Serial Hybrids Are Here!
Just six months after Tesla Motors announced the return of a 100% battery car, the Tesla Roadster, we have another great leap forward. As reported in the Los Angeles Times in a story entitled “GM To Present A Modified Electric Car“ (courant.com) on November 10th, General Motors has announced a serial hybrid car. Early next year they will present a prototype of the vehicle.
If you are wondering just exactly what “serial hybrid” car means, you’re not alone. But this is a car that will take the market by storm. A serial hybrid means that the car has two engines, hence it is a hybrid, but only one engine is connected directly to the drive train, hence it is a “serial” hybrid. By this logic, your Prius is a parallel hybrid, or just a hybrid. For a detailed explanation of a serial hybrid car, including diagrams and energy conversion charts, read our feature from October 2005 entitled “The Case for the Serial Hybrid Car.”
The advantages of a serial hybrid car are huge. They are far, far less complex than conventional hybrid cars, because only the electric motor, with its huge range of usable RPM, is connected to the drivetrain. Another huge advantage is that serial hybrid cars have their second motor, a small, ultra-low-emission gas or diesel engine, connected to a generator to recharge the battery pack while the car is being driven. By doing this, a cheaper and more reliable battery pack can be used, and there is no need for a complex heat management system that is still necessary for the lithium ion batteries.
It is well and good to criticize General Motors for discontinuing the EV-1. But they are back with another green car which is as ahead of its time as the EV-1 once was, and this car is going to attract a much bigger market.
Critics may claim the EV-1 was a zero-emission vehicle, while a serial hybrid car has a small, ultra-low emission onboard motor, and therefore it isn’t as green as the EV-1, or the Tesla Roadster, or any 100% battery powered car. Someday, when all electricity generated everywhere is done so with no combustion or other form of environmental degradation, this concern may be valid, but until that time, this is pure poppycock.
A detail of some interest regarding GM’s bold and groundbreaking new green car initiative are some performance specifications as reported in the Los Angeles Times story. “The new car, if developed as a production model, would be recharged daily by owners and probably would deliver sufficient power from the batteries to cover the typical daily commute of 20 to 30 miles before depleting the battery charge and switching to electricity generated onboard.”
If these figures are true, GM’s planned serial hybrid car could be dirt cheap. Theoretically, a car like this could run on lead-acid batteries. Remember, a serial-hybrid car would only need a two-speed transmission, if that, for the electric motor that provides traction, and no transmission at all for the small gas (or diesel) engine that powers the onboard generator. Maintenance would be negligible. If GM used a nickel-metal hydride battery pack, it is likely that their serial-hybrid car will go much further than “20-30 miles” just on previously stored battery power, and the onboard generator engine could be smaller. The people’s car is here.
However General Motors designs their serial hybrid car, it will be carefully calibrated to create a car with so much value for money that we all want to buy one, and don’t be surprised if they call it the EV-2. Redemption is a sweet thing.
November 12th, 2006 at 5:47 am
IN THE NEXT few years, we will probably begin to see more electric vehicles and hybrid-electric cars on roads most everywhere. Partly, because of unstable and unpredictable gas prices, people are looking for better alternatives to match their day to day driving needs. Most people don’t realize it requires 12Kw of electrical power to refine one gallon of gasoline. According to Electric Power Research, BEVs (battery-electric vehicles) are 97 percent cleaner than gasoline-powered cars. Gasoline-powered cars give off pollutants whenever the engine is running. Just starting your car or sitting in traffic increases air pollution, and filling your gas tank releases harmful fuel vapors. As a gasoline-powered car ages, pollutants increase. A BEV car has low pollutants and remains that way during the course of its life.
November 13th, 2006 at 1:01 pm
The GM plug-in hybrid is good news. . . It’s something that has been rumored for several months, and we still need to see exactly what they’ve come up with before I get too excited about it.
This article, however, is poorly written. The hyperbole is shameful. A sober and realistic assessment of the technology’s potential would be much more helpful.
