a first tubular body connected to the solar panel array;

a second tubular body coupled below the first tubular body and fixed to the top of the pole;

a gear unit to transmit a rotation force to the first tubular body; and

a driving motor fixed to an inside of the second tubular body to provide the rotation force to the gear unit,

wherein the gear unit includes a planetary (PL) gear set including a sun gear connected to a rotational shaft of the driving motor, a plurality of PL gears arranged at a preset interval around the sun gear to be engaged with the sun gear and a ring gear disposed outside of the plurality of PL gears and fixed to the first tubular body to be engaged with the PL gears, and

wherein all of the sun gear, the PL gears and the ring gear have inclined teeth in a circumferential surface and have a tapered structure,

wherein the sun gear has a cross section with a narrow upper part and a wide lower part, the PL gears have a cross section with a wide upper part and a narrow lower part, an inner diameter of an upper part of the ring gear is wider than an inner diameter of a lower part of the ring gear to correspond to an inclined surface of the PL gears,

wherein the rotation device comprises an upper frame installed on the plurality of PL gears to hold the plurality of PL gears, and

wherein the plurality of PL gears moves toward the upper frame during the gear rotation to ensure backlash between the sun gear and the ring gear, and when the gear rotation ends, moves toward the sun gear and the ring gear by a self-weight to prevent backlash.