Comparing BMW i3 vs break-even mileage

Hi,

There is a recent article that correctly claims a Prius Level 2 ECO can be cheaper to operate than an EV:
http://www.torquenews.com/1083/2016-toyota-prius-two-eco-beats-evs-cost-mile-michigan
It has to do with the high efficiency of the Toyota's Gen-4 Prius and local utility and gasoline prices and using a "Leaf" as the EV.

I had already been working on a similar model and their math is accurate. Of course there are other effects to consider. For example, a hybrid typically pays a warm-up penalty in the first 1-2 miles that our BMW i3-REx does not. Understand my model is not designed to cover all test conditions but demonstrate how local utility and fuel rates can enhance or reduce the spread between our rides and a gas, diesel, or other fueled vehicle.


(I will try to make a URL that allows you' all to download the OpenSource spreadsheet.)

The upper sheet has inputs of local electrical costs, fuel cost (could be diesel), and the type of fuel, local quantities and distance units. Then I put in my tripmeter recorded miles/kWh for about +300 miles. It turns out a 2016 Prius Level 2 ECO driven in a similar manner would and could break-even at 74 MPG. The lower sheet does the same analysis using EU typical units. A Prius would have to achieve 2.9 l/100 km based on some German typical electrical and fuel costs.

Now my metrics included a lot of air conditioner usage in our +90F (+32C), high humidity days with an average speed of 28 mph (45 k/h). Change the test conditions and we can move the threshold to either favor or penalize the hybrid or the BMW i3-REx. Other areas have higher or lower electrical rates and fuel costs. But the math model remains a valid approach to compare our rides.

Bob Wilson

ps. Experimental URLs to the OpenSource spreadsheet and a zip file with the OpenSource file.

http://hiwaay.net/~bzwilson/BMW/EV_to_MPG.ods
http://hiwaay.net/~bzwilson/BMW/EV_to_MPG.zip

Your spreadsheet does not account for charging efficiency which is roughly 90% and increases the effective cost of the EV.

In any case, that's a silly article for a number of reasons:

1) Car and Driver (http://www.caranddriver.com/reviews/2016-toyota-prius-two-eco-test-review) only managed 47mph in their 1,000 mile road test.

2) Regular gas in California is about $2.80/gal which puts the break even versus the i3 at 120mpg, or more than twice the EPA rating and 2.5x what C&D experienced.

3) The driving experience is entirely different. The i3 sprints to 60 in 7.0sec, the Prius eventually reaches 60 after 9.4sec.

4) The Prius owner gets to maintain an ICE engine, and and EV drivetrain so lifetime ownership cost will be higher.

Of course the Prius is also cheaper, it's just not an apples to apples comparison.

We could compare my Tesla Model S to the Mercedes E350 Bluetec it replaced and get similar results. At $2.70 / gal for diesel, 90% charge efficiency and the Model S getting about 3.6mi/kWh, the breakeven is 89mpg. Unfortunately the Mercedes averages about 34 mpg all around with a 0-60 of 7.2sec versus the Tesla's 4.2sec. Again the EV's mileage is about 2.5x the ICE. And don't get me started on the cost of Mercedes maintenance.

To equalize cost and performance, compare the Tesla Model S to a Porsche Panamera 4S. The Tesla is still 0.4sec faster to 60, but they are otherwise pretty similar in capacity, performance and purchase price. But the Porsche averages about 22mpg, compared with the 96mpg equivalent using $2.90 for premium fuel for the Porsche. The Tesla is more than 4x better on a cost / mile basis.

It's a nice headline, and I'm sure some ICE owners will be quoting it all weekend, but it's not reality.

Boatguy said:

4) The Prius owner gets to maintain an ICE engine, and and EV drivetrain so lifetime ownership cost will be higher.

Click to expand...

I agree with all your points, but feel this in particular is not adequately stressed enough when long-term benefits are considered. EVs do not have timing belts, egr valves, fuel pressure regulators, vacuum hoses, cat converters, and the list goes on - all things that wear and clog over time, at a minimum requiring per-emptive maintenance and replacement; at worst causing a break-down costing thousands.

Relax fellows. My spreadsheet model is 'back of the envelope'. Certainly I have no problem if you' all add as many additional factors as you want to make it more accurate. I was trying to stay within the scope of the original article.

Now I have no problem with the "90%" efficiency provided it is backed up by a creible source or personal experiment. The irony is I will be doing a home based test in about 30-45 minutes.

So enjoy the article and point out to skeptics that they just endorsed the PRIUS, a car they usually loath. Hoist them on their own pitard. <GRINS>

Bob Wilson

From Electricity Grid the wheels the efficiency is about 75%.

Grid transmission efficiency ~ 98% in the UK, adjust for the US.

Converter efficiency in rapid charger ~ 94% (you can find these on the manufacturers' brochures. Or the Converter efficiency within the car for fast of slow chargers is also about 94% (i3 Tech documentation and also AVT-INEL testing).

