Powerwall2 near the main panel or 200 feet away subpanel?

[EVkid]

Hello,

I need your help in understanding the best location to install the Tesla PowerWall2, Inverter, and the Switchboard in the following configuration. The new detached garage is under construction that will have the subpanel(100Amp) installed about 200 feet away from the main panel(200 Amp) in the main house garage. I am planning to install the 14Kwh Tesla solar panels on the south-facing rooftop of the new garage.

Is it better to have the equipment near the main panel in the garage of the main house or is it okay to install the equipment in the new garage after the subpanel?

EVkid
2022 Tesla Model S Long Range
Cybertruck (deposit)
Tesla Energy 14Kwh + Powerwall2 in plan

 

[BGbreeder]

I am not an electrician, so take any advice as a non-expert.

Have you figured out where you plan to charge your car and truck? The combination could pull a lot of power, as in 96A, if you charged both at high speed at the same time. Having them both in the detached garage is great from the perspective of solar straight to the vehicles, but even best case, you would be pulling a minimum of 38A to the detached garage. I am not sure that a 100A panel would be large enough. You absolutely need to make sure that the charging circuits are installed prior to solar and Powerwalls.

I would look at the question from the perspective of two things a) power loss, and b) loads. The loss is I**2R, where I is current, R is the resistance in the wire. If you expect your Powerwall(s) to absorb large PV power and trickle them to the house, having the Powerwall(s) at the garage will reduce you average losses. From the perspective of loads, if you plan to use the PV to charge your car(s), then that means you will consume much of the power locally to the detached a garage (?), and less average power will leave the garage. If you have a pool, AC, electric heat, dual electric ovens, etc., you may want the Powerwall(s) at the house.

Whatever you do, I would ask, and pay for, having the 200' wire upgraded to a larger size to reduce losses. With two EVs, there is the potential to pull quite a bit of current over a long run. Personally, I would expect to be upgrading all of the panels.

Finally, two things; if you don't have solar on the main house, I would consider adding it now, and go large. Two EVs are a non-trivial load. Adding more solar later is a mess. Secondly, Powerwalls can accept a maximum of 5kW for charging, so a 14kW solar array would need three powerwalls to be able to accept the full solar output in an off grid situation. (PSPS, earthquake, etc.) Otherwise, the Powerwalls are likely to shutoff the solar and not charge well, basically only charging when the home load is large enough to soak up at least 4.7kW of load.

All the best,

BG

 

[EVkid]

I am not an electrician, so take any advice as a non-expert.

Have you figured out where you plan to charge your car and truck? The combination could pull a lot of power, as in 96A, if you charged both at high speed at the same time. Having them both in the detached garage is great from the perspective of solar straight to the vehicles, but even best case, you would be pulling a minimum of 38A to the detached garage. I am not sure that a 100A panel would be large enough. You absolutely need to make sure that the charging circuits are installed prior to solar and Powerwalls.

I would look at the question from the perspective of two things a) power loss, and b) loads. The loss is I**2R, where I is current, R is the resistance in the wire. If you expect your Powerwall(s) to absorb large PV power and trickle them to the house, having the Powerwall(s) at the garage will reduce you average losses. From the perspective of loads, if you plan to use the PV to charge your car(s), then that means you will consume much of the power locally to the detached a garage (?), and less average power will leave the garage. If you have a pool, AC, electric heat, dual electric ovens, etc., you may want the Powerwall(s) at the house.

Whatever you do, I would ask, and pay for, having the 200' wire upgraded to a larger size to reduce losses. With two EVs, there is the potential to pull quite a bit of current over a long run. Personally, I would expect to be upgrading all of the panels.

Finally, two things; if you don't have solar on the main house, I would consider adding it now, and go large. Two EVs are a non-trivial load. Adding more solar later is a mess. Secondly, Powerwalls can accept a maximum of 5kW for charging, so a 14kW solar array would need three powerwalls to be able to accept the full solar output in an off grid situation. (PSPS, earthquake, etc.) Otherwise, the Powerwalls are likely to shutoff the solar and not charge well, basically only charging when the home load is large enough to soak up at least 4.7kW of load.

