Yes, I see. The density of hydrogen at 5000 psi is about 100 g per gallon, or < 1/45 th the density of diesel. So on a weight basis you get three times the mileage, but to travel a given distance you need about 13 times the volume. Also, you need a fuel tank to confine hydrogen at 5000 psi. Not only is the cost of such a tank very expensive, hydrogen at 5000 psi is potentially deadly. So guess what happens if your tank gets a serious leak? That's right, it's happy Hindenberg day!
I dont think it unreasonable to think that many might assume from the first post in the thread that you would need a hydrogen tank of one third the size of a petrol tank to get you a given distance. The reality is a tank about 40 times bigger than the one imagined!
biodiesel:Can be used in existing diesel engines, which have already been in use for 100 years
H2:At least ten years away
Fuel source
biodiesel:Algae farms or other vegetable crops, or waste conversion. Completely renewable process, with no net CO2 emissions.
H2:Electrolyzing water (most likely using fossil fuel energy) or reforming fossil fuels. Most likely non-renewable methods with large net CO2 emissions
Fuel Distribution System
biodiesel:Can be distributed with existing filling stations with no changes. No system currently exists, would take decades to develop.?
H2:Would cost $176 billion to put one hydrogen pump at each of the filling stations in the US.
Overall Energy Balance (each unit of energy put in yields....) [higher is better]
biodiesel:3.2 units (soy)4.3 units (rapeseed)
H2:0.5 units (electrolyzing water into hydrogen with renewable sources)
Large scale fuel development cost analysis
biodiesel:For an estimated $1691 billion, enough algae farms could be built to completely replace petroleum transportation fuels with biodiesel
H2:To produce enough clean hydrogen for our transportation needs would cost $2.5 trillion (wind power) or $25 trillion (solar)
Safety
biodiesel:Flash point of biodiesel is over 300° F (considered "not flammable")
H2:Highly flammable
Time scale for wide scale use
biodiesel:5-10 years
H2:30-50 years optimistic assumption
Cost of engines
biodiesel:Comparable to existing vehicles
H2:Currently 50-100 times as expensive as existing engines. The cost of the fuel cells themselves will come down significantly ? the cost of the infrastructure and making the hydrogen will not
Vehicle performance
biodiesel:Significantly better range than gasoline vehicles, comparable power (roughly 700 mile range for Volkswagen Jetta TDI)
H2:Significantly smaller range than gasoline vehicles (180 mile range for Toyota?s FCHV)
Tank capacity required for 1,000 mile range in conventional sedan
