| The Hydrogen
Economy: An Objective Look Part 1: Hydrogen as Transport Fuel |
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There are actually three different application areas to consider for hydrogen:
In this article, we’ll cover some general issues and then focus on hydrogen as a transportation fuel. A later article will address hydrogen’s potential for replacing natural gas in heating and for use in power buffering.
Hydrogen Basics
Proponents of the hydrogen economy like to lead off with two observations about
hydrogen:
a) It is the most abundant element in the universe, comprising some 99% of all
atoms in the stars and galaxies; and
b) Free hydrogen gas, H2, carries the highest chemical potential
energy, relative to mass, of any chemically stable compound that exists or is
ever likely to exist. One kilogram of hydrogen contains as much energy as about
2.4 kg of natural gas or 2.85 kg of gasoline.
The first point is perfectly true, but academic. We are hardly going to be mining hydrogen from the atmosphere of Jupiter to obtain energy. The second point is also true, but of little relevance unless one is choosing the fuel for an orbital rocket.
Cosmic abundance notwithstanding, the fact is that here on earth, there is no free hydrogen waiting to be tapped for producing energy. It must always be split away from compounds with which it is chemically bound, using some other energy source. Hydrogen for us is not an energy source, but an energy carrier. In that respect, it is like electricity.
The simplest way to get hydrogen is to split it from water, by electrolysis. Current industrial electrolyzers need about 54 kWh of electricity per kg of hydrogen [1]. In the future, better catalysts and electrolytes might enable as little as 40 kWh / kg, but that’s getting fairly close to thermodynamic limits.
Producing hydrogen by electrolysis is of interest because it’s clean, and because the leading renewable energy sources—wind, solar, and hydro—all produce electricity. But unless the electricity is priced below about $0.03 / kWh, the cost of producing hydrogen by electrolysis is greater than the cost of producing it from natural gas or other fossil fuels [2].
Producing Hydrogen
The most economical method for producing hydrogen for industrial use has long
been steam reforming of methane. Steam reacts with methane at high temperatures,
to produce carbon monoxide and hydrogen:
CH4 + H2O ? CO + 3H2
By separating out the hydrogen and adding more steam, the CO can be shifted to CO2 and more hydrogen:
CO + H2O ? CO2 + H2
The method used to separate hydrogen from CO and CO2 strongly influences the cost and efficiency of the process. In the past, the size and complexity of the equipment required made small-scale steam reforming plants impractical. Recently, ceramic membranes have been developed that are highly permeable to hydrogen but not to other gases [3]. Tubes formed from these membranes can operate at the temperatures and pressures at which the reforming and shift reactions are carried out. This avoids thermal cycling and improves net efficiency.
More importantly, it makes small-scale reformers feasible. Potentially, these membranes might enable on-board reformers to produce purified hydrogen for fuel cell vehicles [4].
Following the steep rise in natural gas prices in North America over the last few years, steam reforming of methane is no longer quite so cheap. In principle, it would now be more economical to produce hydrogen from gasification of coal or refinery waste—carbon in the form of “pet coke”.
The basic reactions involved are very similar to those involved in steam reforming of methane, but they start with plain carbon:
C + H2O ? CO + H2
This method isn’t widely used as yet. The capital cost for a gasification plant is high. Because of impurities present in coal and pet coke, the processes are messier and not as mature as they are for steam reforming of methane. Since no one is entirely certain that the cost of natural gas will remain at current high levels relative to coal, there is a reluctance to invest in these plants.
Hydrogen can also be produced from virtually any type of biomass. If biomass is heated to several hundred °C in the absence of oxygen, it breaks down through pyrolysis into a range of volatile hydrocarbons and a solid char that is mostly carbon. If either or both of the pyrolysis fractions is reacted with high temperature steam, the result is the same sort of CO + H2 mix created in steam reforming of methane or in gasification of coal.
Gasification of biomass is economically attractive in certain situations. It’s actually easier than gasification of coal, because the biomass feedstock is largely free of sulfur, mercury, and other contaminants that complicate the latter. But growing biomass for energy requires a lot of land and water. It isn’t a practical replacement for fossil fuels at the rate we currently consume them. However, when a stream of biomass is a byproduct of another process, it can be cost-effective to tap it for local power and heat. Examples are described in [5].
Other Production Methods
Other methods under development are aimed at producing hydrogen directly from sunlight, using the energy of solar photons to split water molecules. Although some of these approaches are regarded as “promising”, efficiencies to date have been low. The amount of hydrogen produced per square meter of sunlight has been far less than what could be produced by high efficiency solar cells driving conventional electrolysis.
