Calculating KWh usage from 120v outlet

[eustachio]

We rent our apartment, which comes with a private garage that has a 120v outlet.

I'm trying to calculage kwh usage with regard to my supplier's (PGE) costs.

We're on a plan that gives us 8.8 kwh per day at "Tier 1", 0.22c per kwh.

If we exceed this, it goes up to 0.28c per kwh, unless we go 4 times above our baseline, it jumps to 0.49c (but we'll never hit this based on current usage patterns)

What would the kwh usage be from a 120v outlet?

 

[brkaus]

We rent our apartment, which comes with a private garage that has a 120v outlet.

I'm trying to calculage kwh usage with regard to my supplier's (PGE) costs.

We're on a plan that gives us 8.8 kwh per day at "Tier 1", 0.22c per kwh.

If we exceed this, it goes up to 0.28c per kwh, unless we go 4 times above our baseline, it jumps to 0.49c (but we'll never hit this based on current usage patterns)

What would the kwh usage be from a 120v outlet?

assuming a standard 15a outlet charging at 12a.

1.44kW per hour.

If you use something like teslafi you can monitor daily. Use my username in the “how did you hear” your free trial doubles.

 

[Akikiki]

Let me make sure I understand what the OP said, please. At highest rate he's going to pay 1/2 of a cent per kWh? And is wondering what his usage would be? Where I live we pay about 30 cents, make sure you read that correctly 30 cents not .30 cents. On average we are paying 61 times what he is paying at his highest point.

 

[brkaus]

Let me make sure I understand what the OP said, please. At highest rate he's going to pay 1/2 of a cent per kWh? And is wondering what his usage would be? Where I live we pay about 30 cents, make sure you read that correctly 30 cents not .30 cents. On average we are paying 61 times what he is paying at his highest point.

I’m pretty sure the decimal is in the wrong place. It is $ and not c.

 

[Rottenapplr]

You can use the stats app to calculate charging and kwh usage. This would be the most economical solution. Just use an excel spreadsheet to monitor kwh used per charging session. That’s how I monitor my charging cost on a daily basis.

 

[AlanSubie4Life]

Where I live we pay about 30 cents, make sure you read that correctly 30 cents not .30 cents

He's from California, so this is clearly a typo on the OPs part.

What would the kwh usage be from a 120v outlet?

Probably what you should really ask is how much it will cost you per rated mile (this is different than driven miles, of course)....however...

At 12A, it will be 12A*120V = 1440W (power), so in 1 hour that would be 1.44kWh (energy).

Plot of charging efficiency vs. input power

So, you need to translate this to a per rated mile (rmi) number. I'll assume you have an AWD/Performance. There are a lot of ways to do this, and the way below isn't really the simplest, but I wanted to answer it in the context of your question.

You'll be getting something like 70% charging efficiency based on above plot. So that means:

kW (battery) / kW (wall) = 0.70 (Same for the kWh ratio FWIW).

kW (battery) = 0.7*1440W = 1.008kW This is what you'll get (power, not energy) into the battery for a 12A/120V outlet.


For an AWD, it's 245Wh/rmi => 1.008kW / 0.245kWh/rmi = 4.11 rmi/hr

Your electric expense for this, per hour, is 1440W *$0.22/kWh = 31.7 cents/hr

So this is 31.7cents/hr / 4.11rmi/hr = 7.7cents/rmi

Also of interest, 1.44kWh/4.11rmi = 35kWh/100mi (but this isn't quite fair to compare to the 29kWh/100mi EPA number, for subtle reasons you have to multiply by ~76/78). But in any case the "penalty" for 120V charging is pretty clear.

Notably, you'll likely end up using considerably more rmi (rated miles) than miles you drive. But this is a starting point. The point is your costs per driven mile will almost certainly be higher than this.

You can use the stats app to calculate charging and kwh usage.

Note that this Stats report does NOT report the kWh from the wall. You have an LR RWD...I could tell without looking at your signature...because 19.37kWh/83rmi = 233Wh/rmi which is the approximate charging constant for the LR RWD - but this is AFTER the AC-DC converter and it ONLY counts energy added to the battery...

If you want to monitor your actual charging costs you can hack it by inflating your per kWh cost in the Stats app, if you always charge from the same place, by whatever the efficiency ratio is.

 

[justsomeguy]

assuming a standard 15a outlet charging at 12a.

1.44kW per hour.

If you use something like teslafi you can monitor daily. Use my username in the “how did you hear” your free trial doubles.

It's 1.44kW or 1.44kWh per hour. Not 1.44kW per hour.

 

[eustachio]

D'oh, apologies, it should read $0.22 above, or 22c. I can't seem to edit my post.

 

[eustachio]

View attachment 450592 You can use the stats app to calculate charging and kwh usage.

Which stats app?


@AlanSubie4Life Thank you for the detailed explanation. My head hurts a little now. Which is no reflection on your helpfulness

 

[AlanSubie4Life]

Which stats app?

It's just called Stats: For Tesla, for iOS devices only.

 

[eustachio]

It's just called Stats: For Tesla, for iOS devices only.

Ah, thanks. And sigh, android is the geek's choice

 

[Rottenapplr]

I’m sure there’s an android alternative right

 

[brkaus]

Thanks @justsomeguy - was rushed, didn't really finish my thought and just simply got it wrong.

@eustachio There are a few apps out there. Also a few web pages. Another recent one is Teslastics. I've just used teslafi forever I haven't looked around recently. I also only have it on one car. Decided it was fun, but not fun enough for both cars. Statistic overload!

You can probably look in the google store or search here. Sorry I can't help I do iOS.

