Curtain walls according to embodiments of the present disclosure integrate a variety of energy producing and/or energy saving features and may be used to clad buildings to achieve net zero energy or low energy ratings. A curtain wall may comprise: a support frame; a grid assembly attached to the support frame; and, panels and cassettes each comprising a prefabricated unit attached to a frame; wherein the assembly is configured for ease of attachment of the frames carrying the prefabricated units. A wide range of different panels and cassettes with different functions can be integrated into the curtain wall, such as glazing, electrochromic, solar, photovoltaic (PV) and aluminum.