One further method for producing hydrogen is thermo-chemical splitting of water. Although not presently used commercially, it’s potentially very important. It is considered a practical way to produce hydrogen from a new generation of very efficient nuclear reactors. The hot coolant from the reactor would drive a thermo-chemical cycle for splitting water. Waste heat from the thermo-chemical cycle would drive conventional power turbines. An overall thermal efficiency of perhaps 60% has been projected for the combined cycles. [6], [7]
The prospect of large supplies of cheap hydrogen from hundreds of such reactors lends credence to the hydrogen economy. However, it dismays some of hydrogen’s original proponents. They oppose large central power plants in general and nuclear plants in particular. The notion that there could be a synergy between advanced nuclear power and the hydrogen economy is unwelcome.
Thermo-chemical production of hydrogen, however, might also work for decentralized power. In Canada, SHEC Labs is developing a small-scale thermo-chemical hydrogen production process. Focused sunlight, rather than nuclear power, drives its thermal reactors [8]. In principle, these reactors should be able to achieve much better efficiency for solar energy to hydrogen conversion than is possible using PV cells and electrolysis. If they can be made cheaply, concentrator dishes around five meters in diameter might supply hydrogen and electricity to small clusters of energy-efficient houses. Unfortunately, the technology is still unproven in mass production.
Hydrogen as Transport Fuel
Despite skepticism from hydrogen’s detractors, the fact is that if one must
use non-fossil energy to produce fuel for transport, then hydrogen really is
about the most energy-efficient way to go. In terms of electric or solar energy
input versus power output at the wheels, no manufactured fuel beats hydrogen
feeding fuel cells to power an electric drive train. The reason for hydrogen’s
greater efficiency is easy to understand: nearly all other candidates for a
manufactured transportation fuel require production of hydrogen as a first step.
For example, to produce methanol without resort to coal or biomass, the reaction
is:
CO2 + 3H2 => CH3OH + H2O
A significant amount of energy is lost in reacting hydrogen with CO2 to produce methanol. It is more efficient if the hydrogen can be used directly.
Another consideration favoring hydrogen is that it can, in principle, deliver to the wheels a much higher fraction of the energy it contains. That’s because it can be burned in a fuel cell to produce electricity at a high efficiency. Electricity, in turn, can be efficiently converted to traction power at the wheels. A great deal of internal friction from pistons, crankshaft, driveshaft, and gears that lower IC engine efficiency is avoided. [9] To realize those advantages, it’s necessary to first solve two formidable problems. The cost and durability of fuel cells for mobile vehicles must be dramatically improved, and a practical means must be found to store enough hydrogen in an acceptably small and lightweight fuel tank.
Pressurized Hydrogen
Many hydrogen advocates feel that the storage problem has been adequately solved
already by the development of high performance tanks for storing compressed
hydrogen gas. Such tanks are filament-wound with carbon fiber for high strength
and low weight. Tanks rated for 5000 PSIG, manufactured by Quantum Technologies
are in use in hydrogen vehicle demonstration programs. Tanks rated for 10,000
PSIG are planned for use in production vehicles. At that pressure, enough
hydrogen can be carried to give a 5-passenger fuel cell-powered coupe a 300-mile
driving range—comparable to today’s gasoline-powered cars.
The two main technical issues with this approach are the energy needed to compress hydrogen to such extreme pressures, and safety. Even with perfect isothermal compression, it takes about one-eighth as much mechanical energy to compress hydrogen to 10,000 PSI as the hydrogen will deliver in fuel cell output. This "energy tax" for compressing hydrogen approaches what would be needed to produce methanol from hydrogen and CO2. Since methanol is easy to store and avoids the safety issues with highly compressed hydrogen, critics suggest that it might be a better just to produce methanol.
It’s possible that the critics are right. But the issue is far from settled. It may actually be possible to turn the “compression energy tax” to hydrogen’s advantage.
Energy Recovery
Before it can be used in a fuel cell, the highly compressed hydrogen from a
pressure tank must be decompressed. A conventional pressure regulator does that
job cheaply and easily, but also wastefully. The mechanical potential energy of
the compressed gas is dissipated in forcing the gas through the regulator’s
needle valve. If, instead, the pressurized gas is used to power a compressed gas
motor, a good fraction of the energy put into compressing it can be recovered.
Directors of hydrogen vehicle research program might wish to give some priority to developing compressed gas motors for use with hydrogen. The payoff from a reliable, cost-effective design would be substantial. If it were able to recover as much as 70% of the compression energy of the hydrogen gas, then it would reduce the size and weight of the hydrogen tanks and fuel cells by about 10%, for the same range between fill-ups.
