Don’t Let Your Soil Eat Away Your Profits
July 6, 2017
Corrosion involves a complex, open system with many variables. Taking the time to do a thorough geotechnical assessment as part of a commercial or utility-scale ground mount solar project can ensure you understand the interaction of these variables and are able to calculate and design a reliable system for long-term performance.
What are those variables? When it comes to assessing the soil from your ground mount project site, geotechnical experts are looking at several key measures of corrosion potential:
Corrosion can’t happen without water. Water acts as a catalyst to drive the reactions that can deteriorate metals. That said, identifying how much moisture is present in your soil, as well as the potential for variable seasonal saturation, is the first priority.
Soluble Salt Content
The second essential element in the corrosion equation is soluble salt. Soluble salt dissolves with water and reacts with steel. During geotechnical testing, soluble salts such as chloride and sulfate are measured in your soil to determine the potential for salts impact the environmental conditions and system design.
Next, it’s important to look at how strongly your soil resists the flow of electric current. Ideally, the soil will have a high electrical resistivity – meaning that the soil resists the flow of current and therefore will slows the reactions that can cause corrosion.
Like any other material exposed to acid, if foundations are exposed to soil that is too acidic, the acid can degrade metal or concrete, speed up electrochemical reactions, and compromise the structural integrity foundations.
Most sites show low potential for premature corrosion. Showing positive corrosion results can lead to more efficient system design and a more bankable project. This is a great outcome that assures all parties in the project’s development that the project should perform well for the duration of its 20-year, 30-year or even longer lifespan.
But what if a geotechnical survey reveals corrosive potential?
By investing in pile testing as part of your diligence phase, you have the opportunity to mitigate corrosion, extend the life of your foundations and design an overall system that can stand up to the elements.
The first line of defense is extra galvanization. Zinc is more difficult to corrode than steel, so adding additional galvanization can slow corrosion.
Similarly, epoxy can serve as a barrier to corrosion. Painting posts with epoxy prevents the water and salts from interacting with the metal.
For utility-scale sites of 15 to 20 MW or more, there are also highly engineered solutions that may make good financial sense. One such approach uses sacrificial galvanic anodes. Sacrificial metal is driven into the soil solely to attract the corrosive elements, in essence distracting corrosion from the galvanized system foundations. Impressed current might also be used, where a DC current is used to drive a protective electrochemical reaction. A corrosion specialist can guide utility-scale developers through a cost-benefit analysis.
Regardless of project size, the key is to know your soil composition and design your system for long-term performance in your site-specific conditions. A geotechnical report by SunLink PowerCare will evaluate your soil corrosion potential from high to low, and can calculate how corrosion factors may impact the lifespan of your solar project.