How much does a hydrogen car cost to run?

Toyota reckons its Mirai will become the Prius of the hydrogen fuel cell car world. That’s a pretty brave claim, given the current lack of knowledge about this form of transport. Many folk seem to equate hydrogen with catastrophic explosions, even though the truth is that hydrogen is safer to carry in a car than petrol.

Once you’ve got them past that misunderstanding, the next thing they ask about is the Mirai is how fuel efficient it is. Again, its relationship with the Prius probably has something to do with that. The Prius is seen as economical, so presumably the Mirai is too?

Like them, we were desperate from the start of our Mirai stewardship to come up with a quotable figure with which to answer this question. As time went on, we came to a kind of realisation that the ‘truth’ of this matter depends on how you measure it.

The most obvious figure to quote is miles per kilogram. From as near to empty as we dare to go, which is about 270 miles after a fillup, the Mirai takes around 4.7kg of compressed hydrogen. It’s easy to calculate from that data that the car does 57.02 miles per kilo of hydrogen – but the trouble with this calculation is that petrol is about eight times heavier than compressed hydrogen.

We saw something in the Mirai brochure that we thought might help. It said that a tankful is the equivalent to ‘roughly’ 60 litres of conventional fuel capacity. That means 4.7kg of consumed hydrogen is roughly equivalent to 56.4 litres, or 10.3 gallons, of petrol. In ‘petrol equivalent’ terms the Mirai therefore returns 26.2mpg over its 270 mile range.

If you’re as bothered about the economy side of things as you are about the green side, that doesn’t sound too brilliant, but it’s important to remember that we’re talking about zero emissions motoring.

A more useful Mirai gauge involves measuring the fuel cost per mile and comparing it with, say, a 40mpg petrol car. You’ll pay £9.99 per kilo of hydrogen, so a 4.7kg fill-up costs about £47. That’s 5.74 miles per pound over 270 miles, or 17.4 pence per mile.

A 40mpg petrol saloon fuelled at £1.20 per litre/£5.46 per gallon would use 8.1 gallons over that same 270 miles, the total cost of which would be £44.20. That works out at around 16.3p per mile – about 90% of what it costs to run the Mirai. Considering how early-days this experimental car is, that seems pretty good to us.