Living with a plug-in hybrid

It's not every day you get to drive a high-performance prestige sedan costing in excess of a quarter of a million dollars.

When you do, fuel consumption figures somewhere north of 15L/100km go with the territory. Yet here was this Porsche Panamera, posting a long-term fuel consumption average of 5.6L/100km.

Pretty decent number that... for anything but a plug-in hybrid. This particular plug-in hybrid is exceptionally comfortable inside, accelerates like a rocket and shrugs off corners with complete disdain, yet it should have achieved an even lower figure (Porsche claims a 3.1L/100km combined figure).

The reason it didn't do better? The Panamera S E-Hybrid, as it's named, is limited to a pure-electric driving range of just 20km around town, which is far less than most all-electric, battery-only electric vehicles (EVs) and also down on most other plug-in hybrid vehicles (PHEVs).

Then again, there aren't many this big and heavy (2095kg DIN unladen), and fewer still that can sprint to 100km/h in a claimed 5.5 seconds on their way to 135km/h without using any fuel (outright top speed is a claimed 270km/h).

In the case of the six-cylinder petrol-electric Panamera, as soon as you drive the car further than 20km between battery charges, the long-term average fuel consumption figure climbs. If you lose the motivation to recharge the Panamera after every (short) trip, fuel economy declines further.

Plug-in hybrids might not come with the range anxiety of a pure EV and, in theory, are the most suitable form of vehicle electrification in a country like Australia, but this is just one of numerous challenges PHEVs present. Some are logistical, some are market-driven, some are values-based.

We all hate taking time out of our day to refuel a car, but it only happens on average about once a week. Recharging a plug-in may end up being a twice-daily ritual, and it may even have ramifications in an emergency.

Need to get someone to the hospital in a hurry? Your time is likely spent more productively tending to an injured friend or family member than uncoupling a recharging unit so you can drive that person to hospital. Roll on inductive charging...

Social considerations? You're bound to be bailed up at some point by some crazed eco-nazi who's keen to tell you that their decades-old Fiat 127 is kinder to the environment than your $300K Porsche, fresh from the factory.

There's no easy answer to that, although you trust that the Fiat probably discharges more CO2 in a day than an average suburban garden can absorb in a week.

Consumer choices? We understand the desire of some people to be seen to be green, but why opt for a Panamera over the market's sole performance EV (currently), the Tesla Model S? The Model S in P85D form is way cheaper and significantly faster in a straight line.

Alternatively, why not purchase two cars: an Audi A3 e-tron for the weekly running around in zero-emissions mode, plus a 'real' Porsche for the occasional weekend blast?

The carbon footprint is probably much the same, since you can only drive one car at a time anyway. There could be cost savings on the combined purchase prices and possibly some gain in resale value.

There's a psychological component to operating a PHEV too. It's easy to become obsessive about saving fuel to the extreme. Let's call it the Jay Leno syndrome, after the American talk-show host who famously boasted he had operated a Chevrolet Volt over 11,000 miles (17,700km) using just 4.65 gallons (17.6 litres) of petrol.

This obsession can affect your focus in traffic, if you're flicking between different screens to check out power flow or distance travelled in the various modes. It's taking your eye – and your mind – off the road.

The Porsche is not alone in encouraging this sort of behaviour, Toyota's Prius makes a virtue of it. It's easy to become fixated with this 'game' too. On different occasions I arrived at my destination without drawing on petrol power at all. That's an average trip of 20km; longer in the morning when dropping the kids at school.

But to achieve that result you have to drive everywhere as slowly as possible... except while coasting downhill. And with 21km of zero-emissions (e-power) range, my morning trip doesn't leave much margin for energy wastage in the event that someone's old Commodore breaks down in the left lane, banking up traffic for 3km of a major arterial road.

On occasions the petrol V6 would kick in when supplemental power was required – making a right turn across a busy road, for instance. Fuel consumption like 0.6 or 0.7L/100km over a 20km drive is roughly equivalent to the petrol engine starting, accelerating hard briefly and then switching off again after 300 metres.

The tactics of tippy-toe driving

As the regular driver you soon learn how to get the most out of the Panamera. On Friday morning my 20.5km run taxed the Porsche's EV range to its limit, and beyond. The petrol V6 fired up just 700 metres shy of my destination.

By the next Tuesday morning, the Panamera reached work entirely on electric power alone – in heavier traffic. There was 0km electric mode range left, but the Porsche made it.

Avoiding heavy traffic is a key factor in conserving electrical energy. Leaving work later on Friday night ensured the Panamera reached home (a 19.6km trip) entirely on electric power and with 3km of EV range in hand.

