What is a series hybrid/extended range electric vehicle?
by Sam Abuelsamid on Apr 2nd 2009 at 11:56AM 
Ever since the debut of the Chevrolet Volt concept in January 2007, the arguments have come fast and furious abut whether it is a hybrid or an electric vehicle. Technically, its actually both. There are those who insist on calling the Volt and similar vehicles from Chrysler, series or serial hybrids. This argument seems to come mostly from those who believe an electric vehicle should have nothing but a battery (or other electrical device) on board for energy storage. Certain proponents of parallel hybrid technology also prefer the series hybrid moniker, since it implies that the system is not that much more advanced than current production systems.
The counter argument from General Motors and others is that this drive architecture is more accurately referred to as a range extended electric vehicle. The premise here is that even there is an engine in the vehicle, it is not connected to the wheels and only the electric motor(s) provides actual propulsion. Let's take a look (after the jump) beyond the semantic argument at the actual technology that moves cars like the Volt.Let's step back for a moment and consider parallel vs series. By definition, parallel lines are always the same distance apart and moving in the same direction. In a parallel hybrid, two (or conceivably more) power-plants can each provide a torque flow path to the drive wheels. Either power-plant can provide torque to the wheels independent of the other (read more on parallel hybrids).
In a series architecture, multiple systems feed into each other in sequence with only one connection to the end point, namely the drive wheels. For example an internal combustion engine would drive a generator that produces electricity. That electricity could feed into a battery which would then drive an electric motor to propel the vehicle. The engine doesn't directly drive the wheels through a transmission the way it can in a parallel hybrid.
Series hybrids are nothing new and, in fact, the very first hybrid used this configuration back at the beginning of the twentieth century with the Lohner-Porsche. Since the 1920s, the most common series hybrid application has been railroad locomotives. These machines use a diesel driving a generator which feeds the motors that drive the wheels. Automotive applications add a battery to the mix.
Depending on the size of the battery, the vehicle may or may not have any zero emissions range. A series hybrid with a small battery could run the engine at constant speed in its most efficient range. The battery could then be used to store extra energy from the engine at light load conditions or from regenerative braking. When extra power is needed for acceleration, the battery can provide this.
Going to a larger battery with plug-in capability can allow the vehicle to operate in zero emissions road for some period of time dependent on the capacity of the battery. A compact car like the Volt with a 16 kWh battery can operate for up to 40 miles without running the engine. In no case does the engine ever send drive torque directly to the wheels. This particular configuration is what GM and others are referring to as ER-EVs.
There are downsides to the series hybrid layout. Having a vehicle operate with an engine running at constant speed can get the best efficiency out of that engine. However, a series hybrid has multiple energy transformations. Every energy transformation involves some losses. A conventional mechanical geared transmission, is generally about 95 percent efficient transferring energy.
Going from an engine's mechanical energy to electrical energy will produce some loss depending on the efficiency of the generator. Similarly, there are losses in a battery as it heats up when being charged. There are also losses going from the battery back to the drive motor. Of course, some of this is offset by recapturing kinetic energy through regenerative braking and the previously mentioned engine efficiencies.
The real benefit comes from having that larger battery that gets charged off the grid. If an ER-EV is operated without plugging it in, it will likely not get any better fuel economy than a conventional similar vehicle. If however, the vehicle is operated largely within its electric range and then plugged in, the reduction in fuel consumption, even when the grid energy is factored in, can be huge.
So,is the Volt an ER-EV or a plug-in series hybrid? Both, really, but who cares? It doesn't matter as long as it works.
Reader Comments (Page 1 of 2)
LaughingMan 12:13PM (4/02/2009)
I made a comment about this yesterday, but I think since this is an article devoted to the Volt's serial hybrid design...
One way of looking at the Volts hybrid system is that the conventional engine, the gas tank, the emission control system in the Volt are dead weight. Just a few hundred pounds of steel, plastic, and gasoline that only serve to exist for the maximal case, and weight down the car to perform less efficiently in the average case.
People blast modern day full hybrids like the Prius for carrying around "dead weight" in the form of the traction batteries... they make the mistaken claim that the extra weight of the battery reduces highway mileage, assuming that the hybrid system does no good in a highway case...
