Berkeley Lab study finds hybrids more fuel efficient in India, China than in US
31 March 2014
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| Improvement in fuel consumption in India of a hybrid vehicle over a conventional vehicle. Click to enlarge. |
In a pair of studies using real-world driving conditions, scientists at the US Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab) found that hybrid cars are significantly more fuel-efficient in India and China than they are in the United States due to traffic and driving conditions in those countries.
They found that driving a hybrid would achieve fuel savings of about 47 to 48% over a conventional car in India and about 53 to 55% in China. In the United States, hybrids are rated to produce a fuel savings of about 40% over their conventional counterparts. Currently hybrid and electric vehicles have a tiny share of the market in India and China and are seen as a higher-end product.
Their results were reported in two papers, “Understanding the fuel savings potential from deploying hybrid cars in China,” published in Applied Energy, and “Understanding fuel savings mechanisms from hybrid vehicles to guide optimal battery sizing for India,” accepted for publication in the International Journal of Powertrains, also co-authored by Berkeley Lab battery scientist Venkat Srinivasan. The studies are believed to be the first of their kind.
These findings could have an important impact in countries that are on the brink of experiencing an explosion in the sales of personal vehicles; the government of India has already taken note of the findings.
Currently greenhouse gas emissions from the transportation sector in India and China are a smaller piece of the pie compared with other sectors. But vehicle ownership is going to skyrocket in these countries. That is why we decided to focus on this area. Hybrid and electric vehicles can significantly reduce carbon emissions and other pollutants.
—lead researcher Anand Gopal
Gopal, working with Berkeley Lab scientists Samveg Saxena and Amol Phadke, used a powertrain simulation model called Autonomie to create a hypothetical hybridized version of the top-selling conventional car in each country—in China it was the Buick Excelle and in India the Maruti Alto. The reason for creating a hypothetical version was to isolate the improvement from hybridization and measure only that benefit.
China study. To represent typical Chinese driving conditions, the researchers selected drive cycles from 11 Chinese cities of different size, with the drive cycles capturing on-peak and off-peak driving times, and road types including freeways, major arterials, sub-arterials, and residential roads. Comparing the characteristics of the different drive cycles against US drive cycles, they found that Chinese driving often involves lower speed driving, a moderate stop frequency and more sudden acceleration and deceleration.
They used the drive cycles as inputs for powertrain models for a conventional engine-only vehicle, a mild parallel hybrid with integrated starter/generator, a power–split hybrid, and a conventional gasoline vehicle with start–stop functionality, then compared the fuel savings potential from each vehicle architecture against the conventional vehicle in US and Chinese driving conditions.
The results show that the driving conditions in China enable hybrid vehicles to achieve significantly greater fuel savings as compared with hybrids in the US, with parallel hybrids producing 25.5% fuel savings in China versus 13.2% fuel savings in the US and power–split hybrids producing 53.6% fuel savings in China versus 32.6% fuel savings in the US.
The fuel savings benefits from parallel and power–split hybrids significantly exceed the fuel savings from conventional gasoline vehicles with start–stop functionality for both the US and China. These results suggest that the increased cost of deploying hybrids will have significantly greater impact in Chinese driving conditions, and hybrid vehicles in China should be seriously considered for incentive programs (perhaps as part of the recently announced 2012–2020 China automotive industry development plan) to accelerate their deployment, they concluded.
India study. For the India analysis the researchers simulated drive cycles in two Indian cities (New Delhi and Pune) taken from published studies and also used the Modified Indian Drive Cycle, the test for the official fuel economy rating. Here also they used the US drive cycle as a basis for comparison.
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| Estimated fuel savings in China from three types of hybrid vehicles over conventional vehicles. Click to enlarge. |
Gopal describes the traffic in India as “pretty slow, pretty crazy, always congested.” The frequent starting and stopping, considerable amount of time spent idling, and low percentage of time spent on highways provide hybrids three ways to save additional fuel.
