Powerwall behavior when charging car

[shingles]

Sorry if my search-fu is lacking.. I tried for a bit but can't get figure out the answers.

New Powerwall owner, have a 15.2kW non Tesla solar. I am curious about the behavior of the PW when charging my Tesla:

Scenario 1) Say it's night time and the PW is above Backup Reserve limit, I plug in the Model X to be charged... will it draw from the PW down to Backup Reserve limit?
Scenario 2) It's night time, you have Tesla Energy and Unlimited Overnight EV charging, the PW is above Backup Reserve, plug in the Model X to be charged, will it draw from the PW down to Power Reserve limit?

In the app, there's a Vehicle Charging setting, but it seems to be for when Off-Grid. I am assuming scenario 1 is yes it draws from PW, but wondering what scenario 2 does?

Thanks.

 

[jjrandorin]

I cant answer the "Tesla energy" question, however if the powerwall can see the load (meaning the outlet / wall connector that is being used to charge the car is a load that the powerwall gateway can see), then yes in both cases the car will draw the powerwall down to its reserve, whatever that is set to.

The vehicle charging setting in the app is only for off grid operation.

 

[bmah]

Sorry if my search-fu is lacking.. I tried for a bit but can't get figure out the answers.

New Powerwall owner, have a 15.2kW non Tesla solar. I am curious about the behavior of the PW when charging my Tesla:

Scenario 1) Say it's night time and the PW is above Backup Reserve limit, I plug in the Model X to be charged... will it draw from the PW down to Backup Reserve limit?
Scenario 2) It's night time, you have Tesla Energy and Unlimited Overnight EV charging, the PW is above Backup Reserve, plug in the Model X to be charged, will it draw from the PW down to Power Reserve limit?

In the app, there's a Vehicle Charging setting, but it seems to be for when Off-Grid. I am assuming scenario 1 is yes it draws from PW, but wondering what scenario 2 does?

Thanks.

Are you talking on-grid of off-grid operation? How are your Powerwalls configured? In particular are they set for Self-Powered or Time-Based Control? What's your rate plan schedule look like? When you plug in "at night time", is that peak, partial-peak, off-peak?

The answers to these questions will have an effect on the answers to your original questions. My first reaction to @jjrandorin's answers were "no those are wrong", and then I realized that we probably had different assumptions to fill in bits of information that your original post didn't have.

"Vehicle Charging when Off-Grid" is used to have your car soak up solar energy as the Powerwall batteries get full and can't absorb any more energy.

Hope this helps. This is a bit confusing because everyone's energy situation is different.

Bruce.

PS. For my setup, on-grid operation, with a time-of-use rate plan (one peak during the late afternoon/early evening and hour of partial peak on either side of that, which is pretty common in California), and time-based control... If I start my car charging at night time (no solar production) during peak, it's going to draw the Powerwalls down to the reserve limit. Start charging at night during partial peak, it might draw the Powerwalls down. If I start charging during off-peak, it'll always charge from the grid and never from the Powerwalls. So for this reason I have my car configured to start charging at the start of off-peak pricing. I'm not familiar with "Unlimited Overnight EV charging", but I presume that pricing is factored into the rate plan that's a part of your Powerwall settings.

 

[jjrandorin]

Are you talking on-grid of off-grid operation? How are your Powerwalls configured? In particular are they set for Self-Powered or Time-Based Control? What's your rate plan schedule look like? When you plug in "at night time", is that peak, partial-peak, off-peak?

The answers to these questions will have an effect on the answers to your original questions. My first reaction to @jjrandorin's answers were "no those are wrong", and then I realized that we probably had different assumptions to fill in bits of information that your original post didn't have.

"Vehicle Charging when Off-Grid" is used to have your car soak up solar energy as the Powerwall batteries get full and can't absorb any more energy.

Hope this helps. This is a bit confusing because everyone's energy situation is different.

Bruce.

