What’s the relation between Solar Rooftop design and December 21
The relation between solar energy generation and seasons are pretty much interlinked. Solar Rooftop is always designed in such a way that we have the maximum generation on the shortest day of the year. And the shortest day of the year is December 21st. Which eventually helps us in getting long generation hours on other days as well.
Sun’s orientation changes every single day of the year. If we stand at a position every day at the same time, the shadow will keep changing.
Img Source: Wikipedia.org
Above image is taken at the same time every day for a year to show the Sun’s Orientation.
Universal truth says Sun raises in the East and sets in the west. This is true with an add-on in it. On June 22nd, the longest day of the year sun raises at East and sets at west travelling exactly through half hemisphere of the earth. If we stand out in Sun at 12:00 PM our shadow is little below us. But if we consider on December 21st shadow is little away from us at the same time.
This happens because Sun travels from the east to west more towards the south. This is causing days to be shorter when date moves towards December 21st from June 20th. And in the same way, day increases with the date moving towards June 21 from Dec 21st.