Your group can pick the topic from the ones listed below it. You can cover some parts of the other sources as well (if they have some common features, for example), but I highly recommend to concentrate on one source to cover it thoroughly enough.

• Solar power: 
• Wind power: 
• Tidal and hydroelectric power: 
• Geothermal energy: 
• Biomass energy:
• Fossil fuels (coal, oil and natural gas): 
• Nuclear power: