JZ, the other two posts answer the question. Short term, I’d add in “clean” coal as well. (See past posts by Una Persson, who retrofits coal-fired plants for a living, on what can be accomplished here in terms of environmental/energy benefits, and why coal is a necessary component of the energy mix in the immediate future.
My point is not that you use hydrogen to generate electricity – that’s silly. It’s that we need energy in portable form to fuel vehicles, and hydrogen is mych more feasible than electric-battery power for this particular use in just basic engineering terms.
Produce hydrogen at fixed points such as nuclear and hydroelectric plants, where energy and water are locally plentiful. Use the hydrogen to fuel vehicles such as locomotives and long-haul big-rig trucks where direct battery-based electric power is not at present a feasible option.
I know an engineer that worked on Ford’s hydrogen car project. What he told me:
The problem with hydrogen is storage. It just disappears when it is harnessed in containers that our current technology can construct. You can’t sell cars where you never really know how much energy you have in the tank and there is no infrastructure to support it.
Also, gasoline is the most efficient and safest form of energy storage that is easily transportable. With current technology, hydrogen isn’t a superior alternative. There is a reason why “big oil” became big. For all of the downsides of gasoline there is yet to be something that really is better.
Hopefully, technology will make gasoline obsolete as the transportation fuel of choice. Until then, it ain’t so easy.
Right, if you ignore the greenhouse gas and limited resource issues (as we largely have up until now), gasoline is an absolutely amazing fuel. It’s got extremely high energy density, compared to anything we’ve proposed to replace it, it can be refueled in minutes, it’s quite safe given how much energy it has, and (for the present, at least) it’s very cheap. Heck, it’s possible that the vehicle system of the future might even involve gasoline synthesized from atmospheric carbon dioxide and water: In principle, that’s not all that different from synthesizing hydrogen, and it has a lot of advantages.
An interesting point about the economics of fuels can be seen from the difference between natural gas (aka methane) and LPG Liquified Petroleum Gas (aka propane). The two have pretty close to the same energy denisity by mass, are both reasonably abundant and exploited around the planet. And yet LPG is worth about twice as much per unit energy as natural gas. This despite it is possible to liquify natural gas (aka LNG.) The big difference is that LPG can be transported at ordinary temperatures and does not require much pressure to maintain it liquid. Methane can only be liquifed and kept liquid with heroic efforts, and whilst it can be transported in huge tankers like this, it is not a viable distribution mechanism.
So, the only reason propane is worth so much more than methane is that it is easy to transport. I live just far enough out of town that my only viable source of gas for home heating and cooking is propane. I buy 45kg cylinders for over $100 a shot. Across the planet, especially in emerging economies, such as India and China, LPG is trucked everywhere. This demand is what pushes the price up. In cities with well integrated infrastructure methane heats the homes at half the price.
In cars the situation is interesting. Here in Oz, our petrol (gas) stations typically sell three fuels: conventional petroleum (alkanes) in various octanes, diesel fuel, and LPG. Many cars run on LPG, although the cost efficiency to a large extent of this comes from a set of different taxation rules. There is however an example of natural gas being used. Many buses are run on methane. They are fitted with large high pressure tanks, and they are recharged overnight by a compressor that connects to the ordinary gas main.
One might note the parallels with a hydrogen economy. Except that hydrogen is always going to be significantly less efficient. The problem with hydrogen is that creating it is well short of 100% efficient. Indeed a naive electrolosys of water is about 30% efficient. The rest of the energy goes into ohmic heating of the water. You can do better, but it isn’t easy.
If you were running trains, running the locomotives of hydrogen derived from electricity would be dreadful. This is why electric locomotives are well favoured. Even with the trasmission losses, powering trains directly with electricity wins. More trains and get the long distance trucks off the roads is vastly more efficient.
No, that was my point. The OP said “Why are we not advancing to this fuel, continuing instead with electronic cars which need charging (using fossil fuel?)” - I was saying that hydrogen is basically the same thing, charging from fossil fuels, so it’s not inherently superior to electric that way. Furthermore electric has a better infrastructure. That was my point.
