Concentrated solar power plants - The challenges of corrosion

As the global demand for clean, sustainable energy continues to rise, renewable energy technologies are playing a central role in reshaping the world’s energy landscape. Among them, Concentrated Solar Power (CSP) stands out as a promising solution for electricity generation.

CSP systems typically use mirrors or lenses to focus sunlight onto a receiver, where a heat transfer fluid (HTF) absorbs the concentrated energy. This thermal energy is either used immediately to generate steam and drive a turbine, or stored in thermal storage tanks for later use, allowing CSP plants to deliver dispatchable power even in the absence of sunlight. This energy storage capability gives CSP a unique advantage over other intermittent renewables, such as wind or photovoltaic solar systems.

In recent years, molten salts have become the most widely used HTFs in CSP plants due to their high thermal stability, favourable heat capacity, and cost-effectiveness. They also enable efficient thermal energy storage (TES), extending plant operation beyond daylight hours. However, the high-temperature environments in which these salts operate—often between 290 °C and 550 °C or above, depending on their nature—pose significant challenges to the durability and performance of structural materials in CSP systems.

One of the most critical issues in this context is corrosion. The interaction between molten salts and the metallic components of the plant—such as piping, heat exchangers, and storage tanks—can lead to various degradation mechanisms, including uniform corrosion, localized attack, stress corrosion cracking (SCC), and stress relaxation cracking (SRC). These degradation processes are exacerbated by the presence of impurities in the salts, cyclic thermal stresses, and the breakdown of protective oxide layers on metal surfaces.

In particular, alkali nitrate molten salts, such as the binary mixture of sodium and potassium nitrate (commonly referred to as “solar salt”), act as electrolytes similar to aqueous solutions, enabling electrochemical reactions at the metal–salt interface. The presence of contaminants like chlorides, sulphates, or dissolved oxygen further intensifies the corrosive behaviour. Over time, these effects compromise the mechanical integrity of critical components, increasing the risk of leaks, unplanned downtime, and costly maintenance or replacement.

Effective corrosion management is therefore essential to ensure the long-term performance, reliability, and economic viability of CSP technologies. Key strategies include the careful selection of corrosion-resistant materials, such as high-alloy stainless steels or nickel-based alloys, the use of protective coatings, and the continuous monitoring and control...