4 ms·
There are three pressing concerns for hydrogen fuel cells, which can be added up to "bullshit". First, energy density. I can't speak to that in detail, but the
by beat 13y ago
There are three pressing concerns for hydrogen fuel cells, which can be added up to "bullshit". First, energy density. I can't speak to that in detail, but the range problem is serious. Then again, the range problem seemed insurmountable for electric cars until Tesla got within spitting distance.
Second, platinum. Traditional hydrogen cells require some platinum in the catalyst, which is fine at lab scales, but unviable at industrial scale. There have been advances in alternative catalysts recently, but until fuel cells can be built without rare and exotic raw materials, they're just a toy.
Third, power source. Hydrogen comes from cracking water, which requires energy. It's just a storage medium for energy provided during the cracking process. What's the end-to-end thermal efficiency of that process? And where does the power come from? Of course, this problem applies 100% to battery-powered cars as well.
- soperj 13y agoIt applies to gasoline cars too, you need energy to process oil into gasoline.
- saalweachter 13y agoOil is a net positive on the energy, even with the energy cost to refine it. Generating hydrogen from water is a net negative on the energy, guaranteed, by thermodynamics. Unless we start stealing it from an extra-planetary source, it is best to think of hydrogen as a battery, not a fuel.
- soperj 13y agoOr if they use algae or a microbial process to produce hydrogen instead, or concentrated solar to dissociate water into hydrogen and oxygen? Electrolysis isn't the only option.
- mchannon 13y agoOil is not a net positive on the energy; gasoline consumes more in electricity during the refining process than it contains; it's just in a much more useful form.
- saalweachter 13y agoThat is a fascinating claim. I've just spent twenty minutes or so trying to track down the origin and veracity of it. As near as I can tell, that is a corruption of the claim "you can drive an electric car further on the electricity which goes into refining a gallon of gas than you can a car on the same gallon of gas". Specifically, the numbers I saw people quoting were that it took between 3 and 7.5 kWh of electricity to refine a gallon of gas, and that an electric vehicle could drive 30-50 miles on that amount of electricity. However, a gallon of gasoline contains far more than 7.5 kWh: approximately 37.8 kWh. So gasoline is still a net positive on energy, even after refining.
- mchannon 13y agoThanks for saving me the trouble of tracking down sources. The claim was inartfully stated at best. However, it all ends up going back to your definition of "net positive". I read "net positive" as getting more out than you put in during the refining process. Neither gasoline nor hydrogen from water is a net positive by this basis. If you extend the "net positive" test to the extraction and refining process, then you have to include the process to make the electricity for hydrogen-from-water or it's not a fair comparison. I can't dig up electricity. In this case both processes are net positives if the comparison is even.
- saalweachter 13y agoI wouldn't go that far. First, to be honest, I don't trust the initial claim. I couldn't find a source for the 3.5 to 7 kWh figure, and their are a lot of ways it could be wrong or misleading. Firstly, you don't refine gasoline in a vacuum; when you refine a barrel of oil, you get roughly 45 gallons of refined petroleum products, including about 19 gallons of gasoline. Are they assigning the full cost to the gasoline, dividing it by volume, or by energy cost? And 3.5 vs 7.5 is a full factor of two. What is the average cost? Even taking the energy cost as gospel, it still tells you a heckuva lot more about the vehicles than the fuel. ICEs peak at about 30% efficiency, so you ought to be able to apply a solid 12 kWh from a gallon of gas to making cars go. If the fifty miles you can push a particular electric car on 7.5 kWh is more than your typical car, that's hardly the fuel's fault. And indeed: the current record for fuel efficiency is 209 mpg. So it's duplicitous to say that electricity is more efficient for running cars than gasoline, or claim gasoline is somehow energy negative. We get so much energy from gasoline we can be extraordinarily wasteful in how we use it.
- gbhn 13y agoSee this link about energy density: http://www.aip.org/tip/INPHFA/vol-10/iss-1/p20.html http://www.aip.org/tip/INPHFA/vol-10/iss-1/p20.html Even liquid hydrogen doesn't come close to the volumetric energy density that seems like it'd be a solution for transportation. And the more compressed or cold you get it has a lot of attendant problems in terms of expansion effects of the gas, or the energy required to compress it. The permeability of hydrogen in containers, especially at high pressure, is also a real concern. Hydrogen escapes through container walls, and has bad (embrittling, usually) effects on them. A brittle 10,000psi H2 tank on board a car is something you really do not want. It seems to me the most feasible path to fuel cell power is to use non-pure-hydrogen fuels.
- beat 13y agoThanks for the link. I've always suspected that energy density was a problem, but never investigated it.