One is regenerative braking, another is being able to turn off the engine when the car is stopped or in low-power condition, and another is that the hybrid system—the electric motor, the batteries—enable the engine to operate at a higher efficiency operating condition,” Saxena explained. “We weighed the importance of these three mechanisms against each other for the Indian vehicles, and found that the ability to increase engine efficiency was the most important reason, second was regenerative braking, then engine shutdown.
—Samveg Saxena, lead author
The engineering results were a little surprising, Saxena said, as they went into the study thinking regenerative braking would make for very unique fuel-saving opportunities.
The authors also carried out a parametric analysis of battery size on fuel savings mechanisms, and found that hybrid vehicles for Indian driving conditions should ideally have a power capacity between 15 and 20 kW, with 10 kW as a lower limit.
The government of India, which launched a national plan last year with the goal of getting 6 to 7 million hybrid and electric vehicles (EVs) on the road by 2020, is already working with the Berkeley Lab researchers to further analyze their results. India is a member country of the Electric Vehicles Initiative (EVI) of the Clean Energy Ministerial, a global forum of governments focused on accelerating the transition to clean energy technologies. Through EVI, Berkeley Lab’s research will guide India in moving forward with its EV plan.
EVs in India. A third paper by Gopal, Saxena, and Phadke also looked at electrical consumption of all-electric vehicles in India. The study lays the groundwork for their next project, which is to analyze how EVs can be integrated into the existing electrical grid and how to minimize grid emissions.
This study uses detailed vehicle powertrain models to estimate per kilometer electrical consumption for electric scooters, 3-wheelers and different types of 4-wheelers in India.
They validated the powertrain modeling methodology against experimental measurements of electrical consumption for a Nissan LEAF. They then used model to predict electrical consumption for several types of vehicles in different driving conditions.
The results show that in city driving conditions, the average electrical consumption is:
- 33 Wh/km for the scooter
- 61 Wh/km for the 3-wheeler
- 84 Wh/km for the low power 4-wheeler
- 123 Wh/km for the high power 4-wheeler
For highway driving conditions, the average electrical consumption is: 133 Wh/km for the low power 4-wheeler and 165 Wh/km for the high power 4-wheeler. The impact of variations in several parameters are modeled, including the impact of different driving conditions, different levels of loading by air conditions and other ancillary components, different total vehicle masses, and different levels of motor operating efficiency.
Resources
Samveg Saxena, Amol Phadke, Anand Gopal (2014) “Understanding the fuel savings potential from deploying hybrid cars in China,” Applied Energy, Volume 113, Pages 1127-1133 doi: 10.1016/j.apenergy.2013.08.057
Samveg Saxena, Amol Phadke, Anand Gopal, Venkat Srinivasan (2014) “Understanding Fuel Savings Mechanisms from Hybrid Vehicles to Guide Optimal Battery Sizing for India,” International Journal of Powertrains
Samveg Saxena, Anand Gopal, Amol Phadke (2014) “Electrical consumption of two-, three- and four-wheel light-duty electric vehicles in India,” Applied Energy, Volume 115, Pages 582-590, doi: 10.1016/j.apenergy.2013.10.043
I am a bit skeptical of the comment about the three fuel-saving mechanisms and their relative importances. Since the authors designed these vehicles, i.e., they were not modeling existing production vehicles, it's possible that their design choices were not optimal. Thus, regen braking may actually be more important if the control strategy, motor, and battery were designed differently. I think that drawing conclusions on the order of importance is inappropriate from this study.
Posted by: canuckinaz | 31 March 2014 at 04:24 PM
I don't know about other drivers, but we consistently are getting around 56 mpg average throughout the seasons for our Prius Gen III. A comparable vehicle like the Corolla would have a combined MPG rating of around 28. So, in our situation, the improvement would be 100% for a power split hybrid vs. a comparable ICEV. Of course, drivers who are not attentive to the fuel-saving features of a HEV may not be able to take full advantage of what an HEV can offer.
Posted by: Roger Pham | 01 April 2014 at 01:07 AM
For direct comparison, our 2009 Ford Fusion ICEV averages about 27 mpg year round. The Fusion is a little bit heavier, though not any roomier.
Posted by: Roger Pham | 01 April 2014 at 01:10 AM
why is this News. all cars are more in India, China than in US.
