A renewable source of energy is an energy source that cannot be depleted. It is an energy source with constant abundance and hence it is always in abundance. What we are saying is that they are energy sources that cannot be used up. Although it might sometimes be that it is unavailable at some instances, this does not take away the fact that it is abundant and cannot be depleted, although the strength at different times may vary. Example of renewable energy sources include solar energy, wind energy, hydroelectric power source etc. These sources are never depleted and are in abundance.
Non renewable source of energy are those sources of energy that can be depleted. A good example of this can be seen in fossil fuels. Fossil fuels are usually burned to produce energy. They are used up in the process and it will require an additional amount of fossil fuel to be restocked for the energy to be continually supplied.
Photosynthesis. Because the plants give off oxygen as a waste product. Carbon dioxide then moves from the air into the leaves of plants through tiny openings in the plants leaves.
