Best Mode for Long Idling?

I don't think I would bother with using charge mode to build up EV capacity. Just use what you have when you get there and then let the ICE top off the HV portion of the battery as needed. People camp out overnight with the A/C running in non-plugins all the time. You'll use a tiny fraction of the gas the other cars will use.

As for the engine not getting cooling air flow, it won't be running enough to make all that much difference, as opposed to the gassers who have to burn fuel full time to keep the engine rotating full time in order to keep the A/C system running full time.

The Prius is a beautiful machine!!

 

It should cost less than idling the gas engine.

 

i think the higher the mpg's, the more efficient the machine is. i don't have any data based on stop and go or idling though.

 

I've been trying to break it down in my head. The answer is no doubt it uses less, but the question is how much less? If the weather were perfect so that the Prius could literally shut down when not moving, the difference could be enormous. And perhaps I've just got an overreaction from being surprised how quickly the (non-Prime) traction battery goes down when just sitting there on a hot day with the A/C on.

What makes for good mileage in a Prius?

1. The Prime can have electricity poured into it to get 25 miles for free. Other than that, all energy the car uses comes from the ICE, directly or indirectly:

2. The Prius ICE runs on the Atkinson cycle, which uses 25% less gas (I think) but would normally be too wimpy for people to tolerate. Fortunately, the Prius has electric motors that can make up for this when accelerating -- particularly from a stop where electric motors have natural torque advantages and an Atkinson-cycle engine is particularly anemic.

3. Through regenerative braking, you can recover some energy that would otherwise be wasted.

4a. The two electric motors and one ICE, under computer control, allow for a continuously-variable transmission (CVT) which is much simpler -- less parasitic loss of energy -- than an automatic transmission, and also

4b. This arrangement also allows the ICE to operate more often within its most efficient range.

5. Aerodynamics, which isn't restricted to hybrids, but the Prius certainly emphasizes is.

In a low-speed situation like the original poster asked about, numbers 1, 3, and 5 have little effect. I think 4a is really only meaningful when moving or when holding the car by using the brakes while in Drive, so if the non-hybrid driver shifted into Park it might be a wash. And 4b is also much less of an issue when not moving.

That leaves #2 and also the fact that the climate control can run when the ICE isn't running.

Energy is wasted when charging and discharging a battery. Is spinning an ICE with gasoline, having it spin an electric motor, and in turn charging a battery 70% efficient? 50% efficient? I've read that electricity from your wall into a hybrid battery is about 80% efficient, so i imagine it's lower than that. So having the motors and the traction battery is a gain, but maybe only half the gain you might expect.

So the Prius starts out using 25% less gas when running the engine at roughly the same idle speed as the non-hybrid sitting next to it. The Prius will have a duty cycle, while the non-bybrid will have to run 100% of the time. So a big question is: on a hot day, what is the duty cycle: the percentage of the time the ICE has to run to provide enough electricity to run the A/C full-time?

An non-hybrid car will have higher parasitic loss than the Prius: 9-volt battery and alternator less efficient, engine hotter requiring more fan and coolant circulation, automatic transmission inefficiencies, etc. But does the Prius idle at higher speed when it's running A/C and also charging the traction battery?

I've read that an ICE approximately the size of the Prius' engine will use about 0.15-0.2 gallons of gasoline per hour just idling (in Park, I assume). I have to imagine there are folks here who know enough about idle speeds, etc, to put it all together, but I don't think we could say that the Prius gets twice the miles per gallon that the average car gets and therefore will use half as much gas sitting in a traffic jam with the A/C running. (Not saying you're saying that, just thinking aloud.)