Hydrogen is really a non starter for domestic vehicles. I'll explain why in a bit. But don't dismiss Hydrogen all together. It is a very useful chemical. It can be used for super high temperature plasma arc welding. Experiments are also in the pilot plant stage to use hydrogen to refine iron ore instead of using Coke. If the hydrogen is produced by electrolyzing water instead of reforming methane, then there will be a significant reduction in our carbon foot print. There are many many other uses, too numerous to include in this blog.
In addition, the production of Hydrogen by the electrolysis of water, if done correctly also produced Oxygen which has a plethora of uses in our modern society.
However, hydrogen can not compete on a cost basis or energy efficiency basis, with simply charging a battery. To charge a battery, you generate power (renewably, of course), transmit it across existing power lines and charge your battery. Let's take a fairly bad case and say we loose 6% of the power in transmission. So 0.94 of the power gets through. We then charge the battery in the car and use this power to drive the car. Taking a worse case scenario, we get 80% or 0.80 of the power we put into the battery out of the battery. Multiplying these two figures together we get 0.752 or 75% of the energy generated is useful energy in an battery-electric car. Of course the situation improves if you have your own solar panels and charge your car right beside them.
Let's look at the situation with Hydrogen.
First you have to split water by electrolysis. We will ignore the steam reforming of Methane since it produced Carbon monoxide. In other words it has a significant carbon foot print. The present efficiency of water hydrolysis is about 80%. In other words, the energy content of the hydrogen produced is 0.80 of the energy used to produce it. If we are talking economics rather than energy efficiency, it should be noted that, if done correctly, the by product of H2 production is O2, a very widely used chemical in a modern society.
Then you have to compress or liquefy the hydrogen. To compress Hydrogen takes up more energy. It takes about 38% as much energy as was used to produce the hydrogen. In other words it's efficiency i 62% or 0.62. Without even shipping the hydrogen, we are down to 0.80 x 0.62 = .49 ie 49% and we also have to multiply by the efficiency of an internal combustion engine using hydrogen or a fuel cell(34% and 60% respectively). Let's ignore using hydrogen in an internal combustion engine as it has poorer efficiency than using a fuel cell.
At this point we are in the same situation as an electric car running on a battery. The electricity produced by the fuel cell is used to power the electric motor of the car.
So the best case is with a fuel cell and we multiply 0.49 times 0.60 = 29% compared to a battery which gives us 75% from renewable energy source to the electricity fed to the electric motor of a car. Note that I have taken the very best figures I can find for the use of Hydrogen and the worst figures I can find for a battery car.
We also haven't taken into consideration the energy or economic cost of transporting the Hydrogen to the hydrogen station.
How about if we decide to compress and cool the hydrogen to liquify it. We start with the same efficiency of electrolysis to produce the Hydrogen of 80%. It takes about 30% as much energy to liquify Hydrogen as it took to produce it. Therefore, it is about 70% efficient. 0.70 x 0.80 = 0.56 or 56%. Looks promising, no? But our troubles are not over. Liquid Hydrogen at one atmosphere outside pressure has a boiling point of minus 253C. And wherever you store the liquid Hydrogen, even in the arctic it is a relatively hot day outside. And we still have to multiply by the efficiency of a fuel cell (60%) so we have 0.56 x 0.60 = 0.34 or 34%. Liquid hydrogen must either be allowed to evaporate to keep it cool or refrigerated down to minus 253 degrees C.
Liquid Hydrogen has a whole raft of other problems associated with it's need for very well insulated containers, the fact that is slowly boils off and needs the hydrogen gas to be re-liquified or you must simply wear the loss and it's danger in an accident as liquid hydrogen will blast freeze anything it touches.
Hydrogen is a very valuable product for a wide range of applications, just not for domestic transportation.
https://www.youtube.com/watch?v=AoXJYPfag1I
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