Early next year, devotees of the Toyota Prius will have their chance to go a step further into greenness. Thatís when the Prius PHV, a plug-in hybrid based on the current Prius architecture, will be introduced.
(To see related content, about the Chevy Volt, go to Drive for Innovation and follow the cross-country journey of EE Life editorial director, Brian Fuller. On his trip, sponsored by Avnet Express, Fuller is driving a Volt across America to interview engineers.)
Design News recently had an opportunity to drive a pre-production version of the Prius plug-in, and the good news is that itís a sensible alternative-fuel vehicle.
First, it should be noted that, as a plug-in, this Prius is half hybrid and half electric. It differs from other plug-in vehicles in that it employs a relatively small battery. At 5.2kWh, the Prius has a battery capacity thatís about one third that of the Chevy Voltís 16kWh and about one fifth that of the Nissan Leafís 24kWh.
There are pluses and minuses to Toyotaís strategy. First, letís look at the downside: The Prius has an all-electric range of just 13 miles. If youíre looking for a vehicle thatís more electric and less hybrid, this isnít it.
The upside, though, is big. Yes, the range is just 13 miles, but the smaller-battery strategy has efficiency written all over it. Smaller means less mass, which translates into greater fuel economy. Thatís particularly important when the driver has exceeded the 13-mile range and the depleted battery is basically dead weight.
It also means the recharging time is a fraction of what weíre hearing from competitors. Instead of an eight-hour recharge at 220V (as is the case with the Leaf), the Prius plug-in recharges in about three hours at 110V or 1.5 hours at 220V.
The 110V recharging setup is a huge advantage, not only in terms of availability, but also in terms of cost. During the week we tested the vehicle, we recharged in three hours twice from a 110V outlet. Thatís very important in terms of cost, because it means owners donít need to get their garages rewired at $2,000 a pop.
The biggest advantage of the smaller battery, however, is initial cost. Toyota engineers told us that more range would have translated into about $500 per design mile. Hereís another way to look at it: Numerous estimates have placed lithium-ion battery cost at between $750 and $1,000 per kilowatt-hour. In terms of initial cost, that converts to between $15,000 and $20,000 to get an extra 20kWh.
During our test drive, we got the advertised 13-14 miles of range. When we drove within that all-electric range, our vehicle estimated its own fuel efficiency at 99mpg. It should be noted, however, that even when we drove within the electric range, the vehicle autonomously shifted back and forth between electric and hybrid modes. The main reason was acceleration. When we stepped deep into the accelerator, the car shifted into hybrid mode for about 10 seconds until a constant velocity was reached, and then it switched back. After a low-speed, 4.3-mile circuit, the vehicleís dashboard display claimed it had been in EV mode 75 percent of the time and in hybrid mode for the remaining 25 percent.
A longer drive was a different matter. As soon as we reached 60mph on a local expressway, the car shifted into hybrid mode and stayed there. The shift was seamless. During a 155-mile ride, the vehicle was in all-electric mode just 4 percent of the time. The fuel efficiency was still impressive, however, coming in at 56.6mpg.
The key to this carís success on the market, of course, will be its cost. Unfortunately, Toyota hasnít announced an exact figure. During an interview with Design News, Toyota engineers hinted at a possible figure hovering at around $26,000 or $27,000. But itís probably safe to say the ultimate entry number will be higher -- possibly landing between $27,000 and $32,000 before tax credits.
The bottom line is that this is a sensible alternative-fuel vehicle for someone who has a short commute to work. Some owners will be able to drive all week in the electric mode simply by recharging every night. Then, when the weekend arrives, they can depend on the car to switch silently to hybrid mode for greater range.
Jenn: I didn't time it myself, but the time is generally assumed to be around ten seconds. The acceleration characteristics of the this vehicle aren't great, but they are no worse than the conventional Prius. The electric powertrain provides about 60 kW. But if you're accelerating full-on, then you'll need about 120 to 150 kW, so the Prius Hybrid Synergy Drive has to kick in to make up the difference.
Hey Chuck, one thing I've wondered about with these batteries is whether there is deterioration over time. After months or years of recharging, will they lose the 13-mile reach? I would think the battery would become less powerful after countless recharges. How do these vehicles hold up in general over the long haul?
