Renewable and Non-renewable Sources of Energy The document discusses renewable and non-renewable sources of energy. Renewable sources, such as tidal power generated from ocean tides, will never run out as their energy comes from ongoing natural processes. Non-renewable sources, including coal, natural gas, and asphalt, will eventually be depleted as they cannot be naturally replenished within human timescales once extracted and used. The key difference is that renewable sources rely on perpetual natural cycles while non-renewable sources are finite.