Pro/Con of backing up two EVSE or not?

[YRide]

Just recently got my system installed here in San Jose (city), Tesla scheduling final inspection. Interconnect was filed in time for NEM2.0….

10.8kW PV, 4x ESS (54kW).

3x EV’s (Model Y).

PGE EV2A rate plan.

Currently have 200A service. 200A main panel (but backed up loads limited to 100A by 100A max branch breaker on the main panel).

Tesla removed the extra load center, and was able to tie all 4 powerwalls directly into the GW2, with the optional sub panel board (that was a nice surprise).

I was also able to convince Tesla to preemptively install #2/0 (instead of AWG #3) for both the main to GW2 and also GW2 to Backed Up load center / distribution panel (which has a 225A bus bar). In theory this should make for an easy upgrade to a new main panel that is 200A as well as 200A rated on a max branch breakers…

If I do that upgrade it would allow me to change the backed up load center to 200A breakers instead of current 100A…and move my two EVSE loads (48A continuous, 60A breaker / OCPD) from the non-backed up main over to the backed up load center.

Question is…is that a good thing, bad thing or moot / don’t care?

I understand that even one EV needing like 60% of charge (Tesla Y’s are like 82kW, right?) will consume my 4x powerwalls…much less 3x EV’s.

And also, in an outage, I’ll likely want to conserve my powerwalls and not charge EV’s (but Tesla kinda manages that with the setting where you can limit EV charging during an outage).

But for Time Based Control to have the most data to make the best monetary optimizations…isn’t it better to have all loads backed up?

Also, that way I can see the EV consumption on the app. If they weren’t backed up I could not.

 

[arnolddeleon]

My current position/recommendation is back up all the circuits if you have a modicum of clue on how things work and have some amount of automation/coordination. This gives you the most flexibility.

In your specific case it sounds like all the vehicles Teslas and Tesla already supports settings that prevent your cars charging from draining your Powerwalls in a grid outage.

 

[YRide]

I guess one benefit…if I ever did need to charge an EV at 4p…then if backed up I am using my own generation instead of paying peak rates.

But if I’m on TBC setting, I probably only have until 6p before the powerwalls have drained to maximize NEM credits at peak.

 

[buckets0fun]

My current position/recommendation is back up all the circuits if you have a modicum of clue on how things work and have some amount of automation/coordination. This gives you the most flexibility.

In your specific case it sounds like all the vehicles Teslas and Tesla already supports settings that prevent your cars charging from draining your Powerwalls in a grid outage.

This.

If you have the space, back it all up. Do the MPU with tesla if you’re able.

 

[YRide]

This.

If you have the space, back it all up. Do the MPU with tesla if you’re able.

Tesla wouldn’t do the MPU. I did find a Tesla approved electrician, HCI Solar, that seemed pretty knowledgeable and I think was quoting like $3.5k. This included all the stucco work and painting (I’m Semi-flush mounted).

 

[buckets0fun]

Tesla wouldn’t do the MPU. I did find a Tesla approved electrician, HCI Solar, that seemed pretty knowledgeable and I think was quoting like $3.5k. This included all the stucco work and painting (I’m Semi-flush mounted).

That’s a great price. Take it and run.

 

[h2ofun]

I have 5 wall connectors on a 200 amp panel. But, even if I get multiple EV's, would probably never charge more than 2 at a time, max.
Not connected to my batteries which is fine wit me.. Do not need to think about it. I try to charge during the day when 7 batteries full and sending 20KWh back to PGE so they do not get. But if I miss, like now, I just set to charge at midnight. I have some much excess it is not worth worrying about, I love it

 

[Vines]

One of the cooler parts of car chargers on the backup side is that they will not charge unless the conditions benefit you.

I personally like another large battery to dump excess solar into during long outages. The Powerwal system automatically turns on my car charger whenever my powerwall batteries get beyond 95% state of charge.

Rather than frequency shift to turn off the solar, the car starts charging and no electrons are wasted.

 

[holeydonut]

I have 5 wall connectors on a 200 amp panel. But, even if I get multiple EV's, would probably never charge more than 2 at a time, max.
Not connected to my batteries which is fine wit me.. Do not need to think about it. I try to charge during the day when 7 batteries full and sending 20KWh back to PGE so they do not get. But if I miss, like now, I just set to charge at midnight. I have some much excess it is not worth worrying about, I love it

When the big earthquake hits and the grid is offline for a month, everybody in Auburn with a Tesla (but no ESS) will be hanging out at your house for suds .

 

[YRide]

One of the cooler parts of car chargers on the backup side is that they will not charge unless the conditions benefit you.

I personally like another large battery to dump excess solar into during long outages. The Powerwal system automatically turns on my car charger whenever my powerwall batteries get beyond 95% state of charge.

Rather than frequency shift to turn off the solar, the car sharts charging and no electrons are wasted.

