Once they’ve established that it’s not prone to imminent explosion (if anything, hydrogen is safer to carry than petrol), the second thing people want to know about the Toyota Mirai is how fuel efficient it is.
After all, the Mirai is quite closely related to the Prius, which has economy at its core. Is the Mirai economical too?
We were keen to find a figure at the outset, but the more we thought about it, the more truth seemed to be carried in the words ‘depends how you measure it’. The easiest figure to give is miles per kilogram: the Mirai takes around 4.7kg of compressed hydrogen when the fuel gauge says it’s as near as we’re prepared to get to bone empty, at which point it has done around 270 miles. That calculation is easy: the car does 57.02 miles per kilo of hydrogen. Trouble is, this doesn’t help much, not least because compressed hydrogen is about eight times lighter than petrol.
Then we spotted a figure in the Mirai brochure stating that a tankful equates ‘roughly’ to 60 litres of conventional fuel capacity. That means 4.7kg of consumed hydrogen equates roughly to 56.4 litres, or 10.3 gallons. It gives you a range of 270 miles, thus in ‘petrol equivalent’ the Mirai returns 26.2mpg. Not impressive, if it matters.
We think a more interesting gauge of the Mirai’s efficiency is to measure fuel cost per mile and compare it with, say, a 40mpg petrol car. Hydrogen costs £9.99 per kilo, so our 4.7kg fill-up costs £47, give or take. Over 270 miles, that’s 5.74 miles per pound, or 17.4 pence per mile. Now consider a 40mpg petrol saloon fuelled at £1.20 per litre/£5.46 per gallon. Over 270 miles it would use 8.1 gallons, which costs £44.20 or 16.3p per mile, near enough.
Ergo, running a similarly sized petrol car costs roughly 90% of what we’re paying to run the Mirai.It seems a steal given that this is still very much an experimental car.