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The recent and apparently continuing surge in oil and gas prices has stimulated fresh interest in the hydrogen economy. But the concept is surprisingly controversial. "The hydrogen economy" encapsulates a vision of hydrogen as a superior successor to fossil fuels for serving the world’s energy needs. That vision has attracted both passionate advocates and passionate detractors. Both sometimes overstate their cases. This article attempts to sort out the key issues.
There are actually three different application areas to consider for hydrogen:
As fuel for transportation vehicles and mobile equipment, replacing gasoline and diesel;
As a replacement for natural gas for a range of industrial and home uses;
As an energy storage medium for buffering electrical power.
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:
Reduction in miles driven as drivers adjust to higher gasoline prices;
A swing back to smaller, higher mileage vehicles;
Increasing numbers of high-mileage hybrid vehicles;
Emergence of “plug-in hybrids” with external battery charging provisions;
Expansion of fuel production from oil sands, heavy and sour crudes, and coal.
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
For information on purchasing reprints of this article, contact sales. Copyright 2013 CyberTech, Inc.
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
Jack Ellis 11.13.04
Excellent, well written and very informative article that cuts through all the misleading rhetoric. On to part II.
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.
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
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... (http://www.dotynmr.com/PDF/Doty_H2Price.pdf)
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.
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.
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.
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:
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.
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.
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.
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.
It had been a while since I had perused Graham's web site on boron as an energy carrier. So I went back and reviewed it again. It's a delightful site. Not the one he references above, which is a shorter technical paper, but the one with pictures and lots of cross links and references. Let's see if I can type in some html here and get clickable link to work. The site is here. And if that doesn't work, the cut and paste is http://www.eagle.ca/~gcowan/boron_blast.html.
Technically, I couldn't find anything wrong with anything I read there. I'll admit that I was reading it pretty quickly. But he writes clearly and seems to know what he's talking about at least as well as I do. (And I *hope* that readers won't take that as an example of "damning with faint praise" ;-) However, my article was about hydrogen, not Boron.
As to the issue of cost for compressed hydrogen, I'll say first that the paper by Dr. Doty is a good one that I hadn't read before. I'm adding it to the page of hydrogen links at my own web site and recommending it to anyone who wants to get really educated about hydrogen issues. But it's not actually all that relevant. All the hydrogen vehicle plans I've seen propose either local hydrogen production right at the refueling station, or centralized production and distribution to refueling stations by pipeline. Which, assertions by hydrogen detractors notwithstanding, is perfectly feasible, presuming investment in the necessary pipeline infrastructure. So that leaves you with the issue of the cost of the on-board fuel tank. That's a formidable issue, as I noted, but it doesn't directly affect the cost of the hydrogen dispensed at the refueling station.
As to the relative merits of liquid hydrogen vs. compressed hydrogen, I think I'd rather save that for another day. A key point, however, is that we're not looking at a two-horse race, where it's one or the other. There are a lot of horses in the race, some of which involve hydrogen and some of which involve "crazy" ideas like a boron-fueled oxygen gas turbine. Looking at the fundamentals--which is all I know how to do--I wouldn't pick either compressed hydrogen or liquid hydrogen as a likely winner. But they have to be taken seriously, if only because there's so much money apparently being bet on them.
Len Gould 11.17.04
After as close a study of Graham Cowan's articles as I'm capable of, I've decided (actually quite a while ago) that boron IS a much smarter energy carrier than hydrogen. There then remain three substantial hurdles, being 1- development of the turbine engine, 2- oxygen separation technology and 3- boria to boron process development. I have the impression that if, as Roger points out, hydrogen didn't have all the hype, the smart money would be working on these three obviously easily surmountable issues and we'd soon have on our hands a permanent transportation fuel solution.
BTW, i love the "truck-flinging" imagery. It could become a stadium event similar to monster trucks. One more reason though, I suppose.