Rather like the other old codger who wanted to know why they didn’t make an electric car with two batteries, one to be charged up by the momentum of the vehicle while the other was being used to drive it. “Don’t tell me it can’t be done!”
A concern with hydrogen fuel I seldom see mentioned is safety in the event of a vehicle accident.
Lower and Upper Explosive limits by % in air
Gasoline 1.4 - 7.6
Hydrogen 4 - 75
Granted hydrogen is lighter than air and won’t pool under a damaged vehicle, and it’s auto ignition temp is around twice that of gasoline so less chance of ignition from contact with hot engine components in a crash. But the storage tank would be under extreme pressure and virtually any concentration of hydrogen in air offers an explosive potential.
Personally I think the press would have a field day the first time a mushroom cloud goes up over an auto accident scene.
There is no free hydrogen available anywhere on earth in any significant quantity. It’s all bound into molecules such as H2O (water) and CH4 (methane). It takes energy to break the chemical bonds that hold the hydrogen in these molecules. You can get the same amount of energy back by recombining hydrogen into molecules. A hydrogen fuel cell is a device that reaps as electricity the energy released by this recombination. That is why hydrogen is often referred to as merely an energy storage medium: all of the energy one gets from using hydrogen comes from something else.
The energy used to obtain hydrogen can come from clean sources such as solar and geothermal. Nuclear is also clean with respect to greenhouse gases. You can also use waste heat from many different sources. But there are arguments against hydrogen fuel cells even if the hydrogen is produced cleanly. It comes down to the question of whether hydrogen is really the best way to store energy. One problem is that hydrogen has a low energy density relative to other fuels. Another is that it’s hard to transport and deliver. It seems likely to me that, for transportation (cars & trucks, for example) liquid biofuels will turn out to be more economical than hydrogen.
BTW, a lot of the hydrogen used in fuel cells today comes from methane. This produces carbon dioxide as a by-product. If this CO2 is released into the atmosphere it contributes to climate change. So, unless the CO2 is sequestered there’s little difference between getting hydrogen energy from methane and just burning the methane as a fuel.
There’s a big difference in efficiency. Big power plants are more efficient than small internal combustion engines or even fuel cells. Transmitting electricity, charging a battery, and running an electric motor is more efficient than cracking or electrolysing hydrogen and then compressing it.
So the overall efficiency works out to something like this:
50% power plant efficiency * 95% transmission eff. * 90% charging eff. * 90% electric motor eff. = 38% overall electric car efficiency.
That figure was assuming rather optimistic fuel cell technology; but currently fuel cells are too expensive and not durable enough to power a practical mass-market vehicle. Electric cars (and hybrids) also have an advantage in that they can use regenerative braking to recover some of the energy that’s lost to any other car.
And for one final bit of comparison, hydrogen has much better energy density than batteries if measured in energy/weight. But hydrogen is also much more bulky, and far worse if measured by energy/volume. In a standard car that basically means you have to replace the gas tank and fill the entire trunk with hydrogen storage to get anywhere near enough.
Those numbers, added to the permeability losses mentioned above (w3hich I had not considered), effectively put paid to my argument. Thank you for spelling out the reasoning, with supporting numbers.
While mushroom clouds are commonly associated with nuclear explosions, they can be produced by any sufficiently large release of heat, whether nuclear or non-nuclear. Rupture a tank of hydrogen gas, ignite the resulting cloud, and you might see one.
The cars fuel tank is one big problem.
Like Hbns states, the explosive mixture has a large bandwidth which means more of the fuel escaping from a container is burning when it ignites. That would produce not a fire but an explosion.
So one big trick in Hydrogen car development is to keep the gas tank from becoming a bomb in the event of an accident.
This is an old article but it shows some of the efforts being made to make the fuel tank safe.
I recall reading something about a solid substance, some sort of aluminium foam I think, that could be used as a storage medium for hydrogen. Basically a “brick” of this stuff could be used as a leak-proof hydrogen “tank”, and it was still light enough for use in vehicles. I can’t find it in Google, maybe the men in black SUVs from Detroit got there first.
