Argonne: longer-range BEVs may be almost as powertrain energy dense as gasoline vehicles by 2045
09 May 2016
An analysis by a team at Argonne National Laboratory (ANL) has found that by 2045, some configurations of battery electric vehicles (BEV) could become almost as energy dense as a conventional vehicle. The team presented their paper at the recent 2016 SAE World Congress.
Hydrocarbon fuels (either fossil- or bio-derived) have high energy densities that are at least 100 times greater than that of a present day lithium-ion battery. Despite projected improvements in battery technology, this form of energy storage is still expected to be significantly less energy dense than gasoline even by 2045. However, the Argonne team argues, the energy density of storage medium (fuel or battery) should not be used as the sole criterion to compare conventional vehicles and BEVs. Rather, powertrain-level energy and power density will be better criteria to compare the propulsion technology used for BEVs and conventional vehicles, they suggest.
This requires assessing the efficiency of the conversion of the stored energy to useful mechanical energy to propel the vehicle.
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| Comparison of powertrain energy density at the wheel of BEVs as a ratio to gasoline-powered conventional vehicle. Closer to “1”—the value for the gasoline vehicle—indicates higher powertrain energy density. Vijayagopal et al. Click to enlarge. |
For the study, the team compared several mid-size passenger cars:
A gasoline-powered car that can run 300 miles on one tank of gasoline.
A BEV with a driving range of 100 miles (BEV 100)—common commercially today.
A BEV with a driving range of 300 miles (BEV 300) to match the range of the conventional vehicle.
The researchers considered two variants of each BEV: a BEV with a two-speed transmission (DM), and a BEV with a single-speed reduction between the motor and wheels (Fixed). Vehicle mass, power, and energy requirements changed slightly between these two options.
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| Powertrain components that convert stored energy to useful mechanical power output. Vijayagopal et al. Click to enlarge. |
They then modeled out, in five-year increments, changes in vehicle weight reduction, battery technologies, powertrain components, power and energy requirements, and powertrain energy and power densities. For each time period, they produced three assumed values corresponding to high, low, and medium probabilities.
They then calculated the “Ratio of the Powertrain Energy Density”: the ratio of the powertrain specific energy (energy consumed divided by vehicle mass) of the conventional gasoline vehicle to the BEV.
They found a significant decrease in energy consumed by the gasoline vehicle over the period, largely due to the addition of start-stop systems that reduce engine idling.
They also found that current gasoline-powered vehicles require about 10 times more energy input per kg of vehicle powertrain mass compared to the energy requirement of a BEV. Even with the projected improvements, the conventional vehicles in 2045 will still need almost twice as much energy input per kg compared to the BEV 300.
In terms of energy-out density, even though the BEV is more efficient than the conventional vehicle, its greater mass results in spending more energy at the wheel per kg of the vehicle powertrain mass.
This ratio, however, will decrease as batteries get lighter and other components become more efficient.
By 2045, BEV 300s will be comparable to conventional vehicles in terms of the energy spent at the wheel per kg of the powertrain mass.
—Vijayagopal et al.
Resources
Vijayagopal, R., Gallagher, K., Lee, D., and Rousseau, A., “Comparing the Powertrain Energy Densities of Electric and Gasoline Vehicles),” SAE Technical Paper 2016-01-0903, doi: 10.4271/2016-01-0903
Engineers can be very ingenious. Synergies in function of components already significantly reduce total vehicle weight. With the flexibility of battery and integral vehicle structural packaging, let alone fleet efficiencies rather than single vehicles, the transition to a more efficient electric transport solution is closer than you many think.
Posted by: GCrispin | 09 May 2016 at 05:17 AM
Way before 2045, clean running FCEVs will be competitive with ICEVs in all aspects.
Clean low cost H2 main and sub stations will be available in all industrial countries.
BEVs will compete as good weather short and mid-range light vehicles.
Of, relatively quick (20-30 minutes) public quick charge facilities will be installed.
Posted by: HarveyD | 09 May 2016 at 08:41 AM
I'm rather surprised that the technology of the EV-1 hasn't gone bigger. Separate motors per driven wheel eliminate differentials and free up a fair amount of room. This makes all-wheel drive a fairly simple option to add.
Specific power of a motor is directly proportional to its drive frequency (rotational speed) so faster = smaller = lighter/cheaper.
The ultimate outcome of this is vehicles either with in-wheel motors or small but powerful motors mounted on the suspension swing arms where they contribute very little to unsprung mass. All the space devoted to drive shafts and differential cases is freed, and wheels can be pushed to the extreme corners where they improve handling. All-wheel steering is no problem. The weight saved from shafts and gear cases goes to batteries, which can go in the vehicle floor where they don't impact usable space.
The BEV is already an improvement over the ICEV, and will only get better.
Posted by: Engineer-Poet | 09 May 2016 at 09:04 AM
OP> By 2045, BEV 300s will be comparable to conventional vehicles in terms of the energy spent at the wheel per kg of the powertrain mass.
Well, if 400,000 Telsa Model 3 reservations didn't wake you up, surely Vijayagopal must. That would be quite an inspiring quote to set as the alarm chime on the morning clock. Maybe Vijayagopal will post an MP3 online. I'm sure it would soon outrank Robin Williams' exalting "Good Morning Vietnam!"
If Vijayagopal will not chant it as a morning raga, maybe we can get a fat lady to sing it.
Gotta start eating my veggies, so I live to see the day...
Posted by: electric-car-insider.com | 09 May 2016 at 09:17 PM
Engineer-Poet,
the EV1 only had 1 motor, plus differential.
There is one gadget in the EV1 that would be nice to have today: automatic tire inflation.
Every wheel had a device which kept tire pressure at the optimum level. That saves a lot of energy, as many people use their cars with under inflated tires.
Posted by: peskanov | 11 May 2016 at 03:17 AM
Strange, I read once that it had a pair of them. Apparently not.
This is not difficult. There is already a patent for a peristalsis pump built into a tire bead, to add air to the tire as the wheel rotates. When the tire is at its rated pressure, the inlet to the pump is closed. This works on any vehicle.
The real question is why this hasn't caught on like wildfire.
Posted by: Engineer-Poet | 11 May 2016 at 08:44 AM
Maybe there is a fear of tires exploding due to malfunction or something similar...
About differentials: I read in several places that Tesla and other car engineering firms prefer differential because you can use the full torque of your motor on curves. With two motors, the one closer to the internal part of the curve should not use full torque.
I think this concept is interesting (electric torque vectoring):
http://www.greencarcongress.com/2014/10/20141015-visom.html
Posted by: peskanov | 14 May 2016 at 12:40 AM
There are these things called "relief valves". The TPMS could provide warning of this as well.
The differential provides the same torque to both wheels unless it is limited-slip, in which case it provides more to the inside wheel (which has less weight on it). A single motor needs a single controller or inverter, which makes it cheaper. However, with power electronics still falling in price this may not be a factor for much longer. The bigger factor will be gear reductions/transmissions; you need one per motor.
Posted by: Engineer-Poet | 14 May 2016 at 03:45 AM
I understand with torque vectoring systems you can balance the torque as you wish, which seems a bit better than having two motors. But it looks quite complex mechanically.
I read Tesla (but have no official confirmation) brakes the inside wheel to allow more torque to be transferred to the outside wheel when needed.
Posted by: peskanov | 14 May 2016 at 09:14 AM
I'd like to see how a hybrid would stack up. I think it would make the ICE engine more efficient and would delay parity even further.
Posted by: TM | 19 June 2016 at 08:57 AM