Murray Duffin 11.18.04
Roger - The bit about high velocity bullets (and truck flinging) is the kind of thing that is an "oh yeah" on cursory reading, but nags at the back of the mind and seems like a big red herring on due reflection. Before commenting let me say that I am not a mechanical engineer, and really disliked strength of materials lab. First, why would anyone use a high velocity bullet, how often might it happen when you were in the car and the car was sitting still, and if the purpose is to kill you why not shoot at you instead of the Tank? If the car was moving you have to add the improbability of hitting the tank. In a lightweight car, the tank is likely to be fitted to a longtitudinal channel in the body shell, which means the bullet would have to penetrate three layers of car and not get deflected before getting to the tank. Then the tank is not brittle. It has a tough polymer liner that will tear under enough force, but will not fragment, The carbon fiber wrapping has very high tensile strength, much higher than lateral shear strength. The bullet might penetrate, but would likely only make a hole through which the compressed hydrogen would escape at high velocity. Of course if it escaped into the car's interior it could blow out a window. Locally weakening the total tensile integrity might cause the tank to rupture, but that would probably be a continuous deformation process not an explosive process. No one worries about someone using tracers or incendiary bullets on a conventional gas tank, which must be at least as probable. My conclusion - that dog just won't hunt. Changing the subject, I think Doty has a lot of weak thinking, presented quite authoritatively. You hit one of the main points, but he also ignores all of the rapid progress being made, exaggerates the inefficiencies, takes no account of drivers like China, and presents a time frame as an implied barrier when it is probably a practical reality. Boron may be a great alternative, but given the vast amount of research happening worldwide, I would expect it to be receiving attention if it really has prospects at least 1/2 as good as hydrogen. That doesn't appear to be happening. Murray
Murray Duffin 11.18.04
One more point. The key is to build hypercars, which will require less R&D and cost reduction than bringing down the tank cost. With a lightweight, low rolling resistance car, you only need 5000 psi, so its more productive and safer to focus on that solution than a heavy car with a 10,000 psi tank. Also I don't understand the tank cost being expressed in $/kg. If a 1kg tank costs $5000. than a 3 KG tank should cost no more than $3100/kg. A 30:1 cost reduction would than be satisfactory, and is probably achievable. Murray
Len Gould 11.18.04
Murray: I don't think I buy it. If we could get drivers to accept cars with 1/3 or less energy capacity onboard, implying 3x or more performance-to-weight, we'd be almost as well off to stick with fossil petroleum. The premise of the hydrogen economy is underpinned by "present performance, present luxury". At that point, go boron.
Also, the present hydrogen "mania" is little different than Tullip bulbs in 1800's, or Internet startups in the 1990's. Many obvious technical hurdles, some like the cost of platinum catalysts and life of membranes being so far from apparent solution as to be possibly insurmountable. I see none of the challenges to the boron cycle being anywhere near as difficult to resolve. But then, a million stock market investors can't be wrong, can they?
Roger Arnold 11.18.04
Murray, the safety issue with the high pressure tank isn't so much somebody firing an armor-piercing round at your hydrogen tank in order to do you in. I agree that's pretty unlikely. The issue is car bombs. Any car with a high pressure hydrogen tank would be a potent car bomb able to be detonated at any time by a properly placed armor-piercing bullet. The idea of a half-inch hole punched into a pressurized tank may not seem that catastrophic, but that's because our intuition doesn't equip us to comprehend the effects of hydrogen gas at 10,000 PSI suddenly finding an escape route. To hydrogen, the air surrounding the tank looks like a slowly yielding solid that the hydrogen gradually pushes away. That slow yielding is called a shock wave.
I agree that Doty writes with an agenda. He cherry-picked optimistic forecasts of hydrogen and fuel cell development in order to show how far they've fallen short. Granted, he didn't have to look all that hard to find unrealistic forecasts, but it's still a cheap trick.
I don't really know whether boron is a practical energy carrier. The closed cycle oxygen gas turbine that Graham describes has some severe technical challenges. Some of them he cites, and some he passes over. There's the little matter of the low temperature heat sink and the recompressor, and how to keep them from becoming fouled with borite glass. But it's an intriguing concept.
James Hopf 11.18.04
Dave Christensen wrote (concerning plug-ins):
DC: "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."
With the H2 approach, where does the hydrogen come from? Neither electricity nor H2 are energy sources; they are only carriers. In both cases, the original energy will have to come from renewables, nuclear, or fossil fuels. The point is the comparison of efficiencies and costs between the two energy carrier approaches. In addition to a much higher infrastructure and equipment investment (or cost), the H2 approach is only about half as efficient ("well-to-wheel") as the electric car approach. Thus, if we go with the H2 economy, we will need about TWICE as much renewable, nuclear, or fossil energy generation to power the whole thing. If fossil fuels are mostly used as the primary energy source, the H2 appraoch would involve roughly double the CO2 emissions. In either approach, however, the CO2 emissions (and air pollution) will be MUCH lower than those of our current, oil-powered cars.
