Getting excited about next Gen. Prius Plug-in

Two questions:

1. Why do you assume the PHEV Prius will recharge itself?
2. Why do think that would be a good thing?

The main advantage of a PHEV over a standard HEV is that it can offset gasoline with electricity from the grid. To maximize gasoline offset, you want to match your battery size to your trip length, so that you always finish your trip with a battery that has just reached empty. That way you are not paying for and hauling around more battery than you need, but you also have as much available capacity to store grid electricity as possible. If after reaching the empty battery point you still have to drive more, you want to run the ICE as little as possible and as efficiently as possible until you can recharge the battery. If you use the ICE to recharge the battery you will burn more gas than you needed to on your trip, and have less room in the battery to store grid electricity for offsetting gas on your next trip.

Your thought that this would double the effective EV range doesn't make sense to me. EV range attributed to electricity generated by burning gasoline in the ICE is not really EV range. Its gasoline range, at a lower efficiency than if the ICE was turning the wheels directly. By that logic the Volt would have infinite EV range, because its always being driven purely by the electric motor whether its electricity is being supplied by the battery from the grid or from ICE turning the generator. IMHO that is the true advantage of the HSD over the Volt. Both will be potentially equally efficient while discharging the battery through the motor, as both will run essentially as series hybrids. Once the battery is empty, the HSD will have a significant advantage. The Volt will have to continue to run in a series mode, with its built in efficiency penalty of converting energy from mechanical to electrical and back, while the HSD can transition into a parallel hybrid mode where the ICE drives the wheels directly with no such conversion penalty.

Here is a rough numerical example to try and illustrate. To keep things simple, assume a Prius PHEV 10 gets infinite mpg on battery, 50mpg while just maintaining a depleted battery, and 25mpg while recharging the battery. For the 25mpg, I assume that it will take the same amount of time to charge the battery back up as it did to deplete it. I also assume that the efficiency improvement from more heavily loading the ICE cancels the conversion and storage loses associated with charging the battery. If the IC is putting out twice the power (1x to drive the car, 1x to generate electricity) then fuel use doubles, mpgs gets cut in half. A regular Prius is calculated at 50mpg.

CS = Charge Sustain, maintaining the battery at a constant level once discharged
RCH = Recharge, cycling the battery back up to 100% every time it depletes
HEV = Normal Prius

Trip - CS gal - CS MPG - RCH Gal - RCH MPG - HEV Gal - HEV MPG
10 mi -- 0 ------ inf ----- 0 ------ inf ----- 0.2 ----- 50
20 mi - 0.2 ----- 100 ---- 0.4 ------ 50 ----- 0.4 ----- 50
30 mi - 0.4 ------ 75 ---- 0.4 ------ 75 ----- 0.6 ----- 50
40 mi - 0.6 ------ 67 ---- 0.8 ------ 50 ----- 0.8 ----- 50
50 mi - 0.8 ------ 62 ---- 0.8 ------ 62 ----- 1.0 ----- 50
60 mi - 1.0 ------ 60 ---- 1.0 ------ 50 ----- 1.2 ----- 50

I think this shows a couple of interesting things. First, in the best case the recharge mode is as good as charge sustain at 10, 30 and 50 miles, but worse at 20, 40 and 60. Its never better. And this assumes that there is no penalty for charging the battery off the ICE, which I think most current gen Prius drivers already know is not the case. In reality the conversion efficiency loses of converting the ICE output to electricity, storing it as chemical energy in the battery, then converting it back to electrical energy to drive the electric motor will probably keep you from even breaking even at 10, 30 and 50 miles.

The other interesting thing to note is that while a PHEV 10 sounds pretty pathetic, its still reducing fuel consumption by 33% at 3X its range and 20% at 5X its range. With the cost probably being a few $k at most, thats not a bad result.

Rob

 

From everything I have read about the factory Toyota Plug-In, they are only aiming for 8-10 miles of EV range. That is less than 1/2 of what the Hymotion system is providing today.

Of course, the Toyota Plug-In will also likely be cheaper than the $10,000 premium of the Hymotion system.

After driving the Hymotion plug-in for the past few weeks, I can say that 20-40 miles is the minimum necessary for this type of system. Most days it is enough for me because I either drive less than that, or I have the opportunity to recharge a few hours during the day while parked at work or at various locations where I am during my daily driving. Only 3 times in the past 3 weeks have I actually emptied the Hymotion battery and been forced to run in stock Prius mode.

