Considering that the salts solidify around 240C, the tanks should be preheated previously to fill them to prevent freezing on the walls of the tank, heaters, pump rotor, etc. Preheating should be done up to 350C, same temperature than the salt in the molten system to minimize thermal shock of the tank during filling.
    After the first hour of the start of the preheating process, it was found that the temperature of the metal wall (under the insulation) in the southern part of the bottom of the two tanks had a slower evolution than other temperatures elsewhere.
    Different reasons were found for this behaviour:
    Not enough turbulence of the hot air due to a non-optimum design of the diffusors.
    Heat losses in that area of the tanks, potentially due to the effect of wind on the tanks