DC: "Is the recharging done at a low rate and off peak, so the existing transmission and distribution system can handle it....?"
Ideally, it's done at night, during times of off peak demand, and minimum load on both the generation and transmission infrastructures. This is also when most people would find it most convenient. Even if they plug in right when they get home, a timer that starts the charging late at night will not be difficult to arrange. It is also likely that a deal would be offered to plug-in car owners, giving them a lower power price if they charge at off-peak times (i.e., a smart metering system). People who insist on charging at peak times will be charged accordingly. No difference between this and any other form of power demand. This new off-peak power application will smooth out the load curve and allow us to get more of our power from baseload units, which are better able to run on domestic sources (e.g., clean coal or nuclear, vs. imported gas). It will also allow us to largely avoid having to build more grid capacity.
DC: "A transportation system that depends on the electric system would increase society's vulnerability to failures in the electric system."
If electricicty is not available, a plug-in hybrid can just run on gasoline (or some other liquid fuel), whether the issue is a power outage, or just a long trip that exceeds the battery range. That's the beauty of the flexible, plug-in hybrid approach.
The ONE thing that the H2 approach has going for it is that it is easier to store H2 than it is to store electricicty. This may allow intermittant sources like wind to play a much larger role in the transport sector than they otherwise would have. But does this one issue justify the enormous costs? This leads me to what is perhaps my final take on the issue. If you're going to use wind to make the H2, go for it. But if you're going to use clean coal or nuclear, then don't. Use those sources to generate electricicty for plug-in (and eventually pure) electric cars instead.
Murray Duffin 11.19.04
Roger - you are right. My intuition does not grasp this shockwave. I visualize a high velocity jet of hydrogen gas escaping very directionally and initially transmitting energy (a directional shockwave?) to the "slowly yeilding solid" air around it, which would rapidly absorb and attenuate the energy from the hydrogen. The shockwave is unlikely to be harmful to anything not in it's direct path, and the first thing in its path will be some wall of the car, which is also made of high tensile strength fibre composite in the case of the lightweight car. I just don't envision a "car bomb". Is there somewhere that I can get a technical analysis or description that would enlarge my vision?
Len - spend 3 or 4 hours researching the R&D and progress in the various aspects of Hydrogen, and it does not read like mania. Very serious people are making very real progress at an astonishing pace. Murray
Graham Cowan 11.19.04
Does anyone know what the, or a, SEED rally was? Because the world's first liquid-hydrogen car was in it, in or shortly after 1975, and the membrane and catalyst problems Gould mentions didn't prevent it from going 2,800 km. (Would that have been a rally in competion with regular cars? Try to imagine one of today's hydrogen fuel cell prototypes doing that.)
Graham, the car ran on liquid hydrogen, but did not use a fuel cell. It had an internal combustion engine. I think you'll find that to be true for any hydrogen fueled car built more than a few years ago.
Roger Arnold 11.19.04
Oh, sorry. I guess that was your whole point. No membrane problems. :-)
Graham Cowan 11.20.04
That's right, and no catalysis problems. A spark is a wonderful H2/air combustion catalyst. I see I goofed up my angle brackets and some of what I wrote came out black-on-purple. If I may I'll repost that part:
... GM Zafira that recently managed to go 250 km on a tankful, under the restrained foot of a journalist who was trying to avoid a repeat of its earlier fit of pining for the fjords after only 185 km. 250 km is a new frontier for hydrogen fuel cells, but on that timeline you can find a burner, the BMW 520h, that could go farther in the 70s.
Combustion is better.
I don't want to pass over any significant problems with boron power, although it must be admitted that the bigger web page does, referring to a B2O3/sulfur vapour reaction that I now know doesn't go. I'm confident someone more skilled in devising chemical heat engines can fix it; or if that doesn't happen, one can always electrolyse. I thank Roger Arnold for pointing out the possibility that some of the liquid B2O3 may get past the power turbine and gum up parts that aren't spinning fast enough to move it. Gas that is being diverted by a turbine blade is feeling strong acceleration, so I think there's a chance the fraction of the B2O3 that doesn't rain out onto them will be very small. We'll have to see.