Sometimes, prolonging the time in EV mode is a balancing act. Wait for the traffic to clear and hope the light doesn't change to amber? Or peel out of the left lane, using extra energy from the battery to get through the intersection before the light changes?

It depends on multiple factors, including the density of traffic on the other side of the intersection. There's no point going feral with the throttle only to come to a grinding halt within 50 metres.

The whole family piled into the Porsche on Saturday afternoon, and we set out for the city via the nearest freeway, without recharging the battery. The Panamera reached the freeway on electric power alone, but I then activated the e-charge mode once the car was up to cruising speed on the freeway.

This starts the Porsche's petrol engine to recharge the battery on the fly, as it simultaneously supplies motive power to the drive wheels through the eight-speed automatic transmission. It's not a particularly efficient or cost-effective way to recharge the battery, but it's certainly better to use e-charge on the freeway than in stop/start traffic.

Fuel consumption averaged 7.6L/100km for the 21.1km drive into the city, with the climate-control keeping the temperature inside the car at 21 degrees on a 31-degree day.

A test run on Sunday night resulted in an average fuel consumption figure of 7.3L/100km, which was due to the petrol engine running in Sports mode at intervals during the 58.6km drive.

The Panamera used an inordinate amount of electrical energy with the headlights on and running up hill. Yet the car travelled 35.9km in EV mode, starting out with 23km of electric mode range and recovering additional energy from braking or coasting on hills and from the petrol engine.

For the final full day of my time with the Panamera, fuel consumption was 0.0L/100km in the morning and 0.6L/100km in the evening, after I tramped it to enter a road ahead of another car fast approaching from the right.

An Airbus moment

Monday night the Panamera threw me a curve ball, as the Americans would say. At the 2.8km mark on the way home the car suddenly sounded an audible alarm and displayed two alternating Airbus-like error messages in the right gauge of the instrument binnacle.

According to the car, the hybrid-drive system had failed and the car's drivetrain management system was observing reduced engine power mode.

There were no signs to indicate what had caused this or what was specifically wrong. The V6 had burst into life, but was supplying motive power only. The trip computer indicated that the battery retained its charge – worth 14km of zero-emissions range – but e-power mode was not available.

The car continued to drive in internal-combustion mode until I found a quiet street, pulled over and reset the system. The car restarted normally and I drove the rest of the way home in EV mode. Fuel consumption for the drive home that afternoon was 8.9L/100km, based on nearly 16km of the 18.8km trip travelled on petrol power.

Porsche puts it down to a 'glitch', since the problem didn't reoccur and was resolved by resetting the system.

How alt-energy cars may shape society

Spending a week with a high-end hybrid like the Panamera has been enlightening. It's a pointer to what the future holds – except hopefully each new technological advance will come sooner than the one before.

The plug-in hybrids of 2020 will be smarter cars, I trust, and maybe they'll be so very intelligent that they'll take all responsibility for driving and monitoring fuel use out of the driver's hands.

At some point in the future, improved plug-in hybrid technology (with capacitors to recover braking energy?) will be matched up with autonomous drive systems. That day will be a blessing for commuters.

Just name your destination in the car's satellite-navigation and have the car plot its own course, taking you there in the most energy-efficient way, without any need for you to monitor energy expenditure – unless you want to do that.

Before that happens, however, governments will have to sort out roads and other infrastructure. It should start with discouraging civil engineers and town planners from implementing 'Maginot lines' of speed humps around our municipalities. Pacifying traffic need only reduce speeds to the speed limit, no lower than that; otherwise local government is contributing to excessive energy expenditure.

There are currently few allowances made for cyclists sharing the roads with cars either. For the sake of safety AND conserving energy, governments need to address the separation of bikes and cars as a priority; the status quo will hobble autonomous cars with conservative operating parameters to ensure cyclists don't get skittled.

And for the sake of everyone's sanity... more roundabouts, fewer traffic lights please. Most traffic-light-controlled intersections make no allowance whatsoever for efficient energy usage – in either hybrids or conventional cars. The programmed time delay and sequencing won't suit future needs.

Oh, and before that happens, we probably need to make public transport more appealing, more cost-effective and more accessible – to take more cars off the road.

Why is this all so important? In a highly urbanised country like Australia, improved traffic flow could make a world of difference to our national energy consumption for road transport.

Having saved my little bit of the world for a week, I'm now looking forward to a wasteful diesel SUV for the next seven days. So are my kids; they recognise that driving a hybrid for optimal efficiency turns drivers into zombies.

Or as the kids see it, Dad's driving a Porsche way too slowly.