November 13th, 2006 at 1:09 pm
If the “EV-2″ has some of the performance features of the brilliant Tesla Roadster, you can count me in! But 20-30 miles isn’t anywhere close to Tesla’s 250! For commuters, a 100 mile range is desireable. And please oh please make it look cool!
November 13th, 2006 at 1:28 pm
Trevor,
We are trying to find out details. But the 20-30 mile range may mean 40-60 round trip. More importantly, the onboard gas generator may replenish the batteries at nearly the rate they are depleted, meaning this car may have a range well over 250 miles.
November 13th, 2006 at 2:55 pm
I am shocked it is GM that is offering this vehicle. When GM introduced the two-mode hybrid concept, they slammed series hybrids. GM criticized the “single-mode” Toyota design because it combines series and parallel hybrids, and electric power is always being used. Here’s a quote: “The relative sizes of these electrical and mechanical power flows are critical, because electrical path efficiency is typically close to 70%, and mechanical path efficiency is typically greater than 90%.”
I don’t know how the other parts of this design are going to overcome the claimed 20+% efficiency deficit of series hybrids. But maybe GM doesn’t care about efficiency, they just want to release something that qualifies as a hybrid.
November 13th, 2006 at 3:47 pm
Americans are eager to buy a GM car that makes them feel proud to own. This could very well do it. Be dedicated to hip styling, put in voice activated and touchscreen GPS, aux input for the i-pod, and bluetooth phone support, and they won’t be able to make them fast enough for the 40 and under crowd.
November 13th, 2006 at 6:19 pm
“The relative sizes of these electrical and mechanical power flows are critical, because electrical path efficiency is typically close to 70%, and mechanical path efficiency is typically greater than 90%.”
“I don’t know how the other parts of this design are going to overcome the claimed 20+% efficiency deficit of series hybrids.”
This is incorrect. The series hybrid is the most efficient way to build a vehicle. GM is in error regarding the 70% electrical efficiency. Yes 90% generator efficiency & 90% motor efficiency & 85% battery storage efficiency yields 70%, however much of the time the generator is directly supplying the PEM DC bus without charging the battery and if ultracapacitors are used on the DC Bus, the 15% charging loss can be eliminated, all that is needed is a 1 kwh capacitor for all normal driving and about a 5 kwh battery bank connected through a DC-DC converter to the DC bus, which would supply energy only for sustained extreme speed travel or climbing mountains at speed or towing a trailer.
A series hybrid recovers almost all the energy from braking, the parallel only a much smaller portion of the energy. The electric motor in a series hybrid supplies acceleration energy & recovers braking energy efficiently at all operating speeds. An Electric Motor delivers to the battery / ultracapacitor about the same current braking 60-0 in 8 secs, as it takes accelerating 0-60 in 8 secs, therefore a robust fully powered electric vehicle is necessary to recover the energy lost in deceleration, that is a fully electric drive. The partial electric drive in a parallel hybrid just won’t do it.
The larger battery pack on a series hybrid is needed to store the potential energy lost by going downhill, so it can be used to power the uphill climb. The small battery pack on the parallel hybrid cannot do this, for example, the .3 kwh (utilized) battery on the Prius, is only capable of storing the energy for a small 1% grade hill for 1.5 km, anything more is thrown away, vs the series hybrid with a 4 kwh utilized battery pack, which could store the energy from a steep 12% grade for 2 km. Also the larger battery pack means lower charging currents / per cell, which leads to higher charging efficiency for braking energy recovery.
The generator engine on the series hybrid can be much smaller, simpler and more efficient than on the parallel hybrid. It only needs to run at optimal charging speeds, does not need good torque or acceleration performance. It only needs to be large enough to supply average energy that the vehicle uses or even less if the vehicle is parked part of the time.
The generator module on the series hybrid can be easily be standardized for all electric vehicles, and mass produced as an interchangeable auto component. It could easily be replaced, exchanged or upgraded depending on requirements or the available technology. For instance, it could be a high efficiency diesel, a FlexFuel Turbine with up to 50% efficiency, a Fuel Cell or StarRotor’s Brayton cycle external combustion turbine (they are claiming 45% to 60% efficiency).