Having some experience in design and testing H2 systems, recall that hydrogen detonates at <5 % in air, and it burns with no visible flame.
"Any H2 leak" is not acceptable. Earlier demonstrations of H2 fueled (IC) cars revealed a tendency for the car's hood to disappear! Maybe you should ask your wife what she think of this discussion.......
Would you let her refuel a H2 powered car?
Keith Moore
Joel Melito 11.25.04
Keith Moore pinpoints the consequence of the issue I found lacking in both the article and the discussion to date. The problem with hydrogen technology (as with any technology) is not the BIG catastrophe; as described here - the terrorist, lunatic, disgruntled postal worker or whomever armed with a large-bore rifle and capable of placing an armor-piercing bullet through the H2 tank of some unsuspecting citizen's personal vehicle. It works great in Hollywood action films and the nightly network news, but in reality the real problem is the accumulation of many small and individually insignificant faults that lead to major failures and accidents. A more practical scenario would find 10,000 vehicles in afternoon summer commuting gridlock, with each vehicle leaking some amount of hydrogen, a thermal inversion limiting diffusion and dispersal (no wind), and somebody keys their cell phone, then BLAM - roasted expressway. Frankly, you don't need high-powered rifle bullets with armor-piercing ammo either, just a rock or piece of roadside debris thrown by a truck, or maybe a piece of roadbed reinforcing steel that suddenly breaks free and springs up in the path of your fuel tank. These are real things that can happen and have happened.
The other part of this conversation that bothers me is the missed opportunity to challenge the context that causes the "thirst for petroleum" problem. Roger Arnold lists three of five bullets including reducing commuter mileage, smaller-lighter vehicles and more hybrids, but then dismisses by stating "their potential for reducing oil consumption is limited." Since when, Roger? Step back and take a look at a larger picture, The only reason there is even a serious discussion of hydrogen-fueled vehicles as a repalcement for gasoline-fueled vehicles is because these vehicles have been elevated to the level of the sacred. In almost every community where I I have lived over the last 40 years, the constant complaint of ordinary citizens is that they have become enslaved to using their cars for even the most basic items necessary for life. "Planning" a community development has long been a bad joke played on private citizens by developers; it really means setting up residential communities so that cars should be sold with houses for all practical purposes. The government has been (local, state and federal) up to their ears in promoting this by so many means they've lost count. Mostly, this is a modern consequence of abandoning cities wholesale in the USA after the end of WW-II. As REAL environmentalists have known all along, suburban sprawl is the greatest problem in almost any context - economic, sociological, environmental/ecological, cultural, criminal, etc. The easiest place to start if you want to end this problem and rewrite the context - get rid of the current income tax system and all of its deductions, especially home mortgage interest deductibility. The idea is not to have everyone return to the big cities. The better answer is to have small cities form as nodes around a central set of facilities - transportation (roads, rail, water, air), energy (or at least main transmission), etc. At the local level, 80 percent or more of the city populace should be able to walk to work, school, and whatever store they need for the basics. Any, today at least if not in the past, the rest is available from "ebay."
Then there is one final issue with hydrogen, and all other alternatives. Why design vehicles that must carry their engine and fuel aorund no matter where they go. I think the work by GM on a form of modular vehicle platform confirms that this is a presumption and not a fact. Must the hydrogen used for hydrogen "powered" vehicles be on board? What if it were not, and along with the fuel cell generating electricity, were a part of the "road" you ride over? Instead of overloading the existing electrical transmission system, or traveling with millions of other unexploded hydrogen bombs, should we answer the demand of the public to hide unsightly electrical gear and embed the transmission system with the highway system (and in what form)?
Frankly, my biggest beef with the hydrogen-car as with any government program is: For what purpose are my tax dollars (and yours) really being spent? Is the hydrogen car just a concept hoping for a real market (like fusion power). I would rather see some honesty - apply tolls to pay for all of the roads and drop the gasoline taxes. Set the tolls for passenger-miles efficiency if that is your real objective - a five passenger Buick getting 26mpg beats a two passenger Chevy Metro getting 60mpg, if it did. And forget speed limits and state troopers patrolling the highways - set the tolls based on highway design speed, the traffic density, and weather, so that you can drive your Porsche at 160mph cross state and pay that $752 toll when you arrive at your destination (next time we'll just pre-bill you as a high-risk driver, o
Graham Cowan 11.26.04
Engines in the road? If you add up the length of, say, the cars in North America -- I guess 300 million of them, average length six metres -- you should get a total length for an all-North-America nose-to-tail motorcade of 1.8 million km. Isn't the total length of the North American road network greater than that? Powering the cars rather than the roads is a sensible choice given limited hardware budgets, I think. Also I'm somewhat disappointed that Melito doesn't seem to understand my forget-hydrogen proposal would definitely solve the issues both of pressure tank explosive rupture and subsequent fuel-air explosion.