If Toyota is only aiming for 8-10 miles, that is gone in a heartbeat. Why even bother?
I would use that up quickly every single day and be driving many miles without the electric boost of a Plug-In battery.

So frankly I think there will always be an aftermarket to boost the power of these Plug-Ins with additional range. I encourage Toyota to improve on the Prius. But their current goal of 8-10 miles is not even close to being sufficient.

 

The system wouldn't force such aggressive recharging.

Taking advantage of electricity available from a plug at home is the point.

.

 

9G-man, I agree that the Prius with 8-10 miles of EV range is a huge improvement over the current Prius. It will be wonderful. But I doubt that will be the standard Prius. It will likely be a premium option similar to the "Touring" option now. Maybe 5% of the Prius vehicles will come that way.

My argument is that the people who want that type of performance actually want much more than 8-10 miles of EV action. Recharging from the gas engine is nice, but also very inefficient. The most efficient electricity in the system is from the outlet where you plug in. A small ICE can never compete with large utility scale turbines in the creation of electricity.

The goal is to minimize gasoline consumption and shift the balance of power to the electric grid, which can be produced from zero carbon sources like wind, solar, nuclear, geothermal, etc.

The Hymotion system still allows regen into the stock Prius NiMH battery, so that energy savings is already present. The Hymotion Prius is using both batteries at the same time. The stock NiMH battery never falls below 6/8 while Hymotion is engaged, but it is still providing energy to the overall system and recapturing energy via regen.

My only opinion on the Toyota Plug-In of 8-10 miles is that it will be gone very quickly based on my experience. I use most of the 30-40 mile range of the Hymotion every day. It is right at the limit of my average day and likely the average day of most Americans. I actively try to plug in everywhere that I park for "opportunity charging" in order to extend my daily Hymotion range. It is a new method of thinking and operating. But this is the future.

There is a reason the Volt is aiming for 40 miles. That is the sweet spot of being functional.

 

I agree with miscrms. There might be improved regen, and better overall efficiency but you can't say that the effective EV range of the plug-in prius is doubled because of "transit charging".

If there is only one battery, it will be interesting to know what SOC the system will try to maintain while in normal prius mode after the 10 mile range is surpassed. The OP appears to think it will shoot for over 90%.

It may be relatively low (under 25%?) (<25% SOC of this new battery equaling something above 60% in the current Prius battery in terms of Joules?).

Going higher would lead to more conversion losses. But can this battery be kept healthy at a low SOC? If not, Toyota engineers might have a problem on their hands.

 

I am hoping there will be a facility where the driver can let the car know whether or not it should specifically degrade mileage to charge the battery. *I* will know if I am going farther than the EV range before I can plug back in, AND whether or nor I'll be able to plug in when I stop, or if it will have to wait until I return. No reason for the car to set a minimum SOC other than battery protection. However, if I'm doing a 200 mile trip, I hope the car can function as it does now, again with me having the ability to end up at my plug in point with little SOC to spare.

 

as a first offering, 9-10 miles is good. it still puts you in all EV for the shorter "run to the corner for a minute" trips which are the worst for your overall mileage.

and i also think that later down the road, extended range options will be provided just like upgrading the stereo is now...

lets see the base plug in at "neighborhood" range of 8-9 miles

then another "city" range of 20-25 miles

and then a "commuter" range of 40 miles

that way, each can choose what they want based on what their specific needs are... better than a "one size fits all approach"..

as little as 8 miles would be, it would work for me, my one way trip to work is 7 miles and i am allowed to plug in at work, so no prob!!

*edit**
one last thing...

sorry, just couldnt resist.

but look at what happened with gm's "all or nothing" approach... maybe Toyota is doing it right by starting out small and manageable, collecting data and then implementing a larger pack option after they are sure they can do it effectively

 

In my understanding, the plug-in Prius works as follows;

1. initial EV mode (called depression mode): Prius runs using battery down to some SOC, say 30%.
2. normal HV mode (called sustaining mode): Prius runs as normal hybrid vehicle trying to maintain the target SOC, say 30%. There is no aggressive charging to raise the SOC because it is not efficient way to do aggressive charging using gasoline.
Please refer to page-14 of following presentation.
http://www.toyota.co.jp/en/ir/presentation/2008/pdf/081002presen_2.pdf

Also, please forget the 8-10 miles of EV range on the current plug-in Prius.
It is just a prototype for field testing using two existing NiMH batteries.
The EV range for the production plug-in Prius using Li-ion has not been announced yet, so we can't discuss about it.

