a double hopper system is disclosed . the double hopper system includes , a first hopper and a second hopper . the first hopper has a first and a second opening , and the second hopper is arranged above the second opening of the first hopper and extends into the second opening of the first hopper . the first opening of the first hopper has a predetermined length and a distribution area , and the second hopper is movably arranged with respect to the first hopper , such that the second hopper is movable over at least ¾ of the length of the first opening of the first hopper .