Road test: Toyota Prius 3 Plug-In Hybrid

Toyota follows competition with a plug-in rechargeable variant of the Prius. 

With more than 5 million hybrid cars sold as of December 2012, Toyota is not only the largest car manufacturer in the world, but also the undisputed leader for a technology that has gone mainstream. It is however with apparent reluctance that the Japanese company moved to launch a plug-in rechargeable version of the Prius, and the competitive pressure coming from General Motors with the Chevrolet Volt (badged Opel Ampera in Europe) and Nissan Leaf probably were contributing factors.

After a large scale test in several markets with a fleet of several hundred cars, Toyota proceeded to the commercial launch of the rechargeable Prius early 2012. As show in the table below, the selected option does not radically increase the battery capacity over a standard Prius III, especially when compared with the Opel and Nissan products where a much larger electric range were part of the technical brief.

It is important to stress that the maximum energy content listed in this table are theoretical. Out of concerns over battery longevity, manufacturers only use a fraction of the total available charge. For instance, we only managed to inject 3.2 kWh of electricity into our test car, from which one must substract thermal and efficiency losses during the charging process. Counting on an estimated 75% efficiency ratio, useful energy is probably only 2.4 kWh, or a smidge over half of the total capacity of the Lithium Ion battery pack.

Charging the Prius on a standard power socket is easy and trouble free. We did not experience any issue at our usual charging locations, the process completes in about 90 minutes at an average 10A of current. Our car drew an average of 3.054 kWh as reported by our external current meter. It is easy also to program the car to charge at a set time during the night and thereby to benefit from the cheaper electricity prices.

Toyota claims a maximum electrical range of 25 kilometers, a distance we nearly managed to replicate, but at the price of extreme eco-drive measures: flat route, extremely gently acceleration, absence of traffic and cruise speed below the limit. By adopting a more realistic – though eco-friendly – driving style, we reached 19 km on flat suburban commutes, and only 14km with a mix of down- and uphill city streets in Lausanne, in spite of a net zero altitude change.

Freeways ? The Hybrid Synergy Drive system, a continuously variable transmission based on planetary gears does not allow to exceed 99 km/h in electric mode, making it difficult to merge into traffic. This maximum speed is also difficult to reach as total electric power is limited any excess pressure on the throttle pedal will spark the gasoline engine. Even if you adopt a slow cruise speed (80 km/h), a long incline can be enough to trigger the 4 cylinder thermal unit. It is difficult to isolate all the factors that can result in a switch from the electric ‘EV’ mode to the hybrid ‘HV’ mode, but these include use of the heating system and other mechanical necessities, translating into a vague message ‘EV mode unavailable – warming up”. A consequence of not-so-extreme winter temperatures ? Difficult to say, but the fact is that imposing EV mode until batteries are empty is not always possible.

The subjective appeal of a rechargeable car is the ability to enjoy electrical drive over extended journeys, without the noise and vibration inherent to an internal combustion engine. The Prius III Plug-In can deliver against this expectation, but in conditions limited not only by its moderate range, but also by other unpredictable factors. I would be inclined to speculate that Toyota has adopted a very conservative approach to the management of the Lithium Ion battery, and that a sustained solicitation triggers a handover to the 1.8 liter VVTi  engine.

Another telltale sign of this conservative approach is the limited torque available on tap. In comparison, the Nissan Leaf and Opel Ampera are much zippier and feel measurably faster off the line than a decidedly very calm Prius. Even if the exercise is in thorough contradiction with the very “raison d’être” of these cars, one of the enjoyable aspects of electric cars is the ample availability of torque and the fun of fast acceleration in near total silence. Nothing such here, petrol is required for swift reactions, electric propulsion is reserved for energy-efficient mobility.

I trust Toyota engineers and the unique experience they have from millions of cars covering hundreds of billions of miles with unquestionable reliability, but the prospective buyer must make his (or her) mind in full knowledge: the Prius Plug-In only offers a fraction of the pleasure to drive an electric car and is rather to be considered as a hybrid on steroids. With this car, electric drive is an opportunity, but cannot be an obsession.

From this angle, the Plug-In Prius displays good fuel economy. We measured 4.72 L/100km (4.4 L/100km at an average speed of 70 km/h according to the on board computer), with an additional 33.6 kWh of electricity drawn from the power grid, the equivalent of 11 charge cycles. There are several ways to analyze these figures.  The eleven charge cycles allowed us to cover around 200km in electric mode at a cost of 33.6 [kWh] * 0.145 [CHF/kWh] = 4.88 CHF, or the economic equivalent, at today’s pump prices, of 1.35 L/100km. The remainder of our 1848 km road test required 87.23L of 95 unleaded, translating into an effective mileage of 5.3 L/100km in hybrid mode. This value is consistent with the 5.44 L/100km measured with a Prius II over 50’000km, and lower than the 5.7 L/100km we computed in our Prius III road test under more severe conditions (passengers, higher cruise speeds, alpine roads in the mix).

Electrical consumption is very dependent on the route and driving style, with extremes ranging from 133 Wh/km in snail-like eco-drive to 229 Wh/km in the Lausanne hills. These values are in line with those measured on the Leaf and the Ampera, in spite of the technology differences between these models. Unlike petrol powertrains, the energy efficiency of these batteries and electric motors seem secondary in comparison with the effort, chiefly the itinerary and the driving technique.

