Renewable forms of Energy are generally seen as much more environmentally friendly than NonRenewables because they don't tend to produce waste that has to be disposed off someway.
Most Renewable Energy can be traced back to the sun. Those forms which use the radiation from the sun directly are called SolarPower. Other forms, such as BioFuels or WindPower, also rely on the sun, although less directly. Finally some forms, like TidalPower, GeoThermalEnergy, OsmoticPower or CapillarityPower don't depend on the sun at all.
Renewable energy can be logically split into two forms: ObligateRenewables and PotentialRenewables. The former, like WindPower, are necessarily Sustainable, while the latter, such as BioFuels can be Sustainable but can also be used in NonSustainable fashion.