 Pernick and Wilder present examples which show that the " clean tech revolution " is already under way . Very large corporations such as <unk> , Toyota and Sharp , and investment firms such as Goldman Sachs are making multibillion @-@ dollar investments in clean technology . <unk> clean tech cities are seen to include Copenhagen , where wind power generates 20 percent of Denmark 's electricity , and Chicago , a leader in " green " buildings saving energy , heating and cooling costs . Statistics from the U.S. and from abroad , especially from China , India , Brazil , and Europe are presented . 