But where are the people making the inverse argument about the "range extender" feature on cars like the Volt? If the hundreds of pounds dedicated to the engine, the gas tank and emissions control were swapped out for batteries, you'd have a 300+ mile range vehicle that performs better to boot. Guys at Tesla have *proved* that.
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oldraven 12:50PM (4/02/2009)
I think GM should offer a pure EV trim level, where there is no range extender, for those who do not think they will ever use the car beyond their 40 mile commute. With the extra weight savings, it either gives it a little better pure EV range than the ER-EV, or the extra space can be utilised for additional batteries to run the car's various systems not related to propulsion, ensuring the added range. If they leave it out altogether, they could sell the EV variant at a discount as well, making the ER-EV version's higher price tag a LITTLE easier to swallow.
Steve 12:53PM (4/02/2009)
Cost
Lets make some general assumptions.
Volt = 40k
Volt - High Tech Stuff = Cruze = 20-25K
High Tech Stuff = Electric Drive System + generator + batteries = 15-20k
Batteries (16kwh) = 10-15k
53kwH = 240 miles (Tesla Roadster)
Batteries (53kwh) = 33-50k
240 mile range all electric Volt = 53 - 75k
GM may have something if they market it as an all electric Converj, but not with the bowtie on the front. They will never get the volume of sales needed from a 50k Chevy Cruze.
For what it is worth a well design 4 cylinder engine should weight 300#s or less. 53kwh of batteries is almost 1000#s.
MT 2:12PM (4/02/2009)
>For what it is worth a well design 4 cylinder engine should weight 300#s or less....
+ transmission + exhaust system + gas tank + 10-15 gallons of gas. And then factor in that you have to design the vehicle around a 2' x 2' lump of metal vs a smaller electric motor and batteries that can be flexibly placed.
oldraven 3:36PM (4/02/2009)
@MT
The 1.4L in the Volt doesn't have a transmission.
win39 3:47PM (4/02/2009)
Dead weight? I think not. A discharged battery and the whole car is dead weight. People responding may be content to buy an electric car and restrict their travel to their local environment, but most people buy a vehicle that will do anything for them. Stopping overnight to recharge every 200 miles is not an acceptable part of the equation not to mention finding lodging that will include a charge. The good part of the Volt design is that the engine design can be tailored just to run a generator to charge the battery in the most efficient manner possible. It can be made small, light and without a transmission. Many of the inefficiencies of internal combustion engines have to do with making them flexible enough to propel a vehicle down the road under varying demands. The bad part is that the Volt will be so expensive is that it will not compete with the other hybrids for cost of purchase and perhaps not even in the operating cost department should Toyota bring its plug in hybrid to market first.
It is interesting that with GM's experience with their diesel electric train locomotives, that they did not choose a diesel engine for the recharging unit. The goal is, apparently, no adaptation needed by the new owner.
MT 3:57PM (4/02/2009)
I was thinking that 4-cylinder comment was comparing to a standard 4-cylinder car. If it's a Volt/Tesla comparison, and we're talking about range-extending engine vs more battery capacity, then the 300 lb engine + misc bits, should actually be compared to the weight of 53-16 = 37kwh of batteries which is the amount of extra capacity the Tesla has which GM is trying to offset by going range-extension.
Matt 12:47PM (4/02/2009)
An inefficient engineering idea?
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oldraven 12:50PM (4/02/2009)
The automotive world isn't really about efficiency or ecological superiority. It's about pleasing the public.
MT 2:21PM (4/02/2009)
It's actually about making money. Sometimes that means convincing the public that what they want is your highest profit margin product (ie trucks and SUVs).
I don't think there are a lot of people begging to increase their risk of dying by cancer, but the cigarette companies have done a great job of product placement and making a horrible product that few people would otherwise want seem cool. Most consumers don't know what they want, they're told what they want.
Bill Max 12:51PM (4/02/2009)
Well, it seems like everybody is fooled by scientists who doesn't understand how market works and businessmen who have no clue in science.
Tesla, Fisker, Volt... all will fail. Because they were fooled. A battery is not advancing that fast as Ellon Musk assumed. Bob Lutz didn't know that Ellon Musk's assumptions were so far from reality. Fisker draws beautiful cars, but doesn't mean he will invent something better than Volt and Tesla.
