A solar module in-roof mounting system, comprising at least two solar modules (4a, 4b) arranged adjacent to one another and at least one retaining rail, the retaining rail being arranged between the two solar modules that are arranged adjacent to one another and including, in the cross-section, a first insertion region, which accommodates a lateral edge of a first solar module, and including a second insertion region, which is arranged adjacent to the first insertion region and accommodates a lateral edge of a second solar module, the solar module in-roof mounting system comprising a further retaining rail and at least one further solar module (4a, 4b), the further retaining rail being arranged abut the first retaining rail in a flush manner, and the further solar module (4a, 4b) being inserted into a first or second insertion region (2a, 2b) of the further retaining rail, the retaining rails, at the respective ends thereof at the right and left lower corners, including notched regions, the retaining rails being shorter than the lateral edges (5a, 5b) of the solar modules (4a, 4b) that run parallel to the retaining rails, characterized in that the solar module in-roof mounting system comprises trapezoidal drain plates (18a, 18b) for the vertical drainage of rain water, the trapezoidal drain plates (18a, 18b) being inserted in a shingled manner between solar modules arranged next to one another, the drain plates (18a, 18b) being inserted into adjacent notched regions of the retaining rails, beneath the butt joints of the retaining rails that are arranged in a line with respect to one another, such that the drain plates (18a, 18b) cover the butt joints. the retaining rail being arranged between the two solar modules that are arranged adjacent to one another and including, in the cross-section, a first insertion region, which accommodates a lateral edge of a first solar module, and including a second insertion region, which is arranged adjacent to the first insertion region and accommodates a lateral edge of a second solar module, the solar module in-roof mounting system comprising a further retaining rail and at least one further solar module (4a, 4b), the further retaining rail being arranged abut the first retaining rail in a flush manner, and the further solar module (4a, 4b) being inserted into a first or second insertion region (2a, 2b) of the further retaining rail, the retaining rails, at the respective ends thereof at the right and left lower corners, including notched regions, the retaining rails being shorter than the lateral edges (5a, 5b) of the solar modules (4a, 4b) that run parallel to the retaining rails, characterized in that the solar module in-roof mounting system comprises trapezoidal drain plates (18a, 18b) for the vertical drainage of rain water, the trapezoidal drain plates (18a, 18b) being inserted in a shingled manner between solar modules arranged next to one another, the drain plates (18a, 18b) being inserted into adjacent notched regions of the retaining rails, beneath the butt joints of the retaining rails that are arranged in a line with respect to one another, such that the drain plates (18a, 18b) cover the butt joints.