Pernick and Wilder define "clean tech" as "any product, service, or process that delivers value using limited or zero non-renewable resources and/or creates significantly less waste than conventional offerings." They highlight eight major clean technology sectors: solar power, wind power, biofuels, green buildings, personal transportation, the smart grid, mobile applications (such as portable fuel cells), and water filtration. The authors explain how investors, entrepreneurs, and individuals can profit from technological innovation in these areas. Pernick and Wilder identify some specific clean technologies, companies, and regions that are leading the way.