Courtesy MIT Press Hydrogen expert Peter Hoffmann shows many sides of the clean-energy debate. Related Links: Peter Hoffmann Responds to Your Questions About Fuel Cells Volvo Designs Fuel Cell Asphalt Paver The world of alternative fuels works in funny ways. Take hydrogen, which was close to gaining hero status a decade ago. In fuel-cell form, it emits little except for heat, electricity and pure water. Hydrogen appeared to be our ticket out of the fossil-fuel cycle for good.Today, however, natural gas, a fossil fuel (albeit a cleaner-burning one than many other mainstream fuels), is the alternative du jour, while hydrogen
Arch dams, classically curved monoliths situated in narrow valleys, are not as common as other types of dams, such as embankment dams and gravity dams. ENR takes a look at some of the biggest arch dams in the world, both completed and under construction.