Wind, solar and geothermal power are called renewable energy sources because

They  are inexhaustible.

Explanation:

Energy sources that are never ending are called renewable sources of energy.  Solar power comes from Sun . Sun light never gets exhausted and is always present . So it is called renewable source. Similarly wind and geothermal energy also do not get exhausted even after using them repeatedly, on a large scale. Using these energy resources does not cause environmental pollution.

But when it comes to energy resources like fossil fuels, they are  non renewable since the resources drain out if used on a large scale, over a period of time.