[NeilBlanchard]

Hi Dave,

A parallel hybrid design has several of choices that run between these three:

1) It can have a big enough ICE to be able to power the vehicle by itself, but it then has to have a transmission that lets work. The electric motor can be kept small, but the only advantages you gain are a small amount of regenerative braking, built in start/stop ability, and the ICE is only a bit smaller than it might otherwise be. The Honda system is close to this.

2) It can use either the electric alone, or the ICE alone to move the vehicle, but this requires each to be larger than otherwise, and the battery must be large enough to run for a reasonable period. It can also be operated in either series mode (see below). The Prius is approximately this design.

3) It can have a big enough electric motor to power the vehicle by itself at lower speeds, but then you have to a have a larger battery, and the small ICE must be used at highway/constant speeds (in order to justify it's use) and it still needs a transmission, if it is needed to climb hills by itself. I think this is going to be the most efficient parallel hybrid.

A series hybrid also has a range of choices:

1) It can use the ICE to directly generate power as required by the electric motor, and have the motor vary is RPM to match. You can even do this without any battery, though it should probably have a supercapacitor, at least, and possibly a small battery. Diesel/electric trains are like this.

2) It can use the ICE to generate enough power to run the electric motor directly and/or to charge the battery.

3) It can use a very small ICE to only charge the battery, and it would run at it's most efficient RPM (so ~37% efficient any time). This is the type that would seem to be the most efficient.

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For either type of electric/ICE hybrid, you can choose to have plug-in charging; and you can choose to have a supercapacitor to get more regenerative braking, because it can instantly absorb as much current as you can generate. This can then be used to either charge the battery (at a rate that is safe), or you can use the supercap to power the electric motor at a higher/faster rate than the battery can.

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In all the parallel hybrid arrangements, you have a larger ICE than in an series hybrid of the third type. And, all the parallel hybrids need a transmission. A parallel hybrid's only advantage is it can have a smaller battery, but it then cannot be a plug-in, and has more limited regenerative braking -- and this would preclude it being the third type that I listed above.

I would love to have lots of both parallel and series hybrids, to base our judgments on. But the fundamentals are that:

* ICE power at low speeds is (much) worse than electric power at low speeds, and they require warm up time, and they require much more regular maintenance.

* Electrics allow you to have regenerative braking.

* ICE is required (for now) to have long enough range to drive non-stop all day.

* Renewable energy sources must be used in order to be sustainable over the long term. Electricity offers more renewable sources right now, that are already more accessible.

Can we agree on these?

It comes down to how you achieve efficiency at highway speeds, and/or over longer ranges, I think.