Concept:
Renewable energy sources are naturally replenished and can be used repeatedly without being exhausted quickly.
Step 1: Coal, crude oil, and natural gas are fossil fuels.
Step 2: Fossil fuels are non-renewable because they take millions of years to form.
Step 3: Wind energy is obtained from moving air and is naturally replenished.
Step 4: Therefore, wind energy is a renewable energy source.
Hence:
\[
\boxed{\text{Wind energy}}
\]