Human waste can be used to make renewable fuels and fertilisers.  The fuels produced, petroleum products, and fertilisers are not clean sources of energy and release greenhouse gases into the atmosphere.  However  they are renewable as there is always human waste.  

Plastics can also be heated at high temperatures to produce petrochemicals.  However as with waste the resulting fuels and the process of producing these fuels releases greenhouse gases into the atmosphere.  The upside is the fuels produced are mobile.  So the bottom line is we do have renewable sources of energy however there is a cost to the environment.