A steam generator having two vaporization chambers filled with molten metal salts for sequential flash evaporation of preheated atomized water through multiple vaporization tubes in said respective chambers. The molten metal salts are heated by secondary solar thermal input from lens assemblies and primary heat input from U-shaped hot air heating tubes within said vaporization chambers supplied by gas fired tube burners. Steam vapor generated by initial vaporization chamber is re-circulated to the secondary chamber outputting super heated steam. The molten metal vaporization chambers are encased in a single pressure vessel with re-circulation of condensate and multiple heat exchangers within.