Electric Cars Battery Capacity and Efficiency: In-Depth Analysis, Graphs

JAN 6 2019 BY DAVID ROPER 29

There are many factors to consider when buying an all-electric car (BEV)

Some of the most important ones are:

• Wells-to-Wheels carbon emissions

• Battery Capacity in kWh

• Battery efficiency in miles/kWh, MPGe, kWh/100-miles. I prefer miles/kWh since kWh is what I pay for and it is easy to memorize.

• Range in miles, which is a function of battery capacity and efficiency

• Price

This article is an attempt to quantify the first five of these factors.

The following graph shows how kWh/100-miles and MPGe are related to miles/kWh:

The value of kWh/100-miles is useful to calculate how much energy in kWh is required to travel a specific distance in miles. The value of MPGe (MPG-equivalent) is useful to compare the efficiency of a BEV to a gasoline car’s MPG. MPGe is calculated using the EPA number that one gallon of unleaded regular gasoline when fully combusted produces 33.7 kWh of heat.

The following graph shows how range (miles) varies with battery capacity (kWh) for seven values of miles/kWh:

Range can be calculated as Range(miles = Battery-Capacity(kWh)*Miles/kWh. Unfortunately, auto companies often do not list range and/or efficiency for their BEVs. Some do not list either. However, reviews by car reviewers often list one or both. But, sometimes the range listed is for the European Driving Cycle (NEDC) rather than the U.S. EPA Driving Cycle. The NEDC range value for a specific BEV is always considerably larger than the EPA range, which means that the miles/kWh is always larger.

To complicate matters the European Union, Japan and India have defined another Worldwide Harmonized Light Vehicles Test Procedure (WLTP), which value lies between the NEDC and the EPA value. It is often not clear in a BEV review article which of the three test numbers is given. So the range numbers in the following graph for range vs battery-capacity for several BEVs may not all be EPA values:

*Note that BEV efficiency (range) varies widely for high battery capacity

Union of Concerned Scientists has calculated the 2016 equivalent MPG for a gasoline car to equal the driving carbon emissions of a typical BEV in various regions of the U.S. The sales-weighted average for the U.S. is 80 MPG, which will increase if electric-power sources become more emissions free. The different regions vary from 38 MPG to 191 MPG. (See the map.) Of course, if you have enough solar panels on your house, the gasoline equivalent MPG is very much higher.

Union of Concerned Scientists have calculated the “Wells-to-Wheels (WtW)” carbon emissions of average gasoline cars and average BEVs in the U.S.. It was found that BEVs have about one-third WtW of gasoline cars for the U.S.

Here is a graph that shows driving costs for BEVs:

The dashed line (3.5 miles/kWh) is my estimate for the average BEV in 2018.

The average cost of electricity for the last several years has been about $0.12 (vertical line).

The average (dashed line) crosses the vertical line at about $0.035/mile.

Compare to this graph that shows driving cost for gasoline cars:

The dashed line (27.4 MPG) is for the average gasoline car in the U.S. for 2016.

The average cost per gallon for the last several years I estimate at $2.50 (vertical line).

The average (dashed line) crosses the vertical line at about $0.09/mile.

http://www.roperld.com/Science/My5BEVs.pdf

http://www.roperld.com/Science/TM3LR_SCChargingCurves.pdf

L. David Roper, ROPERLD@VT.EDU, http://www.roperld.com/personal/roperldavid.htm 4 January 2019

*Above web addresses are not secure.

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29 Comments on "Electric Cars Battery Capacity and Efficiency: In-Depth Analysis, Graphs"

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Driving 25 miles a day, the new 2019 BMW i3 with 150 miles now has 6 DAYS of RANGE.
Range is now sufficient, and the car is a pleasure to drive.

Do you actually get 150 miles of (real world) range out of that 2019 i3? BEV or REX? I took the $10k discount on a 2018 (94ah) model they were offering a couple months back (knowing the 120ah version was coming) but as far as real world range I’m getting maybe 100 miles on a good day (i3s/REX). It is winter (Seattle) so that might get better as temps rise. At freeway speeds ~ 70mph I’ve done way worse… like I understood the concept of freeway speeds equaling less range but I was not expecting a 30-40% hit in range… meaning I can easily deplete the battery in under 75 miles if I’m not taking it easy. Glad to have REX for when those slight miscalculations happen.

I would not call it miscalculation. You just have to learn, his your car’s efficiency reacts to your foot and outside conditions. Being able to pre-heat from plug, makes a world of difference on commutes as well. Of course, if you cannot you pay a penalty through lower range ….

Absolutely, numerically, every car is different, but they all behave the same way … The faster you go in cooler weather, the shorter the range. Some cars range meters are also better at estimating range than others …

It would be really nice if Washington would install the freaking combo plug on the Western Washington Electric Highway.

Not like I can take the i3 to Leavenworth and back. There is no place to fast charge along highway 2.

I consider BMW to be part of the problem.

I have driven 7,000 miles on my 2018 i3s, no range extender. In summer I had about 130 miles of usable range, it winter it dropped to about 105 (I’m in PA). Not surprised with your observation, seems about right. I have calculated about 20% loss in winter, with another 15% of highway driving (with heat on, and seat warmer on).

Freeway driving with 80mph can result in 50-80% less range compared to city driving only

Shame it looks like a freak mobile. Which shows what BMW really think about BEV’s.