Safety
As to the safety issues with highly compressed hydrogen, I think the jury is
still out. There’s probably no need for concern about spontaneous bursting of
the fuel tanks. A fuel-tank rupture would be a worst-case scenario, and would
create a truly horrendous explosion. However, the tanks can be made with a
sufficient margin of safety to preclude spontaneous bursting [10].
Very high pressure is possibly a safety advantage in crashes. High pressure allows the tanks to be smaller. Moreover, to withstand that degree of internal pressure, the tanks must be so strong that, by comparison, external impact forces become less significant.
The plumbing between the tank and the fuel cells is more vulnerable, and would likely be severed in a crash. But Quantum has addressed that problem by developing pressure regulators that mount inside the tank. External lines carry only low-pressure gas. Safety valves at the regulator immediately cut off gas flow if pressure in the external lines is lost. So it seems that the system would be adequately safe for driving. Refilling the tanks is more problematic. The only way to get fast refilling is to have a direct connection between the fuel tank and a high-pressure supply tank. Although it is almost certainly possible to design hoses and connectors that are capable of handling hydrogen at 10,000 PSI, it’s not easy. Equipment of that sort is not something to be handled by untrained citizens at neighborhood filling stations. The potential for disastrous accidents is too great.
Possibly, the refilling issue can be addressed by making the hydrogen tanks swappable. To fill up, a driver would pull up over a sunken bay similar to those now used at fast oil-change stations. A robotic tool would remove the depleted tank and replace it with a full one. The depleted tank would then be conveyed to an underground room where refilling could be done slowly and safely.
Unfortunately, there is in these days one final safety issue with high-pressure hydrogen tanks. A heavy-caliber armor piercing round fired into a car’s high-pressure hydrogen tank would cause an explosion equivalent to at least a case of dynamite. The hydrogen gas itself is not explosive, but pressurized to 10,000 PSI and with a speed of sound four times faster than that of air, it might as well be. It will escape so rapidly and with such force from a pierced tank as to drive an expanding spherical shock wave through the air ahead of it. Hydrogen behind the shock wave will diffuse into the superheated shock zone and burn in a matter of milliseconds. The result would be hard to distinguish from a “true” explosion.
I don’t know it that particular problem has any technical solution.
Other Storage Options
There are other less scary options for storing hydrogen, though none is ideal.
The approaches that deliver good densities all involve binding the hydrogen
chemically. That invariably means some loss of energy, compared to using
hydrogen directly.
The least wasteful of these approaches is probably to bind the hydrogen with nitrogen, producing ammonia (NH3). Ammonia can be used directly in certain types of high temperature fuel cells. The energy required for breaking the ammonia down to hydrogen and nitrogen is supplied by waste heat from the fuel cell, and doesn’t subtract from the electrical output of the cell. Apollo Energy Systems of Ft. Lauderdale, FL, is planning to use alkaline fuel cells powered by ammonia in a line of fuel cell vehicles.
Unfortunately, ammonia is not free from safety issues of its own. In high concentrations it is toxic to breathe. The risk is moderate; ammonia is used for fertilizer, and farmers routinely handle it safely. But pressure is needed to keep ammonia liquid at normal temperatures. It will escape rapidly and disastrously from a broken valve. There have been fatalities due to accidental release of ammonia at chemical plants or in crashes of tanker trucks carrying it.
Two other interesting options are the "hydrogen on demand" system from Millennium Cell, and the lithium hydride slurry approach from Safe Hydrogen LLC. The former uses sodium boro-hydride (NaBH4) in an aqueous solution, while the latter uses a stabilized slurry of lithium hydride particles (LiH) in a mineral-oil carrier. Both are similar in that they produce spent solutions that must be held on board for recycling. In both cases, the liquid fuels are resistant to combustion, and present no fire hazard in the event of a crash. Though much safer than gasoline, the spent solutions are caustic, and can be hazardous if their tanks are breached.
The cost of regenerating fuel is also a significant downside for both approaches. The energy needed is very much greater than that needed to produce the same amount of hydrogen directly by electrolysis of water. Neither company quotes figures, but I suspect that recycling the spent fuel is even more costly than producing methanol from CO2 and hydrogen.
Cost and Durability Issues
Whether hydrogen finds widespread use as a transportation fuel will ultimately
depend on how well certain cost and durability issues can be addressed.
Production of hydrogen at this point is not a killer problem. But both the cost
and durability of hydrogen fuel cells for automotive use are big problems, as is
the cost of lightweight high-pressure tanks. The cost of hydrogen fuel cells
must be cut by a factor of ten before they are cheap enough to be attractive for
automotive use. That won’t be easy, but it may be possible. Over the last five
years, costs have already dropped by one factor of ten; with more research and
tooling for mass production, another factor of ten is conceivable. Some major
players, like GM, are betting on it.