Like the Ampera – and to a lesser extent the Leaf due to its limited range, the Plug-In Prius allows to commute at low energy costs, a radically attractive economic proposition in comparison with a gas or diesel car of equivalent size (almost 4.50m in length, or 24cm longer than a VW Golf). There are however a few important caveats.

First, the range, limited to 15 or 20km depending on conditions. Sufficient for short distances, unless a possibility exists to charge at destination. Second, the capital outlay. The Plug-In version is priced 13’000 CHF (9000 €) higher than the ‘base’ Prius:  51’900 CHF (37’000 €) list price. Our Sol Premium version, arguably well equipped, carries a dizzying price tag of 61’630 CHF !

Is this 13’000 CHF premium economically justifiable ? Let’s consider a favorable case where one can go through two charges a day and cover 40km in electric mode. The difference in daily energy costs places the break-even point at 21 years of 220 business days. It is impossible to build a financial case on the extra cost of this version, furthermore as there is no credible scenario under which the price of electricity would not, over the medium term, fluctuate in tune with the price of gas at the pump.

Focus must then be shifted toward other criteria. Ecological considerations can play a predominant role in the purchase decision for such a car, but can appear more ideological than factual as soon as the origin of electricity is factored into the discussion. In Europe, 55.4% of electrical power comes from fossil fuels, and another 27.8% is nuclear (source: Eurostat 2009) .

Focus must then be shifted toward other criteria. Ecological considerations can play a predominant role in the purchase decision for such a car, but can appear more ideological than factual as soon as the origin of electricity is factored into the discussion. In Europe, 55.4% of electrical power comes from fossil fuels, and another 27.8% is nuclear (source: Eurostat 2009). All that is then left is the luxury of electric drive. Every hybrid car we test emphasizes the point that electric mobility reigns supreme in terms of silence, absence of vibration and comfort. Electric torque delivery can be fun too, but we already mentioned that this is not the Prius strong suit.

Visually, the plug-in version distinguishes itself from a standard Prius III with its charging port on the rear right fender, its logos and the 15 inch rims, the only available option on the catalogue while most hybrid versions get snazzy 17 inch alloys wearing 215/45R17 rubber that go a long way in giving an attractive, sportier stance to the car.

Interior design is very similar to the base version, except a few specific functions. The EV button has been renamed EV/HV, allowing to switch between hybrid mode (where the car will attempt to optimize use of the battery) and EV mode where the driver can attempt to force the depletion of the battery before tapping into the 45L gas tank. The EV City mode is nothing more than a neutered EV mode with limited torque. I enjoyed the ergonomics of the raised center console and its touchscreen, with rapid access to the different functions through the buttons lined on each side. Seats and driving position are comfortable too, a significant progress over the Prius II, in spite of the fact that the steering column can still only be adjusted in angle, but not in reach. This makes for a comfortable freeway car, except for the noise of the Atkinson 4 cylinder engine when it is put to task on uphills. Designed to deliver its peak torque at low revs (142 Nm at 2800 rpm), it can function at extremely low revs under light loads, but its drone can become tiring, for instance when trying to maintain a 130 km/h cruise speed while climbing hills.

We had already noticed that the Prius III had a very optimistic speedometer, and the same is true here with the Plug-In version, to the point where it is strikingly obvious in traffic. After checking tire pressure, we measured, swiss chronometer in hand, a significant mismatch between the vacuum fluorescent display and reality: 90 km/h at an indicated 100, from 107 to 110 at an indicated 120, 113 at 130 km/h, etc … Our measurements systematically show that displayed speed is grossly exaggerated. Even more peculiar, the odometer is quite precise when compared with google maps. Would Toyota try to protect its customers from speeding tickets ? Or entice them to save fuel by enticing them to drive slower than they think ?

Equipped in Sol Premium trim, the Prius 3 Plug-In is an enjoyable car to live with, easy to manoeuver once you factor in its mediocre turning radius (11.2m according to the spec sheet). There is a wealth of storage compartments, one of which is dedicated to the charging cable. Suspension is comfortable, but with spring rates which are not excessively soft. Indulging into spirited driving attempts will quickly confirm that the 65-series tires lack rigidity and translate into predictable understeer. On freeways, the car offers good stability and is more relaxing than a Prius II to drive on long distances. The electrically assisted steering column is light but numb, not too surprising for the target audience.

The Toyota Prius Plug-In is without doubt a polished product which builds on the unmatched technological experience of the Toyota group over time and volume, but this expertise comes at a steep price for a car that is more of a super hybrid than a real electric car. Competition offers more in terms of an electric car experience, both in terms of range and torque, at equivalent prices. If price is no object, then the plug-in version is without doubt a better Prius, but for people in the market for a car delivering on the promise of an electric car experience, the Opel Ampera represents serious competition.

List price of the tested model: Toyota Prius Plug-In Hybrid Sol Premium, metallic paint: CHF 61’630.-

Facing competition

* including eco-bonus ** not rechargeable

We thank Toyota Switzerland for the load of this Prius Plug-In.

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