On 8/24/21 2:56 AM, Martin WINLOW via EV wrote:
Mark: "In pondering what attraction a FCEV might have over a BEV, I hit upon an
extremely minor one. BEVs do not shed mass as they are driven, while
FCEVs do. So, FCEVs should see a very slight rise in efficiency as they
expend their fuel while BEVs do not. I am NOT claiming that it should
be a consideration when making buying decisions. But, since we are
grasping for straws, it is SOMETHING.”
This is only true for ICE vehicles in stop/go (ie urban) driving where you have
to accelerate the mass of the vehicle up to speed and then lose all that energy
braking to a stop again, repeatedly. On the open road and sticking to a
relatively constant speed, the main force using using energy is aerodynamic
drag (and tyre/road friction plus that of the mechanicals of the drivetrain).
In an EV, much of the braking in stop/go energy can be recovered by
regenerative braking, thus the ’shed mass’ argument is severely undermined.
The same applies to hilly terrain.
1) I was comparing FCEVs and BEVs. No consideration of ICE.
2) No consideration of energy flows. Though I believe both FCEVs and
BEVs recover kinetic energy via regen.
3) To try to be clearer: A FCEV is lighter after it has depleted it's
fuel. It has "shed mass". A BEV is the same weight charged and
discharged. Near the end of the fuel supply, a FCEV is slightly more
efficient than when it has a full supply. A BEV should have the same
efficiency when fully charged and near fully discharged.
Significant? No. We are "grasping at straws" for reasons a FCEV might
be better than a BEV.
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