Renewable Energy comes in many forms including Biomass, Geothermal, Solar Energy, Wave Energy, Tidal Energy, Hydroelectricity, etc. Each of these subjects deserves a thesis. Here is a short description of each of the processes together with links to more detailed information: -
Sustainability may be defined as using a resource so that the resource is not depleted or permanently damaged.
Sustainability is also critical in the functioning of a business, a concept which is succulently dealt with by the Financial Times at http://lexicon.ft.com/Term?term=business-sustainability