All the best,

BG

Hi BG,

Thank you so much for highlighting many great points to consider.

Ideally, I wanted to keep the PowerWall2 and Inverter in a detached garage using oversized electrical wires between the main and sub-panels. The issue is the PowerWall2 installer insists that it needs to be within 25' of the main panel. His statement makes me think there must be a good reason for this requirement.

The WallCharger in the main garage will be used for charging the daily use vehicle of Model S from midnight. I hope the solar system can produce enough electricity to send it back into the grid during the daytime and charges Tesla during the night from the grid credit.

I will be installing at least one WallCharger in the detached garage for the future Tesla. The subpanel will supply the electricity to the garage lights, outlets, and two large garage door motors.

I would like to know if the PowerWall2 needs to be close to the main panel or not.

Thank you for any advice,

EVkid

 

[miimura]

It is a simpler install if the Powerwalls are relatively close to the main panel. The main consideration is communication between the Powerwalls and the Gateway. So, your installer is at least partially correct. However, the number I recall is more like 50' to 100' instead of 25'. Putting the solar inverters on the detached garage 200' away should not be a problem as long as there is network connectivity between the buildings to pass the generation measurement data.

 

[EVkid]

It is a simpler install if the Powerwalls are relatively close to the main panel. The main consideration is communication between the Powerwalls and the Gateway. So, your installer is at least partially correct. However, the number I recall is more like 50' to 100' instead of 25'. Putting the solar inverters on the detached garage 200' away should not be a problem as long as there is network connectivity between the buildings to pass the generation measurement data.

I sure like your idea of keeping the Inverter in the detached garage and installing the Gateway and PowerWall2 near the main panel. I was reluctant to install the dedicated PV wires back into the main garage if the Inverter can not stay in the detached garage. It is simpler and less expensive to install the data cable along with large size 4 conductor electrical wires underground before installing the 200' long concrete driveway.

Thank you for your suggestions.

EVkid

 

[BGbreeder]

Thanks @miimura I had forgotten about the gateway to Powerwall bus. The gateway to Powerwall communication bus is a CANbus, or a close relative of it, and the upper limit for that is, IIRC, 20m, but the distance is also dependent on nodes. So,...if you want whole house backup, the gateway and powerwalls all need to be close to your main panel. Oversized conductors to/from the detached garage remains a great idea.

@EVkid just FYI, there is a loss of about ten percent round trip into the powerwalls, so storing during the day and charging at night from Powerwalls is less efficient than sending the power to the grid and then using the banked power later, though you will pay non-by passable charges (NBCs).

All the best,

BG

 

[Rocket_man]

Just fyi.... in my system the panels are on the opposite side of the house from the inverters. They ran over 60 feet of wire from the panels to the inverter and that didn't seem to be much of an issue. I don't know what the maximum distance is, Tesla is going to have to design that for you, really it is up to them. One other thing my installer mentioned is that the Gateway and PW+'s talk to each other over WiFi. I can see the CAN bus wires installed so I'm not sure what he meant by that. It might be wise to have WiFi available in the 2nd garage. Just a suggestion to future proof your 2nd garage, run some Schedule 80 PVC between the two buildings, at least 2 runs if not three. I'm not sure you can run DC and AC wires in the same conduit, not to mention low voltage wires. One last thing, I have a 14.8kw system with 2 powerwall +'s. Each inverter can support 7.6kw, but in reality they can go well over that rating, and the system rarely gets close to 14kw. But having the 2nd battery is key for us. I added panels to the system to charge a future EV, but I wish I had gone a little larger. I have a Sense energy monitor and it really opened my eyes to what the loads in our house are. Our house has two A/C systems, one uses 1.7kw, the other 2.3kw. Of course they are cyclic. Our electric clothes dryer is 7kw! And when it is running it is at a high duty cycle. 7kw is nearly what it would take to charge an EV at a moderate rate. If the dryer and A/C units are running and the lights and always on loads it can pull 10kw constantly. I probably have a lot more A/C than you do, but know your loads as best you can.. and always go bigger! lol.

