Cost to charge at home?

[BentheRed]

Noobie question - I have tiered pricing from Austin Energy (i.e. not peak/off peak pricing) and the highest tier I’m ever in is $0.078 per k/w. If the battery capacity of my SR+ is 62 kwh would the cost to full charge from empty be 62 x $0.078? $4.84? Is it that simple? Obviously I would rarely charge from empty to full, and there is some dispute what the full capacity of the SR+ is, but that would mean most charges where I charge ~100 miles would be $2?
I ask for two reasons -
1) to reassure family/friends whom I’ll charge with over holiday visits that “don’t worry, it’s only a couple of bucks electricity I’m using”, and
2) Austin energy offer a $30 flat monthly fee for home EV charging, but since I don’t drive that many miles a month I’d be better off just paying as I charge.
Thanks!

 

[ewoodrick]

Look at the energy graph and other sources in the car to see what your consumption is. In the summer, you can expect around 250 W/mi if driving well, and up to about 350 during colder temperatures.

250 W/mi is 0.250 kW/mi.

$0.078 * 0.25 = $0.0195, 2 cents per mile

Yep, $2 per 100 miles, $6 for a full charge. Buy them a Latte at Starbucks and call it even!

 

[mchas]

If you’re sure of your rate then yes it is basically that simple. Keep in mind though if you are using a standard 110 outlet that you will use some energy for the overhead of keeping the car awake while it’s charging, so it will use a bit more for that. I have heard from friends that Austin has very cheap electricity - I am jealous. A Tesla makes even more sense there because of that. Enjoy.

 

[jmaddr]

There is some inefficiency in charging so it’s not a simple multiplication. Maybe add 6-12 percent conversion inefficiency, but yes, you have great rates (make sure they include fuel charges as well...my charges are around those number but they also charge an additional 4 cents fuel charge per kWh).

 

[TomB985]

Yup, that's correct.

I have in off-peak circuit for my charging set up, and my rate is similar to yours. During the summer it would cost me an average of $30 to travel 1500 miles. These things are extremely cheap compared to any gas powered car out there.

 

[hugh_jassol]

Noobie question - I have tiered pricing from Austin Energy (i.e. not peak/off peak pricing) and the highest tier I’m ever in is $0.078 per k/w. If the battery capacity of my SR+ is 62 kwh would the cost to full charge from empty be 62 x $0.078? $4.84? Is it that simple?

BTW, the SR+ has a 55 kWh batt. The mid-range has a 62 kWh (no longer made). Here’s the EPA test data: https://iaspub.epa.gov/otaqpub/display_file.jsp?docid=46584&flag=1

SR ≈ 50 kWh (software locked SR+)
SR+ ≈ 55 kWh (EPA test measured 54.5 kWh)
MR ≈ 62 kWh (EPA test measured 63.8 kWh)
LR ≈ 78 kWh (EPA test measured 78.2 kWh)

 

[boriszima]

As an owner living in Los Angeles whose rate is doubled that I am indeed envious of that rate. And for those that drive a lot, $30 flat charge is great which I assume requires a separate meter and level 2 charger?

 

[TomB985]

As an owner living in Los Angeles whose rate is doubled that I am indeed envious of that rate. And for those that drive a lot, $30 flat charge is great which I assume requires a separate meter and level 2 charger?

Just to clarify, you pay double the rate to charge your car than you do otherwise? What are the rates like out there?

 

[iamnid]

Just to clarify, you pay double the rate to charge your car than you do otherwise? What are the rates like out there?

I think he means he pays double the $.08 kwh price used in the calculation. I am also in Southern California and my rates go from between $.11 and $.19 per kwh.

 

[garth_angst]

Just to clarify, you pay double the rate to charge your car than you do otherwise? What are the rates like out there?

I live on Long Island. 19.5 cents per KwH, all hours. Not sure how much I am actually saving since my last car got 41 MPG, but there's nothing I can do about it, so I don't care much.

 

[boriszima]

Just to clarify, you pay double the rate to charge your car than you do otherwise? What are the rates like out there?

