Hydrogen is not an energy resource,[97] except in the hypothetical context of commercial nuclear fusion power plants using deuterium or tritium, a technology presently far from development.[98] The Sun's energy comes from nuclear fusion of hydrogen, but this process is difficult to achieve controllably on Earth.[99] Elemental hydrogen from solar, biological, or electrical sources require more energy to make it than is obtained by burning it, so in these cases hydrogen functions as an energy carrier, like a battery. Hydrogen may be obtained from fossil sources (such as methane), but these sources are unsustainable.[97]
The energy density per unit volume of both liquid hydrogen and compressed hydrogen gas at any practicable pressure is significantly less than that of traditional fuel sources, although the energy density per unit fuel mass is higher.[97] Nevertheless, elemental hydrogen has been widely discussed in the context of energy, as a possible future carrier of energy on an economy-wide scale.[100] For example, CO2 sequestration followed by carbon capture and storage could be conducted at the point of H2 production from fossil fuels.[101] Hydrogen used in transportation would burn relatively cleanly, with some NOx emissions,[102] but without carbon emissions.[101] However, the infrastructure costs associated with full conversion to a hydrogen economy would be substantial.[103]
الأربعاء نوفمبر 14, 2012 12:23 am