Not only do costs have to come down, however; durability has to go up. The best automotive fuel cells are currently good for only a couple of months of driving before their PEM membranes fail. Researchers at Du Pont are working on various incremental improvements for their Nafion® PEM membranes [11]. These have so far been the standard for automotive fuel cells. However, it’s not clear whether incremental improvements will suffice. Current PEM fuel cells prefer stable operating environments. Their membranes are physically and chemically delicate, and don’t stand up well to the repeated swings in temperature and humidity that they encounter in automotive use.
Recently, the British firm PolyFuel has announced the development of a promising new fuel cell membrane. If their claims hold up, they may be able to deliver the improvements in cost and durability that are needed. It’s too early, however, to know.
The most I can say for sure at this point, after surveying fuel cell development work reported on the web, is that fuel cell technology is an active field in which rapid progress is being made. Statements by hydrogen detractors that “researchers have been trying unsuccessfully for 80 years to make fuel cells practical” are unfair and misleading.
The Alternatives
If hydrogen fuel cell vehicles were the only option for dealing with the coming
shortfalls in oil supplies, then their future would be assured. However,
that’s not the case. The following developments could all serve to reduce oil
consumption enough to keep crude oil prices from rising quickly above the $60 a
barrel level toward which they now seem headed:
The first three points are obvious, but their potential for reducing oil consumption is limited. The last point is potentially more significant. I’ll have more to say about it in Part 2, in connection with hydrogen’s use in oil refining and synthetic fuel production. It’s the fourth point, however—the emergence of plug-in hybrids—that poses the most direct challenge for hydrogen vehicles.
Gal Luft wrote about plug-in hybrids in an earlier EnergyPulse article this summer [12]. They are hybrid vehicles whose batteries can be recharged from an external source, like those of a battery electric vehicle. For trips under ten miles or so—which comprise the large majority of trips actually driven—they can run entirely on batteries. Fuel consumption may thus be cut by 85%. That’s substantial enough to allow us to track dwindling oil supplies for quite some time before we’re actually forced to abandon the stuff. That means that, absent a heavy carbon tax on gasoline and diesel fuel, hydrogen as a transportation fuel will have to compete economically with oil at prices not much higher than we see today.
Whether it will be able to do so depends heavily on the hydrogen production and distribution infrastructure we are able to put in place. That, in turn, depends at least partly on issues that will be explored in the Part 2, Hydrogen and Utilities.
Endnotes and References
[1] Summary of Electrolytic Hydrogen Production, http://www.nrel.gov/docs/fy04osti/36734.pdf
[2] Assumes current prices for fossil fuels. Naturally, as competition for
diminishing supplies drive fuel prices higher, the price point at which
electrolytic hydrogen becomes competitive rises correspondingly.
[3] http://www.physorg.com/news906.html
[4] Early efforts to develop on-board reformers as a way to supply hydrogen for
fuel-cell vehicles have fallen by the way. The simple reformers that were
feasible could not produce pure hydrogen, and efforts to develop automotive fuel
cells that would tolerate CO and CO2 in the fuel stream were
unsuccessful.
[5] http://www.eere.energy.gov/hydrogenandfuelcells/pdfs/merit03/30_gti_david_bowen.pdf
[6] http://www.uic.com.au/nip73.htm
[7] http://gcep.stanford.edu/pdfs/hydrogen_workshop/Schultz.pdf
[8] http://shec-labs.com/process.htm
[9] Of course, internal combustion engines and mechanical drive systems are not
the only alternative to hydrogen fuel cell vehicles. See section on
alternatives.
[10] U.S. codes for pressure vessels call for a 2.5:1 safety margin. A 10,000
PSI tank must survive testing to 25,000 PSI. Ultrasonic microphones can monitor
the tank on refilling, and computer analysis of the sound can detect aging tanks
that might be starting to weaken/
[11] http://www.qtww.com/home.shtml
[12] http://www.energypulse.net/centers/article/article_print.cfm?a_id=790
| Mike Johnston 11.12.04 |
I find your analysis of hydrogen fuel
essentially correct but would add a few things in interest of better
understanding the topics that you raise. Consider that we already have two
very efficient hydrogen storage vehicles at hand; one binding the hydrogen
to carbon atoms and two binding the hydrogen atoms to oxygen atoms. The
second is the most renewable storage method and the safest and most
plentiful. Since we have been utilizing the hydrogen/carbon storage system
for some time now I think it is safe to say that we have been using
hydrogen energy for the last 100 years or so and are now looking at ways
to improve the existing hydrogen economy not ways to develop a whole new
energy system. The CO + H2 mix known as water gas or coal gas was the
first gas used in the US and was replaced by natural gas and yes the
reformer reaction is not very different. Tha catalytic converter on your
car is a type of reformer. That demystifies it a bit doesn't it? Please
check out my blog for more in-depth writings on these topics. http://enki.tblog.com
Thank you. MJ
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| Jack Ellis 11.13.04 |
Excellent, well written and very
informative article that cuts through all the misleading rhetoric. On to
part II.