 

[Steve2498]

Hello,

I need your help in understanding the best location to install the Tesla PowerWall2, Inverter, and the Switchboard in the following configuration. The new detached garage is under construction that will have the subpanel(100Amp) installed about 200 feet away from the main panel(200 Amp) in the main house garage. I am planning to install the 14Kwh Tesla solar panels on the south-facing rooftop of the new garage.

Is it better to have the equipment near the main panel in the garage of the main house or is it okay to install the equipment in the new garage after the subpanel?

EVkid
2022 Tesla Model S Long Range
Cybertruck (deposit)
Tesla Energy 14Kwh + Powerwall2 in plan

just FYI-re a configuration that can work. I have a 200 amp main service and a 100 amp sub panel in a detached garage. All my panels are on the house roof, the inverters and GW2 are installed next to the main panel. The PowerWalls are installed on the detached garage, about 100 ft away.

 

[Vines]

Hello,

I need your help in understanding the best location to install the Tesla PowerWall2, Inverter, and the Switchboard in the following configuration. The new detached garage is under construction that will have the subpanel(100Amp) installed about 200 feet away from the main panel(200 Amp) in the main house garage. I am planning to install the 14Kwh Tesla solar panels on the south-facing rooftop of the new garage.

Is it better to have the equipment near the main panel in the garage of the main house or is it okay to install the equipment in the new garage after the subpanel?

EVkid
2022 Tesla Model S Long Range
Cybertruck (deposit)
Tesla Energy 14Kwh + Powerwall2 in plan

In your case I would recommend to leave the PV solar at the detached garage, connected to a dedicated subfeed to the MSP area.

Near the MSP I would put the Powerwalls and associated equipment. Other solutions are just forcing things that don't want to work. The Powerwalls cannot physically be that far from the TEG.

 

[wwhitney]

In your case I would recommend to leave the PV solar at the detached garage, connected to a dedicated subfeed to the MSP area.

So you are proposing two feeders to the garage, one for loads and one for PV?

Cheers, Wayne

 

[Vines]

So you are proposing two feeders to the garage, one for loads and one for PV?

Cheers, Wayne

Yes, that is the way I would design it so you can easily monitor the PV at the dedicated PV gen. subfeed to the GW2.

If you combine the loads and generation sources in the same feeder, you have to monitor it at the garage and the whole system depends on the wifi signal from the neurio CT that captures PV generation, to the TEG. 200' means this might be a flaky wifi connection, and any dropout of this neurio will send the system into error mode.

It is possible to extend the 100A PV CT's over a 200' hardline, which is a great alternative.

EDIT: maybe a better alternative now that I have more coffee.

 

[BGbreeder]

I was told the Tesla CTs max out at 50', and not recommended over thirty, when we were having trouble with monitoring our remote (garage roof) solar panels. Practically speaking, CT wires end up being great antennas, even if twisted, as the input power is so low, which makes measurement over long distance problematic. We had to install a dedicated WiFi access point for the neurio, as its WiFi abilities are so anemic.

I agree that running two feeds would really simplify the monitoring, and the generation feed wouldn't have to be as large as the load feed, would it? Two feeds would also give you both generation and load panels in the garage that would simplify troubleshooting and isolation. (Fewer panels with multiple power sources.) And, yes, I would vote for a third low voltage conduit for Ethernet or fiber or... Once you have trenched it, the additional cost for an extra conduit is a round off cost, and the flexibility would be really nice.

All the best,

BG

 

[Vines]

I was told the Tesla CTs max out at 50', and not recommended over thirty, when we were having trouble with monitoring our remote (garage roof) solar panels. Practically speaking, CT wires end up being great antennas, even if twisted, as the input power is so low, which makes measurement over long distance problematic. We had to install a dedicated WiFi access point for the neurio, as its WiFi abilities are so anemic.

I agree that running two feeds would really simplify the monitoring, and the generation feed wouldn't have to be as large as the load feed, would it? Two feeds would also give you both generation and load panels in the garage that would simplify troubleshooting and isolation. (Fewer panels with multiple power sources.) And, yes, I would vote for a third low voltage conduit for Ethernet or fiber or... Once you have trenched it, the additional cost for an extra conduit is a round off cost, and the flexibility would be really nice.

