A method of installing a solar module to efficiently use sunlight, the method comprising: Determining, by a solar module including a solar cell panel and a reflection plate, a reflection plate tilt angle (θ 1) of the reflection plate so as to be tilted at a certain angle with a first virtual horizontal surface (HS 1) wherein the solar cell panel and the reflection plate are connected at one end, said end defining a segment, said segment being horizontal in a reference system; calculating a second projection distance (PD 2) corresponding to a distance between a second reference point (RP 2) and a second projection point (PP 2) at which a second virtual horizontal surface (HS 2) which is below the first virtual horizontal surface (HS 1) meets sunlight which is reflected by other end of the reflection plate and projected onto the second virtual horizontal surface (HS 2) by using a first projection height (PH 1) corresponding to a distance between the other end of the reflection plate and a first reference point (RP 1) which meets a vertical line vertically extending from the other end of the reflection plate to be perpendicular to a first virtual horizontal surface (HS 1), a second projection height (PH 2) corresponding to a distance between the other end of the reflection plate and the second reference point which meets the second virtual horizontal surface (HS 2) horizontally extending from other end of the solar cell panel, and a first projection distance (PD 1) corresponding to a distance between the first reference point (RP 1) and a first projection point (PP 1) at which the first virtual horizontal surface (HS 1) meets the sunlight which is reflected by the other end of the reflection plate and projected onto the first virtual horizontal surface (HS 1); and determining a panel tilt angle (θ 6) between the solar cell panel and the second virtual horizontal surface (HS 2) or determining a length of the solar cell panel to allow the other end of the solar cell panel to be located at the calculated second projection distance (PD 2) and installing the solar module corresponding to the determined panel tilt angle (θ 6) or panel length, wherein the first projection height (PH 1) is calculated using a trigonometric function based on a reflection plate length and the reflection plate tilt angle (θ 1) of the reflection plate, wherein the first projection distance (PD 1) is calculated using a trigonometric function based on the first projection height (PH 1) and a projection angle (θ 5) of the sunlight with respect to the first virtual horizontal surface (HS 1) or the second virtual horizontal surface (HS 2) at the winter solstice, wherein the projection angle (θ 5) is calculated using the following Equation. Projection angle (θ 5) = 180° + meridian altitude of sun at winter solstice (θ2) - 2 * meridian altitude of sun at summer solstice (θ 1) Determining, by a solar module including a solar cell panel and a reflection plate, a reflection plate tilt angle (θ 1) of the reflection plate so as to be tilted at a certain angle with a first virtual horizontal surface (HS 1) wherein the solar cell panel and the reflection plate are connected at one end, said end defining a segment, said segment being horizontal in a reference system; calculating a second projection distance (PD 2) corresponding to a distance between a second reference point (RP 2) and a second projection point (PP 2) at which a second virtual horizontal surface (HS 2) which is below the first virtual horizontal surface (HS 1) meets sunlight which is reflected by other end of the reflection plate and projected onto the second virtual horizontal surface (HS 2) by using a first projection height (PH 1) corresponding to a distance between the other end of the reflection plate and a first reference point (RP 1) which meets a vertical line vertically extending from the other end of the reflection plate to be perpendicular to a first virtual horizontal surface (HS 1), a second projection height (PH 2) corresponding to a distance between the other end of the reflection plate and the second reference point which meets the second virtual horizontal surface (HS 2) horizontally extending from other end of the solar cell panel, and a first projection distance (PD 1) corresponding to a distance between the first reference point (RP 1) and a first projection point (PP 1) at which the first virtual horizontal surface (HS 1) meets the sunlight which is reflected by the other end of the reflection plate and projected onto the first virtual horizontal surface (HS 1); and determining a panel tilt angle (θ 6) between the solar cell panel and the second virtual horizontal surface (HS 2) or determining a length of the solar cell panel to allow the other end of the solar cell panel to be located at the calculated second projection distance (PD 2) and installing the solar module corresponding to the determined panel tilt angle (θ 6) or panel length, wherein the first projection height (PH 1) is calculated using a trigonometric function based on a reflection plate length and the reflection plate tilt angle (θ 1) of the reflection plate, wherein the first projection distance (PD 1) is calculated using a trigonometric function based on the first projection height (PH 1) and a projection angle (θ 5) of the sunlight with respect to the first virtual horizontal surface (HS 1) or the second virtual horizontal surface (HS 2) at the winter solstice, wherein the projection angle (θ 5) is calculated using the following Equation. Projection angle (θ 5) = 180° + meridian altitude of sun at winter solstice (θ2) - 2 * meridian altitude of sun at summer solstice (θ 1)