PW's and car charging

[NathanielHrnblwr]

My PW's were installed this last Friday and my Wall Connector (And A/C's) are on the non backed up loads panel. To my surprise, my PW's were discharging when my Tesla began it's nightly charge at 10pm. I now understand this is expected behavior thanks to @jjrandorin, but before install I thought the PW's wouldn't try to charge the large loads on the non backed up panel. I guess the non backed up loads are literally just not backed up!

I'm currently using self powered while I figure things out.

What's your strategy for car charging? I do not wish to drain my PW's to the reserve at 10PM when my car starts to charge, but there doesn't seem to be a way to stop it when self powered. One option suggested is to change the car charging time to later in the night and set a reserve so the house runs on the PW's all night, the car begins to charge, PW's drop to the reserve and the car charges from the grid for the remainder.

Any other ideas? I don't want to babysit this daily and move to backup only mode before the car charges. I haven't spent much time with advanced settings as my winter TOU rates are identical for off and semi peak.

On a similar note, the A/C will drain the PW's pretty fast when used. Do you switch out of self powered during this time or just let them drain to the reserve? The next day could be cloudy and not enough to charge the PW's fully and I incorrectly accepted the large loads would just be solely grid tied.

I guess it's six of one, half a dozen of the other in the end, but I expected the large loads to just pull from the grid since my PW's weren't capable of powering them on their own so I'm trying to wrap my mind around the options.

 

[charlesj]

Interesting. But the non backed up panel really applies when grid is down to the best of my short term here. They are wired next to each other practically speaking and unless the grid is down, PW could be charging those loads to the max continuous PW output, 5 kW per battery. Grid down, non backed up will not be energized. But, I could be wrong on this, count two?

 

[jjrandorin]

Interesting. But the non backed up panel really applies when grid is down to the best of my short term here. They are wired next to each other practically speaking and unless the grid is down, PW could be charging those loads to the max continuous PW output, 5 kW per battery. Grid down, non backed up will not be energized. But, I could be wrong on this, count two?

Powerwall can provide power to both backed up and non backed up loads when grid is up. When grid is down, they wont be powered. I dont have a better suggestion for car charging than OP and I already chatted about, and was mentioned by him above. I am interested to see what others say.

 

[bob_p]

Our system has 4 PowerWalls that are providing power to two breaker panels for all of our house circuits, except for EV charging.

Our two Tesla HPWC's are connected to a separate breaker panel that is connected to grid power - not to the Tesla Gateway & the PowerWalls.

We have our Tesla vehicles set to schedule charging for 10PM each night.

When operating on grid, we haven't seen any power from the PowerWalls applied to the HPWCs, otherwise we'd end up with the PowerWalls always sitting at the reserve % by morning.

If you're seeing the PowerWalls providing power to EV charging that is supposed to be directly connected to the grid - what does the Tesla app show when the EV is charging?

If the app is showing the EV charging as part of the house power, then your EV charging is wired to the Gateway and not the grid.

If the app is showing the EV charging as part of the grid power (a negative number), that could be a problem - should something on the grid side of the Gateway be able to pull power from your PowerWalls (whether or not the grid is up)?

I'll run some tests with our system today to see if I can reproduce this. Normally we have our HPWCs pull 48A for each vehicle, which is more power than 4 PowerWalls can provide. I'll try lowering the power below 20A and see if the Gateway routes solar/PowerWall power to the HPWC (which is connected on the grid side of the Gateway).

 

[jjrandorin]

Our system has 4 PowerWalls that are providing power to two breaker panels for all of our house circuits, except for EV charging.

Our two Tesla HPWC's are connected to a separate breaker panel that is connected to grid power - not to the Tesla Gateway & the PowerWalls.

We have our Tesla vehicles set to schedule charging for 10PM each night.

When operating on grid, we haven't seen any power from the PowerWalls applied to the HPWCs, otherwise we'd end up with the PowerWalls always sitting at the reserve % by morning.

If you're seeing the PowerWalls providing power to EV charging that is supposed to be directly connected to the grid - what does the Tesla app show when the EV is charging?

If the app is showing the EV charging as part of the house power, then your EV charging is wired to the Gateway and not the grid.

If the app is showing the EV charging as part of the grid power (a negative number), that could be a problem - should something on the grid side of the Gateway be able to pull power from your PowerWalls (whether or not the grid is up)?

I'll run some tests with our system today to see if I can reproduce this. Normally we have our HPWCs pull 48A for each vehicle, which is more power than 4 PowerWalls can provide. I'll try lowering the power below 20A and see if the Gateway routes solar/PowerWall power to the HPWC (which is connected on the grid side of the Gateway).