Joel Melito: Your post is filled with eroneous assumptions and wishfull thinking. a- Mortgage payments are not deductible in Canada, yet the residential development pattern is identical. b- High pressure H2 storage does not release anything flamable to the atmosphere. You may be thinking of liquid H2, but even that is minimal and only when not running. And no atmoshperic condition will stop free H2 from zooming straight up fast. c- People walking to work in small communities presumes a lot about freedom of choice in the workplace. State planning? d- As Graham points out, powered roads may be feasible on the high-traffic routes, but what if you want to go view the fall leaf colours? Would the available power be sized to start large semi-trailers on an up hill in stop-and-go, or are trucks to continue using huge amounts of fossil?
Support the boron cycle, its smarter, safer, cheaper and will be available sooner than widespread H2 powered vehicles.
Roger Arnold 11.28.04
Keith: I've read what seemed to me credible sources that stated that despite the low concentration at which hydrogen is *combustable* in air, there is very little danger of explosions from leaking hydrogen. I don't *think* it was simply that hydrogen is so light and diffuses so fast that it's difficult to build up even a 5% concentration from a leak. I seem to recall that it was something more fundamental having to do with conditions needed to support detonation, vs. burning. If any reader knows more about that, I'd appreciate hearing it.
In any case, Joel's concern about many small leaks from individual vehicles resulting in a sufficient buildup of hydrogen in the air above a freeway to lead to an explosion is completely non-credible. It doesn't matter how freakishly calm it might get under an inversion layer; the volume of air vs. the volume of hydrogen is just way too large to allow that.
To me, the principle safety issues--for pressurized hydrogen--remain refueling accidents and the relative ease with which a high pressure hydrogen tank could be transformed into a potent bomb. A terrorist wouldn't need to pack a car with C4; they wouldn't even need a high calibre weapon firing an armor-piercing round. All they'd need is a small shaped charge applied to the outside of a full hydrogen tank.
I'll be the first to agree that terrorist threats, in general, have been way overblown and are tragically distorting our domestic and foreign policies. In terms of risk factors, there are a thousand daily hazards more likely to do you in than being the victim of a terrorist attack. But that doesn't mean the threat should be completely ignored. It's just not good policy to make the explosive equivalent of a case of dynamite available to any nut who might rent a car. Not when there are safer alternatives.
Joel: When I said that the moving to higher mileage cars and reducing miles traveled had a "limited potential" to reduce our consumption of oil, I was thinking in terms of what happened the last time oil prices shot up, in the Carter years. There *was* a small reduction in miles traveled--that's when carpool lanes were created--and a short-lived shift to smaller and more fuel-efficient vehicles. But it didn't make a lot of difference. The shift to higher mileage cars took six years before it had gotten far enough to be noticeable, and it stalled out after oil prices collapsed. I don't think we're going to be seeing a comparable collapse of oil prices this time, but I do think that before we see major reductions in miles traveled or major improvements in mileage of conventional cars, we'll see plug-in hybrids coming on strong. They simply have the most potential for reducing net oil consumption with the least investment. I'm not talking about what should happen, only what I think will happen. I personally agree that we'd all be better off with simpler lifestyles, working and shopping close to where we lived. But as Len suggests, you won't see a lot of people rushing to embrace that choice if it's not forced on them by hard economics or coercive state planning.
Graham Cowan 11.29.04
In a world where any significant number of people wanted hydrogen for their own personal rides, hydrogen would never blow up a whole freeway; as Roger Arnold says, there is too much air. Although that world would have to be very different from this one, perhaps enough so that the closest thing to air there is liquid squidge. Anyway if something like that were ever possible it would be so where cars crowd together at high power while moving slowly, i.e. at a traffic light that has just turned green.
