Hydrogen car

From Silent Revolution

Topic: Hydrogen cars are unlikely to become widespread.

In our drive to free ourself from our dependency on fossil fuels, a number of concepts have been proposed for alternate propulsion systems -- namely, the electric car, the compressed air car, and the hydrogen car. The compressed air and the hydrogen car, however, have fallen far enough behind the electric car that it seems to be a dead-end technology. In the case of the hydrogen car, even some of its biggest initial backers have been bailing on it.[4][5]

[edit] Efficiency

Energy efficiencies of different propulsion methods gathered in "Well to wheel study of passenger vehicles in the Norwegian energy system"[1]. Note the unimpressive performance of hydrogen cars (PEMFC and ICE H2) running on ordinary power, in comparison to gasoline and diesel cars, and the excellent performance of electrics.

CO2 and NOx emissions from different propulsion methods, gathered in "Well to wheel study of passenger vehicles in the Norwegian energy system"[2]. Again, note the unimpressive performance of hydrogen cars (PEMFC and ICE H2) running on ordinary power, in comparison to gasoline and diesel cars, and the excellent performance of electrics.

Energy losses in a gasoline vehicle, for comparison[3].

In this section, we will look at the efficiency and environmental consequences of producing hydrogen in different methods -- in order, electrolysis/thermolysis from thermal power, from other sources of power, from natural gas reformation, from bacteria, and from direct solar-to-hydrogen production methods. These are then contrasted with gasoline and electric vehicles.

In terms of environmental impact, especially given an infrastructure of polluting power plants, efficient use of energy is critical to reduce pollution. By this measure, hydrogen vehicles don't even outperform gasoline vehicles, let alone electrics. First, let's look at the chain of how energy is burned in a typical thermal plant and winds up driving the wheels of a hydrogen car, in comparison to an electric. Thermal plants include everything from coal to natural gas to burning biomass to solar thermal, and comprise about 75% of our electricity generation. A heat-based power system also lets us directly compare efficiency with gasoline.

Generation from heat: Modern thermal power plants, including ever-common coal, but also nuclear and solar thermal, today get 40-50% efficiency at producing AC energy, with the more efficient ones tending to be newer plants. 60% is possible. Common older plants get 30%-40%. We'll use 45% as our efficiency number to be representative of the upcoming power grid. Note that efficiency in this context isn't what percent of the fuel is burned (usually near 100%), but what amount of that energy can be recovered and turned into AC.[6][7][8][9]

Transmission: One would assume that hydrogen is generated reasonably near the power plant. Since the average transmission loss in the US is about 7.2% (including transformers)[10], we'll give electric vehicles a 92.8% efficiency number for transmission and hydrogen vehicles a 99% efficiency number.

AC/DC conversion: Electrolysis only runs on DC. The batteries in electric cars need DC. 94% seems a reasonable number for this process with widespread adoption (it can get as high as 96%[11]).

Electrolysis of water into hydrogen and oxygen: Most hydrogen today is made by methane reformation, but the goal is to transfer the load to grid power to eliminate our dependency on more limited fuel supplies and reduce costs, as well as to make it easier to transition to renewable energy. When your source is electricity, you produce hydrogen through electrolysis of water, usually with 50-60% efficiency[12]. The most efficient systems are large ones in which electrolysis is done on hot, high pressure steam (as opposed to the inefficient garage-scale kits that work on liquid water). 85% is about as good as it gets nowadays, so even though these have low output, we'll go with that in order to favor hydrogen.[13]. One company, QuantumSphere, has announced nanoparticles that will allow home kits to reach 85%, and the company thinks it may be possible, in the future, to reach as high as 96%; as of yet, this is unproven.[14]

Note that instead of Generation/Transmission/Electrolysis, an alternative is thermolysis -- direct splitting of water with heat. However, A) this takes very high temperature steam, which is typically only available in a few types of power plants (such as next-generation nuclear), and B) it's not significantly more energy efficient than combining the three above steps. Another alternative is reforming of fossil fuels, which is obviously undesirable. The most common currently is steam reforming of natural gas, due to economics. Perhaps the most environmentally friendly is the Plasmatron, which doesn't oxidize the carbon, leaving it free for cheap sequestration or other uses. Unfortunately, it uses 20% of the fuel's energy in electricity (they're hoping to reduce it to 5%), and given power plant efficiencies (above), it's not really an improvement in system efficiency [15].

