Photovoltaic panel tilt angle calculation method

The optimum tilt angle is calculated by adding 15 degrees to your latitude during winter, and subtracting 15 degrees from your latitude during summer. [pdf]

Photovoltaic panel tilt design specifications

In the Northern Hemisphere, panels should tilt at (latitude × 0.9) – 23.5° in summer. This angle captures more sunlight. In winter, tilt them at (latitude × 0.9) + 29° to catch the sun’s lower rays. [pdf]