What makes renewable energy renewable?

Answer 1

NOTHING!

There is no such thing by the most basic Law of Physics, that energy can be neither created nor destroyed; only released, transferred or converted. Its ultimate fate is conversion to heat.

"Renewable" energy is a handy term for politicians, journalists and school-teachers, most of both of whom have a generally poor grasp of science and engineering so are easily taken in by commercial advertising. After all they, like the advertising copy-writer responsible, can't even see that small radio-telephones are "portable", not "mobile"!

A better term perhaps would be "Inexhaustible Energy". Although that too is scientifically weak, it is true enough in human terms because meteorological and oceanographic processes have been around since the oceans formed, will last far longer than humanity; and the energy we extract from such Natural Resources at a given time are a tiny fraction of that being converted in the process as a whole.

The manner of harnessing that energy is another matter: wind-power is being shown to be nothing more than a small contribution. Hydro-electric power from rivers is clean and efficient but obviously needs sufficiently large, reliable rivers and the effect of building large reservoirs must not be ignored.

Tidal-barrage power is reliable but obviously cyclical, and also at some environmental cost. Tidal-stream power has the same qualities. Wave power obviously demands waves - like wind power, they don't arrive to timetables and always of the right power!

What everyone ignores about fossil fuels is that they are also chemical feed-stocks; and it is hard to see what will replace them when eventually they run out.

Answer 2

it is air Water and sun