Posted by: dursun | 01 April 2014 at 06:41 PM
According to the EPA, the current Corolla Eco gets a 30/42 (average 35) rating, to the current Prius's 51/48 (average 50), so the difference is almost exactly 30% (or $500/year).
It makes sense that hybrids do comparatively better in congested traffic. That's where hybrid powertrains really shine. The Prius's slight highway advantage over the Corolla is mostly thanks to the Prius's slippery aerodynamics and rock-hard tires.
In that way, hybrids may make more financial sense in India and China, provided that fuel costs justify the initial financial hit. As we've seen in other articles, they are definitely beneficial to the taxi industry.
Posted by: Bernard | 02 April 2014 at 07:12 AM
@Bernard,
Our Prius is 2011 model, so, to compare with a 2011 Corolla 4-sp automatic, the following reference stated the combined mpg as 29 mpg for 1.8 liter version and 25 mpg for the 2.4 liter version. See:
http://www.fueleconomy.gov/feg/bymodel/2011_Toyota_Corolla.shtml
So, my number of 28 mpg for a typical ICEV comparable to the Prius 2011 was not off the mark. Driven similarly, our Ford Fusion averages 27 mpg, so we have first-hand actual real-life experiences to compare the overall MPG's of an optimal HEV vs. a typical comparable ICEV of similar size, seating capacity, and internal space.
Please note that a hybridized version of a formerly ICEV will not do as well and was not able to improve efficiency by 100%, for example, the Camry vs. Camry hybrid, or Lexus vs. Lexus hybrid etc...This is because a clean-sheet HEV design is required to optimize efficiency. All other hybridized versions of regular ICEV are compromises only.
Posted by: Roger Pham | 03 April 2014 at 01:08 PM
I am quite skeptical of the conclusions of this studies for the following reasons:
1. Drivers in developing countries tend to be much more aggressive than their American and European counterparts (hard accelerating and braking, less safe distance among vehicles, etc.), thus reducing significantly the potential of battery regen.
2. Traffic congestion in developing countries tend to have more stop-and-go, leaving the car idling more often than in the typical U.S. or European city. Under this condition, the relatively low capacity of a hybrid's battery is critical. Once the battery is depleted and with fewer opportunities of coasting/braking to regen, the hybrid consumes fuel just as a regular car.
As a piece of empirical evidence, I imported my 2012 Camry Hybrid LE to Brazil recently. In the U.S., I did in a couple of months about 39.5 mpg. In Brasilia, a city planned for cars, I did 38.5 mpg during the first year (almost no highway travel). The loss was due essentially to the higher ethanol content of Brazilian gasoline (E25 from E10 in the U.S.) And by the way, I changed my driving style to ecodriving to take advantage of the hybrid fuel savings potential.
A couple of months ago, and due to the incoming Soccer World Cup, a lot of street closings have taken place downtown and the already heavy rush hour became chaos. My travel time almost doubled, and with it, the fuel economy suffered. Now I am making an average for my daily commute of 34.5 mpg. Since I became addicted to the hybrid monitoring screens, I noticed that the main culprit for the lower performance is the battery. In heavy stop-and-go, the battery drains faster, and you are left with a regular gasoline-powered car, making just around 25 mpg. Once the battery reaches the critical minimum level there is no stop/start, the engine is idling just wasting gasoline, and you can watch in the screen how your mpg just is going down fast. I thought hybrids were good to handle snail's pace traffic jams, but they are not. Hybrids need a larger battery!
Finally, this is my experience with a Toyota hybrid, but remember than over 6 million out the 7 million hybrids on the world's roads use Toyota's Hybrid Synergy Drive powertrain technology.
Posted by: Mariordo | 03 April 2014 at 02:27 PM
@Mariordo,
In heavy stop and go, with prolonged stop and little go, all vehicles will suffer from tremendous decrease in MPG. This will be much worse if Air Conditioning (A/C) is used, especially in hot and humid weather.
