# Pleae review my fuel estimates EV vs. gas



## coil_nine (Apr 22, 2008)

Could you review my numbers below? 

I am looking at the economics of EV versus ICE. I know the energy storage unit is very significant, but first I am comparing the simple fuel cost per mile. It seems an EV is 40% of the cost of gas (April 2008, USA). I chose a conservative EV use of 300 watts per mile, based on postings on various forums, and present metric and antique units. My home cost per kWh is $.16, which is much higher than the national average (WMECo, Western MA)

ev_efficiency 186 (W/m) 300 (W/mile)
energy_cost 0.16 ($/kWh) 0.16 ($/kWh)
cost_per_km 0.030 ($/km) 0.048 ($/mi)

ice_efficiency 8 (l/100km) 29.38(mpg)
energy_cost 0.92 ($/l) 3.54($/gal)
ice_cost_per_km 0.074 ($/km) 0.120 ($/mile)

ev_cost/ice_cost 0.4 0.4


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## MrCrabs (Mar 7, 2008)

Sorry to disappoint but would say that is a very over optimistic estimate.

Most Wh/mile calculations are done based on what the battery puts out to move the car. That is useful in figuring out how far you can go based on the batteries capacity.
When you recharge a battery I've seen figures that say you need to put in about 120% of what you take out of them. So for 1000 Wh used you need to put in 1200 Wh. Plus you have to account for the charger inefficiencies which depends on the specific charger.
To do a fair comparison you also need to take into account the cost of the
batteries because they won't last forever. You need to figure out how many miles the battery pack will get you based on expected DOD for a given trip and # of cycles for that DOD.

To do a total cost of ownership comparison you would need to take into account maintenance performed on both and figure out what costs more.


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## coil_nine (Apr 22, 2008)

Thank you, I had forgotten about charging inefficiencies. 

let me understand: AFTER the losses in the charging inverter, the batteries have an inherent charging ineffcienty of about 20%? So the charger is delivering 120A and the batteries are only storing approximately 100A? 

A detailed TCO was next. I had run a few TCO projections with large 1000 cycle battery packs allowing for 80% DOD (Lion LiFePo) and the break even greatly depended on the initial cost and life of the storage units. Any break even was well beyond 100k miles, and those did not account for charging inefficiencies.


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## saab96 (Mar 19, 2008)

The cost of batteries totally eliminates the cost advantages of owning an EV over a gas car. Batteries have to be made to last longer. It's kind of sad what's happening with the altair nanosafe batteries. A123 is wiping the floor with them. If the nanosafes really last as long as they say they will then they would be a far better technology than the lifepo4's which max out at 2,000 cycles. It's like the difference between the longevity of an incandescent bulb (lead acid) vs. a CFL (lifepo4) vs. LED (nanosafe or ultracaps).


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## mattW (Sep 14, 2007)

but don't forget the rate of increase of fuel prices compared to the decrease in the price of Lifepo4's and comparatively slow rises in energy costs. Although you might crack even at today's fuel prices, I wouldn't bet on it staying the same for the next 8 years!


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## coil_nine (Apr 22, 2008)

Addressing the question, I will allow 0.80 charging efficiency for direct fuel comparisons. Thank you all for answering my question and pointing out TCO, which few people seem to think about.

The rest of this post is my rational for considering EVs, not hard data. 

Saving money:
My wife works some distance away. We calculated she works one day per week for fuel money. We will save more money changing our workplaces than any fuel efficient cars. So immediate fuel savings are not my entire reason for EVs. (Rant: over the next 10 years of my life, do I really want to spend another 150,000 miles in any friggin' car? And I am soooo tired of fixing my ICEs, changin oil, and plugging tranny leaks. End rant)

Fuel costs, TCO, and personal security:
I am planning for fuel costs to reach 5 $US per gallon by the end of 2008 because I think the heating season will drive them up. I hope I am wrong, but I must plan ahead so my family can stay warm. We can argue whether it is the dollar devaluation or global demand that is the cause; my family members will not care if they are cold.

Even at 5 $US the TCO of an electric may be slightly more than a fossil fuel car, but it is more stable and more within my control. My electric power company WMECo raised its rates 30% in the past year, and they use coal! Rising fuel costs will jump it again but slower than the gas pump. If grid power goes up, PV panels may be competitive, again coming within my control. If my glider falls apart or is damaged (I will have an accident over 150,000 miles), I can transfer the motor and remaining storage to another glider of any make or model. Again, a little more personal control and security.

Battery design and TCO:
I am a newbie and already I see A123's are the buzz, although Altair Nanosafe technology is the better product over the life of the vehicle. I think the auto companies are truly looking at lifetime costs including resale value, e.g., the Subaru concept car is designed with Nanosafes.


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## MrCrabs (Mar 7, 2008)

coil_nine said:


> let me understand: AFTER the losses in the charging inverter, the batteries have an inherent charging ineffcienty of about 20%? So the charger is delivering 120A and the batteries are only storing approximately 100A?


Thats my understanding. I need to keep better notes and bookmarks.. but i've seen that figure somewhere... but it makes sense because batteries get warm while charging, which would indicate wasted energy. If the charger puts on 120 Ah and the battery stores 100 Ah, those 20 Ah go to wasted heat.

I'll post back if I can find the source of this info


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## mattW (Sep 14, 2007)

Hmmm no I think the total efficiency of charging is 20% including inverter losses and heat losses in the battery... I.e. from AC to stored DC you lose 20%


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## CPLTECH (Sep 14, 2007)

For what it is worth, this is my experience:
In the past year, drove 4,350 miles and consumed 2,700KWH in a S10 with 1400# of lead. Do the math. A car with better drag ratio would use less.
Also, as for the cold MA weather, have never known of a battery that performs well in the cold as it does in the warm.


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## MrCrabs (Mar 7, 2008)

Is that 2700 kWh from the wall, measured by a Kill-A-Watt type device?


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## coil_nine (Apr 22, 2008)

CPLTECH said:


> In the past year, drove 4,350 miles and consumed 2,700KWH in a S10 with 1400# of lead. Do the math.


OK, that is 620 W/mile, and I've read several places the S-10 is a good choice for a conversion vehicle. I guesstimated 300 W/mile for a sedan. The guesstimate difference is much more significant than a 20% loss from the wall socket. I must search for more real-world power use.


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## ngrimm (Oct 19, 2007)

So at an average of 15 mpg on his s10 (my Dakota quad cab 2wd averages 13 mpg city) that would come to about $1000 at $3.50 per gallon. At $.16 that would be around $430. for electricity. Our electricity in Oregon costs only $.04 per kwh but gasoline is $3.80. So the comparison here would be $108 electric and $1100 for gas. No wonder there are so many evs in Oregon. Norm


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## CPLTECH (Sep 14, 2007)

To answer the question as to how the 2700KWH was calculated:

I installed a meter (similar to the utility's) in the garage so the true grid usage is known. The Link 10 E-Meter only gives the amount the motor used.


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