Within the scope of EU-Project “RAISELIFE: Raising the Lifetime of Functional Materials for Concentrated Solar Power Technology” researchers from DECHEMA-Forschungsinstitut (DFI) developed a novel Ni-rich coating via electroless deposition. The patented coating showed significantly improved corrosion resistance of cost-efficient candidate alloys during isothermal and dynamic exposure tests and prevents the formation of toxic hexavalent chromate species and their dissolution into the solar salt.
On June 19, 2020, this coating concept of DFI researchers received the award „Great EU-funded Innovation” (see www.innoradar.eu/innovation/37195) from EU Innovation Radar. The innovation was listed as tech-ready indicating its applicability to industrial scale. With the ultimate goal of “climate-neutral Europe by 2050“, concentrated solar power (CSP) technology is qualified as a very promising energy generation method due to the establishment of thermal energy storage.
One focus of the RAISELIFE project was to increase the lifetime of structural components utilized in CSP plants. The development of coating systems improving the optical properties i.e. absorptivity or reflectivity depending on the application unit as well as corrosion and erosion resistance enables an extended lifetime of components.
Nitrate salt mixtures are currently used as state-of-the-art heat transfer and storage medium in CSP plants owing to their beneficial thermophysical properties such as a high heat capacity and low viscosity. While enabling a continuous power generation and thus high dispatchability, their employment restricts the material choice to higher alloyed systems due to accelerated corrosion attack at temperatures around 580°C, thereby decreasing the cost-efficiency of the CSP technology.
The pioneer commercial CSP plant utilizing nitrate salts as heat transfer medium (Gemasolar, 19.9 MW) was commissioned in Andalusia, Spain in 2011. In the following years, the up-scaling of the nominal capacity was achieved such as for the 150 MW NOOR III CSP plant in Ouarzazate, Morocco.
The optimization of the plant design plays a key role in increasing the competitiveness of CSP technology in the renewable energy market. For that matter, the choice of structural materials creates a challenging task, since corrosion resistance and mechanical strength of candidate alloys have to be considered together with cost factors. Particularly for cost-efficient materials such as 9% Cr steels, the corrosion rate is higher in molten nitrates compared to expensive Ni-based alloys. Nonetheless, since chromium is present in almost all technical alloys, its dissolution into the salt melt in the form of toxic chromates creates a major problem for the CSP technology.
As the Member of the Executive Board and the Head of the Research Group “High Temperature Materials” Associate Prof. Dr.-Ing. Mathias Galetz commented on the reception of the award: “We are delighted to be acknowledged from the European Commission for our innovation. With this award the European Union honored the application-oriented basis of our research institute and the associated know-how transfer with the energy industry”.
Photo credits: © DECHEMA-Forschungsinstitut (DFI): Ni-P coated P91 steel after 750 h exposure in solar salt at 565°C