But Arnold should look up "deflagration-to-detonation". My impression was that hydrogen is rather good at this transition, i.e., while 2.5 grams of propane blowing up in your face can singe your eyebrows, a gram of hydrogen doing the same can break your little toe. Same energy, different result.
If any prototype hydrogen car's hood has disappeared, although as yet no reason for accepting this as fact has been presented, the brisance of hydrogen-air explosions occurring under it might be the explanation.
In addition to doing the adiabatic expansion work that Arnold and I have respectively described as case-of-dynamite-equivalent, and able to fling a truck, kilograms of hydrogen escaping suddenly from a very high-pressure tank tend to ignite promptly, and even so, still progress to detonation. So when a car's worth of hydrogen at only 600 psi escaped near these two unfortunate men, the coroner found "Multiple injuries to lungs and other areas of both bodies... Due to explosion of hydrogen cloud that caused shock wave injuries".
I'll tell you what I know about "ignitable" hydrogen concentrations.
I've worked briefly on a situation where hydrogen generation was an issue, and we had to show complaiance with safety regulations related to hydrogen ignition. The regulations state that in any closed area/volume where there may be a source of hydrogen (due to H2 generation or perhaps a potential leak), it had to be shown by analysis that the concentration of H2 in air would never exceed 4% (or was it 5%?). This was referred to as the "ignitable" threshold. There is a good chance that these regulations are conservative, but the idea is that ignition is not possible at lower concentrations, and thus safety is assured.
Once again, the regulations are probably conservative, and the 4-5% limit may be based on some hypothetical optimum conditions under which ignition at those concentrations is possible. Under other, perhaps more common conditions, a higher concentration may be required. Perhaps under some conditions, and at some concentrations, burning as opposed to detonation (an explosion) may occur, as you suggested above. Nothing is possible under 4-5%. All that said, however, my guess is that most of what makes an H2 leak relatively safe is the bouyancy and dispersion you mentioned above (although it may not be the entire reason).
Len Gould 11.30.04
James: Agreed. There seems to be a lot of confusion between flamability/ignition concentrations (quite a wide band around 5% to 75%) and explosive concentrations (significantly narrower).
Graham: I think the "hood disappearing" thing you refer to is the early experiments on trying to burn H2 in Otto IC engines using the CNG carberator systems. The intake valves are not fast enough to reliably isolate the manifold from the combustion chambers at all speeds and power settings, resulting in some spectacular explosions, and several professors swearing never again. Only reliable solution is serious de-rating of the engine (eg. Ford and BMW), or direct injection. At one time i'd designed a modified spark plug with an attached H2 injection valve for direct H2 injection alternate fueling (either H2 or gasoline) as a retrofit but decided the auto safety bureaucracies and mfgr warranty issues would never allow it to make a profit. Too bad, it was a cheap re-fit. Still have the patent application around here somewhere.
Roger Arnold 12.12.04
Well, this is embarassing. I wrote this article to help sort out fact from myth, and now it seems I'm guilty of spreading a myth myself, regarding the safety (or non-safety) of high pressure hydrogen tanks.
Here's what I now know to be a fact: AT LEAST ONE FULLY FILLED 5000 PSI CARBON FIBRE COMPOSITE HYDROGEN TANK HAS UNDERGONE TESTS WHERE IT WAS PENETRATED BY ARMOR-PIERCING BULLETS. IT VENTED RAPIDLY, IN A MATTER OF SECONDS, BUT THERE WAS NO BIG EXPLOSION.
The tank remained intact, and stayed strapped to its pallet on the test stand. Craig Webster, director of Gas Systems Engineering at Powertech Labs, was kind enough to send me a video clip of the test. Powertech is a respected independent testing lab, not affiliated with the maker of the tank, so I have no reason to doubt Mr. Webster's statements to me or the authenticity of the video.
I'll try to write more about the physics of what goes on when a bullet penetrates one of these tanks. As soon as I can figure it out.
Len Gould 12.13.04
Roger: Crazy canuks at it again huh? Go figure.
From the picture i saw of the tank penetrated by the sniper bullet, it doesn't immediatly obviate the issue Graham raised, eg. what happens to the vehicle if the total energy of compression is quickly released as a jet in a downward direction. Calculations indicate such an event (with no chemical explosion at all) should release enough energy to "fling" a vehicle a good distance. The test they show had the test tank quite securely strapped to a very well anchored bunker.
