How to compare electric vehicle with fuel vehicle on cost?

1934 Views 19 Replies 12 Participants Last post by leave, Jun 3, 2014

Sunrise

Discussion Starter · May 23, 2014

I need to develop android app of displaying on the screen of comparing fuel and electric vehicles. I am considering parameter as fuel cost versus charging cost. Can I determine charging cost from state of charge, battery voltage or battery current? I can get these values from CAN messages.

Can anyone suggest me ideas on how to approach?

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Paul

· #2 · May 23, 2014

It's quite complex. Smarter folk than me may pop in and add to the help/advice but you have many factors at play. Cost per kWh of the electricity and the miles/km per kWh at any given time and/or on average (real world) then the cost cost per litre or gallon of fuel and the current or average miles/km per litre/gallon (real world) of an ICE vehicle. Do you then also factor in other service costs broken down by the mile, don't know. Where you would get these figures would be another challenge.

All possible, I think Nissan have produced an iOS app which tries to tell you what you'd be saving by having an EV, can't recall it's name though, sounds similar to what you're looking to achieve.

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Lee Dalton

· #3 · May 24, 2014

Pretty much as Paul said. Miles per kWh of electric, compared to miles per gallon.
Electric at whatever price per unit, and fuel at current petrol/diesel prices.

To get to the miles per kWh I think you need to know the starting point, ie. the max usable battery capacity, then work backwards using the state of charge. Presumably you can pull mileage out of the CAN messages ?

Robwiz

· #4 · May 24, 2014

It's even more complicated. You need to factor in the car's charger efficiency to determine the actual kWh drawn from the supply used to charge the car.

Ian

· #5 · May 24, 2014

Whilst I can appreciate that some people are interested in the cost comparison I feel it would be better to compare efficiencies by lining up electric kW/mile against fuel kW/mile. Also many would be interested in CO₂ output comparisons as well as that appears to be the criteria governments are keen on promoting.

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Paul_Moxhay

· #6 · May 24, 2014

I think it needs both comparisons. Many people are not at all interested in how many mpg their car gets and are only interested in how much it costs them. Others will be interested in the MPGe as a more direct comparison of efficiency.

Ian

· #7 · May 24, 2014

That was what I said!

Paul_Moxhay

· #8 · May 24, 2014

Ian said:
That was what I said!

I know... I am supporting your view

BarryP

· #9 · May 25, 2014

One factor that is ignored in virtually all advertising is the cost per mile of the battery. There is either the extra capital cost of an EV versus a ICE, or, the rental cost of the battery. In the case of the Nissan Leaf it works out at around 9.3ppm (Pence per mile) ,using Nissan figures.This needs to be added to the stated 2.3 to 5 ppm claimed by the Manufacturers.
Using those figures shows that my Leaf is more expensive per mile than a small diesel car at 60 mpg.
Just as well I didn't buy an EV simply to save money.

The problem as I see it is that by claiming such low 'fuel' costs for EV's the various bodies involved in setting pricing policies for Public charge points are being misled as to the margins available. Look at Chargemasters pricing policy to see how wrong they have got it. Since the idea of using Public money to install charge points is to encourage the expansion of EV sales there needs to be less emphasis by us drivers as to how cheap the cars are to run and more on the environmental aspects.

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Paul

· #10 · May 25, 2014

I think cost of a car is different to efficiency/cost per mile.

However if you go down that route, what really matters is residuals, say over three years. Not purchase price, but depreciation. This probably isn't a great thing in terms of EVs (at the moment), but it's fairer than saying, for example, a MINI is more expensive per mile than a Fiesta because it costs more like-for-like size and feature wise.

It's also really complex and model specific, so maybe WAY beyond the scope of an app.

Sunrise

Discussion Starter · #11 · Jun 2, 2014

Lee Dalton said:
Pretty much as Paul said. Miles per kWh of electric, compared to miles per gallon.
Electric at whatever price per unit, and fuel at current petrol/diesel prices.

To get to the miles per kWh I think you need to know the starting point, ie. the max usable battery capacity, then work backwards using the state of charge. Presumably you can pull mileage out of the CAN messages ?

Can you please elaborate on how to calculate miles per kWh?

