By Dave Valenti, RBI Solar Inc., Cincinnati, OH
When designing a PV racking structure, it is important to determine how much soil corrosivity needs to be accounted for in order to ensure the life expectancy of the mounting structure. Several factors need to be measured on a site by site basis. Soil pH, moisture content, chlorides, and resistivity all determine the service life of hot-dipped galvanized steel piles embedded in the ground. If every variable is not taken into consideration during the design of solar mounting systems, then failure before the target service length is reached is a very real possibility.
The lower the pH values of soil the higher the rate of corrosion and vice versa. The larger the presence of chloride ions the higher the level of corrosion that will be seen on galvanized piles due to the relationship between resistivity and chloride ions. Chloride ion activity is also largely affected by the moisture content of the soil. In addition, the lower the resistivity the higher the soil corrosivity with the soil’s resistivity being defined as the soil’s ability to resist electric current passing through it. The service life of galvanized steel posts embedded in the soil will be determined through the analysis of all the parameters mentioned above and can only be determined by a licensed corrosion engineering specialist.
It is very important to use protection measures to shield ground mount solar posts from soil corrosion. Once the service life is determined to be insufficient for a target design life, then additional measures need to be also considered such as a layer of corrosion retarding epoxy, embedding in concrete, or even the use of zinc galvanic anodes. It is highly recommended that corrosion potential be considered when designing a PV racking system, and the soil analysis from each site will dictate the type and level of this protection. It cannot be overstated that this required protection can only properly be determined by a licensed corrosion specialist.