Storage and Transportation: Hydrogen needs to be stored (compressed) and transported as necessary to filling stations. Let's be nice and say that only 10% of the energy is lost in all of these stages -- 90% efficiency (90% is normally what's needed for one stage of compression/storage alone[16]).

Getting hydrogen in and out of the vehicle: In a hydrogen vehicle without a storage medium, just a pressure tank, losses from fuelling are generally low -- 5% or so. If the vehicle stores the hydrogen in a storage medium, energy losses from either getting the hydrogen in or getting it out can be significant. We'll assume that it merely uses compressed storage and go with 95% efficiency

Storing electricity in batteries: Only applies to electric cars. Modern lithium ion batteries are extremely efficient at storing and discharging electricity, at about 99.9% each way.[17]

Fuel cell: Fuel cell stack efficiencies typically range from 40-60% (individual cells can be higher if run at very low loads and with bottled (pre-compressed) oxygen, but that's not a realistic proposition). Let's be incredibly nice and use 65% efficiency.[18]

Electric motor: A brushless DC electric motor can run at over 90% efficient, although 85% or so efficiency is more common. AC motors can get 95% efficient. This is efficiency in optimal driving conditions. Let's say 80% average efficiency.

Now we need to put it all together.

Hydrogen: 0.45 * 0.99 * 0.94 * 0.85 * 0.9 * 0.95 * 0.65 * 0.8 = 16% Electric: 0.45 * 0.928 * 0.94 * 0.99 * 0.99 * 0.8 = 31%

To compare with a gasoline vehicle, you have 30-35% combustion efficiency but a lot of miscellaneous losses, leading to an overall system efficiency (well to wheel) of 15-20%.[19][20] (Note: Do not confuse combustion efficiency with how completely the fuel is burned. Almost all of the fuel is burned, but due to Carnot's law, only a fraction of the energy released from that combustion can be turned into mechanical energy[21],and engines only turn a fraction of their theoretical maximum power into wheel torque) While these comparisons don't account for the (relatively small, except on synfuels) cost to produce, transport, and refine gasoline, they also don't count for the 10-20%[22][23] loss of hydrogen during production and transport.

Note that the combined fuel cell efficiency and electric motor efficiency given our hydrogen-friendly numbers are 0.52. Reality currently isn't generally that kind. Currently, 45% is more common, and only at low loads. When driving a driving cycle like the NEDC, the current numbers are more like 36%[24].

The results are unimpressive for hydrogen, to say the least -- worse than gasoline and half the efficiency of an electric car at best. In terms of the environment, this is a disaster. The only advantage the hydrogen car can claim, in terms of the environment in such a situation, is displacing the pollution to outside of cities -- but that won't be any benefit concerning the CO2 emissions (barring sequestration, which is a very expensive and technically challenging endeavor which doesn't work equally well (if at all) in all locations).

One can tweak the numbers to their will, but most of the process is the same for both vehicles. The real losses for hydrogen vehicles come from the combination of electrolysis and fuel cells, plus higher storage losses. Electrics just don't have these losses. Instead, they have very minimal battery losses.

We can consider some alternative hydrogen generation methods. You can get a little better system efficiency using natural gas reformation to produce hydrogen, but still not nearly the efficiency of an electric; you might as well just burn the natural gas directly. You could use photovoltaic power and cut out the AC/DC stage, but that benefits electrics (and if this is photovoltaic power from your home, you have to cut the efficiency of your electrolysis stage for hydrogen vehicles since small electrolysis setups are less efficient).

Let's not kid ourselves here: environmental effects of a given transportation alternative from a given power source are all about energy efficiency. Every power source, even "clean", "renewable" sources, have consequences. Destruction of natural land landscapes. Waste and emissions from component manufacture. The environmental "carrying load" for the planet of the people involved in building, operating, and maintaining them. The more energy you consume to accomplish a given task, the worse the environmental consequences for doing that task, even when using "clean" power. Of course, most of our power currently is distinctly not green.