The series hybrid can readily be made a true all wheel drive vehicle, without the complexity of multiple drive shafts / differentials, by using wheel hub electric motors. Added benefit of zero turning radius by running wheels on one side backwards to wheels on the other side. Also the wheel motors run >90% efficient, with NO DRIVETRAIN LOSSES, which amount to 30% to 50% of the I.C. Engine shaft horsepower in a parallel hybrid or standard ICE powered vehicle. This cannot be done on the parallel hybrid.
You can calculate the fuel economy of a Series Hybrid by using the Tesla Electric Car data, modified to assume an onboard fuel generator instead of a utility powered charger, which would replace 85% of the Tesla’s 44 kwh battery pack. At 7.85 km per kwh of utility energy, this would yield 68 miles per gal with a 35% mechanical efficiency diesel generator. This would be higher in actual fact because the generator would be substantially lighter than the replaced battery pack. Accounting for the generator energy directly supplying the DC bus, this would push the fuel economy up to about 73 mpg, using ultracapacitors this would increase to 78 mpg. The Tesla was designed for high speed (130mph), and so the 2 speed transmission. Using wheel motors to replace the transmission & rear differential should push the fuel economy up to at least 90 mpg. Replacing the Diesel Motor with a Fuel Cell, high efficiency turbine or the StarRotor type motor would push the fuel economy up to 115 to 155 mpg. Not bad for a 0-60 mph in 3.9 sec sports car.
November 16th, 2006 at 11:17 am
I look forward to this innovation. But I also remember the GM prototype which offerred multiple platforms on a generic chassis in a hybrid drive. It never saw the light of day’. So this can be very good news for both GM and the public, but I just hope they actually produce this thing rather than use it for simply publicity events - to tell the world how environmentally sensitive they are - kindof like the ‘compassionite conservative’ we all know now. So bring it on GM - I might actually buy it if you actually sell it. Assuming my Prius is worn out by then….
November 18th, 2006 at 12:08 pm
In the 1960s, when I worked for an engine and generator manufacturer, I tested the efficiency of one of the DC dynamometers. It was basically an externally excited DC generator which could also run as a motor and was capable of producing about 45 KW on a continuous basis. It was designed in about 1940.
The efficiency was about 91%. Considering that it was a DC machine designed about 65 years ago, it can safely be assumed that more modern motors and generators would be significantly more efficient, probably about 95% over a reasonable range of speeds. 95% * 95% = about 90%, so I think that the efficiency from the generator to the traction motor(s) could be about that high, even with the losses in the electronics required to make it work.
November 18th, 2006 at 10:36 pm
WBH just about sums it up. If GM can execute on their series hybrid design they will have a much more flexible platform than Toyota. Toyotas design requires a vary close integration of the transmission, engine, and motor, while a series hybrid is completely decoupled. You may even have no engine if the customer does not see a need for ever going more than maybe 200 miles. Just use the space that the ‘fuel converter’ would use for more batteries. A customer could also opt for a 5-6 kW fuel converter if they may go more than 200 miles once or twice a year. A 25-30 kW fuel converter would allow full speed operation over a range of 600 to 700 miles a day with the only penalty of reducing the all electric range to maybe 40 to 50 miles.
November 20th, 2006 at 8:49 am
How come nothing on this site is speaking of Human Power? With all the awareness of how out of shape and obese people are becoming and the need to improve the nutritional content and awareness of what nutrients do in the human body I think its a travesty to go on pushing for these “Lazy Mobiles” that help humans become large road raging Amoeba’s instead of fit, serene, calm and beautiful creatures that truly enhance the planet instead of jamming it up with large boxes of steel and plastic while bored to death.
