Electric Hypermiling vs ICE Hypermiling

Does anyone with knowledge of both want to comment about any differences in technique between the two? Slow and smooth seems to be the general rule for both.....

Both require anticipation but the idea is to conserve momentum - more so in ICE cars as there are no energy benefits from braking. Even on i3 there is a spot on the accelerator where you can "glide" between power on and regen braking. Slow uphill, fast downhill, slow into headwind, fast tailwind.

High efficiency doesn't always mean slow. Stop start traffic suits EVs, but some journalists got speeding tickets doing a eco test drive in Spain during A2 launch back in 2001:

http://www.telegraph.co.uk/motoring/4749588/A-little-fuel-for-thought.html

Aero affects both but I wouldn't get too close - you need to anticipate when the guy in front will brake - i.e: see ahead of them.

Good video for tips on city driving using a Lupo 3L:

http://youtu.be/THkVciVpmxs

Good question. It seems like the general approach must be similar, but I suspect the penalty for being "sub optimal" with your inputs is more with an ICE. Regen braking is the biggest factor, but I also wonder about the relative penalty for fast acceleration.

By this, I mean that if you accelerate at 0.3G instead of 0.15G in an ICE and thereby use X% more gas, if you did the same in the i3, would the (relative) incremental kWh used be higher or lower than X%?

Chrisn said:

... I also wonder about the relative penalty for fast acceleration.

By this, I mean that if you accelerate at 0.3G instead of 0.15G in an ICE and thereby use X% more gas, if you did the same in the i3, would the (relative) incremental kWh used be higher or lower than X%?

Click to expand...

This is one of the really great things about EVs. Electric motors maintain essentially the same (very high) efficiency throughout their power and RPM range, in contrast to ICE vehicles that spew more pollutants than power at low RPM and high demand.

Bottom line is that any efficiency loss due to rapid acceleration is more a result of aerodynamic losses as a result of the greater time spent at the final speed achieved than is due to the acceleration itself. Fact is, acceleration in an EV at twice the rate of an alternative run between points to a speed lower than that which would need to be achieved at the lower acceleration rate in order to decelerate to a stop in the same time and distance, would actually use less energy:



There's an old thread that discusses this, with detractors (mostly from a solar energy background) bringing up fun concepts like "internal resistance" and "Peukert effect" - which are very real issues with lead-acid batteries, but insignificant when talking about not only the vastly superior chemistry of Lithium Ion, but the fact that these bursts of speed last only a few seconds, and that any temperature related ill effects are countered by not only the short duration but by the incredible technology of the BMW's refrigerant based cooling system.

A bit of the old discussion repeated for your benefit:

Many folks interested in EVs come from a solar energy background where internal resistance of a given battery is a very big deal, and a significant factor in sizing a lead acid battery bank. The higher the discharge rate, the higher the internal resistance, the greater the heat generated, and the lower the total energy storage capability of the battery. The capacity of a lead acid battery discharged quickly, say in 2 hours, is roughly 58% of the capacity of that same battery discharged slowly, over the course of 100 hours. For this reason, lead acid battery spec sheets do not state a single ah capacity, but rather a broad range of them based on discharge rate, with most manufacturers standardizing somewhat on the 20 hour rate for comparison purposes. So, how does a wise EV engineer deal with internal resistance?

• 1. She chooses the right battery technology for the job. Ever wonder why Lithium Ion battery capacity is never stated at a "20 hour" rate but rather as a single number? It is because all of the factors (to include internal resistance) that might otherwise contribute to reduced capacity at high discharge rates are inherently so small that they do not significantly affect a Lithium Ion battery's capacity. Consider this comparison of AGM (a lead acid technology) to lithium ion:
  
  
  
  
  
  2. She chooses the best battery chemistry for the job. The NMC (Nickel-Manganese-Cobalt Oxide) chemistry BMW chose for the i3 has the lowest self heating rate of any Lithium Ion battery chemistry currently available for use. It is lower than the LOM chemistry used in the Nissan Leaf and Chevy Volt. (http://batteryuniversity.com/learn/article/types_of_lithium_ion)
  
  3. She sizes a massive battery bank so that even at high total discharge rates, each individual cell is discharged relatively slowly. Ever wonder why a 60 kWh Tesla Model S accelerates more slowly than an 85 kWh model? Them Tesla engineers are some smart folks, and intentionally limit the maximum discharge rate of individual cells, making the power draw on each cell similar for the two cars even though they are capable of accelerating at different rates.
  
  4. She designs an effective thermal management system. No current EV manufacturer can hold a candle to the effectiveness of the refrigerant system of the i3.
  
  5. She limits the maximum power draw. Ever wonder why power is limited to 170 hp and top speed is limited to 93 mph / 150 km/h? It ain't because it is significantly more expensive to make a more powerful motor. It is more likely to limit power draw on the battery bank.

Some people never get the idea of smooth transitions...ever ride in a car where the person was always (may be slight, but still there) accelerating, decelerating, and can't hold a steady rate? On an old car with a carburetor (are there any new ones being built these days?) that could trigger the accelerator pump to be constantly injecting extra fuel. WIth today's fuel injection, that isn't as big of an issue, but creeping up and down around your desired speed means lots of little acceleration events that add up. With an EV, it isn't so much how fast you get to speed, it's that you do it smoothly, and also don't constantly creep up and down around your average cruising speed. The Eco modes on the i3 limit the motor's response to those requests for more speed, and is one big reason (other than disabling or reducing creature comforts) they add efficiency.

For ICE (especially modern diesels), rapid acceleration to optimum cruise speed and highest gearing is best for max MPG and lowest emissions overall. "Gliding" = freewheeling also helps hugely. That's how the VW Lupo hyper-miler in the link achieves 2l RME biodiesel per 100km (141 Imp MPG/111 US MPG).

For EV, there are issues with Li Ion batteries especially if very cold: Harsh acceleration/high demand can cause formation of metallic lithium dendrites in the SEI (anode side of the batteries) which ulitmately could penetrate membrane and short circuit the cell.

In terms of pollution, if NYC or Hawaii petroleum based electricity used then not really better than an efficient ICE. If CA USA Solar - a very different story.

Below 40 mph aerodynamics have very little to do with range. However, we have seen real world, the i3 BEV and REX soon use up charge at highway speeds.

Overall the smoother the better - in range terms it is actually better to glide with momentum than use harsh regen or worse, braking.