I agree with
@digilotus and to answer the efficiency point …..
I agree batteries are generally more ‘efficient’ that cracking hydrogen and then burning it - with any thermal engine the laws of thermodynamics (Carnot cycle) will limit the efficiency. The same applies to actually generating electricity using thermal power in the first place.
However, the key issue I think is not necessarily efficiency but one of overall environmental impact and that’s actually really hard to figure out. I’m sure folks would agree that hydrogen is pretty darn abundant as water so let’s ignore any H2 ‘resource’ issues - especially since burning it just makes water again. Also, since we don’t have a H2 economy yet let’s also set aside the practical issues of bulk storage, distribution and supply of hydrogen which would admittedly require huge investment.
So the environmental balance is
- the environmental cost of producing hydrogen (typically by cracking water and there’s various ways of doing that)
vs
- the environmental cost of making batteries PLUS the environmental impact of producing the electricity to charge them with when driving
If you have a surplus of renewable energy then producing hydrogen becomes quite cheap and has minimal environmental footprint, so if energy is lost in the production / distribution / use cycle it doesn’t matter. However, if you don’t have plentiful renewable energy, then producing hydrogen is not so good.
Batteries (at least current technology) use rare earth metals that have to be mined and have a finite supply. There are other technologies like supercapacitors and next gen batteries but they are quite a way off commercial viability yet (AFAIK - it’s quite commercially sensitive!). Also, recycling of batteries has yet to properly get going so there’s still a question mark over how many times the base materials of a battery can be recycled into new batteries. Plenty of research and development is going into it but there’s no definitive answer yet. The generating electricity bit is the same as for hydrogen, but since you lose less the generation / distribution / use cycle is more efficient.
So in my mind if you have lots of renewable energy available then hydrogen is good, if you don’t then it‘s a balance between the environmental impact of a battery lifecycle vs the efficiency gains by direct power storage in a battery.
Sorry this is a bit long winded but as with many things in life, nothing is simple!