The standard installation (as much as you can have a "standard installation" is for both backed up and non backed up breaker boxes to be connected to the grid, and in series. The powerwalls can provide power to non backed up loads when the grid is up, in most cases, unless one has an electrical system with sub panels that are not being measured at all.

 

[jboy210]

While our HPWC is backed up, in the event of an outage I plan on doing no time based charging. There are numerous Superchargers near me and I would rather drive a few miles and use one of those than drain the Powerwalls. If I do need to do some home charging I will try to do it manually when I assess that the solar production will replenish what the charging uses.

Of course, this is the plan. Reality may be significantly different.

 

[bob_p]

I reviewed the electrical diagrams the installer prepared prior to installation - and also again what they submitted to our local utility to achieve PTO.

The house breaker panels are connected to the Tesla Energy Gateway (TEG), along with the solar panels and PowerWalls. The TEG serves as a smart switch automatically routing power between the grid connection, home, solar panels and PowerWalls, based on the settings for the TEG and how much power is being generated or used by the various connections.

Our EV panel is connected on the line the "grid" connection between the TEG and our smart meter.

I just ran a test, lowering our HPWC down to 12A, so that it is low enough to be handled by our PowerWalls - and verified that when our S started charging, there wasn't any change in the status display in the Tesla app for the TEG. All of the solar power continued to be going only to the home and PowerWalls - and nothing was being drawn from or sent to the grid connection to the TEG. Stopping the HPWC charging also didn't show any difference. So at least while there is grid power, the TEG (at least in our configuration) will not provide any power to the breaker panel for our two HPWCs. And that's how it's supposed to work, otherwise every morning, our PowerWalls would be drained, because they don't store enough power to recharge our S and X.

One test I can't easily do is verify what happens when the grid power is out. It's possible to simulate a grid outage by throwing the breaker switch in the TEG panel. But that disconnects the grid connection to the TEG and because our HPWC breaker panel is on that line, the HPWC panel will still be getting grid power while the rest of the house is running off-grid.

So I'll need to wait until the next real power outage - and when that happens, will run another test to see if the TEG supplies any power to our HPWCs when the grid is really down.

With the information provided by the Tesla app, it should be easy to verify what's happening. If an EV is charging and shows up under the Home power consumption, then the EV charger is on a circuit powered by the TEG.

 

[jjrandorin]

I reviewed the electrical diagrams the installer prepared prior to installation - and also again what they submitted to our local utility to achieve PTO.

The house breaker panels are connected to the Tesla Energy Gateway (TEG), along with the solar panels and PowerWalls. The TEG serves as a smart switch automatically routing power between the grid connection, home, solar panels and PowerWalls, based on the settings for the TEG and how much power is being generated or used by the various connections.

Our EV panel is connected on the line the "grid" connection between the TEG and our smart meter.

I just ran a test, lowering our HPWC down to 12A, so that it is low enough to be handled by our PowerWalls - and verified that when our S started charging, there wasn't any change in the status display in the Tesla app for the TEG. All of the solar power continued to be going only to the home and PowerWalls - and nothing was being drawn from or sent to the grid connection to the TEG. Stopping the HPWC charging also didn't show any difference. So at least while there is grid power, the TEG (at least in our configuration) will not provide any power to the breaker panel for our two HPWCs. And that's how it's supposed to work, otherwise every morning, our PowerWalls would be drained, because they don't store enough power to recharge our S and X.

One test I can't easily do is verify what happens when the grid power is out. It's possible to simulate a grid outage by throwing the breaker switch in the TEG panel. But that disconnects the grid connection to the TEG and because our HPWC breaker panel is on that line, the HPWC panel will still be getting grid power while the rest of the house is running off-grid.

So I'll need to wait until the next real power outage - and when that happens, will run another test to see if the TEG supplies any power to our HPWCs when the grid is really down.

With the information provided by the Tesla app, it should be easy to verify what's happening. If an EV is charging and shows up under the Home power consumption, then the EV charger is on a circuit powered by the TEG.

I think you are missing something here. In many installations (likely most regular installations), just because a load is not "backed up" does NOT mean it is not able to be powered by the powerwall.

Just because something can be seen by the gateway does NOT mean it is backed up. Your electrical system does not sound like a "standard track home" type of system. Thats fine, I am not disputing how your system works. I am saying that, whether the system provides can provide powerwall power to a device is not tied to whether its in the "backed up" panel or not.

 

[GenSao]

What's your strategy for car charging?