 

[srs5694]

There are probably Android alternatives to Stats, but one that works on anything is TeslaFi. This provides a Web-based interface, so it's accessible from a desktop/laptop computer, tablet, or cell phone. I don't know about more app-centric alternatives, but TeslaFi lets you set a home address, and it can therefore distinguish between charges at home vs. charges away from home. It can then report them separately. This can be important if you want to track your home electricity use specifically, separate from any charges at public Level 2 or Superchargers.

Another way to get at this issue is to use an electric meter on whatever outlet you like. If you're charging on a regular 120v outlet, you can use something like a Kill-A-Watt meter. I've got one of these, although I've never used it to measure my Tesla's electricity use. This might not be the best tool for measuring monthly use because it might be accidentally reset (I think it'll be reset during a power outage, for instance), but it should at least measure everything that comes from the wall, vs. what ends up in the battery or is used by the car, which as others have said will be less than what comes out of the wall. If you just want to measure for a month or two to get an idea of what your car is using, this might be adequate.

 

[brkaus]

Here is an example of a report from Teslafi.

 

[darth_vad3r]

We rent our apartment, which comes with a private garage that has a 120v outlet.

I'm trying to calculage kwh usage with regard to my supplier's (PGE) costs.

We're on a plan that gives us 8.8 kwh per day at "Tier 1", 0.22c per kwh.

If we exceed this, it goes up to 0.28c per kwh, unless we go 4 times above our baseline, it jumps to 0.49c (but we'll never hit this based on current usage patterns)

What would the kwh usage be from a 120v outlet?

How much do you drive? That’s kind of a really important factor here

If you don’t drive you’ll use 0 kWh to charge

How much energy do you use today, and does your 8.8 kWh per day cover the combined apartment and garage outlet? Are they metered together? Trying to picture how this works in an apartment scenario.

 

[eustachio]

My question boils down to, how many kwh are used per hour from a 120v outlet. According to @justsomeguy and @brkaus answer above, it's 1.44 kw.

Currently we use about 4-5 kw per day. That means I charge for about 2 hours at home before hitting the 8.8 limit.

Our 8.8 kw does cover the apartment and garage.

I'm trying to ultimately figure out how much I can charge at home without going into the higher tier. I can charge at work for free, but typically only get about 9 kw of charge, and only drive to the office 3 days a week.

It's 1.44kW or 1.44kWh per hour. Not 1.44kW per hour.

This gets me every time. I don't understand the distinction.
1.44 kWh per hour expands to "1.44 kilowatt hour per hour"?

 

[AlanSubie4Life]

Ah, thanks. And sigh, android is the geek's choice

I don’t think I would worry about it too much unless you really like to track this stuff. For rough estimation, which will be close, for your P3D Stealth:

1) 29kWh/100mi based on EPA, which assumes about 87% efficient charging. Might be a bit better efficiency assumed; there is potentially some rounding error in the EPA numbers.

2) Add 300kWh/10000mi/0.87 for vampire and feature drain. This is assuming you do 10k miles of driving a year (plug in different value above if you drive a different amount).
Works out to 3.5kWh/100mi. So 32.5kWh/100mi.

3) Due to 120V inefficiency, multiply by efficiency ratio of 0.87/0.7

32.5kWh/100mi*0.87/0.7 = 40.4kWh/100mi

4) Multiply by your electric rate $0.22/kWh

40.4kWh/100mi * $0.22/kWh = 8.9 cents/mi

Note this is different than my prior answer because I included vampire drain, so this is not per rated mile - it is per driven mile.


The above assumes average driving efficiency of 235Wh/mi on the trip meter for AWD. If it is higher, you will need to increase the estimates above by the ratio of your actual efficiency and the baseline 235Wh/mi (but only multiply up the EPA 29kWh/100mi portion, then follow steps 2-4).

You’ll find this process/formula ends up very close to your actual additional electricity costs, once you have that baseline “per mile” cost. And of course you can also use it to calculate additional kWh of use due to EV charging, if you want, for assessing whether it will push you into higher tiers.

 

[AlanSubie4Life]

Currently we use about 4-5 kw per day. That means I charge for about 2 hours at home before hitting the 8.8 limit.

This gets me every time. I don't understand the distinction.
1.44 kWh per hour expands to "1.44 kilowatt hour per hour"?

Sorry, missed your questions prior to last post. It is just units.

kW is just power. kWh is energy.

Energy is power * time.

Power in this case is volts * amps.

So draw 1.44kW of power for 1 hour, and you use 1.44kWh of energy.

To answer your first question, you have 3.8kWh of energy available to use before hitting the limit assuming you charge every single day.

That would be 3.8kWh (energy) / 1.44kW (power) = 2.64 hours of charging each day.

 

[darth_vad3r]

My question boils down to, how many kwh are used per hour from a 120v outlet. According to @justsomeguy and @brkaus answer above, it's 1.44 kw.

Currently we use about 4-5 kw per day. That means I charge for about 2 hours at home before hitting the 8.8 limit.

Our 8.8 kw does cover the apartment and garage.

I'm trying to ultimately figure out how much I can charge at home without going into the higher tier. I can charge at work for free, but typically only get about 9 kw of charge, and only drive to the office 3 days a week.



This gets me every time. I don't understand the distinction.
1.44 kWh per hour expands to "1.44 kilowatt hour per hour"?

kW is power. That’s an instantaneous thing, like horsepower.
kWh is energy. It’s just power x time.

1 kW for 30 minutes is 0.5 kWh
2 kW for 30 minutes is 1.0 kWh
1 kW for 60 minutes is 1.0 kWh

You have 8.8 kWh daily budget. You use 4-5 kWh per day.

8.8 kWh minus 5 kWh max daily use before charging = 3.8 kWh left for charging.

If you charge at rate of 1.44 kW, the math is:
3.8 kWh / 1.44 kW = 2.6 hours, 2h38m.

This is maybe 13 miles of rated range added.