Question

Why the law of conservation of energy can mean that you do not have unlimited sources of energy?

Answer 1

the law of conservation of energy means that energy can neither be created nor be destroyed it can only be converted from one form to another so we can't produce energy and by sources we mean that from it we can extract energy there are many forms of energy from which we cannot extract energy from the technologies we have today.
if the energy gets converted into those forms than it won't be beneficial for us
so energy can't be lost but the sources of energy could
thus the law of conservation of energy can limit the availability of sources