Hydrogen economy

"One alternative to fossil fuels is ‘green’ hydrogen, which can be produced through water electrolysis by using an electric current to split water into hydrogen and oxygen with no greenhouse gas emissions, provided the electricity used to power the process is entirely from renewables. Hydrogen’s high mass energy density, light weight, and facile electrochemical conversion allow it to carry energy across geographical regions through pipelines or in the form of liquid fuels like ammonia on freight ships ... Across sectors as it can be used as a chemical feedstock, burned for heat, used as a reagent for synthetic fuel production, or converted back to electricity through fuel cells. Furthermore, hydrogen’s long-term energy storage capacity in tanks or underground caverns ... makes it one of the only green technologies that can store energy across seasons."

"Although in many ways hydrogen is an attractive replacement for fossil fuels, it does not occur in nature as the fuel H2. Rather, it occurs in chemical compounds like water or hydrocarbons that must be chemically transformed to yield H2. Hydrogen, like electricity, is a carrier of energy, and like electricity, it must be produced from a natural resource. At present, most of the world’s hydrogen is produced from natural gas by a process called steam reforming. However, producing hydrogen from fossil fuels would rob the hydrogen economy of much of its raison d’être: Steam reforming does not reduce the use of fossil fuels but rather shifts them from end use to an earlier production step; and it still releases carbon to the environment in the form of CO2. Thus, to achieve the benefits of the hydrogen economy, we must ultimately produce hydrogen from non-fossil resources, such as water, using a renewable energy source."

"There are three different primary energy-supply system classes which may be used to implement the hydrogen economy, namely, fossil fuels (coal, petroleum, natural gas, and as yet largely unused supplies such as shale oil, oil from tar sands, natural gas from geo-pressured locations, etc.), nuclear reactors including fission reactors and breeders or fusion nuclear reactors over the very long term, and renewable energy sources (including hydroelectric power systems, wind-energy systems, ocean thermal energy conversion systems, geothermal resources, and a host of direct solar energy-conversion systems including biomass production, photovoltaic energy conversion, solar thermal systems, etc.). Examination of present costs of hydrogen production by any of these means shows that the hydrogen economy favored by people searching for a non-polluting gaseous or liquid energy carrier will not be developed without new discoveries or innovations. Hydrogen may become an important market entry in a world with most of the electricity generated in nuclear fission or breeder reactors when high-temperature waste heat is used to dissociate water in chemical cycles or new inventions and innovations lead to low-cost hydrogen production by applying as yet uneconomical renewable solar techniques that are suitable for large-scale production such as direct water photolysis with suitably tailored band gaps on semiconductors or low-cost electricity supplies generated on ocean-based platforms using temperature differences in the tropical seas."

"While industry players have already started the market introduction of hydrogen fuel cell systems, including fuel cell electric vehicles and micro-combined heat and power devices, the use of hydrogen at grid scale requires the challenges of clean hydrogen production, bulk storage and distribution to be resolved. Ultimately, greater government support, in partnership with industry and academia, is still needed to realize hydrogens potential across all economic sectors."

"Unlike CH4 and CO2, ammonia is not a greenhouse gas. In the atmosphere, it quickly forms hydrogen bonds to water vapor and returns to the ground in alkaline rain. However, NH3 is toxic, chills its surroundings rapidly on vaporizing, and releases heat on contact with water. Engineering a safe fuel tank for an ammonia-fueled vehicle would be a key priority. Ammonia is an excellent material for hydrogen storage. ... the volume density of hydrogen in liquid NH3 is more than 40% greater than in liquid H2, and the comparison becomes much more favorable when one considers the weight of the required fuel tank and peripherals. Unlike H2 gas, ammonia explodes in air only over a narrow range of concentrations. Shipping ammonia from production site to point-of-use does not require a great deal of cooling or high pressure. Thousands of miles of NH3 pipeline in the US stand as evidence that reliable infrastructure for NH3 transport and storage has been engineered. In sum, liquid NH3 is not just an excellent hydrogen-storage material but also an ideal medium for moving hydrogenic energy from place to place."

"The medium of energy transport from an atomic reactor to sites at which energy is required should not be electricity, but hydrogen. The term "hydrogen economy" applies to the energetic, ecological, and economic aspects of this concept. The concept envisages reactors held on platforms floating on water. They are in water sufficiently deep to make heat dissipation easy/ The electricity they make would be converted on site to hydrogen and oxygen by hydrolysis. The hydrogen would be piped to distribution stations and thereafter sent to factory and home. Reconversion to electricity would take place in on-site fuel cells, the only side product ebing pure water."