I use the Time of Use (Cost Savings) mode. Set your peak, shoulder and off-peak times (including weekends) to your actual TOU rate schedule. Depending on historic usage, your Powerwall will always cover Peak Time of Use and some (if not all) shoulder times. Shift large loads to off-peak times (cloths dryer, EV charging, etc.). I am OK with the Powerwall covering AC usage during peak period and some of the part-peak period.

Car charge is set during off-peak times. Ideally the powerwall will never discharge during the off-peak period. To be friendlier to the grid, charging is set to start at 1:00 a.m.

As we have PG&E's EV-A rate schedule with off-peak in the morning thru 3:00 p.m. on the weekends, sometimes the car is charged with the morning sun (utilizing solar production) to minimize NBC ( approx. $0.03/kWH).

 

[miimura]

You only have two options if you want your car to charge from the grid:

1. Make the Powerwalls blind to the EV charging load. This requires careful placement of the Grid CTs so that the charging load is not measured. This may not be practical with your electrical system layout.
2. Use Time Based Control and charge during the Off-Peak time period.

I previously did #1 when my system was initially installed and the CTs were placed on the Gateway Grid input, but now I use TBC-Balanced and my system does not discharge the Powerwalls during the Off-Peak period.

This chart shows two cars charging back to back with slight overlap. The Model 3 starts at 00:15 and the other one starts at 03:00. There is almost no grid draw between 3pm and midnight and any solar after 4pm goes straight to the grid. This is on PG&E EV2-A.

 

[NathanielHrnblwr]

This time of year, my semi peak and off peak at basically the same. $.244 and $.248. This changes a bit in summer, but what is consistent is 10p-6a is off peak. So ideally, I would use the app to say 10p-12a or 10p-1a is off peak to give the car a window to charge from the grid, then the PW's can come back online at 1 to discharge until sunrise.

It would be great to be able to schedule modes - have the PW's go into backup mode at a certain time and switch back to another mode at another time to allow for cases such as this.

Thanks for the feedback. If other strategies are used, please feel free to share them.

EDIT: I switched to time based with 10p-12a as off peak and now (9p) it isn't pulling from the PW, just the grid. I must be misunderstanding how to set this properly

 

[power.saver]

Grey is part-peak (shoulder), you need to pull the blue (off-peak) around so it goes up until 12pm. Like this:

 

[NathanielHrnblwr]

According to the app, it treats off peak and shoulder the same? I.e. both periods are discharge when it feels it needs to make room for the next day’s forecasted solar production. Am I right that if it believes it has enough room, it won’t discharge during these periods? Is that what I ran into last night?

 

[power.saver]

Off-peak will never discharge under Cost Savings.

 

[NathanielHrnblwr]

Ok, so in the screen shot in my previous post, I set off peak for 2 hours - the time the car charges. why wasn't the Powerwall discharging during shoulder prior to off peak?

 

[power.saver]

Because you had no higher priority period (i.e. peak) in your schedule. The system works best with peak and off-peak. Shoulder can work, especially after peak, but its operation is dependent on what is ahead in the schedule, so it may charge, discharge or do nothing. To alleviate this, I use only peak and off-peak, and the behavior is consistent and repeatable.

 

[NathanielHrnblwr]

Because you had no higher priority period (i.e. peak) in your schedule. The system works best with peak and off-peak. Shoulder can work, especially after peak, but its operation is dependent on what is ahead in the schedule, so it may charge, discharge or do nothing. To alleviate this, I use only peak and off-peak, and the behavior is consistent and repeatable.

ok that makes sense. I'll play around with it after this rain passed. thanks!

 

[ra88it]

While our HPWC is backed up, in the event of an outage I plan on doing no time based charging. There are numerous Superchargers near me and I would rather drive a few miles and use one of those than drain the Powerwalls. If I do need to do some home charging I will try to do it manually when I assess that the solar production will replenish what the charging uses.

Of course, this is the plan. Reality may be significantly different.

This is what I do in practice, with a combination of charger, vehicle, and the solar app.

Sometimes it works well, there are a few new EVSE that allow this to be done better, but those are still low amperage (and j1772) options.

EDIT: it seems as though ChargePoint has thrown their hat into the ring with a 50a option that has a rather slick interface. Not a paid post in the slightest, just something I found while researching this a bit more.

 

[NathanielHrnblwr]

Bumping this in case someone else is looking to do something similar as I found a solution that works for me.

I set up HomeAssistant on a rPi and installed the Powerwall module so HA can see the PW data. I set up an automation in HA that moves the PW to backup mode if the total load is above 11kW for 30 seconds and then set it back to self consumption when the load drops below 8kW for 30 seconds. So far it works fine and I'm sure I can tweak the rules further.