Likely we’re not going to experience many outages here in SJ. And when they do, usually resolved in 10’s of minutes.

I’ve only had the system running for two weeks, and the weather continues to be weird (not full blue sky every day) this year, but it seems like full-on sun day is getting me 63.3 kWh. When I get some time I’ll go back and double check my PVWatts theoretical numbers and see how this compares for a May day.

Multiply 63.3 by the average days per month (30.42) and I’m at 1925kWh in a month, maximum.

With home loads and 3x EV, we’ve been pulling between 1900 and 2000 kWh a month since last November….so it would seem I’ll never net generate, unless in the summer months my consumption rate is less then Nov-Apr (haven’t lived in house long enough to know what May-Nov consumption is like).

The plan was mainly to use the PW’s to time shift the solar generation into the peak hours + cover the non-EV charging home loads during peak.

63.3 kWh minus the 54 kWh we have in PW capacity means only 9.3kWh headroom on a daily cycle that accounts for reserve + peak home loads.

So it would seem in theory that I don’t need to backup the EVSE as a generation sync, but then I do lose all the consumption data in one easy to use place to track.

 

[CrazyRabbit]

Why did Tesla derate your main panel? You say easy to update, maybe not be. Do you have two PW+’s.
My chargers are on non backed up panel. I have a 240v/50amp receptacle in garage and would us the L2 cord in grid out. I didn’t want to split my system into two systems/gateways like tesla wanted to do, so the house panel is backed up. I had tesla use 3/0 cable!

 

[YRide]

Why did Tesla derate your main panel? You say easy to update, maybe not be. Do you have two PW+’s.

Even though it’s a pretty new 200A panel (new house, ground up 5yrs ago) it’s 1) center-fed onto the busbar and 2) max branch breaker of 100A. So thus the “branch” of the backup load center is limited to 100A.

 

[CrazyRabbit]

Even though it’s a pretty new 200A panel (new house, ground up 5yrs ago) it’s 1) center-fed onto the busbar and 2) max branch breaker of 100A. So thus the “branch” of the backup load center is limited to 100A.

Your non backed up panel should be monitored, why do you say that.

picture…. Make and model of panel.
What service do you have? 200amp?

 

[Vines]

Your non backed up panel should be monitored, why do you say that.

picture…. Make and model of panel.
What service do you have? 200amp?

It is widespread for the service panel to be limited to a 100A breaker on the bus, especially with low profile and skinny center-fed service panels.

However, I agree your car charger and other non-backed up circuits should have meters to capture the loads so you can see and offset them with battery power.

 

[CrazyRabbit]

widespread is not a reason. Give a reason please. Because changes to service panel should not result in nuisance trips.
Op should do the panel upgrade and perhaps service upgrade at same time.

 

[YRide]

Your non backed up panel should be monitored, why do you say that.

picture…. Make and model of panel.
What service do you have? 200amp?

200A service (overall system details in 1st post).

When you say monitored…you mean have additional Neurio in my main panel with two CT’s connected into it?

 

[YRide]

It is widespread for the service panel to be limited to a 100A breaker on the bus, especially with low profile and skinny center-fed service panels.

However, I agree your car charger and other non-backed up circuits should have meters to capture the loads so you can see and offset them with battery power.

Just have two non-backed up loads…two Tesla EVSE’s, 48A cont / 60A OCPD each.

Do you mean there should be a Neurio in my MP, with two CT’s, one on each load, informing the the GW2?

 

[Vines]

Just have two non-backed up loads…two Tesla EVSE’s, 48A cont / 60A OCPD each.

Do you mean there should be a Neurio in my MP, with two CT’s, one on each load, informing the the GW2?

Yes, or a single CT that measures both loads. I would want it that way but I cant say its wrong or right otherwise. We setup 100% of our systems so the customer can see the whole home load.

 

[YRide]

Yes, or a single CT that measures both loads. I would want it that way but I cant say its wrong or right otherwise. We setup 100% of our systems so the customer can see the whole home load.

Tesla install team never mentioned it. I wonder if I can call them back?

Weird thing is they had left a spare Neurio on top of my GW2, with two CT clamps. But then when they came back to fix the other Neurio’s (which I had actually already fixed myself) they took the spare Nuerio home!

Does it not cause any issues in the switching algorithm for the GW2 to “see” extra home loads but not be able to allocate solar or ESS power to them?

 

[Vines]

Tesla install team never mentioned it. I wonder if I can call them back?

Weird thing is they had left a spare Neurio on top of my GW2, with two CT clamps. But then when they came back to fix the other Neurio’s (which I had actually already fixed myself) they took the spare Nuerio home!

Does it not cause any issues in the switching algorithm for the GW2 to “see” extra home loads but not be able to allocate solar or ESS power to them?

The system is designed when on-grid to send PV or powerwall power to offset those loads which are not backed up. I would say it causes issues with the algorithm for there to be large house loads that are NOT monitored.