Estimated gas savings

[mknox]

The car will use more energy in the winter for a number of reasons: Cold air is denser and it takes more energy to push through it. The rolling resistance of colder tires might be worse. Even with the cabin heat off, the battery heater may very well be on in order to maintain proper temperature to ensure longevity of the battery. If there is snow or slush, that will take a toll too.

 

[ZBB]

I also don't like how Tesla is using $10k over 5 years as gas savings. I understand why they are doing it -- since its better to compare the cost of the car and the fuel when cross-shopping an EV with an ICE. But the fixed $10k doesn't take into account variation between cars, regions, etc.

Before I ordered a couple years ago, I made an estimate of the fuel savings. I kept MPG logs for my cars, and used 2.5 years from my previous car as a proxy for the estimates. During those 2.5 years, I averaged 23.1MPG, spent an average of $194/month on gas at an average price of $3.55/gallon, and drove an average of 12.5k miles per year. I also estimated I'd use 426 kWh in the Tesla, which would cost me ~$30/month for the same mileage using my overnight TOU rate (a hair under 7 cents per kWh fully loaded). So I was estimating $164/month in savings, which is $1,968 per year -- and pretty close to Tesla's $2k/year average.

So what am I seeing after almost 2 years (I'm about 6 weeks shy of my 2 year anniversary delivery…)? I'm driving more miles -- I'm just shy of 35k miles in 22.5 months. But about 7k of those miles were road trips mostly on Supercharger or other no-cost charging, so I've charged ~28k miles at home , which is still ~15k miles per year and higher than my previous car. I compared our electric bills from before getting the Tesla to after, and my estimate of ~$30/month to charge was just about spot on (even with the extra miles). But gas prices have fallen -- so I'd say my savings are closer to $100 a month, not $160… Its still savings, but at a $6k run rate, not $10k!

 

[jerry33]

Has anyone analyzed in some thread why it takes so much more power in the winter to propel the car?

1. Colder air is denser. Just ask any pilot how easy it is to take off when it's -10 compared to +40.
2. Roads are often wet, or covered with snow which vastly increases rolling resistance.
3. People often don't compensate for the air shrinking in their tires.
4. Cabin and battery heating (even with preheating) takes more energy than cooling.
5. Days are shorter so you're using the lights more. (Yes, this one is very minor, but it's not zero either.)
6. Roads have more potholes as the winter progresses since they are typically not patched till summer.

 

[Aljohn]

One can debate the mileage savings....it is dependent on individual situation and what one "would have been driving". I have no issue with Tesla offering up a estimate. However, I find it misleading to show the price of the car $10,000 cheaper based on wide-ranging assumptions. It is the same with the tax rebates-- Tesla is showing a savings of $5,000 for my State and $7,500 for the Federal rebates. First Georgia has repealed the State rebate, so the $5000 is not correct. They have also imposed a road use tax (as has other states) on electric vehicles of $200/year. The Federal Tax Rebate is also very individual... One's tax situation (Income, deductions, taxes owned Alternative Minimum Tax, etc.) will cause the Federal to vary between $0 and $7,500 due many complex situations.

My point is --- it is somewhat misleading for Tesla to show the price $22,500 less the the cash needed to buy the car. I have no idea whey Tesla went to this strategy. They were taking to task a couple of years ago for the same thing. Shame.

 

[brucet999]

Why are they talking about 5 years when the warranties are 4 and 8 years?

Probably because, people keep their cars on average for 5 years and Edmunds.com runs all of their TCO calculations to 5 years, so it is easy to get comparatives. Also, their assumptions (bottom of Design Studio page) work out to a nice round $10,000. Note that they even assume 10% of charging free at Superchargers.

It's marketing, for pity sake.

 

[yobigd20]

So apparently it takes 268 (feb) / 172 (jul) = 1.55 times as much energy in the winter vs. the summer to drive the car, i.e. range is reduced by this factor. I assume you use the heater in the winter. Do you also remote start or precondition the car in the winter before starting out? Do you generally leave the car plugged in all the time during the winter?

it's purely from the cabin and battery heater. i'd say its about 20-30% range loss in winter. thats normal...

 

[mknox]

it's purely from the cabin and battery heater. i'd say its about 20-30% range loss in winter. thats normal...

It really depends on your driving patterns. If you park where it is very cold, and only drive a few miles at a time, it might be 400% worse in the winter. On the weekends, when I'm not commuting, I may just make odd trips to stores or restaurants and see way higher consumption than on my weekday 45 mile (each way) commute.

 

[mibaro2]

it's purely from the cabin and battery heater. i'd say its about 20-30% range loss in winter. thats normal...

Yes, 20-30 % is normal. I find the battery heater is the big spike for the first 10 minutes or so. The further you drive, the better your wh/km will be since the battery heater turns off. The short trips really spike your battery usage.
Whenever I talk to people about the car, I tell them to expect to lose 25% in the winter.

 

[brucet999]

4. Cabin and battery heating (even with preheating) takes more energy than cooling.

I don't understand this. It takes much less energy to heat a house than to cool it by the same number of degrees from ambient air temp because insolation pumps heat directly through the roof and windows at a hugely greater rate than the delta T of air would do. So why would heating a car take more energy than cooling it? Are you looking at much greater delta T in winter than in summer?

 

[jerry33]

I don't understand this. It takes much less energy to heat a house than to cool it by the same number of degrees from ambient air temp because insolation pumps heat directly through the roof and windows at a hugely greater rate than the delta T of air would do. So why would heating a car take more energy than cooling it? Are you looking at much greater delta T in winter than in summer?

When heating the car, you also need to heat the battery. The battery is liquid cooled, so it's mainly cooled by convection though the radiator.

And yes, the Delta T is greater. In summer: 40-21=20 In winter: 21--10 is 31. (Picked some non-extreme numbers for both summer and winter. These may or may not agree with the climate where you live.)

Also the heating and cooling mechanisms are somewhat different. My understanding is that the A/C can use up to about 3 or 4 kW. The heating can use up to 11 or 12 kW.

 

[lphe]

I am continuing my original query about mileage in the winter in this thread:

http://www.teslamotorsclub.com/showthread.php/46208-Cold-Weather-Impact-on-EV-range