Anyway, I prefer Toyota version of plug-in than any after market ones, such as Hymotion or DIY things because...
- It'll have Toyota warranty.
- The warranty length will be as long as the vehicle life.
- It'll offer pure EV mode up to 100km/h(62mph).
- It'll have sophisticated charging/discharging system to maintain maximum battery life.

Ken@Japan

 

Those excited about new Prius can sign up for email updates at:

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I am not sure why the Volt is even a concern seeing what kinda of shape GM is in right now. I doubt it will get off the ground, GM may not be around by the start of next year. Of course if they get bought out, then the project may carry over to the new company.

the new prius should be great.

 

If the auto manufacturers can agree on a common external charging configuration, so that all plug-ins can use the same attachment, then local cities might be talked into putting up charging posts than any any hybrid or fully electric car can plug into. Placing a dime or quarter into the post and receiving a charge while at work, shopping, etc., might solve many of the problems discussed in this thread, IMHO.

 

No - 40 miles is 40 miles. Even stupid people know that going somewhere 20 miles away and coming back equals 40 miles.

Eh?

Don't Volt bash for the sake of it - it's a good system. I'm excited at the prospect of there being more technical options available - that is, a series or a parallel hybrid. There are possible advantages to the series hybrid in that the recharging engine can be specifically tuned for max efficiency at one specific engine speed, and that never need change. Don't forget that the Prius runs one motor as a generator into another - which is lossy too.

As for 8-10 miles not being enough - I bet 80% of the journeys in the town where I live would be covered. It's only 4 miles into town from where I live, which is right on the edge.

 

Interesting discussion. Got me thinking.

Our Prius gets driven appx 35 miles/day, that is daily use excluding vacation roadtrips.

Suppose a plug-in hybrid gets 100 mpg in EV mode, has an "X" mile range in EV mode, then gets 45 mpg in hybrid mode, and suppose the car starts the day fully charged but is not re-charged until nighttime, also no regenerative charging. The curve of cumulative mpg in a given day is a flat line at 100 mpg up to X miles/day, then drops off sharply and asymptotes down toward 45 mpg for miles/day above X. This is the curve shown in the slidepack linked by Ken, page 14.

If the plug-in Prius has X = 10 miles, then at 35 miles/day the cumulative mpg is 52 mpg, only a 7 mpg improvement over the 45 mpg of a non-plug-in hybrid. If X = 20 miles, then at 35 miles/day the cumulative mpg is 62 mpg, a 17 mpg improvement.

Depending on the extra cost of the plug-in feature, a 7 mpg improvement may not be enough for me to care. My 08 works fine, after all. But a 17 mpg improvement would get my attention.

 

Also, the slidepack shows the results of a survey that Toyota did. 22% of users expected EV range of 10 km, 30% said 20 km, 20% said 40 km. So even a 20 km EV range would satisfy barely over 50% of users' expectations.

This makes me hopeful that the factory plug-in Prius will have EV range greater than 20 km (12.5 miles), since otherwise the car would fail to meet the expectations of nearly 1/2 the potential owners. Hopefully that is how Toyota will look at it, anyway.

 

I think that the facts and figures may be getting in the way of the realities. Most people who take polls really don't consider the depth of the question or do they have little knowledge of their actual driving needs. The first thing that must be done is to get the general public in the right frame of mind to reverse the average American's love affair with big and/or powerful cars. When gas went over $4.25 in my area, I started seeing less and less big pickup trucks and large SUVs, and it even lasted for a while as the price dropped into the $3's, $2's and then under $2, but as the price got to $1.75, I noticed a lot of large pickups and SUVs returning to the streets.

The car manufactures must get the electric and hybrid cars out there and then as technologies improve, the people will come around. Battery technology will be the sticking point for quite a while. Many years ago, I read about a battery that could be drained and refilled in an operation similar to fueling a vehicle with gas. If that technology comes to fruition, then there will be no need for hybrids, but as long as batteries can not give the driving consumer his daily needs between overnight recharging, there will be a need for hybrids.

I mentioned earlier in this thread the need for charging posts so that people can recharge their electric cars while shopping and while at work. That can be an intermediate step in the transition from pure internal combustion to pure electric.

 

PS: I got the latest "Consumer Reports" today and I read the very interesting article about their conversion of a standard Prius to Plug-In.