Quote:
Originally Posted by Draigflag
So I've been thinking about "the future of the automobile" and although most of the focus is on electric, I'm beginning to think hydrogen powered cars make just as make sense.
Benefits? Slightly longer range than fully electric cars, 300 to 400+ miles per fuel up on about 1kg of fuel, fuel ups take about 5 minutes, no tedious charging times, hydrogen is the most abundant element in the Universe, no worries about running out, tailpipe emissions consist of water vapour only, electric cars in some countries still rely on burning fossil fuels to generate the electricity to power them. There are more benefits of course. What do we think?
|
The Mirai's 312 mile range is on a little under 5kg of hydrogen. One kilogram would have been awesome, since such a little amount would get around one issue of hydrogen car design; the fuel tanks.
Hydrogen's energy density by mass is of the highest in the universe. But its volumetric energy density sucks anywhere outside the center of a sun. In order for a car to carry enough of it to attain ranges that approach a gasoline car's, the hydrogen needs to be liquidified or compressed to really high pressures.
Since personal cars don't have the space to dedicate to insulation, all liquid hydrogen in their tanks will eventually boil off; BMW's bi-fuel hydrogen ICE car's hydrogen tank would empty in about a week.
So the current hydrogen cars use compress hydrogen to the tune of 10k psi. For comparison, CNG vehicle tanks are at 3500 psi. To contain those pressures, the tanks end up heavy even with the use of light weight materials like carbon fiber. A DOE goal is for the weight of a filled hydrogen tank to be 5% hydrogen. They aren't quite there, but if they were, a 5kg tank would be 95kg or 209 pounds.
On top of that, the physical requirements of the tanks for containing high pressure gases limits the shape of the tank to spheres and cylinders. Making the required space on the car higher than for a like amount of liquid fuel. The Mirai's exterior dimensions are very close to a Camry's. The hydrogen tanks mean losing the middle rear seat. Toyota never released the passenger and trunk volumes, but the EPA calls it a subcompact. It is also over 500 pounds heavier than the Camry.
High pressure tanks for vehicles also have a limited service life for safety concerns. The longest lasting CNG tanks are rated for 25 years from manufacturer date; the shortest, 10 years. Going by the label on a Mirai filler door, it appears its tanks are good for 15 years.
Hydrogen is everywhere, but we have to break up molecules to get it in pure form. The cheapest method is to break up natural gas for it. Toyota plans to use Australian coal to provide hydrogen for the Japanese market. Using renewable electric for electrolysis is a possible avenue. it is just very inefficient compared to using the electricity in a plugin car. The electricity to move a hydrogen FCEV one mile would propel a plug in 4 miles. So more renewable electric would need to be built for the same number of cars. There are other possible renewable methods, but they are mostly still in the lab now.
The biggest hurdle for hydrogen powered personal cars is the cost of infrastructure to distribute it. First, it pretty much needs to be built from scratch. Second, hydrogen's physical and chemical nature means constructing and maintaining any pipe lines and tanks will cost more than equivalent ones for other fuels. Third, the equipment required to fill up these high pressure fuel tanks, will make a hydrogen station more expensive to built and run than a current gas one. This all adds up to a pretty big price tag.
Note that my 'little' rant was against hydrogen, not fuel cells. A Volvo partnership has developed a diesel powered fuel cell that they plan on using in long haul trucks and boats to replace the generator. Methanol and natural gas powered fuel cells also exist. The fuel cells and on board reformers are still too bulky for personal cars, but there is no reason for continuing development not to get to the point where they will work.
Those fuels can be make from renewable electricity like hydrogen too. Switch the personal vehicle fleet over to plug in hybrids where a pure BEV won't work, and the reduced amount of fuel used by the ICE on them can make the costs of these renewable fuels more acceptable to the public. Replace the ICE with a fuel cell when they are commercially ready, and the increased efficiency makes the switch to 100% renewable 'fossil' fuels even more likely.
Linear Mode
