Powerwall and Solar Provisions for Future

[mkgrady]

I'm getting ready to wire an entire home renovation/addition. It's on old BIG Victorian house on the coast of Massachusetts. The plans call for provisions for a future powerwall and solar. For the solar they spell out an empty conduit from the basement where the main panels will be to the roof. For the powerwall they just say make provisions.

I have no experience installing solar or power walls and I won't be involved in the future installations. I did wire a Tesla car charger at this location and that charger will become part of the final installed wiring. Right now it is powered from a temporary service that also feeds temporary power for construction. The service for the house is specified as 400 amp. My plan is to use two 200 amp main panels. Part of the reason for the 400 (320 continuous) is the car charger. They were also talking about maybe a snow melt system for the driveway. I'm thinking they are expecting to get more out of the solar than is possible. Not much of the roof faces south and some of them are cone shaped like is often seen in old victorian homes.

A couple of interesting things about the job is that they are doing their HVAC from geothermal and that this very large house has been jacked up, had new foundation walls and footings and has been lowered back down. They went from having a 4-7 foot basement to having a ten foot basement height.

My question about the solar conduit is what size I should consider. Even if they can cram a lot more panels up on the roof that seems possible is 1-1/4 likely large enough? Do I just run it up through the roof and put a cap on it and a rubber boot flashing fitting> Should it be near the bottom of the roof slope or near the top?

I think my question about the provisions for a powerwall are more complicated but I really don't know. Does a power wall just connect to one of the 200 amp main panels? Doesn't that mean only one of the panels can take power from the powerwall during an outage? Should I be using a 400 amp panel instead of two 200s? Are power walls used when power is not lost? Meaning they get charged by the solar during the day and they feed loads at night in lieu of from the POCO? Is one powerwall going to be useful? Does this job call for more than one?

I can't ask the customer any of these questions. They don't know. They just know they want to be green. Any help would be appreciated.

 

[jaggedben]

Most residential systems don't need more than 3/4" to the roof, especially if, as you imply, the roof is too small for a big system. 1" would be reasonable and conservative for using larger conductors to save sone voltage drop. 1-1/4" would be overkill in my book.

Storage... I'm gonna post this for now and start a second reply, lol.

 

[Barbqranch]

Personally, if it were me and if there is an attic, I would run the 1 inch conduit into the attic and let the solar installer penetrate the roof where they want, and you won't be responsible for any leaks, either.

 

[jaggedben]

Okay, energy storage and backup power...This advice is fairly generic, not too specific to Powerall. ( It is specific to planning for a backup micro-grid, not just energy storage for time-of-use management.)

Yeah, people underestimate the detail involved in these systems and how much it changes how you have to think about everything, and cost, to provide aforementioned 'provisions'. Detailed advice is really beyond the scope of what's possible in a forum like this. Broadly speaking though, you need to choose between two general stategies, or some combination thereof:

1) Separate out a limited number of circuits that would be priorities for being backed up, and put them on different distribution than other circuits.
2) Run all branch circuit load wiring into a central gutter, to allow easy rewiring of loads later on to be on or off the micro-grid.

Strategy 2 is better for maximum flexibility later, Strategy 1 might be somewhat more in line with your normal material and labor budget, if the customer is willing to put in some time and make some commitments. The basic point though, is do not wire the air-conditioner (for example) into a subpanel in the middle of the house that is otherwise just lighting and plugs; because then someone is going to have to demo some drywall to get that A/C wiring relocated later.

A couple other things...
-Ideally, do not put any branch circuits in the main service equipment. Use a disconnect or main breaker enclosure.
- Leave plenty of additional wall space for a gateway and backup panel later on.

 

[mkgrady]

Personally, if it were me and if there is an attic, I would run the 1 inch conduit into the attic and let the solar installer penetrate the roof where they want, and you won't be responsible for any leaks, either.

Sounds like good advice. Thanks

 

[mkgrady]

Okay, energy storage and backup power...This advice is fairly generic, not too specific to Powerall. ( It is specific to planning for a backup micro-grid, not just energy storage for time-of-use management.)

Yeah, people underestimate the detail involved in these systems and how much it changes how you have to think about everything, and cost, to provide aforementioned 'provisions'. Detailed advice is really beyond the scope of what's possible in a forum like this. Broadly speaking though, you need to choose between two general stategies, or some combination thereof:

1) Separate out a limited number of circuits that would be priorities for being backed up, and put them on different distribution than other circuits.
2) Run all branch circuit load wiring into a central gutter, to allow easy rewiring of loads later on to be on or off the micro-grid.

Strategy 2 is better for maximum flexibility later, Strategy 1 might be somewhat more in line with your normal material and labor budget, if the customer is willing to put in some time and make some commitments. The basic point though, is do not wire the air-conditioner (for example) into a subpanel in the middle of the house that is otherwise just lighting and plugs; because then someone is going to have to demo some drywall to get that A/C wiring relocated later.

