Investigation of mechanical and environmental durability on self-cleaning coatings based on superhydrophobicity for solar thermal applications

A glass cover which is placed at a certain distance from the Solar Selective Absorber (SSA) can protect the SSA and play a role in heat preservation. However, reflection and absorption of the glass cover can affect the performance of the solar thermal system. In practical application, the outdoor working environmental condition is rather dirty, and the accumulations of surrounding dust on the glass cover reduce the transmittance of normally incident light, which can largely decrease the performance of the solar thermal system. Thus, getting rid of the glass cover can improve the performance of the flat plate solar collector and also a self-cleaning, superhydrophobic coating on SSA i.e., aluminium alloy substrate (Al alloy-2014) can maintain the efficiency in a practical outdoor working environment without affecting the performance of the solar thermal system. Prior to Superhydrophobic coating, aluminium substrate can be modified by proper texturing by which surfaces appear rough and absorb solar energy while appearing highly reflective and mirror-like to thermal energy. The emittance can be adjusted by modifying the microstructure (microcrystallites) of the coatings. The superhydrophobic coating on the modified aluminum substrate results in a water contact angle of above 150° and the sliding angle is less than 5° .Thus the the flat plate solar collectors using this SSA without glass cover can solve the problems of incident light loss and dust accumulations and also have good weather resistance. (author)