1. Where You Live Matters
The shape of the Earth causes solar fasts to vary among 120 countries; the sun is nearly directly overhead at 90 degrees over the equator, but at the poles will rise (or be above) at a small angle, hardly above the horizon; thus to maximize your solar panel system, determine the lattitude of your installation site. When installing your solar system, the angle to achieve maximum solar input depends very much on the latitude at which it is being installed; in tropical lattitudes, as with Brazil, you would want to have a about 30 degree pitch on your panels, while in Canadian/Scandinavian locations you would place a 15-degree pitch to catch the relatively weak winter sun.
2. Seasons Change, So Should Your Setup
Summer brings longer days and higher sun angles - perfect time to angle panels upwards. But when winter arrives with its short, low-sun days, lowering the tilt by 10-15° helps panels "see" the sun longer. I've seen northern homeowners get creative - some even install adjustable racks that let them tweak angles monthly. One friend in Minnesota swears by his seasonal adjustments, claiming it boosts winter output by 25%.