A system for mounting a solar panel(s) may include a panel mounting bracket(s) having a base to be positioned on a building and a vertical extension including spaced apart vertical sidewalls extending vertically upward from the base and defining a cavity therebetween with a cross-support member extending laterally between the vertical sidewalls across the cavity. An adjustable height extension device is also provided which may include 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 solar panel(s), and a vertical height adjustment member including a head carried by the upper portion and a shaft threadably received by the cross support member to cause the lower portion to slide vertically within the cavity to adjust a vertical height of the upper portion as the vertical height adjustment member is rotated.