Looks pretty cool, Chuck. Question for you: My dad owns the original Prius. Any sense of whether this new offering would compel an existing Prius owner like him to want to trade up to the new model or whether this is more a play for attracting new Prius converts?
A few months ago, I read a very-interesting book called "Electric Vehicle Technology Explained" - a very good wrap-up (although slightly out-of-date) of EV technology. Probably about a third of the book was about various battery technologies.
Short summary, battery deterioration over time can comes, mainly, from two sources: heat and overcharging, both of which can cause electro-chemical degrade over time. I'm pessimistic about Nissan's claim that the Leaf's battery doesn't need any form of cooling system. Chevy and Tesla seem to be convinced that very considerable cooling systems are critical. The fact that Nissan designed its battery in modules makes me wonder if they anticipate a need for it to be replaced over time, and tried to reduce the impact by allowing you to replace only portions of it. I don't know, but I just have to wonder...
For whatever it's worth, my 2009 Prius' NiMH has a very-definite, but simple, cooling system - just convection cooling. Existing-Prius batteries have a long history of not showing very much degrade over time. This new one, however, uses an all-new chemistry, and presumably a different architecture, which could affect the effects of overcharging, a certain amount of which is unavoidable (unless you put the cells of the batteries purely in parallel, which is not realistic).
My personal guess would be that it won't degrade much over time, but I don't have any really specific information to base that guess upon.
When I first heard Chevy say, "the Volt is not any kind of hybrid, it's an EREV [extended-range electric vehicle]," I rolled my eyes back into my head. "Don't give me all that marketing hype; it's simply a series hybrid with a big battery."
However, as I read more about the Volt, the Leaf, and the plug-in Prius, I'm starting to accept that it really isn't strictly marketing fluff. The lifestyle differences for these vehicles really is very significant. It's clear to me that the plug-in Prius is still fundamentally a hybrid: A car with multiple, heterogeneous power sources, with a computer system that attempts to find the optimal balance between those sources. In short, it's a vehicle whose goal is to harvest the best aspects of each power source. The only big difference is that they beefed up the battery and made it externally rechargeable.
Although the volt is in fact a (series) hybrid, clearly it's design goals are totally different: To give you a limited range of pure-electric driving, with a gasoline backup. The Leaf, obviously, is intended for a less-limited range, but with no backup. The plug-in Prius does not appear to be intended to function for any significant period of time completely free of gasoline, so it is still truly a hybrid vehicle.
By the way, Mr. Murray, I doubt if the "99.9"MPG number you saw was a true reflection of the mileage you were getting. Priuses have always had mileage displays, instantaneous and cumulative, that "peg out" (saturate) at 99.9MPG. In other words, you were actually getting over 99.9MPG, with no indication of how much more.
Question: Does this Prius insist upon buring gas just simply to warm up the engine after you fire it up? Yes, yes, I understand why they do this: The Prius' power-split-device-based drive system means that the engine turns over most of the time that you're not a complete stop, even if it doesn't get fuel or spark. So they decided that you have to warm up the oil or the engine will suffer excessive wear and cause drag. In this particular case, however, where the real benefit is that short trips (and I for one make a lot of very-short trips to the grocery store and such) use hardly any gas at all. If they do insist on warming up the engine, it would pretty nearly negate any benefit, it would seem.
Beth: This vehicle is truly different than its predecessor because it enables certain drivers, especially those who make a lot of short trips, to run in pure electric mode for a high percentage of the time. Theoretically, it's possible that your father wouldn't have to add gasoline for weeks or even months, depending on how diligent he is about recharging. That said, it's not for everyone. People who have a longer drive to work -- for example, 15 or 20 miles each way -- would probably be better served by the old Prius powertrain architecture.
Rob: Battery deterioration is a slippery subject. It depends on age, mileage and repeated deep cycling of the battery. The advantage of this battery, however, is that it should be less costly replace than, say, a Volt or Leaf battery, because it's significantly smaller.
Thanks Chuck. Has the electric vehicle (EV) world matured enough for consumers to take battery replacement into account as part of the price of owning an EV? With traditional vehicles, consumers have a pretty good idea how often they will have to replace various part of the car. And they have a pretty good idea of the relative cost of that maintenance. Has battery replacement become part of the consciousness of the EV owner?
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