Probably the hardest to compare are the proposed "sunlight to hydrogen" methods, such as farming bacteria. You can't really have an apples to oranges comparison with this in terms of efficiency since electrics can't follow the same path. However, you can do an economics comparison, and in general, rarely have things involving farming photosynthetic bacteria proven particularly profitable. Even where industry uses bacteria to produce products, such as drugs, they're typically grown in vats and fed sugar solutions. It's just cheaper that way. Check out what's needed to get below the DOE price target for hydrogen here -- an order of magnitude reduction in reactor price, no pressure swing adjustment unit, a direct pipeline connection with no hydrogen storage anywhere and ambient pressure operation, thin film (i.e., easily destroyed by wind and at serious risk for degradation) coverings, and perfectly optimized bacteria. All of these are, quite simply, ridiculously kind assumptions. Note that, by far, the major factor is capital costs.

A variant on this technology involves solar cells that produce hydrogen instead of electricity. Normal silicon solar cells are about $4.80 a watt, and most of this cost is due to the price of silicon. This produces electricity significantly more expensive than grid power. Yet these cells are about ~20% efficient. The hydrogen solar cells have their own expensive component -- a special glass -- and are only about 8% efficient.[25][26] It should be obvious that without an order of magnitude reduction in prices, this will never be cost effective. To top it all off, the materials must be resistant to corrosion. Oxygenated water on its own is bad enough at causing corrosion, let alone having hydrogen (which embrittles metals and causes all sorts of other probems) as well. And we haven't even mentioned the ever-common problem with any sun-exposed water source -- algae growth. Nor do we discuss where the water is supposed to come from, given that the sunniest places also tend to be the driest, and in the US, the optimal location (the US desert southwest) is already overconsuming its freshwater resources.

Finally, with either of these technologies, the other problems with hydrogen, from embrittlement to low storage density to safety (see below) to vehicle efficiency and so forth still remain.

[edit] Range and Charge Time

The main reason why hydrogen has been pushed over electrics was because of what were considered to be the two deadly weaknesses of electric vehicles: charge time and range. When hydrogen first began to be pushed, most electric vehicle proposals were using nickel metal hydride batteries. These were good, reliable batteries (and are still used today in cars like the Prius), and outperformed lead-acid batteries in terms of energy density, but still weren't nearly good enough. At highway speeds in a NiMH-powered EV1, you could get perhaps 80-150 miles in warm weather conditions, but only half that in cold-weather. After that, it would take hours to recharge. The combination of short range and long charge time were seen as major roadblocks to replacing gasoline vehicles. Despite the complications involved, hydrogen was seen as a solution to these issues; it could fill vehicles quickly and get 150-250 miles range.

From left to right: 1992, 1994, 1998, 2002, 2002, 2004

Unfortunately for hydrogen, electric vehicles have advanced much faster in terms of range than hydrogen vehicles. Electric vehicle designs today typically involve lithium-ion batteries. Much like moving from NiMH batteries to Li-ion batteries helped scale down cell phones from heavy bricks to pocket lightweights, they can provide a far greater energy density to electric vehicles as well. Even lithium-ion itself has advanced over the years; laptop batteries have gotten lighter and longer lasting while delivering more power to the computer, all at the same time.

Lithium ion chemistry is not without its problems, however. LiCoO2 cathode li-ion batteries, as used in laptops, can be subject to runaway heating and thus significant fires and should be cooled for automotive applications. They also have limited lifespans. To deal with these issues, two approaches have been taken. Some EVs, like the Tesla Roadster, are designed for more wealthy consumers who can afford battery replacement. These use laptop batteries in great numbers with significant charge management. Other EVs are turning to more passively safe li-ion chemistries, such as lithium-iron-phosphate. In exchange for a little bit of energy density, these batteries provide a decade or more of service without any serious risk of runaway decomposition. A123 rates their automotive packs for 10+ years and 7000+ charge cycles.

Present-day tech puts the existing (or practically existing) EVs nearly on par with equivalent hydrogen vehicles for range -- 150-200 miles for electrics, and 200-250 for hydrogen. And while Honda's FCX promises 270 miles with a storage medium[27], AC Propulsion's tzero gets 300 miles with lithium ion batteries, and is no bulkier or heavier (but is far better performing). Yet, Honda only gets their range by using a hydrogen storage medium, which lowers hydrogen efficiency still further. And while virtually any improvement in storage medium density is almost guaranteed to decrease system efficiency for a hydrogen vehicle, there is a great deal of improvements in batteries currently in the process of being commercialized.

