Answer to Question 1
The tilt of the earth's axis causes the difference. When the sun is at its maximum elevation in the northern hemisphere, it is at its lowest elevation in the southern hemisphere and vice-versa.
Answer to Question 2
Answers depend on student location. The optimum angle for a non-adjustable flat plate is generally at the latitude angle from the horizontal but can be set steeper to optimize solar input for winter or flatter to optimize solar input for summer.