By the way to learn more about Human Powered Vehicles (HPV’s) go to www.BentRiderOnline.com
To learn more about properly fueling a Human Powered Engine go to www.LiveJohn1010.com
November 20th, 2006 at 9:47 am
“Large road raging Amoebas!” Very good Erskien! The whole issue of bikes as an alternative form of transportation is complex, however. Certainly there are many people who can commute on a bike to work, but the vast majority of people probably can’t - weather, distance and road conditions make it impossible for bike transportation to significantly replace automotive transport. But they can make a dent…
What might be an interesting type of hybrid is a safe, freeway-capable compact electric car that with controls similar to those on a recumbent bike. Then the driver could pedal, adding some KWH to the battery pack. In most cases, the additional energy contributed by the driver wouldn’t add much to the overall energy requirement, but it would help, and more importantly, one could then combine their exercise with their commute!
November 20th, 2006 at 10:47 am
With all this stored battery power in the garage, and a generator to boot, maybe I don’t need a home backup generator any longer. All I need is an appropriately sized power inverter and we can power (a portion of) the house off the car systems during those pesky winter storms.
November 20th, 2006 at 12:08 pm
I hit the link to “The Case For The Serial Hybrid Car.” In that article, you appear to be highly optimistic about the prospect that future progress in battery technology will overcome present limitations (despite the fact that extensive research over many years has yielded only modest practical results.) However, there is no parallel discussion about possible future improvement in fuel cell efficiency. Is there some theoretical limitation that precludes this development? I am interested in learning more about this issue.
November 20th, 2006 at 4:04 pm
How long do the batteries last and how much does it cost to replace them? What does this add to the cost per mile?
November 20th, 2006 at 8:09 pm
With Moore’s law causing computing power to double every year and the exponential growth we now see in science and technology information, the serial hybrid will only be a brief flash in the pan of our movement away from fossil fuel. By the time it hits the streets it will be like our brand new computers-obsolete.
November 21st, 2006 at 5:31 am
I have been mentioning this “new” series hybrid idea (Circa 1905) technology to my pals since I was a teenager with everybody laughing at me. I also have designed a concept for ideal electric traction EVs during the CARB’s “Shootout in the EV corral”, and constantly upgrading them… and nobody cares.
Keep on laughing…
I am pretty sure somebody someday will come up with similar ideas.
Please open www.ev-motion and click on Pac-Man EV.
November 21st, 2006 at 1:27 pm
Thomas Johnson: I wholeheartedly agree with your belief that we will see technology provide us with unanticipated solutions to many of our current energy and transportation challenges. A serial hybrid car however is a fairly advanced technology - it depends on new zero emission super-efficient diesel engines to turn the generator, and a battery pack with sufficient energy density to make the whole package have a viable range without requiring an oversized genset. At the same time, the serial hybrid has a far less complex transmission than a parallel hybrid - it will cost less to build and require less maintenance. So what is your vision? Are you saying we’ll have batteries that can get a kilowatt-hour or more per kilogram and charge in minutes, eliminating the need for a genset? Are you suggesting hydrogen fuel cells will actually be perfected? What is your alternative?
November 27th, 2006 at 1:59 am
i want one!
November 28th, 2006 at 2:21 am
[…] Serial Hybrids Are Here!EcoWorld.com, CA - Nov 10, 2006As reported in the Los Angeles Times in a story entitled GM To Present A Modified Electric Car (courant.com) on November 10th, General Motors has … […]
November 30th, 2006 at 10:08 pm
[…] What we really were looking for when listening to the GM Chairman Wagoner deliver his keynote in Los Angeles was any indication that GM was going to deliver a serial hybrid car, as rumor has it - read “The Serial Hybrid Car is Here.” […]
December 1st, 2006 at 12:29 pm
Serial hybrids are the future. If or when a hydrogen fuel cell is perfected the genset is easily replaced with it. The biggest problem now for the hydrogen fuel cell is its low well-to-wheel efficiency of only 22% compared with the best diesels of 25%. It just takes too much energy to produce hydrogen for it to be environmentally sound. When it can be done with non-polluting energy such as hydro, wave or solar power it will be a better choice.
Knappen