Ars Technica has a interesting writeup on a study of the life cycle of alternative energy sources, and their total environmental impact. The article is called The ‘greenness’ of alternative energy sources. It looked at the “flow of material and energy used in the construction, operation, and ultimate decommissioning of a renewable energy supply. In addition to these terms, it takes into account the impact of manufacturing the materials needed to extract energy, as well as waste generated by the process.” The quick summary: wind and geothermal do the best, with solar needing wide scale use before its efficiency gets to fossil fuel levels – but dramatically lower on the pollution side, of course.