The Five Myths of the Hydrogen Fueled
Vehicle
Lindsay Leveen December 30, 2003
Introduction
The purpose of this paper is to provide facts to policy
makers, professionals, and the public on the possibilities for vehicles fueled
by alternates other than petroleum liquids.
Present global consumption of crude oil exceeds 3.2 billion gallons each
day. The US alone consumes more
than 830 million gallons a day of crude oil.
As China, India and other countries industrialize, and further develop
their economies the quantity of petroleum based
liquids needed for the global
vehicle fleet will increase.
Hydrogen fueled wheelchairs are even on the market though an
electric wheelchair is still the bigger seller as of now. Putting
aside global warming and environmental concerns, something has to be done to
mitigate the growth in demand for petroleum liquids, if we are going to avert an
impending energy crisis. Much
debate on hydrogen as a substitute fuel has taken place based on the hope of
this clean fuel alternative.
Unfortunately much of debate has been based on myth so it
hooks you in, and not on facts.
Linus Pauling said it best Facts
are the air of scientists. Without
them you can never fly.
Myth 1. The
Internal Combustion Engine will always be inefficient
This argument is central to most of the reasoning behind
the need to substitute fuel cells (FCs) for internal combustion engines (ICEs)
in vehicles. FC proponents often
argue that ICEs have efficiencies of the order of 15%. The Toyota Prius, a popular production
hybrid automobile that
seats five, has an efficiency approaching 40% (source Toyota).
This is just the beginning of the “hybridization” of the automobile
fleet. Direct injected diesel
engines coupled with hybrid energy accumulation systems will have efficiencies
exceeding 55% (source US DOE). To simply discount the ICE due to inefficiency is incorrect
and shortsighted. Perhaps the best
policy would be to allow Toyota to power most vehicles with their hybrid
technology, just as Intel powers most personal computers.
This winning technology applied over tens of millions of vehicles a year
can only become less expensive as it becomes mass-produced.
Myth 2. The
overall efficiency of FCs is greater than 75%
If hydrogen is a primary energy source, and it is not, the
overall efficiency of a FC system approaches 75%. The problem is that hydrogen is an energy carrier, and must
be produced from other primary energy sources.
The most economical method to produce hydrogen is by steam methane
reforming (SMR) technology. This
technology recovers approximately 75% of the energy in the methane used to
produce the hydrogen. Compressing
hydrogen requires electric power. Compression
requires approximately 10% of the energy content of the hydrogen in the form of
electricity. Power generation from
natural gas is at best 50% efficient so that the equivalent of 20% of the energy
in the hydrogen is used up in the natural gas used in generating the power to
compress the hydrogen. Liquefying
hydrogen is even more energy intensive requiring 50% of the energy content in
the form of electricity or 100% of the energy content in the form of natural gas
to generate the electricity for compression.
The overall efficiency of producing, compressing, and using
the hydrogen in a fuel cell is 46.9%. This
is not much greater than the 40% efficiency of the Prius hybrid and well below
the efficiency of a diesel hybrid. Researchers
at Massachusetts Institute Of Technology (MIT) have reported that diesel with
hybrid is more green than hydrogen fuel cell vehicles.
Myth 3. Proton
Exchange Membranes (PEM) FCs will soon be sold for $100 per kilowatt of output
Presently, PEM FCs cost about $5,000 per kilowatt of output
and require one gram of platinum for a kilowatt of output.
The likely PEM FC power plant for a vehicle will need to be sized at 60
kilowatts. This will require two
ounces of platinum and presently costs $300,000.
There will be significant improvement in the cost of fabricating FCs but
the $100 per kilowatt target is in all probability unachievable.
A more likely cost for the PEM FC is $1,000 per kilowatt within a decade
and $500 per kilowatt within two decades. It
has been argued that the famous “Moore’s Law” that applied to integrated
circuits (ICs) will apply to FCs. The
fabrication of ICs has relied on the miniaturization of the circuitry as well as
the increase in size of the silicon wafer substrate.
This is a much different mechanical system than the fabrication of FCs.
The hydrogen atom stripped of an electron is a proton with known physical
shape, size and characteristics, that cannot be miniaturized.
The membrane, the platinum, and the fabrication steps of the FC cell can
and will be improved, however the learning curve for such mechanical systems is
likely far less rapid than for ICs. Moore’s
Law postulates a halving in cost per unit of performance of ICs every 18 months.
The likely rate at which FCs will experience a halving of cost per unit
of performance will be three or four times longer than experienced in ICs.
Myth 4 – Hydrogen has a higher energy density than
gasoline or diesel
Hydrogen has more energy per unit mass than other fuels (61,100 BTUs per pound versus 20,900 BTUs per pound of gasoline). The problem with hydrogen is that it is much less dense (pounds per gallon) than other fuels. A gallon of gasoline has a mass of 6.0 pounds, the same gallon of liquid hydrogen only has a mass of 0.567 pounds or only 9.45% of the mass of gasoline. Therefore one gallon of gasoline yields 125,400 BTUs of energy while a gallon of liquid hydrogen yields only 34,643 BTUs or 27.6% of the energy in a gallon of gasoline. The Space Shuttle uses hydrogen as a fuel, because its mass is low, and the fuel is carried in an external fuel tank that is jettisoned during lift off. Automobiles can not have external fuel tanks that are discarded, and the energy per unit volume is used to determine a fuel’s energy density in automobiles. Compressed gaseous hydrogen is even less dense than liquid hydrogen. At 5,000 psi of pressure gaseous hydrogen only has a density of 0.25 pounds per gallon or one twenty fourth the density of gasoline. Gasoline and diesel are far superior fuels to hydrogen in this regard.
Myth 5 – Hydrogen does not have any greenhouse gas
emissions
Burning hydrogen does not create any carbon dioxide
emissions. However, producing
hydrogen typically does create carbon dioxide emissions.
At the November 17, 2003 Ministerial Meeting in Washington
DC hosted by the US DOE’s International Partnership for the Hydrogen
Economy (IPHE), The World Resources Institute (WRI) presented a paper entitled Environmental
Imperatives in a Hydrogen Economy. The majority of the data in this WRI paper was sourced from
SLS Partners Inc. Figure 1. below shows the pounds of carbon dioxide emissions
associated with various forms of hydrogen production
Figure 1. Pounds
Carbon Dioxide Emissions Per Pound of Hydrogen Produced
One can see that only electrolysis using renewable sources of energy such as wind, solar, hydroelectric or geothermal have no carbon dioxide emissions associated with hydrogen production via electrolysis. As more than 55% of the electricity produced in the USA is based on coal as the fuel, there are significant quantities of carbon dioxide emissions even when the hydrogen is produced via electrolysis. Steam Methane Reforming (SMR) is the most common method of hydrogen production and each pound of hydrogen produced emits 9.42 pounds of carbon dioxide.
Conclusions
There is immediate hope for improved fuel economy and lowering of greenhouse gases from the vehicle fleet. The improvements will first come from the hybrid propulsion systems and then from dual fuel vehicles. Weight savings and the use of substitute lighter materials will also result in lighter and more fuel efficient vehicles. Direct injected diesel and gasoline ICEs with and without hybrid energy accumulation systems will be introduced that have improved fuel efficiency. Hydrogen fueled vehicles will not play a major role in fueling the road transportation fleet over the next couple of decades. Hydrogen is an expensive substitute fuel, but will play an important role as a chemical feed stock to synthesize and produce cleaner liquid fuels for transportation.