Hybrid technology is not new, yet it’s not always been practical. But now there’s three new Mercedes-Benz plug-in hybrids.

WE HAVE run the numbers many a time, and the average hybrid doesn’t make financial sense. In short, the extra premium you pay isn’t recovered until after many, many years of use by the average owner. This is because most hybrids are expensive and simply use their second motor to reduce the fuel consumption of the primary engine, rather than as a true alternative means of propulsion. Yes, hybrids can run purely as electrical vehicles (EVs), but most of them are lucky to make it more than a kilometre on electrical power alone.

Mercedes is changing that game with the release of three new hybrids; the C350 sedan/estate, the S 500 e luxury large car, and the GLE 500 e SUV. Compared to the average hybrid, these cars support a much stronger business case for purchase for three reasons.

The first reason is because they are fairly close in price to their conventional equivalents. The C350 e hybrid is only 2 to 4% more expensive than the petrol and diesel equivalents, so it doesn’t have a huge gap to bridge. The second reason is shown below:

These cars are plug-in hybrids. The fact you can recharge the car at rest instantly helps the financial case. Yes, electricity is not free, but it’s so cheap it may as well be. If the car wasn’t plug-in, then there’d be no way to charge the battery without using petrol or diesel, which rather defeats the point.

The third reason is a usable range of around 30km, which for many people is all they need to do the school run, get to the shops or even commute to work. You can’t always recharge at your destination, but so you might consider the range as 15km there and back. Even if it’s longer, then you can run for the first 30km on electrical power, and then when the battery is depleted the car will still be more efficient in around-town driving. That’s because it uses the standard hybrid fuel-saving techniques such as harvesting energy when decelerating to recharge its battery,  and extended stop/start engine power management in heavy traffic.

The combination of a long (for a hybrid) range of 30km and the plug-in capability means that using these cars as purely electric vehicles is actually a real possibility, and that’s what makes the equations look more convincing than usual for a hybrid.

So with all that considered, here’s the numbers using the C 350 e estate as an example and its diesel and petrol equivalents:

The prices are exclusive of onroad costs, but will serve well enough for comparison, and the fuel is the ADR 81/02 combined cycle figure. As ADR fuel consumption figures do not represent reality we’ve added 20% to both the C250 and C250d. Fuel price is assumed to be $1.15/L.

The figures show that you’ll need to drive 28,000 to 40,000km on pure electrical power to recover the extra cost of the hybrid, but as ever with simple models, there’s a couple of things missing. First, even when not purely on electric power the hybrid will have a lower consumption than either of the other two, unless it’s in steady-state cruise on the freeway in which case it’ll be somewhere between the diesel and the petrol. Also, no allowance has been made for the cost of electricity, or car resale, or interest on additional funds required to purchase the more expensive vehicle.

Yet all that aside, these quick calculations show that the C350e is very likely to make financial sense over a three, certainly five year ownership period if there a substantial number of short trips, say under 50km.

So with the hard numbers out of the way, are you compromised by a hybrid? We had only a short drive, but the answer is an emphatic no. We put the 0-100 sprint times in the table above which show the hybrid is the swiftest, despite weighing 250kg more at around 1850kg (still less than say an RS6). It drives beautifully, although on a back-to-back around a racetrack you’d surely notice the extra weight. As a daily, practical car the only drawback is a slight loss of boot room. And for some, the fact it can’t tow anything, unlike the conventional cars.

Part of the reason these hybrids are more practical is because the reserves of electric power can be put to good and intelligent use. There’s four driving modes:

• Hybrid – the car will balance use of both internal combustion (IC) and electric power.
• E-Mode Electric – car works purely on electrical power, only using the IC engine if the battery is depleted or extra power is needed. In normal driving this will not be the case unless you make a habit of foot-to-the-floor acceleration.
• E-Save – the car will not let the battery drop below a given charge level. This is very useful if you want to preserve some battery power for a future point in your trip; for example, coming to a CBD where electric-only power is required. Or sneaking home quietly after a night out…
• Charge – the car will actively charge the battery as quickly as possible.

These modes give the driver useful control over the car’s electrical systems, and again that’s a difference to most other hybrids. Even better, you can set a destination for the car and it attempts to arrive there having used up its electrical power, because there’s no point arriving with full batteries if you know you’ll be recharging. Mercedes are also looking at other intelligent routing and energy use strategies such as use of maps to determine how and when electrical power should be used. The vehicles will also “sail” which is when the internal combustion engine is shut down, and the car harvests power. 

Here’s a cutaway of the S 500 e which shows the car’s basic design:

The electrical drive system is entirely separated electrically from the conventional electrical systems, even down to the separate 12v battery in the boot, just like any other car. The battery is also behind the rear wheels in the boot. This is not ideal from an engineering perspective, but like most hybrids the S 500 e has had electrical power added to it after conception, not designed from the ground up as a hybrid. If it was, then the battery, or batteries would be distributed throughout the car and there’s no doubt many other design features would be up for improvement leading to further efficiencies and even better value.

Mercedes do have some expertise in this sort of engineering as their Formula 1 team has been world and driver’s champions in dominant fashion for the last two years, and seems set to repeat that success in 2016.

As an example of the technology, the modern Formula 1 car runs a mere 1.6L engine (albeit revving to 15,000rpm) and with its companion electrical motor develops around 700kW of power. There are a raft of technical regulations designed to keep the engineering development on energy management rather than peak power, such as limiting the maximum fuel flow. Mercedes didn’t say, but you’d have to assume that some of this research is flowing into their roadcar programme.

Here’s the specifications for the three hybrids:

Mercedes-Benz Plug-in Hybrids: specifications

The total power and torque for hybrids is never the sum of the two engines as they produce their peak outputs at different revs per minute.

These cars are not the first plug-ins on the market. In February this year BMW announced plug-in versions of the 330 sedan and X5, which are priced even closer to their conventional counterparts than the Mercedes equivalents, and have similar electric-only range. At the other end of the scale there’s Mitsubishi’s Outlander PHEV which has a longer 50km range, but at a premium of over $10,000 compared to a normal Outlander, owners will need to drive a very long way before they recoup the extra costs.

Still, hybrids are going to need charging, however efficient they are. Here’s part of the answer, a Wallbox fast charging unit which about halves the charge time of 3 to 4 hours from a standard household 240v socket.

Fast charging aside, the big question about electricity is where the source energy comes from. Mercedes-Benz have an answer, and have set this up as an example at their regional HQ in Mulgrave, Melbourne:

Solar panels generate electricity which is stored in Mercedes-Benz batteries, and then the cars are charged. The charging station can be seen in the title photograph for this story. It is interesting to see that Mercedes are making a significant push into battery storage units (as indeed are Tesla), something we’ll need as electrically powered cars become more common. It is a cliche, but true nevertheless; the future is here today.

Practical Motoring attended a Mercedes-Benz Tech Day. This is first report; the others will focus on the new E-Class and Mercedes-Benz’s new active safety technology. The video below is a quick ride in the S 500 e:

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