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| Len Gould 11.14.04 |
I agree with Jack. kudos. I'm curious why
you left out liquid hydrogen, with which the europeans esp. BMW appear to
be quite enamoured of. I also hadn't realized how short-lived the nafion
membranes were, though I think I know that the platinum catalyst in them
runs about $1,000/kw with little hope of reduction unless a different
catalyst entirely can be developed. I still think the best near-term use
for hydrogen is attaching it to carbons, ideally non-fossil.
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| Wallace Brand 11.14.04 |
Excellent paper, however the author
overlooked one very promising possibility for distributed generation of
hydrogen along with distributed generation of electric energy:
Distributed Generation of Hydrogen Using High Temperature Fuel Cells By Fred C. Jahnke, Stephen Torres, Pinakin Patel of FuelCell Energy, Inc. Presented at The National Hydrogen Association’s 15 th Annual U. S. Hydrogen Conference, April 17, 2004 ABSTRACT: FuelCell Energy is investigating a novel high temperature fuel cell system (DFC®-H2) for providing a distributed supply of both hydrogen and power. The DFC-H2 concept offers a practical and cost effective solution to facilitate a hydrogen infrastructure. The DFC-H2 concept is based on FCE's Direct Fuel Cell (DFC®) technology and modifies the standard DFC unit for on-site production of hydrogen as well as electricity using high temperature carbonate fuel cells. This configuration offers attractive efficiencies and better economics for both power and hydrogen. in full: www.fce.com/downloads/distrib_gen_hydro_2004.pdf
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| Graham Cowan 11.14.04 |
Consider the situation a non-experimental
hydrogen motorist, if there were one, would face. He'd pay at least the
same price as a welding shop:
Introduction. For the past half century, most cities of population over 100,000 in industrialized nations have had dozens of industrial and research users regularly purchasing pressurized hydrogen gas in heavy steel cylinders containing about 0.5 kg H2 per cylinder. The price of this hydrogen has been reasonably stable at about $100/kg plus cylinder rental...
That is to say, he'd pay about a dollar per kg, plus $99 shipping and handling. He might not have to rent the supplier's cylinder, since his car would have its own, very special internal one, costing "$20,000 to $50,000" according to http://www.freep.com/money/autonews/hstore6_20030306.htm. Such tanks can hold typically 2 kg of hydrogen, so their amortization over 1,000 loads would be a significant extra cost per kg, if anyone were ever going to refill one a thousand times.
Arnold would like someone to investigate recovering the pressure-volume energy in very high-pressure motor fuel hydrogen. This might sensibly be done in the same cylinder the hydrogen was being burned in, except very high-pressure hydrogen lines would then have to extend to that cylinder, and as many others as there might be. Multiplying and lengthening 10-kpsi plumbing seems undesirable.
But if the hydrogen were liquid at moderate pressure, extending liquid-hydrogen lines to each combustion chamber doesn't seem quite as silly. At startup they'd be gaseous-hydrogen lines, of course, but I guess they'd soon cool down.
Arnold notes power losses specific to internal combustion engines that are sidestepped if fuel cells and electric motors are used instead. However, this is misleading unless fuel-cell-specific losses that this change introduces are also noted: ionic and electronic resistance, incomplete hydrogen oxidation at the anodes, much increased gas pumping losses.
No-one interested in hydrogen energy should forget the recent GM Zafira exercise where futuristic fuel-cell efficiency was demonstrated by having the vehicle run out of hydrogen several km short of its planned 190-km trip leg, and the liquid hydrogen tanker come back to meet it.
--- Graham Cowan, former hydrogen fan
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| Roger Arnold 11.14.04 |
To Len's comment, the reason I didn't talk
about liquid hydrogen is that I was trying to keep the article short, and
I didn't feel I had anything very insightful to say about it. It would be
a costly solution, both in terms of the "energy tax" one pays
for cryogenic liquifaction, and in terms of the cost of cryongenic dewars
suitable for use in autos. The latter might conceivably yield to
technology and mass production, but it's hard to see any way around the
former. The energy advantage that hydrogen theoretically has over other
synthetic fuels isn't so overwhelming that one can swallow big
inefficiencies and have it still come out ahead. If cryogenic
liquification is what it takes to achieve adequate storage density for
hydrogen, then I strongly suspect that we'd be better off going with
methanol.