PS. For my setup, on-grid operation, with a time-of-use rate plan (one peak during the late afternoon/early evening and hour of partial peak on either side of that, which is pretty common in California), and time-based control... If I start my car charging at night time (no solar production) during peak, it's going to draw the Powerwalls down to the reserve limit. Start charging at night during partial peak, it might draw the Powerwalls down. If I start charging during off-peak, it'll always charge from the grid and never from the Powerwalls. So for this reason I have my car configured to start charging at the start of off-peak pricing. I'm not familiar with "Unlimited Overnight EV charging", but I presume that pricing is factored into the rate plan that's a part of your Powerwall settings.

Ahh, yes, I always tend to forget that my experience is a bit different because I use self powered mode and have never used TOU mode (because I am still on NEM 1 and a tiered electric plan).

Thanks for the correction there.

I have no idea if they have TOU setup in Texas so I should probably have refrained from answering.

 

[lodar]

Congratulations on the new Powerwall!

In self-powered mode, the EV will drain the Powerwalls down to its reserve. Then it will fall back to the grid if available. Solar would be diverted to the EV, but it is difficult to keep up with a hungry EV in a feeding frenzy.

In Time-Based Control, during peak hours, the EV will drain the battery down to its reserve. The solar power would be diverted to the grid to maximize profits.

In Time-Based Control, during off-peak hours, the EV will charge from the grid. Solar will be busy charging the batteries.

EV charging before and after Powerwalls doesn’t change much, you want to pull from the grid off-peak. Bonus if you have free charging overnight.

I made the mistake doing a Tesla firmware update during peak hours. It must have triggered a fail-safe charging mode and drained my 3 Powerwalls until the Tesla regained its sanity after the update.

If you have a newer Tesla, they have a new “Charge on Excess Solar” mode that is supposed to divert excess solar to your Tesla when the batteries are full and you haven’t hit peak hours yet. My 1st gen Teslas don’t support it so I cannot speak from experience there.

The vehicle charging setting is for when the power is out. You definitely want to be careful with an EV feeding frenzy at that time.

 

[miimura]

I have two Powerwalls and use Time Based Control. My Off-Peak period is Midnight to 3pm. Here are two different examples of how the systems works, which happen to be on two adjacent days that required a lot of charging.

First day, two cars recharging overnight, a bunch of driving, and one car needing more energy for the evening. First chart is Home usage, second is Powerwalls. You will notice that the overnight charging exclusively uses Grid energy. At 3pm, the Powerwalls started powering the house and the solar was exported. When the car started charging at 4pm, the remaining solar in the late afternoon was used in addition to a lot of Powerwall energy to charge the car. I reduced the Reserve extra low to allow the car to use that energy. This was only done because there was a critical need. Using the battery energy was cheaper than Supercharging.

The following day, the car that needed charging in the afternoon was recharged overnight. Even though the Powerwalls were lower than I normally let them go, they were fully charged before the Off-Peak period ended. This was only possible because of my newly expanded solar system. My small 10 year old solar system never would have been able to replace all that energy in one day during this time of year.

 

[shingles]

Thanks all for the answers. In Texas, we rarely are used to single flat rate throughout the day, so I didn't consider effects of peak/off-peak and time control impact. I was really trying to understand the system behavior, thinking it'd be better to avoid charge cycles of the powerwall. I was considering on-grid operation as I understand the behavior during off-grid.

Tesla is a "rertail electric provider" here in Texas, so they can sell electricity in deregulated parts of the state (parts that don't have an electric co-op). Teslas plan DOES introduce peak/off-peak periods. Off Peak is 13.2/kWh (7P to 4P), Peak is 17.9/kWh (4P - 7P). They also offer a $25/mo "unlimited EV charging at home" add on, from 10P - 6A.

So based on what I am learning here, if I set it to time-control, have peak/off-peak setup, it will draw from grid during off-peak time of charging and will draw from batteries when trying to charge during peak period.

Thanks!