A couple other things...
-Ideally, do not put any branch circuits in the main service equipment. Use a disconnect or main breaker enclosure.
- Leave plenty of additional wall space for a gateway and backup panel later on.

Thanks. The one big gutter makes a lot of sense for maximum flexibility. See any drawback to using two 200 amp panels instead of one 400 amp? They are already asking for a sub panel on the second floor. Normally I would do this but now some decisions will have to be made about critical loads off that panel. It's probably better to have all circuits come back to the the main panel(s) area. This is frustrating because I don't know the capacity of the Powerwall because I don't know how many they will install or how many the solar can charge.

Maybe I should treat the circuits like I was wiring for a small standby generator. Just run everything critical to one sub panel in the basement. I'm really confused because I don't understand the Powerwall. Does the stored power get used (for free) at night when the solar isn't producing? If that is the case I would think they would want to use up all they could every night. That would mean I should connect more than critical circuits to this system.

 

[shortcircuit2]

How do you plan to comply with the 2020 230.85 and outside ED's with 2 x 200-amp panels?

 

[chrismarcellino]

See the installation manual for the current PowerWall:

https://www.tesla.com/sites/default/files/pdfs/powerwall/Powerwall_2_AC_BU_NA-EN_Installation_Manual.pdf

Especially starting page 12, and see the diagram page 40. The crux of it is is that there are two pieces:
1) backup gateway - a electrically actuated "generator" transfer switch driven by the powerwall for powerfail mode to isolate the home from the grid (usually rated up to 200 amps)
2) the powerwall itself. needs a 30 amp breaker and can go anywhere downstream of the gateway

Most people with a 400 amp service will split the loads into one panel (ie the "house panel") that will be backed up, since you don't want the car chargers, and other workshop loads, maybe AC and hot tub on the PowerWall side since it would trip it in a backup situation (and you are limited to 200 amps through the current gateway.)

So basically put the house on one panel, and the car chargers, and hot tub etc on the other. If they have a heat pump, should be backed up since you want emergency heat in a disaster.

Can often put a CSED on the outside of the house to meet 2020 firefiredisconnect that has two 200 amp breakers to your feeders. Then they can put the Gateway in attached to the panel on the outside, and feed the "house" panel. The gateway is surface mount, so reasonable to put outside.

Best to have the Powerwall in a reasonably conditioned space.

The last big gotcha: need to have a class 1 or class 2 ethernet cable that connects the gateway and powerwall, and if planning to but these in very far away places (e.g. gateway at the meter, and PowerWall in the basement where the solar inverters are for temperature control), run this or leave a conduit that you can fill later if you can do it without 360 deg of bends, etc. The Tesla installers use an ethernet cable that has a mains insulation rating so they can put it in the high voltage conduit. Note that you cannot just use regular ethernet cable even outside of a conduit since the instructions require class 1 wiring methods for the comms.

For the solar inverters and powerwall, just have a 60-100 amp subpanel in the basement. Watch out for the 120% rules etc. depending on your code cycle or just keep the solar/powerwall subpanel light (e.g. only the furance, and these future things.)

Sorry for the rushed message.

 

[PWDickerson]

Yes, just run a 1" conduit from the PV inverter location to the attic below the likely solar roof surface. This conduit needs to be metal unless the plan is to use micro-inverters.

You will need to think about how rapid shutdown is going to work. We usually install SolarEdge, and we run the AC circuit through a switch at the exterior.

The other replies have just scratched the surface with regard to the PowerWall. You will want to read up on that. I like the idea of putting all the large loads (oven, dryer, car charger, hot tub, heat, snow melt) in one of the 200 A panels, and everything else in the other. Make sure you can install the backup Gateway between the meter and the panel to be backed up. Also, if the PV system is big and there are multiple PowerWalls, that may require a "generation panel", which is a panel dedicated to just that equipment. It is in parallel with the backed up panel and might need to be rated at 200A.

Run an ethernet cable to the PV inverter location as well as the PowerWall location.

 

[mkgrady]

How do you plan to comply with the 2020 230.85 and outside ED's with 2 x 200-amp panels?

Permit was pulled in December 2019 so the 2020 code does not apply

 

[mkgrady]

Yes, just run a 1" conduit from the PV inverter location to the attic below the likely solar roof surface. This conduit needs to be metal unless the plan is to use micro-inverters.

You will need to think about how rapid shutdown is going to work. We usually install SolarEdge, and we run the AC circuit through a switch at the exterior.

The other replies have just scratched the surface with regard to the PowerWall. You will want to read up on that. I like the idea of putting all the large loads (oven, dryer, car charger, hot tub, heat, snow melt) in one of the 200 A panels, and everything else in the other. Make sure you can install the backup Gateway between the meter and the panel to be backed up. Also, if the PV system is big and there are multiple PowerWalls, that may require a "generation panel", which is a panel dedicated to just that equipment. It is in parallel with the backed up panel and might need to be rated at 200A.

