How to supply and configure an energy economy and infrastructure for a world of more than 10 billion inhabitants by mid-century is perhaps the principal long-range issue facing human civilization today. The challenge will be finding the most environmentally benign way to supply that energy.
A key variable in this socioeconomic equation is the extent to which Earth's remaining fossil fuel reserves can be exploited. Even though the link between observed increasing global temperature and increasing carbon dioxide emissions is debatable, all agree that such a link is plausible. The Kyoto Protocol represents a first attempt to limit climate change; coming decades are likely to see worldwide adoption of national carbon caps that could severely restrict the use of fossil fuels for both transportation and the production of thermal and electrical energy. One major harbinger of this trend is accelerated efforts to develop technology to displace hydrocarbons with hydrogen for fueling surface transportation. An example is California's Hydrogen Highways initiative.
But there is a downside to the hydrogen equation that must be considered. Production of sufficient hydrogen—either by electrolysis or by thermal splitting of water or methane—to displace current consumption of petroleum by automobiles and trucks in the U.S. alone would require increasing by 50% the nation's current electricity generation capacity. Given the massive amounts of CO2 that would need to be sequestered should hydrogen be generated either directly or indirectly from fossil fuels—and given the enormous land areas needed for new biomass, wind, or solar plants that such an expansion would require—only nuclear power can feasibly enable a complete hydrogen economy.
In a certain sense, hydrogen and electricity can be considered "mutually fungible." In a number of instances, each can replace or be transformed into the other—hydrogen as potential energy, and electricity as kinetic energy. However, it will be most realistic to provide both and let the end user decide which to use. Figure 1 depicts just such a scenario on an urban scale. The electric portion of the grid would use high-current DC superconducting cables for power transmission, with liquid hydrogen as the core coolant. The electric power and hydrogen would come from nuclear and other power plants spaced along the grid. Electricity would exit the system at various taps, connecting into the existing AC power grid. The hydrogen would also exit the grid, providing a readily available alternative fuel, perhaps for the next generation of fuel cell–powered automobiles.
1. The grid of the future? In this conceptual drawing, an urban community's entire electricity supply comes from a nuclear plant and rooftop photovoltaic panels. The nuclear plant also generates hydrogen, which is distributed along with the electricity by a SuperCable ring bus. Source: Dr. Paul Grant
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