Battery round trip efficiency is ~ 90% - see AVT-INEL testing

EME efficiency is ~ 94% (i3 Technical Documentation)

Motor efficiency ~ 97% (i3 and i8 presentations from BMW)

transmission efficiency 98-99% (generic single stage locked-train gear)

From Grid to Wheels = (grid) 98% x (rectifier) 94% x (battery) 90% x (EME) 94% x (Motor) 97% x (Transmission) 99% = 75%

These are maximum efficiencies and do reduce and vehicle speed and motor speed reduces and also decreases under hard acceleration.

On that simple comparison, the numbers may work or not based on the relative costs of electricity and liquid fuel, I'll leave the US members to argue that but based on the first two posts, a gallon of liquid power in the US appears to be somewhere between 17 and 27 times the cost of a unit of electricity.

In the UK where I live, liquid is around 55 times as expensive as a unit of cheap rate tariff electricity.

It's a no brainer over here, an ICE or PHEV would have to do hundreds of miles to the gallon to get anywhere near the same fuel running costs. And everything I see regarding real world mpg on PHEVs just doesn't match the official quoted numbers.

This is a little dated but still very relevant article, THE EV WEDGE, showing the comparative benefit of EV over ICE across various countries.http://www.theenergycollective.com/...sidered or costed in many of these equations.

Gif said:

. . .

In the UK where I live, liquid is around 55 times as expensive as a unit of cheap rate tariff electricity.

It's a no brainer over here, an ICE or PHEV would have to do hundreds of miles to the gallon to get anywhere near the same fuel running costs. And everything I see regarding real world mpg on PHEVs just doesn't match the official quoted numbers.

Click to expand...

Excellent data point.

Lithiumman said:

This is a little dated but still very relevant article, THE EV WEDGE, showing the comparative benefit of EV over ICE across various countries.http://www.theenergycollective.com/...ive the Prius or the BMW i3-REx. Bob Wilson

Click to expand...

When factoring in the externalized costs of oil lets include wars of choice and rising sea levels. If Iraq had had no oil there would never have been a Saddam Hussein with enough money to make a nuisance of himself, let alone an Iraq war at, say, a US$ trillion and counting. What's the trade-in value for what will once have been Florida? How much for sea walls around Manhattan, Shanghai, Hong Kong, Venice? What's the value of polar bears; the snows of Kilimanjaro, the Great Barrier Reef? Please, factor these into your spreadsheet.

johnnylingo said:

I agree with all your points, but feel this in particular is not adequately stressed enough when long-term benefits are considered. EVs do not have timing belts, egr valves, fuel pressure regulators, vacuum hoses, cat converters, and the list goes on - all things that wear and clog over time, at a minimum requiring per-emptive maintenance and replacement; at worst causing a break-down costing thousands.

Click to expand...

EV batteries degrade, and need to be replaced at some point, and they're not cheap to replace.

We just haven't had any EVs around long enough to really see that in action.

There definitely seem to be fewer moving parts in an EV to maintain, but I think it's erroneous to brush away the cost of a replacement battery yet include oil changes, scheduled maintenance, etc.

FWIW, once the battery pack in an EV has degraded enough so that it needs to be replaced, in most cases, it still has significant additional life in other energy storage applications as evidenced by various schemes, several from BMW included. So, while the outright purchase of a new battery pack might be substantial, I do expect there to be a pretty good core return value that brings that cost down considerably. Plus, when the time comes to recycle it, as opposed to smaller batteries used in say the Tesla, those chosen for the i3 should be easier to recycle and reuse some of the components. Tearing apart many thousands in a Tesla battery pack verses around 100 in an i3...the cost/benefit at least seems to weigh in to benefit the i3 when it comes time to recycle.

Well the week of 'no pay for play' ended with 352.0 miles and not one paid kWh. I arranged my normal trips to include 'free' chargers and the problem was solved.

It felt a little strange starting each morning with less than 100% SOC, sometimes under 80%. I was also surprised to find the Whole Foods chargers turned off at midnight. Also the 'broken display', Blink charger stopped working on Monday (someone finally turned it off?) But the others worked just fine.

Bob Wilson

i3an said:

When factoring in the externalized costs of oil lets include wars of choice and rising sea levels. If Iraq had had no oil there would never have been a Saddam Hussein with enough money to make a nuisance of himself, let alone an Iraq war at, say, a US$ trillion and counting. What's the trade-in value for what will once have been Florida? How much for sea walls around Manhattan, Shanghai, Hong Kong, Venice? What's the value of polar bears; the snows of Kilimanjaro, the Great Barrier Reef? Please, factor these into your spreadsheet.

Click to expand...

+1

The lifetime consumption of my BEV 12,000+km is 12.8kWh/100km. We live up a hill, (300m/1000ft), so we would be getting even higher efficiency if we lived on the flat.
Our BEV is powered by solar PV. We produce more PV power than we consume for the whole household including powering the EV. If we had to buy fossil fuel to power a Prius, we would be cash and environment negative. No thanks.