Toyota Mirai

[ZeGato]

5,6kg la capacité des réservoirs....

[emss]

'Lut,

Une réponse sur le forum de PH expliquant pourquoi l'hydrogène n'est pas une solution, de la part d'un mec qui a apparemment travaillé dans ce secteur

Hmm.

I'm curious as to why you believe the solution to not having to spend a fortune on weakening batteries is hydrogen?

Would it be fair to say that you consider hydrogen as a like-for-like replacement for liquid fuels in terms of user friendliness?

There have been a couple of fairly lengthy hydrogen threads in the EV/alternative fuels sub-forum running for a couple of years now. The EV vs hydrogen discussions have now started to migrate to GG, so we seem to be covering a lot of old, fairly basic ground again.

A passenger car needs something like 5 kg of hydrogen on board to have a decent enough range. That sounds like a pittance, until you you consider that at ambient pressure, that would require a 55,000 litres fuel tank. That is not a typo btw.

Using Toyota as an example, they have chosen to store the hydrogen in three separate tanks with a combined internal volume of 80 litres at 700 bar. These tanks are constructed as domed-end cylinders from aerospace grade carbon fibre composite with wall thicknesses approaching 20 mm. There is literally no other way to store a compressed gas at 700 bar, i.e. 700 times atmospheric pressure.

The cyclic hoop stresses in these tanks as they discharge and refill through their life are so high that eventually the resin matrix that is used to hold the fibres together will start to suffer from fatigue due to this cyclic stress. Due to the relative variability of quality seen in serial manufactured composite structures (compared to isotropic materials), it is necessary to put a lifetime limit on these tanks. Your hydrogen car will thus come with a 'do not refill after' date specified for their tanks. Do weakening hydrogen tanks concern you as much as weakening batteries then? Bear in mind also that unlike Lithium batteries that can be almost entirely recycled, the tanks are throwaway items.

I'd also encourage you to consider exactly how much real estate in the car is consumed by the hydrogen storage tanks. Here is a link with lots of images of that car's underpinnings.
https://www.thedrive.com/news/37872/now-with-three...

In addition to the tanks, the car also has a large fuel cell under the bonnet, all fuel cells degrade with time and use. Do weakening fuel cells concern you?

Lo and behold, there is also a buffer battery between the rear struts to deal with regenerative braking and the fact that the fuel cell can't change it's power output rapidly enough to match the demands from the drive cycle. Do weakening batteries on board hydrogen cars concern you as much as weakening batteries on board EVs then?

Admittedly, the Mirai battery is relatively small. If however, your car is more performance oriented, the battery size will need to increase accordingly. For the premium brands, the battery looks like it is somewhere between 30-50% of the size of the the battery in a pure EV of the same size car.

The final point I will make is that 5 kg of hydrogen is the equivalent of 100 kg of TNT. So you will be carrying a highly pressurised, highly explosive gas that will ignite over a wide range of conditions and has a very low ignition energy. Remember, this gas is undetectable, being both colourless and odourless, and will rise very rapidly in a leakage scenario. It also has one of the smallest molecules, making it an expert at seeking leakage paths through many materials, particularly as they age.

In the event that an ageing car was to leak its fuel into an enclosed space such as a tunnel or underground car park where the hydrogen could be trapped in a ceiling space, there is a major risk of unintended ignition.
For this reason, hydrogen cars are currently banned from tunnels, including Eurotunnel. Here is a 100 kg equivalent TNT explosion to give you an idea.

Now imagine a tunnel full of hydrogen cars where just one of them was to have a leakage/ignition scenario.

All of this to have a car that achieves around 30% utilisation of the original electricity used to produce the hydrogen, vs 80% for an EV.

You can of course avoid some of the shortcomings of the fuel cell by using an ICE, but the efficiency will drop. You now need even more hydrogen on board to achieve the same range, and you have the increase in maintenance that a reciprocating engine brings.

Maybe now you might understand why those amongst us who have worked in the field of alternative propulsion and energy storage systems for passenger vehicles are very skeptical about it, particularly for the UK market, where achievable EV range already meets the vast majority of users.

Éric aka Alf

[Neubauten]

Ma boite investit fortement dans l'hydrogène néanmoins... Vu les millions qui passent dedans je pense que l'équation n'est pas si simple.
Mais en effet je pense que la mise en œuvre est aujourd'hui un gros obstacle pour concurrencer sérieusement les BEV.