EnviroKarma.org - Electric Vehicle (EV) Conversion '...it's (NOT) hard to be Green' - what Kermit should have said


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    If you consider the batteries as 'consumable', then you need to consider their contribution to the 'operational cost' per mile. If I had been willing to live longer with the reduced range as the lead-acid batteries aged, I could have gotten more miles out of them; but I really wanted at least 25 worry-free miles. It was getting to the point where the original 40 mile range had dropped to 25 and the last couple miles the voltage would be 'sagging'. With lead batteries the life-cost, including what I was able to recover by re-selling the batteries to an off-gridder, worked out to about:
    $1400/7,500 miles = $.19/mile for lead-acid

    I decided to upgrade my pack to 120v worth of 100ah LiFePO4 for $5416, delivered. Increasing voltage from 96 to 120v for better performance, more energy on-board, losing about 500# which helped with performance, suspension, and charge efficiency, should last 10x longer (about 75,000 miles or more), and increase max daily range to about 50 miles. The prismatic cells are rated for 3000-5000 'cycles', and I think mine will provide closer to the high end since my typical use is less than 50% Depth of Discharge (DOD)... which may yield 100,000 to 125,000 miles of use if I get 5000 cycles of 25 miles average daily use! This puts the 'operational cost' of the Li about:
    $5416/100,000 = $.054/mile for LiFePO4, or down to .043 if they go 125,000 miles.

    The much longer cycle life of the Li brings up the debate whether you want to consider the batteries a 'consumable', or a 'lifetime' capital expense since they'll probably last about as long as the donor mechanical parts will go if you start with something that already has 100k miles on it. If you don't amortize the batteries in the 'operating cost', then the only real operating expense is the electricity, which is obviously far less expensive than gas...


    The residential rate in NM (2011) is right about $.09/kWhr from PNM. With Lithium batteries the worst case consumption I see 'at the plug' is 2 miles per kWhr. This takes into account all losses in the charger, motor, controller, drive with a heavy foot, and use the heater and headlights. This would mean
    $.045/mile for electricity at worst. I usually get closer to 3 miles per kWhr, which would lower this to
    $.03/mile for electricity usually.

    ...but in my specific case, my electric use is completely offset by my PV installation!

Comparing to running on gasoline

    My little Swift used to get right around 40 mpg. So at a mythical gas price of $3.50/gallon, I would spend
    .088/mile for gas

    but then you also have to add in cost of oil changes... say $30/3000 miles gives:
    .01/mile for oil changes

    and allow at least $1000/60,000 miles for maintenance like belts, filters, plugs, etc
    .017/mile for minor maintenance

    and factor in a serious overhaul for at least $2000 for water pump, rings (rebuild) to get a gas engine to 200,000 miles, which would be easy with an electric motor... which would only require a set of brushes for about $40 under normal circumstances.
    .01/mile for major rebuild to reach 200k miles

    ...adds up to at LEAST $.125/mile on gasoline if no major engine repairs are required and the price of gas averages $3.50 per gallon versus $.10/mile on electricity at MOST, probably closer to $.09/mile... and a lot less if you have PV!

    This figure ignores the 'depreciation' of the vehicle itelf. The typical gas vehicle starting from 'new' basically loses the entire sticker price over 200,000 miles, where the conversion probably started with a 5 or 10 year old car worth less than $5k, but then you put $6k-$8k in parts plus another $5k for batteries into it, so that is sort of a wash except it doesn't 'depreciate' on the normal scale any more.

So the net of it is that saving .03/mile adds up, but not real fast. Lets say you use the car an average of 150 miles/week... thats 7800 miles /year, so only about $234. savings in operational cost. On the bright side, it doesn't cost MORE to operate with Lithium as it did with lead-acid, and it does have all kinds of positive environmental impact. Besides, it gets better and better as the price of gas goes up!

The savings also gets better if you would be parking a more typical gasoline vehicle getting perhaps 20mpg while using the EV for daily trips around town... which would have an operational cost closer to $.213/mile giving savings of $.11 or $.12/mile with the EV, or closer to $860 savings per year. By parking the SUV, the little EV would basiclly pay for itself over a 10 year life, and the SUV retains higher value with fewer miles on it.


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