A system for mounting at least one solar panel on a building may include at least one panel mounting bracket including a base to be positioned on the building, and a vertical extension having a proximal end coupled to the base and a distal end vertically spaced apart from the base. The vertical extension may have a cavity extending vertically therein. The system may also include an adjustable height extension device for the at least one panel mounting bracket including a lower portion carried within the cavity of the vertical extension and vertically slidable within the cavity, an upper portion carried by the lower portion to be connected with the at least one solar panel, and a vertical height adjustment member carried by the upper portion to cause the lower portion to slide vertically within the cavity to adjust a vertical height of the upper portion.