Why cannot a waterfall be considered to be never ending source of energy? A waterfall is converting it's potential into kinetic energy and if we "take out" some of it's kinetic energy while the water is falling down and use it to move a turbine of a generator, we get electricity. Why are we worried about saving energy then?
Let's see, A river has its origins in hilly areas and mountains. The mountains get back water from the clouds. The clouds get water from the sun. So the work in bringing water back to hill is done by solar energy. If the sun is doing our work for us, and sun has a lot of energy and it wouldn't possibly end in a billion years, why do we not see waterfalls as an almost 'infinite' energy source?
I know this is a very basic question.
This question may be similar to the previously asked questions but I couldn't find a satisfactory answer, so I'm asking this.