Wallace's comments about DFC-H2 pertain to issues that I cover--albeit briefly--in Part 2. The issues surrounding different classes of fuel cells are complex, and I'm not an expert on the subject. To me, the question of what type of fuel cell is best for stationary power generation is still very much open. Graham has some interesting arguments in favor of boron as an energy carrier for transportation. It would help his credibility if he would stop refering to bottled hydrogen from welding supply houses as an appropriate measure of the cost of hydrogen, if hydrogen were to be widely employed as a transportation fuel. Obviously, those working on h2-powered vehicles are counting on vastly better economics than that, and they're not total idiots. One can legitimately question whether they'll be able to achieve the levels of improvement needed to make hydrogen practical for transportation--especially when weighed against alternatives like methanol. Or boron, for that matter. But using the cost of welding supply hydrogen as a basis for projection to something so different in scale is insulting.
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| Roger Arnold 11.15.04 |
I just checked out the second link that
Graham gave above. It's to a pretty good article about the challenge that
Quantum Technologies faces in trying to reduce the cost of their high
performance compressed hydrogen tanks from the $20,000 to $50,000 dollars
that their current 5000 PSIG and 10,000 PSIG tanks cost to the $200 and
$500 dollar figures that auto manufacturers want to see. The article talks
about automated production and better methods of winding, but clearly
there will also have to be a hefty reduction in the cost of carbon fibre
itself.
One statement that really surprised me: it said that their current tanks had already passed government tests of "being thrown into a bonfire, subjected to extreme cold, and pierced by a gunshot." I'd like to see some details about that last point. I can imagine that one of these tanks might stand up to small arms fire without being pierced. But if it was fully pressurized with hydrogen, I can't imagine the results of actually piercing the tank being anything less than a disaster.
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| James Hopf 11.15.04 |
This article was very informative
concerning many of the lesser known details and challenges associated with
the H2 economy. Also, I wholeheartedly agree with everything that was said
in the "alternatives" section, especially the 2nd to last
paragraph. I'm also glad that the Mr. Arnold considered the
merits/arguments in favor of the plug-in hybrid alternative that were
presented in the Gal Luft article (and perhaps, the follow-on commentary
:-) ).
At the moment I must say that I am extremely skeptical of H2 as a transport fuel right now. I believe that an evolutionary path from hybrid car, to plug-in hybrid car, to (finally) pure electric car is clearly the better approach. The above article discusses many of the issues (and costs and energy losses) associated with getting the H2 into and out of fuel tank storage, as well as compressing and shipping the H2 around. Even before these issues/losses are considered, the H2 approach seems rather dicey. In addition to the enormous costs associated with creating and entirely new, gaseous fuel infrastructure (as opposed to just using our existing liquid fuel and power grid infrastructures) the H2 economy is extremely energy inefficient, and would require at least twice as much primary energy input (i.e., coal, nuclear, or renewable capacity and associated fuel consumption) to power the transport sector, versus the plug-in hybrid or pure electric car alternative. These arguments are presented in greater detail in my comments on the Gal Luft article, at: http://www.energypulse.net/centers/article/article_display.cfm?a_id=790 The article pointed out that, in a purely non-fossil scenario, using pure H2 was cheaper and more efficient that creating any type of liquid (recycled hydrocarbon) fuel. My reaction to that (before reading the last section) was to say "well yeah, if you insist on an absolute, 100% non-fossil scenario, but why is that necessary?". That would be a case of the quest for perfection getting in the way of the vastly less expensive, "good enough" solution. As this article (and Gal Luft's article) points out, plug-in hybrids could reduce fuel consumption by 85% (corresponding to an equivalent MPG of ~200). Such a car would use electric power for most of its mileage, with this electric portion having at least double the well-to-wheel efficiency of the H2 approach. For the (rarely used) engine fuel, such a car could use gasoline, diesel, or domestic biodiesel, alcohol or some other synfuel. It would use our existing liquid fuel and electric power infrastructures. The refueling process (for the driver) would not change, except for remembering to plug it in at night. My educated guess is that such a car would also have ~1% the air pollutant emissions, compared to average car on the road today. With respect to fuel use (i.e., energy dependence), CO2 emissions, and air pollution, this plug-in solution is clearly good enough, and can be had at a tiny fraction of the cost of the H2 approach, and with none of the huge infrastructure investments or changes in driving/refueling habits. With such a dramatic reduction in oil consumption, we will have several decades, possibly a century, before we would truly run out of petrol. By then, I believe that we will be ready to move to pure electric cars, or at a minimum, be able to produce liquid biofuels that can handle that remaining 15% of energy demand. Even in the unlikely event that we have to use a non-biomass, non-fossil means to produce our transport fuel, the "more expensive, less energy efficient" liquid fuels that the Mr. Arnold mentions may still be a better option than H2, since they would avoid the massive infrastructure investments/changes that the H2 approach would require. This is especially true given that the (plug-in hybrid) system is already using the (far superior) direct electric power transmission approach for most of its mileage, and we're only talking about a higher cost for the small amounts of fuel that are used. Making the huge H2 infrastructure investment only to cover this small portion of the overall energy demand is probably not worth it. The final consideration is that it is probably not worth it since we will be moving to pure electric in the not-so-distant future. For the time being, using these "more expensive" liquid fuels will be worth it. That way, we can get away with avoiding a massive infrastrucutre development/retooling altogether.
