Are hydrogen tanks superior to batteries?

The difference is not a great as you claim. But the point is that if you have plentiful free energy - which we have - then its cost is that of the equipment needed to collect it.

That is falling dramatically, so one would expect the cost of electricity and hydrogen produced to fall as well. The cost of raw electricity might fall faster, but the point comes when the cost of even the more expensive hydrogen is so low that it ceases to be of concern to anyone.

To take this to extremes, hydrogen may still cost ten times what electricity costs, but if ten cents worth of electricity will take you ten miles and hydrogen costs you $1 to go the same ten miles, it makes little or no difference to the driver. he will choose a car that he likes and the hell with the fuel cost. Both are negligible.

I think you will agree that at the present 99 out of 100 car owners buy ICE vehicles which cost a lot more than battery cars to run. This, I think, is clear proof that fuel cost - despite perpetual whining about it - doesn't count for very much to drivers in practice.

The other advantage of hydrogen is that we are increasingly having to accommodate more electricity than we need. Storing it in batteries is expensive and bulky, so it is not done much. However, using it to produce hydrogen is much simpler. You need little more than an electrolyser which will tolerate a high pressure on the hydrogen side with atmospheric pressure on the oxygen side, some simple dewatering kit and a tank. The cost of the plant, per kWh stored, can be far lower than a bank of equivalent batteries. The resulting hydrogen can either be sold to FCVs or used in fuel cells to supply the grid.

Inefficient? Of course it is. But if the cost of the returned energy is lower than a battery can manage, it will prevail.

You seem to think that efficiency is the dominant consideration. In fact it isn't. Convenience and the attractiveness of the vehicle is what sways the customer. Ask any car salesman.

 

Casting my mind back to school chemistry days, I was (hopefully) able to work out that splitting up 18 g of water (one mole) will yield one mole of oxygen (16 g) and two moles of hydrogen (2 g). This will cost about 242 kiloJoules of energy as an irreducible minimum.

Thus to produce a kg of hydrogen will cost - at least - about 121 MegaJoules of energy or in kWh, about 34 kWh

In practice, electrolysis is only about 80% efficient so you would need about 43kWh of energy to produce a kg of hydrogen.

Then you have to compress this. It turns out that to compress 1 kg of hydrogen to 100 MPa requires, in theory, a surprisingly (to me anyway) small amount of energy. About 1.5kWh! HP differential electrolysers are more efficient than compressors, but I don't know how much better they are. Reciprocating compressors manage about 56% with a motor efficiency of 92%. About 52% overall. So if we add this onto our energy bill so far, we require about 46kW to produce a kg of hydrogen at 70MPa in the car's tank.

This will take you 60 miles or so in a modern FCV.

Looking at battery cars, the best estimate I can come up with for 60 miles is about 18kWh. This, I think, is the power actually expended during the drive, and as the round trip efficiency of lithium ion batteries is only about 80%, with a 95% efficient charger, the power actually expended in total is about 24kWh

So overall, I think battery cars - in terms of the electricity they need to run them - are rather less than twice as efficient as FCVs. Quite a big difference but nowhere near the ratios implied by some posters here.

 

Well, Neil,I don't think there is much difference between 46 and 48 kWh. And I think you are adding in compression costs twice. I also neglected the advantage a high differential pressure electrolyser confers. And you have also neglected the losses in charging your battery, so I am prepared to stick with the figures I worked out.

One further point is that carrying fuel by road tanker is MUCH more energy efficient than the 92% efficiency you claim for electricity transmission. I haven't figures for hydrogen, but consider a road tanker which can carry 10,000 gallons of petrol. Over - say - 100 miles it may burn as much as 20 gallons of fuel which gives an efficiency of 99.8% Hydrogen involves heavy tanks, so it will be worse, but still far better than electrical transmission losses.

I'm glad, Teslainvestor, that you are pleased with your FCEV, and look forward to hearing your longer term experiences with it. Hopefully more hydrogen stations will allow you to travel outside California with it in the near future.

 

I just read through another thread here - Battery Life / Cycling - which discusses the best ways of extending battery life. It makes very interesting reading. There is a lot of advice and experience there, some of it conflicting, but it illustrates very well I think why battery cars are unpopular.

If you are an enthusiast, I guess this sort of thing is part of the fun, but the ordinary car user who really doesn't care what makes the thing go as long as it DOES go, sees all this as angst and hassle that they can do without.

 

Be fair, he did go on to say you have to look at the cost of replacing the hydrogen tank too.

I think we have to face the fact that the energy expended in making ANY sort of car is unlikely to be recovered by savings in the fuel used to run them.

Of more interest, possibly, is the comparative weight of hydrogen tank+fuel cell versus battery pack+cooling. I have no idea which weighs more, at the moment, but I would imagine as the weight of a gas tank goes up slower than the volume, whereas the weight of batteries goes up directly with the rise in stored energy, there will come a point where hydrogen wins even if it isn't ahead already.

You will be able to make a bus or a semi a lot lighter with a hydrogen solution than with a battery one. Whether this applies to cars I know not.

 

I could certainly drive across Europe in one, Neil.

Fuel costs even more in an ICE, yet people overwhelmingly insist on buying them. Surely an indication that fuel costs are pretty unimportant to the general public.

I think you have to accept that people have NOT taken to electric cars. Despite heavy advertising, and various financial and other blandishments and a wide choice of models, seven years of pushing them have NOT caused sales to take off.

It's probably too soon to tell whether hydrogen cars will suffer the same level of rejection, but initial indications are rather more encouraging. We shall see in due course.

 

Well, there may be a clue in the words "It's probably too soon to tell...".

I don't know what will happen. I think it is YOU who are projecting, judging by your declaration: "... and they never will."

 

As to fuel costs, variations in the price in the UK don't seem to affect the amount sold. People still insisted on driving horrible great SUVs that gulp down fuel when the cost of it was approaching £2 a litre!

As to 'conversion' to battery cars, I am not so sure it is always very permanent. Certainly not in Japan according to this:

https://www.tokyotimes.com/most-japanese-electric-car-owners-will-never-buy-another/

I can speak with certainty only in my own case. My reason is that they are a lot less convenient than an ICE (or a hydrogen) car. I simply can't be bothered with nannying a battery and fiddling about with cables and chargers at the car's convenience rather than mine. I would much prefer to pay through the nose for it at a filling station, cheering myself up with the thought that I am still saving money by not having bought a very expensive car that depreciates extremely fast.

However, I DO worry about the pollution and will seriously consider an FCV when they hit a reasonable price and I can refuel it.

 

Well, Tesla's next car is always going to be THE one that makes the difference. I don't wish him any ill, but a lot of people think he's already spent too much investors money and given them very little in return. That sort of thing can't go on forever.

 

Apropos hydrogen tanks, this seems a good approach. The conventional shape of existing hydrogen tanks is awkward to incorporate into cars. This company - http://voluteinc.com/our-tanks/ - allows designers to fit the tank to the shape of the vehicle more easily and the result should be a rather more voluminous vehicle.

I expect conformal tanks cost more, but who knows what economies of scale and material advances might achieve? Graphene reinforcement rather than carbon fibre perhaps??

 

I knew it was old, but I don't think things have improved much for EVs there. Heres's a piece from October 2017. It looks like Japan is going for broke on hydrogen.

https://www.ft.com/content/98080634-a1d6-11e7-8d56-98a09be71849