The 34.5 mpg may be very good when you compare this to what a regular Camry V-6 would do with this type of stop and go...perhaps a Camry V-6 can barely produce 15-17 mpg! Remember that if a car just sits and idle, it consumes fuel without covering any distance, and MPG will drop drastically. However, if a HEV just sits in hot and humid weather condition, the A/C consumes a lot of energy and the battery will soon be drained and the engine will have to kick in to charge the battery...This will drop the MPG, but not as much as would in an ICEV, because the engine in an HEV will run at a more efficient point in the map for only a short period of time to charge up the battery and then will shut down, instead of an idling engine that consumes fuel all the time while idling.
Posted by: Roger Pham | 03 April 2014 at 08:14 PM
Hmmm... A/C? Could that be the reason drivers of hybrids get better MPG in India & China? Do they buy cheaper models with no A/C or simply not do not need to use it because they are acclimatized to their region? The US is in a temperate zone, a mild climate, but you go from winter to summer faster than the body can adapt so a lot of people need climate controls for their cars. India on the other hand is tropical, the climate is warmer but it changes less between the seasons so people feel more comfortable without A/C.
BTW this is pure guessing on my part, I really have no clue.
Posted by: ai_vin | 03 April 2014 at 11:46 PM
@ai vin,
In the USA, we consistently obtain 100% improvement in fuel efficiency for a Prius vs a comparable ICEV. In the summer and winter, both HEV and ICEV show some reduction in mpg, but the ratios are quite comparable. I suspect that the lower efficiency improvement of HEV vs ICEV in the USA is due to higher percentage of lead-footed drivers in the USA due to more open roads and less traffic congestion. When the streets are wide and the freeways are spacious, people tend to accelerate and drive faster.
Posted by: Roger Pham | 04 April 2014 at 03:20 PM
I must hasten to add that the situation in the USA will improve with more PHEV's market penetration. PHEV can do much better energy recuperation when brakes abruptly, and a more powerful electric drive train will help the ICE to consume less fuel during brisk acceleration, during which time, the ICE must be richen in an ICEV to prevent engine knock. In a PHEV, the engine won't be pushed to the limit, hence won't be richen during a brisk acceleration.
So, the solution for lead-footed-but-still-green driving is PHEV.
Posted by: Roger Pham | 04 April 2014 at 03:26 PM
Roger,
I think that the more fair comparison is between current models, not past models. That's the choice that a current consumer will face.
It's also fair to compare the Prius to the most fuel-efficient Corolla. One assumes that fuel-economy-conscious consumers will compare these two options rather than comparing a Prius to a rental-spec Corolla. It also brings the price difference closer to the $5,000 range which is more reasonable.
Comparing fuel economy of cars that are more than $10,000 apart is artificial. $10,000 is 20 years of Prius fuel savings (according to the EPA). You may as well invest the $10K and get a "free" 2034 Prius (or two).
Posted by: Bernard | 05 April 2014 at 06:26 AM
@Bernard,
The Corolla Eco version is brand new for 2014 for a new Corolla design with new body and new CVT instead of regular 4-spd auto tranny. The 2014 Prius is the same design since 2009 and will soon be due for replacement, perhaps by 2015. Rumor has it that the new Toyota 5-seat concept car Ft-Bh, capable of 118 mpg, will be available after 2015. See the following link:
http://www.greencarreports.com/news/1073969_toyota-to-sell-ft-bh-hybrid-subcompact-at-60-mpg-plus-after-2015
A commercial model of the Ft-Bh may have mpg reduced from 118 mpg down to perhaps 70-80 mpg, which is still double that of the latest Corolla Eco capable of 35 mpg combined driving. So, a new, dedicated, clean-sheet-design HEV will still triumph with over 100% improved efficiency over a comparable ICEV model!
Posted by: Roger Pham | 05 April 2014 at 11:43 AM
Roger,
Don't put too much trust in rumors. Lots of people speculated that the current (gen 3) Prius would get nearly 100 mpg. In actual fact, it gets almost exactly the same mileage as the gen 2 Prius, and the later Prius C is somewhat worse, given its smaller size.
That's why I find it more appropriate to compare cars that are available right now.
Posted by: Bernard | 07 April 2014 at 06:20 AM