I think he means he pays double the $.08 kwh price used in the calculation. I am also in Southern California and my rates go from between $.11 and $.19 per kwh.

Correct, I pay double for my electricity. Currently i pay $0.174 per kWh for Tier 1 which is first 1,000kWH and there are 2 more tiers which are more expensive. I am in process of switching to what is called Time of Use, where rates are based on the time of the day you use up electricity. There are 3 Tiers, Low, Base, and High

If you are bored and have LADWP you can search and get this document. Here you can add up to see what it costs
http://rates.ladwp.com/UserFiles/Rate Summaries/Electric Rates Summary (effective July 1, 2017).pdf

I got Solar and its helping out a lot to keep me in Tier 1. LADWP also offers a free separate meter to hook up your Level 2 Charger to save 1.5cents per kWh. Of course puling permits and work needed to make it happen usually is not worth it unless once drives enough miles to offset the cost over x amount of years.

 

[TomB985]

Gotcha, that makes sense. I do install a separate meter and circuit for my EV charger to take it vantage of the time of use charging. It was worthwhile because they had a $500 credit towards installation costs and the rate goes down to 7.3 cents for off-peak instead of 11.7 cents normally.

The downside is that it gets prohibitively expensive during the peak times. $.45 per kilowatt hour from 4 to 8 PM on weekdays.

 

[boriszima]

Gotcha, that makes sense. I do install a separate meter and circuit for my EV charger to take it vantage of the time of use charging. It was worthwhile because they had a $500 credit towards installation costs and the rate goes down to 7.3 cents for off-peak instead of 11.7 cents normally.

The downside is that it gets prohibitively expensive during the peak times. $.45 per kilowatt hour from 4 to 8 PM on weekdays.

I misspoke above, LADWP drops rate by 2.5 cents of whatever the rate is during Tier or TOU. For you it seems 11.7-7.3 = 4.4 cents savings which is a whole lot more compared to what i get. As we know this adds up very quick.

LADWP does offer $500 towards Level 2 Charger installed, so its pretty awesome for those that are getting Telsa one, getting your money back for the device minus taxes
They also offer TOU rebate of $250 which covers... their meter
https://ladwp.com/cs/groups/ladwp/documents/pdf/mdaw/njyw/~edisp/opladwpccb660683.pdf
https://ladwp.com/ladwp/faces/ladwp...l-state=lsoprmhaz_25&_afrLoop=279963633676205

I did a good job at hijacking this thread, but wanted to put that information out for Los Angeles owners, as there are many of us.

 

[StealthP3D]

Noobie question - I have tiered pricing from Austin Energy (i.e. not peak/off peak pricing) and the highest tier I’m ever in is $0.078 per k/w. If the battery capacity of my SR+ is 62 kwh would the cost to full charge from empty be 62 x $0.078? $4.84? Is it that simple? Obviously I would rarely charge from empty to full, and there is some dispute what the full capacity of the SR+ is, but that would mean most charges where I charge ~100 miles would be $2?
I ask for two reasons -
1) to reassure family/friends whom I’ll charge with over holiday visits that “don’t worry, it’s only a couple of bucks electricity I’m using”, and
2) Austin energy offer a $30 flat monthly fee for home EV charging, but since I don’t drive that many miles a month I’d be better off just paying as I charge.
Thanks!

Yes, it's pretty cheap. To calculate how much electricity you are actually drawing from an outlet it would be:

kWh into the battery plus about 10% for charging overhead. When using a 120v outlet you might want to figure 12% overhead. My wife's LR RWD Model 3 is sitting at 235 Wh/mile for it's 20,000 plus miles. Adding 10% for charging overhead brings it to under 260 Wh/mile or about 5200 kWh which is only around $520 for 20K miles of fuel. At 20 mpg that would be 1,000 gallons of gasoline. A gas car would also need around three oil/filter changes in that time. Our Model 3's over 33,000 miles have needed $0 of service!