All the best,

BG

Agree, we try to not have super long CT runs whenever possible, and to keep them in a dedicated conduit. The maximum length of a CT is a pretty involved discussion and depends on which of the 3 CT styles you are using. Certainly, there are wifi and hardline options for more than 200' though.
We have been bitten by wifi extender solutions that sound good on paper but they drop out and the system loses its mind.

Solar CT's need to be rock solid, unlike additional CT's that might be set for self-consumption of non-backup loads and the system could work at reduced function without them. Solar CT's must also not have any significant load on them, this also triggers an error state.

 

[wwhitney]

The only real performance downside of a separate load feeder and PV feeder to the detached garage is the inefficiency when there is significant load at the garage contemporaneous with PV production. Then you have 400 feet of extra I^2*R losses. However, if the primary garage load is EV charging, and that occurs at night, then significant contemporaneous load is not so likely.

As for conduits, there's no particular reason to separate the load feeder and the PV feeder. Putting them in the same conduit would incur a 0.8 derating factor for 4-6 current carrying conductors, but assuming THWN-2 conductors or the like, that derating would start at the 90C ampacity, higher than the normal 75C ampacity.

For example, if there's 14 kW DC of panels, then the inverters might be 11.5 kW (a multiple of a standard increment of 3.84 kW), which means 48A continuous AC rating, and a 60A PV feeder is required. For short distances, you could use #1 Al (75C = 100A, 90C = 115A) for the 100A load feeder, and #4 Al (75C = 65A, 90C = 75A) for the 60A PV feeder. With the 80% derating for being in the same conduit, those would only be good for 92A and 60A respectively. Which would actually suffice if the calculated load is 92A or less, and the load feeder could still be protected by a 100A breaker (or a 90A breaker if desired and the calculated load is under 90A).

But at 200' I would think you'd want to upsize at least one size, in which case the ampacity of the load feeder would be over 100A (1/0 Al has 75C = 120A, 90C = 135A, so with 0.8 derating the ampacity is 108A). An online voltage drop calculator tells me that at 200' one-way, #1 Al at 240V at PF=1 has a voltage drop (or rise for the PV inverter) of 2% at 48A. So for the PV feeder you'd likely want at least #1 aluminum to minimize voltage rise, and the load feeder could be #1 or #1/0.

Cheers, Wayne

 

[miimura]

I agree that having separate AC circuits for the solar and loads to the detached garage is preferable. Having to put special remote directional WiFi antennas on the Neurio can get wonky fast. Aiming them is another issue. Being able to use CTs measuring the solar circuit very close to the Gateway is far better.

 

[EVkid]

I agree that having separate AC circuits for the solar and loads to the detached garage is preferable. Having to put special remote directional WiFi antennas on the Neurio can get wonky fast. Aiming them is another issue. Being able to use CTs measuring the solar circuit very close to the Gateway is far better.

Hi Everyone,

I am so lucky to have you all sharing your ideas and recommendations for the issue I am having before the open electrical trench closes. Tesla Energy canceled my order before I had a chance to access one of the advisers for the underground wiring requirements for the solar panel system size of 14.3 Kwh or 16.8Kwh that I wanted to order. The sales representative told me to re-submit the order after the building is complete.

Here is what I need to do with your input:
1. Clear out the space in the main garage for the Tesla Gateway, 2 x Powerwall 2s.
2. Install the PV cable/cables from the detached garage back to the main garage using #1 Aluminum wires in a separate conduit. I am not sure if I need the multiple PV cables to support 40 panels. The inverter takes up to 600Vdc input while each panel's maximum output is 40vcd.
3. I don't know how the Tesla installer will be connecting the 40 panels of PV wires into two inverters in the PowerWall2.
4. Install a separate data cable(Ethernet) in a small size conduit for future use.
5. Install the WallCharger2 in the detached garage for the future EV.

Thank you for eveyone,

EVkid.

 

[wwhitney]

Are you saying you already have an open trench with a feeder supplying the garage? What size conduit and conductors? What loads do you plan for the garage, anything beyond lights, receptacles, garage door opener, and WallCharger2?