Charge time seemed destined to remain a problem for electrics until just a few years ago. Already, AltairNano's 5-minute charge lithium ion batteries are on the market. At $2.50/Wh, they're quite expensive currently, but this is considered solely due to limited production. They better ramp up quickly, because they'll be facing their share of competition -- in March of 2008, industry giant Toshiba is expected to start delivering their "SCiB" batteries with similar charge times that could be used in electric vehicles. There's about a dozen different manufacturers of fast charging lithium phosphate batteries. And let's not even get into EEStor's EESU or the Stanford silicon nanowire anode. In fact, it seems like essentially every new lithium ion chemistry that has some out has had the potential for rapid charging.

[edit] Safety

There's generally little to be concerned about in terms of safety with an electric vehicle. Assuming that passively safe li-ion or other batteries are used, the only possible risk it would seem is electrocution. This is essentially eliminated is fuses -- fuses in the vehicle wiring, in the packs, and sometimes to the cells themselves. Furthermore, you're sitting in a giant faraday cage; even if a short didn't go through the battery itself, and even if it didn't go through the battery compartment's casing itself, you're still the path of most resistance for current flow. Likewise, when charging, even fast charging, there's no reason why one wouldn't expect the charger to not allow current to flow until the plug is connected to the vehicle itself, or that they couldn't use an outer sheath that if damaged, stops current flow through the core. Not as though we're not exposed to potentially deadly currents in every outlet in our house as-is with far fewer safety precautions in place.

While it can be a bit difficult to compare electrics with gasoline or hydrogen in practice without a lot of people on the road in both types of vehicles, it is quite easy to compare hydrogen with gasoline. After all, hydrogen vehicles would need to be able to earn acceptance from the drivers of gasoline vehicles to be accepted, so the comparison seems to be called for. For hydrogen safety and handling, let's turn to NASA[28]

The most common methods for storing hydrogen proposed are in low-temperature, high pressure containers; liquid hydrogen; and in storage mediums.

Ignition:

• "Hydrogen-air mixtures can ignite with very low energy input, 1/10th that required igniting a gasoline-air mixture. For reference, an invisible spark or a static spark from a person can cause ignition."
• " Although the autoignition temperature of hydrogen is higher than those for most hydrocarbons, hydrogen's lower ignition energy makes the ignition of hydrogen-air mixtures more likely. The minimum energy for spark ignition at atmospheric pressure is about 0.02 millijoules"

Mixtures:

• "The flammability limits based on the volume percent of hydrogen in air (at 14.7 psia) are 4.0 and 75.0. The flammability limits based on the volume percent of hydrogen in oxygen (at 14.7 psia) are 4.0 and 94.0."
• "Condensed and solidified atmospheric air, or trace air accumulated in manufacturing, contaminates liquid hydrogen, thereby forming an unstable mixture. This mixture may detonate with effects similar to those produced by trinitrotoluene (TNT) and other highly explosive materials"
• "Explosive limits of hydrogen in air are 18.3 to 59 percent by volume"
• "Flames in and around a collection of pipes or structures can create turbulence that causes a deflagration to evolve into a detonation, even in the absence of gross confinement."
• Deflagration limit of gasoline in air: 1.4-7.6%

Leaks:

• "Leakage, diffusion, and buoyancy: These hazards result from the difficulty in containing hydrogen. Hydrogen diffuses extensively, and when a liquid spill or large gas release occurs, a combustible mixture can form over a considerable distance from the spill location."
• "Hydrogen, in both the liquid and gaseous states, is particularly subject to leakage because of its low viscosity and low molecular weight (leakage is inversely proportional to viscosity). Because of its low viscosity alone, the leakage rate of liquid hydrogen is roughly 100 times that of JP-4 fuel, 50 times that of water, and 10 times that of liquid nitrogen."

Hydrogen also has a tendency to collect under roofs and overhangs from even minor leaks. Combined with its tendencies to leak and even to enter other pipes and then follow them to where they let out, plus its ability to ignite from very weak ignition sources, building codes for anywhere that hydrogen will be stored tend to be very stringent (see 6.5.4: Buildings). This would apply to garages (both home garages and public garages), parking shelters, eaves, overhangs, etc.

