Re: Roof tank?
I'm all in favor of energy and recycling ideas that make economic sense. If something has a reasonable payback or (in the case of recycling) recycling a material is cheaper than making it new I'm all in favor of it. In fact there are some really interesting products, such as deck planking, that are made almost entirely from recycled material that otherwise would have just gone into a landfill.
However global warming does not figure into my rate of return calculations at all. I'm REALLY skeptical about the notion that we are having a significant effect on the climate of a whole planet, and even more skeptical that anyone can come up with accurate figures on how much impact any single project would have on the Earth.