We pay about $0.10/kWh for our two Model 3's and it costs only about 1/4 what we were paying for gasoline in our Volvo S80 and Mazda CX-5. I have free Supercharging for life in my P3D but have only taken advantage of it a handful of times in the last year-plus that I've owned it because the added cost to our electric bill is so insignificant.

 

[cwerdna]

OP and ewoodrick, can you please get your units run? "k/w" makes no sense. W/mi and kW/mi also are wrong. It should be watt-hours (Wh) per mile or kWh/mile.

The folks who used kWh are correct.

kW and kWh are very different metrics. It's the same as confusing gallons with horsepower. Think of kW = horsepower, kWh = gallons.

If one charges at 1 kW (or 1000 watts) for 6 hours, 6 kWh came out of the wall. If it's at 6 kW for 1 hour, it's also 6 kWh. If it's 1 watt for 6000 hours, it's also 6 kWh.

Watts or kilowatts are a measure of power. Watt-hours are a measure of energy.

One pays for electricity at home in cents per kWh. There are a few utilities w/residential plans where they not only bill per kWh but also have demand charges, but that's rare and complicates calculations. (Demand charges aren't unusual on many commercial plans.)

1 hp = ~0.746 kW. 1 gallon of gasoline has 33.7 kWh of energy content.

 

[toolman335]

At my rate of .09 I figured out that it's around $30/month. The easy thing to do is it averages out to a dollar per day.

 

[AlanSubie4Life]

Noobie question - I have tiered pricing from Austin Energy (i.e. not peak/off peak pricing) and the highest tier I’m ever in is $0.078 per k/w. If the battery capacity of my SR+ is 62 kwh would the cost to full charge from empty be 62 x $0.078? $4.84? Is it that simple? Obviously I would rarely charge from empty to full, and there is some dispute what the full capacity of the SR+ is, but that would mean most charges where I charge ~100 miles would be $2?
I ask for two reasons -
1) to reassure family/friends whom I’ll charge with over holiday visits that “don’t worry, it’s only a couple of bucks electricity I’m using”, and
2) Austin energy offer a $30 flat monthly fee for home EV charging, but since I don’t drive that many miles a month I’d be better off just paying as I charge.
Thanks!

No it is not that simple. Though your final number was basically exactly correct.

The EPA document for 2019 (not the same as your vehicle exactly but very close) shows that it takes 62kWh to replenish the 54.5kWh of battery energy (so you are correct about the 62kWh, though it is not the battery size). This is assuming you are using 240V charging; it will be worse with 120V (relevant for your scenario and motivation for the question).

So for a 2019 SR, this is not entirely correct, but assume:

62kWh/247rmi = 250Wh/rmi. (EPA)

Matches the EPA sticker.

For 2020, it is 240Wh/rmi. Those won’t exactly be equivalent to the miles you see displayed in the car due to the buffer but close enough.

https://austinenergy.com/ae/residential/rates/residential-electric-rates-and-line-items

Looks like your stated rate is correct. So cheap!

So it is likely a minimum of:

240Wh/rmi*$0.08/kWh = 2 cents per mile added.

If you were to fully charge your car it would cost 62kWh*$0.08/kWh = $5

These numbers will be about 15% higher at 120V. So call it $6 to fully charge.

 

[iamroy]

The plan I have is free nights from 8pm to 6am. Rate during the day isn't great, but we are at work/school so it's not bad. We run the washer/dryer, dishwasher, and charge the car at night.

 

[ewoodrick]

As an owner living in Los Angeles whose rate is doubled that I am indeed envious of that rate. And for those that drive a lot, $30 flat charge is great which I assume requires a separate meter and level 2 charger?

And you also pay about twice as much for gas, so the comparisons stand.

Everything costs twice as much in CA, some people get paid about twice as much as other markets.

 

[hezza8]

wow some people's highest rate is cheaper than my cheapest off peak rate... And free night charging!!! Wow.. That's just unheard off.

I have an EVPS that tells me how much energy I use each month, but probably an overkill for most folks.