$2.50 per gallon is only temporary.
But if it stays than Alaska oil production and exploration should drop to zero.
All the most expensive places to drill will be shutdown.

We are paying $1.80 per gallon right now (assuming regular). 😉

Agree, won’t stay that low forever.

Joe the plumber is saying, the gas price will keep going lower because of decrease in demand.
When gas price is so low that it becomes unprofitable, oil companies will shut down their production to maintain the price or some oil companies will even go bankrupt

Axis should be labeled in graphs to make them easier to read. Blink charges $0.49/kWh L2, $0.59/kWh DCFC, Electrify America is about $0.45/kWh, some places charge far, far more, and tapered to hell Leaf after spirited drive could be $1.50/kWh. Graph should extend to those values.

Keep in mind that EV must take charging efficiency into account if mi/kWh is read from the car. That varies from bit under 80% (L1) to about 85% (L2). Bolt shows about 3.3 mi/kWh at 70 MPH, but taking charging into consideration, it’s effectively 2.64 mi/kWh (L1) and 2.8 mi/kWh (L2).

Of course, EV does lot better on average, and my Bolt shows 4.9 mi/kWh average (3.9 on L1, 4.2 on L2) after 7K miles. With $0.23/kWh San Diego, that’s about equivalent to 60 MPG gas car when gas is $3.25/gal. SparkEV showed 5.5 mi/kWh after 30K miles.

If you look at the EPA MPGe figure, it factors in charging efficiency and is actual number. Dash number will be misleading as you say.

“With $0.23/kWh San Diego”

Wow! Sounds like a great opportunity for solar. Back in 2016 you could get solar with 0 down and an agreement to pay 15 cents per kWh here in Northern California. If you have decent exposure I would think Southern Cal would be even better being closer to the equator. It was 12 cents kWh if you financed youself.

If you don’t have solar you might want to check out Google’s project sunroof.

https://www.google.com/get/sunroof#p=0

So – the Take-away – in Simple Terms, from the two relevant lines near the end:
“The average (dashed line) crosses the vertical line at about $0.035/mile.” &
“The average (dashed line) crosses the vertical line at about $0.09/mile.”

$0.035/mile (BEV) vs. $0.09/mile (ICE) – So ‘Just over 1/3rd the Cost per mile for the Average EV to drive, versus the Average ICE!’ Or – Saving about 60% in Operating Costs per mile – Energy Use Wise!

Now, if we could just see an article with as much information about the amount of energy used to operate a Home – sized from 400 Sq. Ft, up to 4,000 Sq. Ft. – with them laid out with charts & graphs – by Energy Use Cost & Type, Region, and R-Value Insulation Levels!!

Ends are not equivalent. EV ends at $0.30/kWh but electricity is $0.50/kWh peak in SoCal (and forget about super peak), and also many public charger. Very few places in US gas is $4/gal.

Well to wheel calculations are wrong. It takes into account the electricity generation but not oil production. A Tesla P85D consumes electricity similar to 1.8 liters of gasoline. ( half a gallon). 1 liter of gasoline needs 5 kwh of electricity in the refinery. And from Well to refinary you need to account for consumption, as well. Long story short, it’s not one third, more the one tenth comsumption with respect to ice cars!
My two cents..

Well made well-to-wheel studies include all these factors! Read some scientific papers.

Please don’t repeat the refinery myth. Refineries use a lot of heat energy per gallon produced, but very little electricity.

At 5 kWh per liter US refineries would consume more than 100% of US electricity generation.

“At 5 kWh per liter US refineries would consume more than 100% of US electricity generation.”

….please recheck your math. According to Wikipedia 5kWh per gallon would amount to about18% of US electricity consumption.
(142 x 5) / 3,912

Max allowed DoD is not included, which renders that whole article pointless.

No EV uses 100% of its battery capacity and the allowed depth of discharge varies.

Pointless, really? You just like hyperbole statements, eh?

Jopp:

Your point that “No EV uses 100% of its battery capacity” routinely is entirely valid.
But the article “pointless”??
A standard for comparison applied in a uniform manner across all EVs is hardly pointless. It’s just a useful parameter.

Yes, it behoves all of us to recognise that the devil is in the details. And it can be tricky for newcomers to the field to
understand how all of that will impact their EV usability.
But fortunately, with new vehicle battery capacities getting larger by the year, the chance of getting trapped in a disappointing EV purchase, through ignorance, is becoming more and more unlikely.

All this complexity is why the EPA introduced MPGe. Simple for most people to grasp.

I like miles per kwh also. MPGe doesn’t really stick.

Looks like the average electric car costs 3.5 cents per mile, in comparison to my Prius, which costs 5 cents per mile. Figuring 100,000 miles or so of ownership, that’s $1500 in savings over the ownership of the vehicle.

Around here regular grade gas is close to $3/gal. At 55mpg, that is 5.55 cent per mile.
So over 100K miles the difference is $2000.
If the gas price fell to $2/gal, the difference would be $100.
If the gas price falls to below $2/gal, ICE would cost less to fuel.

In Columbus, Ohio gas is $1.89/gal – that’s crazy.

What the hell is a mile? 43,759 big toes ?!?
Come on the ignorance in presenting an article in an outdated system of measurement used by only two counties is epically frustrating!!

Perils of reading an American Blog.