Lee Howard

· #12 · Jun 2, 2014

Miles per kWh vary considerably with the weather, driving technique, road conditions, and terrain. Some days I see 2 mi/kWh... other days I can easily see 5... both without varying my driving technique or road conditions much... (mostly a weather change).

I'm not sure of the purpose of the Android app is besides showing comparisons between cars, but especially when considering a new purchase it does take a long, long time to recoup the added initial cost of the EV from the savings in purchasing fuel. Even when considering a used EV for me it looks like about 10 years before that cost is recovered.

That said, there is a tremendous value in the convenience of "fueling up" at home, and I don't think that should be neglected. I believe that Tesla factors this into it's "savings" equations by multiplying a wage by the time saved away from a petrol pump.

I'm sure others could go on about societal costs of running our nations' vehicles on petrol... and they'd be right. However, I don't know how one could quantify that on an Android app.

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Paul

· #13 · Jun 2, 2014

Lee Howard said:
Miles per kWh vary considerably with the weather, driving technique, road conditions, and terrain. Some days I see 2 mi/kWh... other days I can easily see 5... both without varying my driving technique or road conditions much... (mostly a weather change).

As does MPG, so despite all that it's a fairly reasonable way to compare.

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Lee Dalton

· #14 · Jun 2, 2014

Sunrise said:
Can you please elaborate on how to calculate miles per kWh?

You have to take a point in a journey, and work out the number of miles covered since the start if the journey, divided by the kWh of power used.
I think if you try to calculate it continuously, you will get a wildly varying number, much like the instantaneous read out on a petrol car.

PMC Paul

· #15 · Jun 2, 2014

I prefer to do this type of thing on actual usage - you never run a fuel tank dry (intentionally), so there is no point in calculating of tank capacities, etc.

So for petrol/diesel, start at the petrol station with an tank which is as "empty" as you would normally risk taking it. Reset the trip and fill it up. Keep the receipt in your glovebox, ashtray, etc.

Next time you are back to roughly the same "empty", clock the milage and write it on the receipt. Rinse and repeat a few times. Work out the average.

The last time I did this in my Golf GTD, it worked out at £67.45 / 437 = £0.154 / mile.

According to the calculator on the Tesla website, at £0.13 / kWh, 435 miles would cost £19.79 = £0.045 / mile.

A very rough estimate of the EV costing a little less than 1/3 the cost of ICE.

Obviously, Tesla are assuming some sort of normal driving style to get the estimated range from the charge. You'll only get a figure which is accurate for your driving style by actually measuring the kWh at its source and recording your mileage.

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derekb

· #16 · Jun 2, 2014

aren't we making this more complicated than it need be? To compare the relative costs it is simply the cost of fuel / the miles travelled (the output is pence per mile). This works for both petrol and electric and is a perfectly valid comparison. This way you dont need to fiddle about with Kw / mile which may get a number no-one really feels they understand or can compare easily with petrol.

Also no need to run to empty or near empty to calculate the petrol use you - whatever you put in is how much you've used since you last filled up! Divide the cost of that by the miles you drove...

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PMC Paul

· #17 · Jun 2, 2014

Isn't that what I said?!

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ScottHelme

· #18 · Jun 2, 2014

If you look on our homepage https://evstatus.com/ you can see how I calculate cost of electric and money saved compared to petrol. Just click on the link for each one to see an explanation.

derekb

· #19 · Jun 3, 2014

TeslaChallenge said:
Isn't that what I said?!

yes yes you did - more of a comment on the overall thread rather than your specific post!

leave

· #20 · Jun 3, 2014

BarryP said:
One factor that is ignored in virtually all advertising is the cost per mile of the battery. There is either the extra capital cost of an EV versus a ICE, or, the rental cost of the battery. In the case of the Nissan Leaf it works out at around 9.3ppm (Pence per mile) ,using Nissan figures.This needs to be added to the stated 2.3 to 5 ppm claimed by the Manufacturers.

If we're taking battery costs into account, then surely ICE servicing costs and replacement ICE components (due to wear & tear) need to be taken into account too? I spent a fortune having my Volvo D5 engine rebuilt a few years ago... at 60,000 miles, with a full service history...

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