
Fixed photovoltaic structures made with pregalvanized metal are unsuitable because of two reasons:
- Galvanization thickness does not exceed 15 μm at best. In a C3 area this translates to a 7-year lifespan, far below the desirable 20-year service life for a photovoltaic park.
The following table displays service life estimates for various cases:
2. The cut edges of pregalvanized metal are not protected against oxidation. Oxidation occurs quickly in these spots, and progresses further into the metal below the galvanized surface, reducing service life even further. DIN 55928-8 paragraph 7 states that cut points of metal sheets over 1,5 mm thickness must be protected. The only way to achieve this is hot-dip galvanization post-production.