A step in the right direction. Hopefully the Panamera will be designed with hybrid in mind instead of retrofitting like this Cayenne and reach even better mpg. Currently the EPA ranks the 2008 Cayenne at 14 mpg at best, and 12 mpg (both city) for V8 turbo models.

Maybe it'll send a strong sign to other automakers as well. Has Mercedes, BMW, or Volkswagen released any hybrids?

I still won't like this yuppie-mobile until it goes around actually cleaning the air and shooting $100 bills at everyone it drives by. But good for them.

I am confused. TFA says:

"The Cayenne Hybrid will feature a full-hybrid parallel design in which the hybrid module (clutch and electric motor) is positioned between the combustion engine and the transmission rather than having a branched or split hybrid power concept."

I would say (perhaps wrongly) that the cayenne is a series design and that a Prius, where the elements can work independently or together, is a parallel design.

While 24MPG is a significant improvement, it is still a low number in absolute terms for a personal transportation vehicle. Hybridization does not really make SUVs acceptable, because fundamentally no-one genuinely needs a luxury off-road vehicle at all. It's a contradiction in terms.

For the same money (or a lot less), you can buy a similarly powerful car-based wagon featuring better on-road handling, lower weight, lower rolling resistance, better aerodynamics, greater crash safety and better fuel economy. Too bad every wagon Detroit ever produced handled like a fishing trawler, earning them automatic demotion to mere shopping trolleys. Modern wagons are very popular in Europe.

Rafael - have to take you to task once again:

"A power converter transmits the electrical power to the drive motor at the required frequency. The generator and motor each need to be rated at the same or higher power than the ICE, making this a very heavy driveline."

As I've labored to explain before, with EV-based series hybrids the genset does NOT provide current on demand for the drivetrain. The addition of a battery totally changes this dynamic. The genset's ICE can be very small and light, thus dramatically reducing the needed size for the generator - and reducing the cost of both.

Your definition might be relevant to older, more traditional series hybrids applications, but their structure is fundamentally very different from the concepts being currently demoed.

"Transmission efficiency is low" - once again, where are these mystery inefficiencies coming from? The ICE is tuned to run very efficiently, the generator operates at nearly 95% efficiency, there is little power lost in the charging/recharging of the battery, and the direct drive motor only has a single gear reduction unit (more simple than even the most basic of manual transmissions), versus the much more complex parallel hybrid's power split device.

@AES -

yes, the addition of a very large battery to a series hybrid lets you operate the engine more efficiently and make do with a smaller generator. However, that very large battery also adds a lot of bulk, weight and cost to an already heavy and expensive drivetrain.

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Back-of-the-envelope efficiency estimate for series hybrid:

Efficiency for electric generator: 0.8-0.95. The low number applies at very low RPM, high number at optimum point. Figure 0.92 on average as used in a genset, because load cannot be kept completely constant at all times.

Efficiency for power converter: 0.8-0.93. High number applies only if the device is actively cooled. Let's assume it is.

Charging efficiency of Li-Ion battery: 0.6-0.92 depending on SOC, charge rate and temperature. If SOC variation is kept low to achieve longevity and battery temperature is controlled, figure 0.88 on average.

Discharging efficiency: roughly the same, figure 0.88.

Drive motor incl. reduction gear: 0.75-0.95, depending on operating point in map. Figure 0.88 on average in official duty cycles.

These are rough estimates intended merely to show real-world transmissions efficiency.

(a) power flow w/o battery buffering:

0.92 * 0.93 * 0.88 = 0.75

(b) power flow w/ battery buffering:

0.92 * 0.93 * 0.88^2 * 0.88 = 0.58

These substantial losses are not due to mechanical friction but rather, magnetic flux in the electric machines, semiconductor switching in the power converter and electrochemical reactions at the battery electrodes.

Compare this to a purely mechanical step-by-step transmission that achieves ~0.94 incl. the final reduction stage.

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Now figure that the gasoline ICE in the genset is always operated near its point of optimum efficiency, roughly 0.35. The battery has to filter out most of the variation in actual vehicle load, so figure half of all power produced by the ICE takes the scenic route.

Total efficiency: 0.35 * (0.75 + 0.58)/2 = 0.233

Alternative: figure the ICE is exposed to 2/3 of the load variation and therefore only achieves 0.28 efficiency on average, but the battery can be smaller and will last longer.

Total efficiency: 0.28 * (2 * 0.75 + 0.58)/3 = 0.194

Conventional drivetrain: ICE is exposed to full load variation, achieving just 0.2 average efficiency.

Total efficiency: 0.2 * 0.94 = 0.188

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Conclusion: the fuel efficiency gains due to a series hybrid drivetrain with battery buffer are modest once the ICE is running. Using a small battery makes little sense in this context, only the full fat version delivers substantial fuel economy gains.

For example, the Volvo ReCharge concept (based on the C30 w/ 1.6L gasoline engine) that will be unveiled in Frankfurt this week achieves 5.6L/100km in the NEDC *once the ICE is active*. The conventional drivetrain needs 5.7L/100km in the highway portion but comes in at 7L/100km for the whole cycle. This illustrates how the battery in the series hybrid is used to level the load on the ICE.

Verification: 7 * 0.188/0.233 = 5.65, so my assumptions are not far off.

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The real fuel savings in Volvo's PHEV concept come from the fact that the first portion of the trip is driven on grid electricity alone. Of course, the savings apply only to gasoline fuel, because electricity must be produced. In the real world, renewable energy constitutes just a small fraction of total electricity production except in a very few countries. That means either CO2 or radioactive waste is produced at the power stations. Plus, even though electricity is cheaper per kWh than motor fuels, it is not free.

