Solar Energy requires the area to be free of trees so the sun can get through to the collector. The collector can block the sun robbing plant life of valuable nutrients. This is very limiting to it's usability, however as new technology emerges we may see less of this impact and it may become more feasible. Wind energy requires wind which sometimes we have, sometimes we do not. Again the usability is limited. Hydro power: well Hoover Dam is already built, and the ecosystem there has already been messed up, and replaced with a new one. It can stay, but I hope we don't go destroying anymore ecosystems for this power source. Geothermal heat, there is still a lot of learning to do here. In some locations where experiments have been done the area has cooled down. I can't be sure that we fully understand what effect the cooling of these geothermal hot spots will have on the environment, and surrounding ecosystems. The creation of mass amounts of steam might turn a desert into a wetlands, or rain forest if done on a large enough scale. Biofuels, everyone thinks they are the wave of the future. If we do not produce enough foods to feed the starving now, then why take away from our food source to move cars? Methane, I believe this might prove to be one of the most viable renewable energy sources we have. Most animal's feces give off this gas (including humans) and a lot of it is just released into the environment. A lot of cow and hog farmers are building smaller power plants on their farms, and selling the power to the power company. It's probably feasible for cities to attempt this at municipal waste treatment facilities too. I don't think it would be feasible for the average joe to attempt this in his back yard though.