Math Questions Regarding Chargers and Solar

[Sully151]

Hi!

I suck at math and most things associated with math. That's why I perform and teach Improvisational Theater, Sketch Comedy, and puppetry for a living. This is also great because I don't have to add a lot of large numbers from paychecks.

My wife and I are going to make a major change and go all EV and add solar to our house. R1T for me and the MINI Cooper SE for her ( I get to play with the MINI too).

We have been shopping Solar with the hopes of charging our cars and running our house. The solar companies I have talked to say we will be more than doubling our usage when we get the EV's. One said we would be using up to 10,000 extra Kwh a year to charge the two cars. Is this true?

Is there a simple math equation that I can use to guesstimate how much we will use based on battery size, annual miles driven, etc.?

Also, they mentioned that I may need to go to a 200 amp electrical box.

Finally, what would I need to do to charge two cars at the same time? Is this possible?

I wish there was an easy tutorial about all of this. I think there will need to be something in the future to make this less confusing.

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[jjwolf120]

Is there a simple math equation that I can use to guesstimate how much we will use based on battery size, annual miles driven, etc.?

Annual miles driven times # of watts per mile. For example, the R1T uses 480 watts per mile (if I remember correctly), so if you travel 10,000 miles per year and only charged at home, you would use 4,800,000 watts or 4,800 Kilowatts. The MG will use less.

 

[PastyPilgrim]

R1T gets 300 mi on a 135 kWh battery = 300/135 = 2.22 mi/kWh. Mini is 110mi / 33kWh = 3.33 mi/kWh.

With those numbers, 10000 kWh is 22k miles for your R1T or 33k miles for your mini. That seems excessive even if split between the two cars.

If you put 10k miles on each per year and only charge at home, then that'd be: (10000 mi) / (2.22 mi/kWh) = 4505 kWh for the R1T and 3003 kWh for the mini. That puts you at needing ~7500 kWh of extra juice which isn't that far from the estimate and could be reasonable if they only deal in units of 5000 kWh/yr or are providing for room to grow.

 

[DucRider]

Using the EPA numbers (those are "from the wall" and reflect what it takes to charge).
R1T is 48 kWh/100 miles. If driven 10K per year (below average) that equates to 4,800 kWh. Add 10-15% if you go with the 20s.
Mini SE is 31 kWh/100 miles or 3,100 kWh.


To break it down:
For every 1,000 miles you will drive the R1T, multiply x 480 (or ~525 if on the 20s)
For every 1,000 miles you will drive the Mini, multiply x 310

If you drove closer to an average of 12K/yr on both vehicles and had the Rivian set up on the 20s, it would be 10,020 kWh/yr
525 x 12 = 6,300 kWh
310 x 12 = 3,720 kWh

 

[Sully151]

Thanks!

Yeah, we both drive quite a bit, probably 30,000 miles a year between the two of us. My jeep takes a brunt of the miles, and at 12 mpg and a 400 mile weekly commute it adds up. I put $160 in my tank last week. I suppose the $1200-1400 that I may pay extra in electricity over the year after solar does its job won't be too bad. Sadly, we just don't have the roofs footage to add more than about 25 panels, and while we are pretty efficient for most of the year, summer is rough.

Now I need to figure out how to charge two cars at the same time.

 

[MoreTrout]

Keep in mind that solar doesn't have to go on the roof. If you have sufficient yard space you can do a ground array too.

Also, you are probably overestimating the need to charge two vehicles at the same time. Based on your current weekly miles, that comes out to about 57 miles a day. Just having a 240v outlet for the 16mi/hr with the charging cord would cover that in under 4 hours. With Rivian's home charger giving 25/hr it would be just over 2 hours.

 

[SANZC02]

Thanks!

Yeah, we both drive quite a bit, probably 30,000 miles a year between the two of us. My jeep takes a brunt of the miles, and at 12 mpg and a 400 mile weekly commute it adds up. I put $160 in my tank last week. I suppose the $1200-1400 that I may pay extra in electricity over the year after solar does its job won't be too bad. Sadly, we just don't have the roofs footage to add more than about 25 panels, and while we are pretty efficient for most of the year, summer is rough.

Now I need to figure out how to charge two cars at the same time.

25 is a lot of panels. I just installed a 17 panel array (275 watts per panel) in SoCal, I have been averaging over 32 KW a day with that, 25 of these panels would probably be generating between 45ish KW a day this time of year.

 

[Caymanwent]

Hi!

I suck at math and most things associated with math. That's why I perform and teach Improvisational Theater, Sketch Comedy, and puppetry for a living. This is also great because I don't have to add a lot of large numbers from paychecks.

My wife and I are going to make a major change and go all EV and add solar to our house. R1T for me and the MINI Cooper SE for her ( I get to play with the MINI too).

We have been shopping Solar with the hopes of charging our cars and running our house. The solar companies I have talked to say we will be more than doubling our usage when we get the EV's. One said we would be using up to 10,000 extra Kwh a year to charge the two cars. Is this true?

Is there a simple math equation that I can use to guesstimate how much we will use based on battery size, annual miles driven, etc.?

Also, they mentioned that I may need to go to a 200 amp electrical box.

Finally, what would I need to do to charge two cars at the same time? Is this possible?

