Hydrogen vehicles - future road vehicle system to tackle oil security and environment problem:
Many vehicle manufacturers are currently researching the feasibility of building hydrogen cars, as more and more environment-friendly, clean, emission-free motor vehicles are needed to fight global warming. Hydrogen vehicles hold the promise of curing the world's oil dependency while making transport-related air pollution and CO2 emissions history. But skeptics say that hydrogen is clean only if produced from renewable sources of energy.
A. Potential sustainable vehicle fuels – (a) Oil can not be expected as energy for sustainable transportation system due to its un-renewable. (b) Renewable primary energy can not be used as vehicle fuel directly. (c) Second energy carriers which have most promising sustainable “fuels” for vehicles are (i) Biomass fuel (ii) Electricity (iii) Hydrogen. In fact, combination hydrogen and electricity have been recognized by many manufactures for the best option for future road vehicle system.
B. Hydrogen has many benefits; such as (i) It is the most abundant element on earth; (ii) it is a versatile energy carrier that can be produced from any source of energy; (iii) it would reduce oil dependency, and bring transport-related air pollution and greenhouse-gas emissions to virtually none, and; (iv) it can be stored and easily kept over time.
C. A hydrogen vehicle is a vehicle that uses hydrogen for motive power. The power system of hydrogen vehicles converts the chemical energy of hydrogen to mechanical energy (torque). A hydrogen vehicle uses one of the following two methods for such conversion to mechanical energy,
(a) Combustion - In combustion, the hydrogen is burned in engines in fundamentally the same method as traditional gasoline cars.
(b) Electrochemical conversion in a fuel-cell - In fuel-cell conversion, the hydrogen is reacted with oxygen to produce water and electricity, the latter of which is used to power an electric traction motor. This process is the reversal of the electrolysis of liquid water and should provide an open circuit voltage of 1.23 Volts per cell.
The fuel-cell conversion system in automobiles is preferred among above two systems. Because fuel-cell has advantages such as, large heat exchanger needed for fuel cells and their limited load change and cold start capability, they are certainly first choice as range extender for battery electric vehicles.
D. The molecular hydrogen needed as an on-board fuel for hydrogen vehicles can be obtained through either of many (i) thermochemical methods utilizing natural gas, coal (by a process known as coal gasification), liquefied petroleum gas, biomass (biomass gasification), by a process called thermal decomposition, or (ii) as a microbial waste product called bio-hydrogen or Biological hydrogen production.
Hydrogen can also be produced from water by electrolysis. If the electricity used for the electrolysis is produced using renewable energy, the production of the hydrogen would (in principle) result in no net carbon dioxide emissions and the process is renewable. Researches have been made successfully for on-board decomposition to produce hydrogen, when a catalyst is used.
E. Recent progress in R&D for hydrogen Fuel Cell Vehicle -
(a) Fuel cells stack power density improved by 20 times. Size and weight of fuel cell engine can be integrated in vehicle, nearly equal to diesel level.
(b) Noble metal is used as the primary catalyst for fuel cells. In recent year, the amount of platinum usage has been reduced significantly by 10 times.
(c)Power efficiency of fuel cell engine reaches to 45%- 50%, plus high efficiency of driving motor, therefore, power efficiency from tank to wheel is one time higher than petrol vehicle.
(d) Reliability and durability of Fuel Cell Vehicles have been increasing as research inputs are flowing in.
F. Major challenges in development of hydrogen Fuel Cell Vehicle -
(a) Hydrogen produced from renewable energy: Great progress are being achieved in solar-hydrogen direct producing technology.
(b) Hydrogen storage: (i) Compressed hydrogen currently available to 700 Bar for longer range; (ii) Metal hydride storage weight rate 7%; (iii) Storage hydrogen by nano technology, such as nano fibers and tubes.
(c) Infrastructures: It is estimated that, quite large investment is needed in infrastructure for setting up large number of hydrogen fuelling stations. Experts predict that such investment in infrastructure would be returned in ten years.
(d) Competitive cost: Experts predict that, Fuel Cells stack cost would drop down to the almost same price of gasoline, 30 USD/kw by the year 2010.