Some policymakers see the eventual switch to hydrogen-powered cars as inevitable, and the Bush administration has allocated $1.7 billion to the development of automotive hydrogen fuel cells for commercial use by 2020. But the road to hydrogen dependence is a bumpy one:
** Steam reformers, which are used to break down natural gas into hydrogen and CO2 molecules, are only about 85 percent efficient; 15 percent of energy in natural gas is lost during the process.
** It costs about $5 to produce enough hydrogen equivalent to the energy potential of one gallon of gasoline.
** Hydrogen's low density would require 21 tanker trucks to haul the amount of energy delivered by a single gasoline truck today, and a hydrogen tanker traveling 500 kilometers would use an amount of hydrogen equaling 40 percent of its cargo.
** At room temperature, hydrogen takes up 3,000 times more space as an energy-equivalent amount of gasoline, therefore, compressed or liquefied gas must be used in vehicle tanks; but tanks on today's hydrogen vehicles take up to eight times as much space as a normal gas tank to store an equivalent amount of fuel.
Furthermore, the necessary infrastructure to fuel about 40 percent of American car would cost about $500 billion.
Hydrogen-powered vehicles will not reduce greenhouse gas emissions if the hydrogen is produced through electric power plants that burn fossil fuels. But using solar or wind power to generate hydrogen is expensive; indeed, solar power still costs 10 times more than coal, in spite of its cost declining substantially over 20 years.
Source: Robert F. Service, "The Hydrogen Backlash," Science, Aug 13, 2004.
Electricity Beats Hydrogen for Power Storage/Delivery
A new study finds that major applications for hydrogen envisioned in hydrogen-economy scenarios could be more efficiently accomplished with technologies that use electricity directly. It concludes that in key roles envisioned for hydrogen as an energy carrier -- namely transmission of remote renewable resources, storage of intermittent renewables or for use in vehicles -- electricity offers options that are more energy-efficient and might preclude mass-scale emergence of hydrogen technologies.
The study -- Carrying the Energy Future: Comparing Hydrogen and Electricity for Transmission, Storage and Transportation - was issued by the Institute for Lifecycle Environmental Assessment and was funded by the John D. and Catherine T. MacArthur Foundation. It found that energy penalties incurred in manufacturing hydrogen place it at a competitive disadvantage compared with electricity. "The first and most important understanding about the proposed hydrogen energy system is that hydrogen is not an energy source," say study authors Patrick Mazza and Roel Hammerschlag. "It is an energy storage medium and carrier. And like the only other commonplace energy carrier --electricity -- hydrogen must be made."
The study compares the actual energy available when hydrogen and electricity carriers are employed and finds that electricity delivers substantially greater end-use energy. Advocates of hydrogen portray it as a means to transmit abundant renewable energy resources located distant from markets, such as sunlight in the Southwestern U.S. or wind in the Great Plains region. Electricity generated in solar panels or wind turbines would be converted to hydrogen via electrolysis, a process that uses electrical current to break the bonds of hydrogen and oxygen in water. Electricity would be recovered through electrochemical reactions generated when hydrogen and oxygen join in a fuel cell. However, when energy penalties are taken into account, says the study, only 45 - 55% of original energy remains compared to 92% if transmitted as electricity. Therefore, electrical transmission provides roughly twice the end-use energy.
The study concludes that even though the use of hydrogen as clean vehicle fuel is the most prominent of its foreseen uses, relative inefficiencies of hydrogen compared with direct electricity play out in vehicle technology too. "Using electricity to charge electric vehicles (EVs) provides twice the miles per kWh than employing electricity to make hydrogen fuel," says Mazza. "While conventional wisdom has it that the EV is a technological dead-end, hobbled by limited range and extended recharging times, advanced battery technologies could substantially extend ranges and meet the needs of a more substantial share of the market than is commonly understood. Lithium ion batteries developed for portable electronics are now working in prototype EVs that go nearly 250 miles between charges."
The study distinguishes between hydrogen and fuel cells. While a hydrogen fuel system is hindered by multiple inefficiencies, fuel cells can form an important part of highly efficient systems that convert biofuels or fossil fuels to electricity. Fuel cells can operate as stationary electrical generators, potentially at significantly higher efficiencies than central power stations or other distributed generators. Emergence of a substantial fuel cell market is in no way conditioned on mass application in vehicles or development of a hydrogen network. The study recommends that hydrogen and electricity advocates focus on complementary development that can support both pathways. This includes rapid expansion of renewables, improvement in hybrid vehicle technology, vehicle-to-grid applications that employ parked vehicles as grid energy storage, and development of biomass supplies from which liquid vehicle fuels and hydrogen can be made.
Source: Power Engineering/SEPP, August 2004
EFN comment: Keep your eye on : 1/ chemical cycles such as the Sulfur-Iodine process for the fabrication of hydrogen with high-temperature nuclear reactors 2/ the development of fuel cells that can use methane or methanol directly to generate electric power. 3/ the possibility of fabricating methane from coal (as was done during WWII).