Based on the numbers for the ReCharge regular full series HEV with large batteries can deliver a 20% improvement in gasoline consumption. With a plug-in option, total fuel cost and CO2 emissions can be reduced even further. However, because the ICE is already running efficiently, the delta is no longer quite so dramatic. Figure a 25% aggregate improvement in CO2 emissions over a conventional drivetrain.

However, the combined cost of the electric motors, power converter and the large battery needed for a PHEV will be sky-high. This is true even if you factor in that you no longer need a clutch, manual transmission, starter motor, alternator and that peripherals like water pump, power steering and even the a/c compressor can all be electric.

Concepts such as two-mode full hybrids and series hybrid PHEVs are great marketing tools to burnish a brand's green credentials by showing what is technically possible. However, for the incremental manufacturing cost of one such showcase drivetrain, you could equip ~10 cars with a micro-hybrid yielding ~4% improvement each (btw, Ford Europe's numbers, not mine).

Fuel consumption factor conventional drivetrain: 1.0
For M/VM hybrid: 0.96
For PHEV: 0.75

Now produce 11 cars and compute the fleet average:
11 * conv / 11 = 1.0
(10 M/VMH + 1 * conv )/11 = 0.9636 (gain of 3.64%)
(1 * PHEV + 10 * conv) = 0.9773 (gain of 2.27%)

Aggregate gain comparison: 3.64%/2.27% = 1.6

Ergo, in terms of the *actual* impact on national energy security/climate change, very modest but inexpensive solutions deliver *much* bigger bang for buck than high-falutin' extreme-tech concepts. Plus, M/VM hybrids force everyone to chip in for the common good.

Hybrid technology will be introduced faster with political support. For instance, if there were a legal requirement for plug-in hybrids, most of the car and light truck/SUV fleet could be converted in 5 years. Without leadership, it could take a century. Reality will be somewhere in between. In short, every vehicle should be a volt concept. If we believe in this technology, shouldn't we be actively and politically supporting this technology? Supporters should have access to form letters and the physical address of every congressman and- yes- even the president's and VP's office. These letters will be stronger if they are a petition with as many constituent signatures as possible. So, does anybody have any further ideas?

Raf-

Where are you getting 0.88 as an average for Li-Ion charging/discharging efficiency? That 0.88^2 is the biggest drain in your calculation. Most sources I have researched have put it more at 0.999 as opposed to between 0.66-0.88 for NiMH (both on the pack and individual cell level).

Replacing 0.88 with 0.999^2 actually puts out an electrical efficiency of ~0.75 - the same as without battery buffering. And gives an overall efficiency of 0.26.

This is qualitative, of course, but I don't think 7.2% is something to be sneezed at, especially since that's almost double a "microhybrid". The fact that the vehicles will also be EV dominant is also a huge bonus factor in their favor - something you yourself point out using the ReCharge as an example.

As far as cost is concerned, the infrastructure and materials supply could easily build a series PHEV pack for less than 10 grand, so getting the rest of the car to market for less than 30 grand is very doable.

Moreover, despite the "modest" increases in efficiency in hybrid mode, the series hybrid architecture represents, I think, a much better strategic platform for taking advantage of future improvements in solid-fuel engines. For example, many alternative engines - external combustion, microturbine, HCCI - have the key disadvantage of becoming very inefficient or underpowered at variable loads and speeds. Or in the case of HCCI - overly complicated. The simplified task of the genset gives the opportunity to take full advantage of each technology's efficiency gains. The 100 mpg EV1 microturbine series hybrid with a recuperator is a great example of this.

Awesome... now put it into a Cayman instead. ^_^

Charge / discharge efficiencies >98% are routinely demonstrated for lithium-ion and lithium-polymer.

eg http://www.dn-power.com/v2/Battery/PLIB-intro.asp
http://sciencelinks.jp/j-east/article/200107/000020010701A0276378.php

The newer chemistries are particularly efficient - Altair recently charged a 35 kWh pack in 10 minutes (210 kW power input!) at a press demonstration and the pack didn't even get warm.

As for Tesla etc, even 2% heat-losses for a 150 kW output battery is 3 kW, which is enough that would need a cooling system and radiator. Cycle and calender life for some battery types are also critically dependent on storage temperature, and this (rather than waste heat) is the main reason for the excessive regulation.

@ clett, AES -

I guess I owe AES an apology, the Japanese in particular appear to have made significant advances in Li-Ion charge/discharge efficiency since I last researched this. Afaik, Li-Ion polymer chemistries are only used for low-power consumer electronics.

However, it is not clear to me if these numbers apply to batteries for consumer electronics products (which are always trickle-charged and can get away with life expectancy of 4 years or less) or for automotive applications, which stress the batteries much more severely. In particular, high power demands are usually problematic for batteries of all kinds, because of the intense electrochemical reactions involved. The Japanese research suggests the chemistry presented is intended for a "secondary" battery, not sure what that means exactly.

Valeo indicates efficiencies of "over 90%" for the automotive Li-Ion cells it evaluated for its Stars-X micro-hybrid project, ultimately choosing a combination of a small supercap bank and a 14V AGM lead-acid battery instead.

@ Rafael:

"Secondary" cell is, as far as i know, just another term for a rechargeable cell. A primary cell would be a non-rechargeable cell.