# Forums

## Can you help me do math?

Because I'm an idiot.

My question is this - how much am I spending preconditioning the car (warming the cabin) to ~72F for 1 hour? Just a best guess is all I'm asking.
~40F in my garage.
Here's how much I pay per my Xcel Energy statement (MN)

Electric/kWh per Day 70.2
Electric/Cost per Day \$9.58

I'm just curious how much warming the battery is costing me every day (ROUGHLY).

TIA

jimglas | 14/11/2019

Not much

andy.connor.e | 14/11/2019

For 1 hour?

≤ 6kWh

Mike UpNorth_ | 14/11/2019

what is that in \$?

andy.connor.e | 14/11/2019

And you're paying roughly 13.6 cents per kWh, so ~\$0.8188/day.

andy.connor.e | 14/11/2019

Sorry less than or equal to 81 cents per day.

Mike UpNorth_ | 14/11/2019

GTFOH! Sweet. There goes that worry.

Mike UpNorth_ | 14/11/2019

and THANK YOU

Mike UpNorth_ | 14/11/2019

shit, I might as well prewarm for 2 hours. 2 bucks.

andy.connor.e | 14/11/2019

For future reference, you listed kWh and \$ usage per day

So \$9.58 / 70.2kWh = \$0.136/kWh

Cabin heater is a 6kW heater running for 1 hour so thats a maximum of 6kWh you could use.

\$0.136 x 6kWh = \$0.818

andy.connor.e | 14/11/2019

Ya its only \$2. But its \$60 every month. or \$720 per year for a preheated cabin.

Mike UpNorth_ | 14/11/2019

Gotcha.
Strange my statements don't say/show the \$0.136/kWh. Why make me do math....

andy.connor.e | 14/11/2019

Thats why there are forums. You're welcome.

Mike UpNorth_ | 14/11/2019

Agreed. It can add up. But in my mind for some odd reason I was ready to hear \$5/day for an hour of cabin warming. So less than \$1 was awesome to find out.
I'll never really prewarm for 2 hours...Just was happy how little it did cost for 1 hour.

Effopec | 14/11/2019

Cost depends on your electric pricing. For me it's about \$0.10/kWhr, so 6 kWhr is about \$0.60.

Next question is why are you running it for an hour? The cabin should warm up within about 5 minutes. If you use the new "finish by" charging strategy you can use your charging to warm the battery. I'm not Minnesota cold (garage is usually in the 50's on cold mornings), but even if it finishes charging close to an hour before I leave I generally don't have any regen dots when I leave. Now if I can just get the timing a bit better I'll be all set. I put in finish by 7:30 & it has been done between 6:20 and 7:00 every day so far. I don't care if it goes all the way to my set point, so I'll probably move the finish line to a bit later to be sure it is pretty warm when I leave.

andy.connor.e | 14/11/2019

No worries. After yesterdays 15 degree temperatures, leaving work i definitely can see the benefit of preheating my cabin for even just 5 minutes.

Mike UpNorth_ | 14/11/2019

And it wouldn't be for a full year. Probably ~5 months. So \$300/year.

but I love regen that much :)

Mike UpNorth_ | 14/11/2019

@Effopec

If I do nothing I have 0 regen (all dots) when I start driving.
If I prewarm + charge for 1 hour before leaving I get about half or more regen back (~50% or less dots). For less than \$1/day I'll take that improvement.

Mike UpNorth_ | 14/11/2019

***I should mention this is after the car sits all night in the freezing cold. Taken from someone else on here a 'cold soaked battery'

andy.connor.e | 14/11/2019

Even this week when it was 12 degrees in the morning my garage was about 55 degrees. So i can imagine i shouldnt have a horrible time with cold battery packs.

hokiegir1 | 14/11/2019

And really -- while that's the max on the heater, my TeslaFi preconditioning losses are *significantly* less than that for 30 minutes to an hour (usually .1 kwh, though there was one morning it was 1.1kwh used), so you'd be looking at closer to 30 cents/hour "real world".

Mike UpNorth_ | 14/11/2019

garage insulated to some degree? I am planning on doing mine just to help my car :)

Mike UpNorth_ | 14/11/2019

@hokie

Back to 2 hours of prewarm for 60 cents! :)

andy.connor.e | 14/11/2019

Ya definitely to some degree. There are typical cinder blocks up to i think 2'-6", but from there its insulated drywall. Garage is also underneath the house, raised ranch style, and there are ducts that run into the garage despite that i have the vents closed. Even better my main panel is directly next to where i park so a charger installation will be a breeze.

andy.connor.e | 14/11/2019

I'll take the 2 hours for 60 cents plz

hokiegir1 | 14/11/2019

With our 1.5 cents/kwh TOU plan here, it's well worth it to me. ;)

Mike UpNorth_ | 14/11/2019

@andy

My panel is in the garage too. My buddy who's an electrician hooked me up so I only paid like \$150 for materials.