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| Akihiko Inoue 11.15.04 |
I agree with you about the future
importance of hydrogen fuel instead of gasoline. However, I understand
that hydrogen as energy carrier will be produced by electrolysis of water
using nuclear energy. Other means for producing hydrogen must emit carbon
dioxide. So they are meaningless from the viewpoint of global warming.
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| Roger Arnold 11.15.04 |
Akihiko, I agree that we should be doing
as much as we can to reduce carbon dioxide emissions. But note that if we
use nuclear power to produce hydrogen, then it's more efficient to use the
thermo chemical method rather than electrolysis.
It's true that it would require using a newer generation of reactor, so it can't be done within the next several years. But neither can nuclear power from current generations reactors be used to produce hydrogen, given that current nuclear capacity is 100% utilized for commercial power. Any that was diverted to produce hydrogen would just have to be replaced by electricity generated by some other means--most likely gas or coal. But in that case, you'd have generated less CO2 if you had used the gas or coal to produce hydrogen chemically. One thing I didn't mention in the article is that chemical production of hydrogen from hydrocarbons (e.g., coal) can produce a nearly pure CO2 waste stream. That makes it more economical to capture and sequester the CO2, if and when countries get serious about reducing CO2 emissions. Also, don't discount the ability of wind and solar energy to produce hydrogen with no CO2 emissions. The cost of doing so is almost entirely due to the cost of capital. If central banks were willing to fund wind and solar power developments at the interest rates at which they're willing to fund loans to banks, then wind and solar power would be cheaper than power from gas and coal. It would be cheap enough to produce hydrogen--or methanol--as cheaply as it is produced from natural gas. Finally, note that there's one way to produce hydrogen whose CO2 emissions are effectively negative. That's by steam reforming of the volatile fractions given off during low temperature pyrolysis of biomass. There's some CO2 produced by the reforming step, but the amount of carbon emitted is less than the carbon that remains in the pyrolysis char residue. When that char is used as a soil builder, the carbon in it remains sequestered more or less permanently. It isn't digested by soil bacteria, but provides "habitat" for them and helps to retain nitrogen and other soluble fertilizers in the soil. The reforming step can also be controlled to produce methanol, rather than hydrogen, with no CO2 emitted at all.
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| Len Gould 11.16.04 |
Roger: Dead right in your point re: cost
of capital being the only thing stalling the switch to a sustainable
energy infrastructure. We are fine with providing free money to
profit-making lending instutions and not calling it a subsidy, but just
try and bypass them, then suddenly "free market" raises it's
head.
|
| Dan Casale 11.16.04 |
Do you plan to address metal-hydrid's in a
future article. Although very heavy, metal-hydrides can store hydrogen at
near liquid hydrogen densities with pressures less than 200 psig. An
interesting article can be found on the homepower magizine site, in the
downloads section. http://www.homepower.com/magazine/downloads_hydrogen.cfm
entitled: Hydrogen Storage (Make a Hydride Storage System)
|
| louis joannette 11.16.04 |
The best way to get the hydrogen economy
in transportation is the developpement of alternator generator , that
would supply enough energy to a electrolyzer using water as fuel, in
direct injection. This innovation would minimyse risk , no storage of gas
, the engine would burnt at will , increase safety .But there are other
useful virtue and apllication of the hydrogen flame . For instance on our
infrastruture roads,bridge, overpass ect with the hydrogen flame , from
scientist by brazing steel with the flame is much more impervious to rust.
