EV Versus FCV- Calculating CO2 Emissions and Volumetric Energy Density
This is an EV site. It is called InsideEVs and it is for EV enthusiasts. Some have argued that FCV articles shouldn’t be posted here. I disagree. I’m an EV enthusiast but I also want to know what the competition is up to and how the vehicles compare.
We’ve heard these kinds of comments on previously posted articles about Toyota’s FCV:
“The hydrogen used in Toyota’s FCV will be made by steam reformation and therefore the FCV is just as bad as an ICE car when it comes to CO2 emissions.”
In order to test the validity of that statement I have put together some calculations that should bring light to the comparison.
Have you ever read a detailed well to wheels comparison? It can be a dizzying discussion. Do we need to include the CO2 that was emitted from making the tires on the transport truck? Are all the energy losses from transmission of the electricity included? What power plant did you assume when calculating your EV’s emissions…….and on and on.
The presentation I have put together is fairly simple. The numbers are easily checked by the reader. The only engineering calculations that need to be made are some unit conversions.
The EV and the FCV energy consumption numbers are included. The EV power plant emissions are included.CO2 emissions from the steam reformation process of making hydrogen are included. Transportation losses and line losses are not included. Leaving out the transportation and electric line losses would affect the absolute value of the numbers presented here. However, since the transportation and line losses are not included for both the FCV and the EV the RELATIVE values should still be valid for purposes of this discussion.
What are the CO2 emissions of the steam reformation process used to make the hydrogen? Reference 6 shows that a good round number is 10 lb of CO2 emitted for each pound of hydrogen produced.
We also need to know how much hydrogen Toyota’s FCV uses per mile ie miles/kg of H2.
It took some searching to answer the miles/kg of H2 question for the FCV. Probably the best source is an actual test done on Toyotas 70 Mpa Hylander- adv FCV. (see ref 5) (hat tip to Mr. Martin).
A value of 70 miles/kg of hydrogen is probably a reasonable H2 consumption rate for Toyota’s soon to be produced FCV.
Knowing the hydrogen consumption and the reformer CO2 the emissions are easily calculated as shown in slide 2. The CO2 calculation for the Prius and an EV are also presented as a comparison in slide 2.
However, comparing a FCV using steam reformation hydrogen is not really a fair way to compare the FCV because the California Air Resourced Board (CARB) has passed legislation that required 1/3 of all hydrogen to come from renewable sources as shown in slide 3.
Slide 4 includes the CO2 emissions calculated for the FCV with 30% renewable hydrogen.
One should note that both the EV and the FCV have low CO2 foot prints. Therefore it is the author’s conclusion that, from a CO2 emissions point of view, there are really no issues when it comes to EV versus FCV.
Volumetric energy Density Comparison:
One would think that Hydrogen is a fairly dense fuel BTU wise. After all we used it in the space shuttle. The difference is that a FCV doesn’t use liquid hydrogen. It uses compressed hydrogen at 70 Mpa (10,000 psi). Ten thousand psi is pretty a high pressure but, even at 10,0000psi, hydrogen is not all that energy dense compared to gasoline on a volumetric basis. As shown in slide 5it is 1/7th the density of gasoline.
Personally, I’ll take an EV. I live in a sunny climate and solar PV works well and integrates nicely with my Volt. However, if one lived in a colder climate with not much sun and had access to hydrogen made from renewables then a FCV might be a good choice.