But yeah, I need to 'finish' my garage. Get that temp up another ~20F

Rikki-Tikki-Tavi | 14/11/2019

lbowroom | 14/11/2019

Since you have the real answer already, Is it ok if I joke that by my alternate math it could be as high as 3.99/minute?

Iwantmy3 | 14/11/2019

How do you get 60 cents? Two hours @ 1kW is only 2 kWh @ \$.136/kWh. That is just 27 cents for 2 hours (or 7 cents for 30 minutes which is more than enough).

andy.connor.e | 14/11/2019

@lbowroom

I think thats a moderately appropriate mathematical conclusion. :D

andy.connor.e | 14/11/2019

@Iwantmy3

I think the 60 cents is coming from the proposed 2 hours of preconditioning Mike was saying he wanted to do. Then @hokiegir1 said that the cabin heater usage for her had been much lower than the maximum 6kW, so to fairly estimate less than half of the proposed usage to arrive somewhere around the arbitrary 30 cents. Could be more could be less but thats a good estimate.

jdcollins5 | 14/11/2019

@MikeUpNorth - do you really use 70.2 kWH a day? Almost a full battery charge or about 300 miles per day? Just curious.

hokiegir1 | 14/11/2019

@Iwantmy3 - Lots of rounding and very fuzzy math. My estimates from TeslaFi were for 30 minutes mainly (I might have run it longer a couple times)....so 1.1kwh @ 13 cents/hour for half an hour of preheating, doubled (to make the hour) comes to 26 cents -- rounded to 30 cents. For 2 hours, that's 60 cents.

hokiegir1 | 14/11/2019

@jdcollins - I think that's his whole house usage, not just the car.

Mike UpNorth_ | 14/11/2019

@Andy yeah, if its a good guess - 30 cents/hour - I'll go with it. Just looking for a ballpark estimate.

@jdcollins it appears so. I work from home. Wife doesn't work and we have 2 kids (2 and 7 months) - so she's home a lot....~72F all day/night. Lights on, computer, electric stove top (sucks)......The electric company sends me these notices comparing me to my neighbors. Lets just say I'm not efficient.
But I don't drive *that* much. ~11,000 miles in 13 months.

Mike UpNorth_ | 14/11/2019

What Hokie said

Rikki-Tikki-Tavi | 14/11/2019

Using a lot of electricity. My usage from yesterday was 29 Kw. And we have cold weather right now in GA. Also house is 3500 sqf plus pool pump working for 2 hours a day.

Rikki-Tikki-Tavi | 14/11/2019

kW*

Mike UpNorth_ | 14/11/2019

well, maybe there's an electricity fairy stealing some of mine. no idea.

andy.connor.e | 14/11/2019

@Mike

Electric heating?

Rikki-Tikki-Tavi | 14/11/2019

I have low e windows, updated hvac, also thermostats set on energy efficient levels, whole house LED lighting. Probably that's why. Who knows )

hokiegir1 | 14/11/2019

We use about 64 kwh per month, including car, electric heater, electric dryer, electric water heater, and electric stove (granted -- we only cook a couple times a week) -- also in GA.

hokiegir1 | 14/11/2019

*per day. 2000/month, on average.

Rikki-Tikki-Tavi | 14/11/2019

House size?

hokiegir1 | 14/11/2019

@WhiteWi - there you go wanting relevant info that I forgot. ;) About 1100 sqft townhouse, built in 1968 -- but we've replaced windows and doors in the last 2 years with efficient ones.

andy.connor.e | 14/11/2019

I've got gas heating and hot water. 335kWh last month, 30 therms of gas.

Mike UpNorth_ | 14/11/2019

I have old windows and the house is a bit drafty. So there's that.
I do have LEDs in every light.
@andy Not baseboard heat, regular furnace.....
~2500 sq feet.

Damn this thread took a turn....

Mike UpNorth_ | 14/11/2019

wait a second....andy, you only use 11k/day and I'm at 70?! Maybe I should look into the culprits....

hokiegir1 | 14/11/2019

@Mike - I think having someone home all day is a pretty big factor. Hubby is home most days, and I work from home one day a week. The car averages about 350-400kwh per month, too....and in 19 months, we've got 41,500 miles on it, primarily local.

Mike UpNorth_ | 14/11/2019

Agreed Hokie.