Same with concrecrete this gas flame by glazing concrete rendering it
impervious to acids and other corrosives will greatly extendeng the
concrete useful lifespan.[REF] Offering by Envirotech System division of
Electricar Canada/marine
|
| N L Williams 11.16.04 |
One way to avoid the impact problem of
vulnerable fuel tanks could be to create a tank within a tank. A high
callibur armor piercing would only pierce the first outer shell and not
the inner tank which holds the fuel. In addition a tank within a tank
within a pressurized tank could also provide an easy solution to the
reduction in pressure energy loss by a mechanism which reduces pressure in
increments from the first tank, to the second, to the third. I understand
tanks are quite expensive and creating a tank within a tank within a tank
is undoubtedly costly, however, the tank within a tank feature reaches the
safety issue adequately.
Good article, it provided food for thought.
|
| Dave Christensen 11.16.04 |
There were a couple of comments about plug
in hybrids and using the existing electric infrastructure for recharging.
There are some serious questions that need to be addressed in order to
evaluate that approach. Where does the electricity come from - fossil,
nuke, renewables, or maybe even demand side management programs? Absent
any new renewables, nukes, or DSM programs, it would seem to have to come
from fossil, with the result of increasing CO2 and other emissions, and
drilling and mining. Is the recharging done at a low rate and off peak, so
the existing transmission and distribution system can handle it, or would
people want to recharge at the office and shopping center, during the
middle of the summer peaking loads when the electric system could be
pushing its limits. There is already concern with the reliability of the
grid. A transportation system that depends on the electric system would
increase society's vulnerability to failures in the electric system.
|
| Roger Arnold 11.17.04 |
Dave, one argument that EV and PIHV
advocates make is that the large battery capacity that would be online at
any given time, and whose charging rate and schedule was somewhat
discretionary, could serve as the equivalent of a "spinning
reserve" for stabilizing the grid. It would permit higher penetration
by wind and solar sources, but would also reduce the need for peaking
units and facilitate investment in higher quality baseload units.
To minimize capital cost, lightly used peaking units are normally simple gas combustion turbines. They're less efficient than combustion turbines with steam bottoming cycles, which are used for base load. But utilities are wary of over-building baseload capacity, because power would be wasted during periods when demand was below base load. The biggest obstacle to this type of operation is probably the need for a new command and control infrastructure for the grid and the tens of thousands to millions of vehicle charging units that would be connected at any given time. It would be an interesting problem for which to develop algorithms and modeling tools...
|
| Graham Cowan 11.17.04 |
I have no information about the costs of
an automotive
liquid hydrogen tank, but it should be much cheaper than very
high-pressure carbon-filament ones for ambient-temperature gaseous
hydrogen. It's more complex -- there must be provision to catalytically
oxidize vented hydrogen, in the unlikely event that it isn't used within a
few days, and if it is used quickly, there must be a small
electric heater to prevent the liquid from getting too cold, and its
vapour pressure too low.
But for the same hydrogen load its internal volume is less than half that of a 10,000-psi tank, less than a third that of a 5-kpsi, and it can be made of aluminum and steel, not carbon filament, since the greatest pressure it ever needs to contain is ~200 times less.
Further to Arnold's "disaster" remark: it's interesting to note that the force pushing the two halves of carbon-filament automotive hydrogen tank apart, when it's full, exceeds the weight of all the highway electric vehicles ever made. If you could wedge one under an 18-wheeler and get it to let go at the right moment, that truck could fly. And not just a little. You probably can't throw a rock as far.
My example of welding shops wasn't well chosen; I see the Doty paper doesn't mention them. I meant them to stand for all the users who now-a-days get hydrogen trucked to them, roughly 100,000 tonnes per year of it in liquid form in North America. But when Arnold says wide use of hydrogen as transportation fuel would be "so different in scale" from that of welders that I shouldn't make the comparison, he is ambiguous. If a day comes when a million hydrogen cars are in real-world service, it will necessarily be preceded by a day when there are 5,000. On that earlier hypothetical day hydrogen could indeed be in widespread use as motor fuel, but the fleet's total demand would be very different in scale from that of margarine makers, etc., by virtue of being smaller.
Arnold wants to ignore liquid hydrogen because of the extra energy it takes to make; the energy premium of insanely compressing it is only about half as much, and this energy, he thinks it would be interesting to recover, perhaps even with an engine separate from the main oxidation-powered one. But if it's good to put 1.2 time the energy in, and devote time and effort to not wasting the 20 percent, wouldn't it be still better, wouldn't that effort be more worthwhile, if the extra energy one was trying to recover was 40 or 50 percent rather than 20 percent? And possibly the whole recovery effort, oxidation and all, is done with one engine?
Plus you get the much smaller tank, of non-exotic materials, with no truck-flinging potential. Hydrogen-car efforts that don't involve liquid hydrogen are not serious.
--- Graham Cowan, former hydrogen fan |
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