Solar panels collect their energy directly from the sun, from sunlight. Orienting the PV panel to the best tilt angle to maximize its exposure to direct sunlight will optimize the efficiency of the panel. The panel will collect solar energy most efficiently when the sun's rays are perpendicular to the panel's surface. As we all know the angle of the sun and the hours of sunlight varies throughout the year. So, the optimal tilt angle for a Solar panel in the winter will is different from the optimal tilt angle for the summer. This angle will also vary by Location.
The farther North the greater the angle in the winter to optimize the energy produced by the panel. Using a tilting panel mount will allow you to get the most production from your solar panels.