The main reason is that the USA is in the Northern Hemisphere & Australia is in the Southern Hemisphere. It has all to do with the tilt of the earth as it revolves around the Sun. Summer happens in the hemisphere tilted towards the Sun, and winter happens in the hemisphere tilted away from the Sun.
Because they both lie in different hemispheres.When there is winter there in Australia it is summer here because due to hemispheric climate in different places and also due to being far from sun
Solar power is not the best option in some countries because places like Rjukan (Norway) that do not recieve enough sunlight because of where they are located.
