No hope for hydrogen
In his informative piece about fuel cell development for cars (Under the Skin, 24 April),
Jesse Crosse rightly described the elephant in the room as being the lack of a hydrogen refuelling network. However, consistently ignored in the FCEV debate is the elephant’s bigger brother, which is the fact that an
FCEV will consume around three times as much electrical energy per mile as a BEV.
Why? Because the process of making hydrogen via the electrolysis of water is around 70% efficient, while compressing the hydrogen to 700 bar for on-board storage is 85% efficient (ie it requires pumping energy equal to 15% of that contained in the gas itself) and the efficiency of the fuel cell itself is around 50%. Multiplying those factors together gives an overall efficiency value of 0.3. In the case of a BEV, the equivalent efficiency value for getting electrical energy to the motor is the battery charging efficiency, and this is around 90%, or a figure of 0.9. Dividing 0.3 by 0.9 results in a comparison ratio of 0.33 – ie one-third, as I stated above.
So until the price of electricity drops to insignificant levels (like never) or governments decide to hugely subsidise FCEVS in some way, BEVS will remain the only real option. A third elephant is that the cost, packaging and safety challenges involved in storing the hydrogen tanks in the vehicle are just as formidable as they are for batteries.
And by the way, burning hydrogen in a combustion engine, rather than using a fuel cell, almost makes the overall energy equation twice as bad again: ie five or six times overall. Michael Appleyard
Via email