The only comparison in which gasoline could possibly win in terms of safety is that gasoline can pool given a (much more difficult to achieve) leak, while hydrogen, if somehow not ignited by whatever caused the leak, and if not pooling in the engine or even the cab of the vehicle or in any outside structures, will escape. If there were then a delayed ignition source, hydrogen could win in this (rather improbable) safety comparison.

Contrary to popular myth, and unlike traditional li-ion batteries, automotive li-ions are not fire-prone.[29]

One final safety note: proponents of hydrogen sometimes still cite the bizarre theory proposed by Addison Bain that hydrogen wasn't the cause of the Hindenburg disaster. This theory holds no water.

While gasoline leaks are indeed somewhat poisonous and can contanimate water if allowed to leak into it, any hydrogen leak is essentially guaranteed to do significant ozone damage[30][31]. As covered above, hydrogen leaks two orders of magnitude more readily than gasoline.

[edit] Economics

The economics of electric vehicles is relatively simple. In terms of capital costs, EVs get to lose large, complex internal combustion engines (ICEs) in exchange for small, simple electric motors. On the downside, they lose a light, simple gas tank in exchange for large, heavy batteries. In all but the "laptop battery" EV proposals and the outdated lead-acid "Neighborhood Electric Vehicle" (street legal golf cart) proposals, the batteries involved have lifespans as long as the vehicle, so maintenance is not an issue with the batteries. Given the simplicity of the drivetrain as a whole, the capital costs of the batteries are offset by greatly reduced maintenance (no fan belts, no radiators, no motor oil, and sometimes not even a transmission due to the ability of electric motors to provide high torque at varying RPMs), as well as the extremely cheap price of electricity per mile ($0.02/mi at 200Wh/mi and $0.10/kWh; compare with $0.10/mi for a 30mpg gasoline vehicle at $3.00/gal)

With hydrogen, the case isn't that simple. Hydrogen cars get to lose some (but generally not all) of the batteries, but in exchange they must carry a stack of fuel cells. These typically contain small but relevant amounts of precious metals such as platinum and are a significant contributor to hydrogen vehicle price (with fuel cell stacks usually costing over $10/W, a stack powerful enough to run a car generally costs hundreds of thousands or more). As a real-world example of an unsubisidized fuel-cell vehicle, fleets can now lease the Toyota FCHV-adv for the low price of an extra $7,700 a month[32] (depending on depreciation, this implies a purchase price of around $500,000). An alternative to fuel cells is a hydrogen ICE (internal combustion engine), but this makes the systen efficiency problem even worse and reduces range correspondingly. While research is ongoing to reduce the amount of precious metals required for fuel cells, it is still significant. As for the fuel, while electrics run much cheaper than gasoline, hydrogen vehicles run much more expensive than gasoline. Not only must hydrogen be made at a loss from other energy sources, but storage poses particularly problematic issues for hydrogen: it's incredibly bulky, explosive, leak-prone, metal-embrittling, and in general much more difficult than gasoline to work with. This translates into extra expense. To top it all off, for the same reasons, hydrogen vehicles themselves will require regular maintenance to ensure safety, detect hydrogen embrittlement, and so forth. Hydrogen vehicles lose on all counts.

One somewhat bizarre claim that sometimes gets mentioned to promote hydrogen cars over electrics is that "copper is a limited resource, and electrics use a lot of it". This claim is rather strange. Not only is copper not required for EVs (it's ideal, but other metals can be used instead), not only is the amount needed no more than is used in a number of household appliances, not only is it not particularly limited (see Peak Oil for discussion of resource extraction), and not only could EV use displace other, less important uses of copper, but the whole argument falls apart when one realizes that hydrogen vehicles use an electric drivetrain; there's just as much copper in a hydrogen vehicle as an electric. In addition, hydrogen vehicles use platinum in addition to the copper -- platinum being several orders of magnitude rarer than copper. What are electric cars supposed to run out of -- lithium? The platinum in hydrogen cars may be reduced, and in the future, eliminated by upcoming technology[33], but that would merely put them on par with EVs in terms of required resources.