Clean Energy. ‘Clean energy’ may have a specific definition in your mind — you may think it’s synonymous with ‘renewable energy’ (i.e. wind energy, solar energy, hydro energy, and geothermal energy). This is, generally, how I use the term.onetheless, despite its malleable nature, ‘clean energy’ is becoming an increasingly popular term. Indeed, I think I use it more than ‘renewable energy’ now (and, as I said, to discuss the same energy sources or technologies). So, I will briefly explain why I use it like this, and why I use it so much.