I wish there was an easy tutorial about all of this. I think there will need to be something in the future to make this less confusing.

Are you tying to offset your grid usage or are you trying to zero it out? Adding any solar will decrease your costs long term but you need very large array(with battery backup) to be energy independent.

 

[Dark-Fx]

The 10k estimate is probably pretty close in that situation if you drive around the average distance an American does in a year. My family has 72k total miles on our two efficent evs in 3ish years and we've put 24MWh through our chargers. Some of our charging hasn't been at home.

 

[ajdelange]

Since the Rivians are going to take about half a kWh to go a mile the math is pretty simple. Ten thousand miles is going to be about 5,000 kWh., You will learn what your actual average consumption is pretty quickly and can adjust up or down. But if you do nominal driving the EPA rating (actually 0.48 kWh per mi) will be pretty accurate, IOW EPA did a pretty good job in developing the rating system.

It's pretty simple on the solar too. Each panel will give you about 1/4 of a kWh for each hour of full equivalent sunshine. You can find maps (search NREL solar) to find how many hours per day you can expect in your location averaged over the year and by month. You will probably have 6 but being conservative you could use 5.

Now when you ask about actual charging it starts to get complicated because there are so many ways to configure charging systems. You will want to upgrade to 200A service. There are "chargers" that will allow you to just come home and plug in and will manage sharing between cars automatically.

 

[Ray R]

Clipper Creek makes dual cord charging stations. And they have a pretty good reputation for reliability.
https://store.clippercreek.com/dual-ev-charging-station-nema-14-50-plug

 

[Mjhirsch78]

Clipper Creek makes dual cord charging stations. And they have a pretty good reputation for reliability.
https://store.clippercreek.com/dual-ev-charging-station-nema-14-50-plug

I have one. It does the job for one EV. I’ll see what it does when we add the R1T.

 

[ajdelange]

Looks good but Oy! on the price tag. A pair of Tesla HPWC would save you $350 on the hardware but then you would have to have two separate installations and that would probably wipe that savings out. OTOH the two will still share even though they are in different parts of the property (one in a garage, one in an outbuilding) as long as they are on the same WiFi network.

 

[Smithery]

One said we would be using up to 10,000 extra Kwh a year to charge the two cars. Is this true?

Depends on how much you drive.
That's 21,000mi in the R1T by itself, or 32,000mi in the Mini by itself.
Or something like 10,500mi in the R1T and 16,000 in the Mini.

Is there a simple math equation that I can use to guesstimate how much we will use based on battery size, annual miles driven, etc.?

Yes, and it's actually straight forward.

R1T rated to use 480 Wh/mi.
Multiply 480 x (number of expected annual miles)

Mini rated to use 312 Wh/mi.
Multiply 312 x (number of expected annual miles)

Your answer may be way less than 10,000,000 additional Wh, or it could be more.

Also, they mentioned that I may need to go to a 200 amp electrical box.

Usually somebody being told they need to upgrade to a 200A panel currently has a 100A panel (or more rarely 60A)

Let's pretend you install a 48A charger for the R1T (which will work fine to charge the Mini as well) and only charge one car at a time.

That means your 100A service becomes "basically 52A service" while the truck is charging.
Quite inadequate for modern electrical demands.

A space heater and a microwave at the same time uses up 30A of that. Hope you don't also have an electric range (30A+), or central A/C (30A+), or an electric clothes dryer (30A).

Finally, what would I need to do to charge two cars at the same time? Is this possible?

Definitely possible.

The most basic charging setup would be two chargers, each on a dedicated circuit. R1T at 48A, Mini at 32A.

Both at the same time draws 80A, which basically eats up most of your upgrade from 100A to 200A service.

In other words - Keep using your home as you do today, plus you're also charging a couple of EVs.

There are also various power-sharing charger setups out there. I have (2) Wallbox Pulsar Pluses networked together and sharing a 60A circuit. They handle our Tesla Model X and any visitors EV (which is any of our parents on any given weekend) and will dynamically split the available 48A between the cars.

I wish there was an easy tutorial about all of this. I think there will need to be something in the future to make this less confusing.

It's still a brave new world. More and more experience is out there, but we're not to the tipping point of "common place" quite yet.

 

[lg3103]

Hi!

I suck at math and most things associated with math. That's why I perform and teach Improvisational Theater, Sketch Comedy, and puppetry for a living. This is also great because I don't have to add a lot of large numbers from paychecks.

My wife and I are going to make a major change and go all EV and add solar to our house. R1T for me and the MINI Cooper SE for her ( I get to play with the MINI too).

We have been shopping Solar with the hopes of charging our cars and running our house. The solar companies I have talked to say we will be more than doubling our usage when we get the EV's. One said we would be using up to 10,000 extra Kwh a year to charge the two cars. Is this true?

Is there a simple math equation that I can use to guesstimate how much we will use based on battery size, annual miles driven, etc.?

Also, they mentioned that I may need to go to a 200 amp electrical box.

Finally, what would I need to do to charge two cars at the same time? Is this possible?

I wish there was an easy tutorial about all of this. I think there will need to be something in the future to make this less confusing.

funny...my wife is getting her Mini SE in two weeks (changing over from Countryman PHEV) and I'm waiting for my R1S LE...Go all EV households!!!

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