Cheers, Wayne

 

[EVkid]

Are you saying you already have an open trench with a feeder supplying the garage? What size conduit and conductors? What loads do you plan for the garage, anything beyond lights, receptacles, garage door opener, and WallCharger2?

Cheers, Wayne

I have the excavator crew starting tomorrow and I am not sure what order of tasks they will start. I am trying to be a little ahead of them to define the electrical underground cabling requirements.

As the load wire size from the 200amp main panel to the 125Amp sub-panel in the detached garage is #2 or #1 copper wires when I had a discussion with the electrician. Although I call this detached building a garage, I will not be doing any major or heavy work that uses lots of power. I don't think I will have any air conditioning units or a heating system in the garage initially. I am thinking of installing a medium-sized Heat pump system after observing electricity production data for a year. I will have a few ceiling fans for the air circulations. The heaviest power user in the detached garage is the second WallCharger2 for the future EV, one 17-gallon size air compressor, and the next power user is the Class C motorhome that is stored most of the year.

My original naive plan was to install the oversized Tesla solar panel system in the detached garage with about 40 solar panels on the south-facing rooftop and assume two units of integrated Inverter PowerWall2 packages connected to the subpanel load line. And only the Tesla Gateway2 is to be installed next to the main panel and the meter.

After learning from you all, it was more complicated than my simple idea.

It would have been great if Tesla Energy's advisor can help me define the wiring requirements for the new building under construction. I like the best Tesla product and its price. I try to prepare the best I can for the proper and easy installation later.

Please let me know if I am missing anything else.

Greatly appreciate your help.
EVkid

 

[wwhitney]

Using copper wire instead of aluminum is a waste of money.

I'd suggest running PVC conduit buried, either (2) 1-1/2" minimum runs for separate feeder and PV, or (1) 2" minimum run for both together. 1-1/2" PVC will hold (4) 1/0 conductors, 2" will hold (7). Assuming the price difference between #2 AWG, #1 AWG, and #1/0 AWG Al XHHW-2 or THHN-2 conductor is minimal, run #1/0 ungrounded conductors for the both the feeder and the PV. Not sure if the PV inverter needs a neutral reference, and if so what size is required (if it's for voltage reference only, it only needs to be minimum sized, the same as the EGC). The feeder neutral can likely be one or two sizes smaller than the ungrounded wires if desired. The EGC size will depend on the actual OCPD used at each end; for a fixed wire size, the smaller the OCPD (and hence greater the ratio of size used to minimum possible size), potentially the larger the EGC you need.

Run a separate conduit for data, not sure what a reasonable size is, maybe 1-1/2"?

I've not actually done any of the above before, so I'm only 95% confident in the numbers, it's possible some things should be one size larger for an even greater margin of error.

Cheers, Wayne

 

[EVkid]

Using copper wire instead of aluminum is a waste of money.

I'd suggest running PVC conduit buried, either (2) 1-1/2" minimum runs for separate feeder and PV, or (1) 2" minimum run for both together. 1-1/2" PVC will hold (4) 1/0 conductors, 2" will hold (7). Assuming the price difference between #2 AWG, #1 AWG, and #1/0 AWG Al XHHW-2 or THHN-2 conductor is minimal, run #1/0 ungrounded conductors for the both the feeder and the PV. Not sure if the PV inverter needs a neutral reference, and if so what size is required (if it's for voltage reference only, it only needs to be minimum sized, the same as the EGC). The feeder neutral can likely be one or two sizes smaller than the ungrounded wires if desired. The EGC size will depend on the actual OCPD used at each end; for a fixed wire size, the smaller the OCPD (and hence greater the ratio of size used to minimum possible size), potentially the larger the EGC you need.

Run a separate conduit for data, not sure what a reasonable size is, maybe 1-1/2"?

I've not actually done any of the above before, so I'm only 95% confident in the numbers, it's possible some things should be one size larger for an even greater margin of error.

Cheers, Wayne

Thank you for the conduit size and wire size recommendations.
I will share this information with my electrician.

EVkid