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jharlan 1:03PM (4/02/2009)
By the time this thing hits the Market it should be wearing the Cadillac badge. That way people who can afford it won't be ashamed to be seen in it.
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ziv 10:54PM (4/02/2009)
It seems like the weight and cost of the ICE in the ER-EV is critical. Volt1 can be a success with a 1.4L engine, but if they are going to get this to work as efficiently as possible, the Volt2 will probably have a high performance engine that is significantly smaller than 1.4L. But even so, until battery prices and sizes drop significantly, the ER-EV will be the better idea. But if LiIon batteries drop to less than $250 kWh installed with a pack management system, then it will make more sense to go with a BEV. On the 10% of the days you use more than the AER, you will still have fast charging to fall back on. The problem with assuming battery prices will continue to drop rapidly is that the low hanging fruit have already been plucked, and further drastic improvements are going to be increasingly difficult to achieve.
If GM survives long enough to build the Volt, it will be a huge success for the first few years, giving Chevy 2 nameplate cars, the Volt and the Corvette. The tough part will be getting enough economies of scale to allow the car to be built cheap enough that the Volt2, the Orlando and the Cruze will be able to sell ER-EV versions without too great an increase in cost over traditional ICE cars, especially if the government allows the federal tax credit to run out. Eventually the Silverado will probably have an ER-EV version, even ranchers & builders will need to cut gas useage when it gets up to $4 or $5 a gallon.
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jpm100 2:09PM (4/02/2009)
For the Volt, the engine is present primarily to compensate for the limited range a practical sized battery currently has.
On a hybrid, the not only is the system restricted by battery size but by the operating range where the engine must run.
Battery limits aside, the amount time the engine must run on a Volt for most driving conditions will be tiny compared to its hybrid competitors.
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LaughingMan 3:08PM (4/02/2009)
Yes, but the fact that the engine is run so little, yet still weighs as much as as a 1.4L engine in a small car is troubling. That means that the engine will be little utilized, but will weight down the car even though it's hardly ever used.
Jason 4:37PM (4/02/2009)
LaughingMan: That's an argument for ditching the electric-only capability altogether and running the engine constantly. That way it's not dead weight. Should lower the overall cost too, as those batteries are absurdly expensive.
GoodCheer 4:41PM (4/02/2009)
"Ever since the debut of the Chevrolet Volt concept in January 2007, the arguments have come fast and furious abut whether it is a hybrid or an electric vehicle. Technically, its actually both."
...er, if something is "both", isn't it then, by definition, a hybrid?
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fatchance 3:50AM (4/03/2009)
it's a hybrid because it uses two different forms of fuel , although different from a prius. you can deisgn simpler like the apple ipod then it'll be cheaper so get rid of the volt and get the ev1 back on the road
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aerotexan 5:30PM (4/02/2009)
LaughingMan: Your comment about the ICE components of an ER-EV being "dead weight" are the same as calling the battery of a BEV "dead weight" when it coasts to the side of the road, out of power. The addition of an engine-driven generator greatly increase the flexibility, and thus public acceptance, of an EV. There are too many unknowns with a BEV, and too many trade-offs. When you put a BEV in real world conditions - 70mph traffic, AC in the summertime, stereo playing and headlights on hi-beam - it'll cut the range dramatically, severely restricting it's utility. Only when the cost and chemistry of batteries improve enough that they can directly compete with the flexibility of an ICE or ER-EV will the pure BEV be accepted by the general public. At least the ER-EV will get the public to more readily accept and BUY electric vehicles, without severley restricting their driving habits.
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Steve 7:50PM (4/02/2009)
Hybrids are simply a place holder until tech evolves enough to replace ICE with electric only vehicles. Hybrids will go the way of VHS. If a 125 miles is the current range for an affordable Battery, 5 years from now that range will be 250 miles, and 10 years from now the 500 miles will be the range at the same price. At that point, it will be pretty stupid to have a generator in your trunk to run your electric motor. Fast Charging stations will be in place for those on a cross country trip. If government policy and funding falls into place it will be even faster than 10 years. There won't be a single personal production ICE vehicle available in 15 years.
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