Run an ethernet cable to the PV inverter location as well as the PowerWall location.

Holy cow. That is a lot to absorb and much appreciated Thanks to you and Chris for the thorough replies.

 

[PWDickerson]

If you specify main panels with a 225A bus, that will allow you to load-side connect a larger PV system than you would otherwise. Still won't be enough if you go with multiple Powerwalls.

 

[mkgrady]

Tomorrow I will try to draft a one line diagram of what might be a versatile setup. I’m sure there will be lots wrong with it due to my inexperience with solar and powerwalls. I will welcome any suggestions.

 

[wwhitney]

The main points for making an installation "Powerwall ready" have already been covered, but I would express it like this:

Arrange for a feeder that can be intercepted for installing the Backup Gateway that is (a) 200A or smaller and (b) feeds all the loads that you want backed up, and only the loads you want backed up. Make sure that feeder lands in a panel that can accept a main breaker, and that there is room for a generation panel.

The Backup Gateway has one set of lugs on the line side but two sets of lugs on the load side, so in my opinion the most efficient way to interconnect everything is to use the 705.12(D) provision for feeders. You can have separate 200A load and generation panels, all connected to a 200A feeder.

Cheers, Wayne

 

[GoldDigger]

Thanks. The one big gutter makes a lot of sense for maximum flexibility. See any drawback to using two 200 amp panels instead of one 400 amp? They are already asking for a sub panel on the second floor. Normally I would do this but now some decisions will have to be made about critical loads off that panel. It's probably better to have all circuits come back to the the main panel(s) area. This is frustrating because I don't know the capacity of the Powerwall because I don't know how many they will install or how many the solar can charge.

Maybe I should treat the circuits like I was wiring for a small standby generator. Just run everything critical to one sub panel in the basement. I'm really confused because I don't understand the Powerwall. Does the stored power get used (for free) at night when the solar isn't producing? If that is the case I would think they would want to use up all they could every night. That would mean I should connect more than critical circuits to this system.

During normal grid interactive / time shifting mode operation the PowerWall can supply current for any loads within its capacity, not just critical panel loads.

Sent from my XT1585 using Tapatalk

 

[mkgrady]

So the powerwall knows to only power a separate critical load panel when normal power is interrupted?

 

[GoldDigger]

So the powerwall knows to only power a separate critical load panel when normal power is interrupted?

Yes, in the sense that when grid is present the transfer switch to the critical load panel does not transfer, so critical and normal are in parallel.
Remember that the PowerWall operates just like a normal grid interactive inverter (but with the addition of local storage as an option) when the grid is present. It is only when the grid goes away that the transfer switch opens and PowerWall operates in stand-alone mode to power only the critical panel.
Note that the term transfer switch is not quite appropriate here, since the inverter stays connected to the critical panel at all times. It is really more appropriately called an isolation switch. But the function is very similar to that of a transfer switch.

 

[PWDickerson]

Yes, the Backup Gateway is more accurately described a an isolation switch rather than a transfer switch. The PowerWall will power everything on the load side of the Backup Gateway during a grid outage. And you can have two 200-amp panels on the load side of the Backup Gateway, a 200A panel with loads, and a 200A panel with PV and PowerWalls (called a generation panel). Alternately, you can have a single panel with both loads and generation (PV + PowerWall) if the 705.12 calculations allow.

 

[jaggedben]

If you specify main panels with a 225A bus, that will allow you to load-side connect a larger PV system than you would otherwise. Still won't be enough if you go with multiple Powerwalls.

This is among the many reasons I suggested not having distribution in the main. Another reason is the ease of installing site consumption CTs on the load side. What Wayne talked about is another possible reason.

As has been noted, there are so many details at stake that it's not really possible to cover everything, although with the multiple replies we are getting closer.

 

[jaggedben]

See the installation manual for the current PowerWall:

https://www.tesla.com/sites/default/files/pdfs/powerwall/Powerwall_2_AC_BU_NA-EN_Installation_Manual.pdf

The last big gotcha: need to have a class 1 or class 2 ethernet cable that connects the gateway and powerwall, and if planning to but these in very far away places (e.g. gateway at the meter, and PowerWall in the basement where the solar inverters are for temperature control), run this or leave a conduit that you can fill later if you can do it without 360 deg of bends, etc. The Tesla installers use an ethernet cable that has a mains insulation rating so they can put it in the high voltage conduit. Note that you cannot just use regular ethernet cable even outside of a conduit since the instructions require class 1 wiring methods for the comms.

It's not actually an ethernet connection. It's a modbus connection. You can use a 4 conductor shielded cable with one twisted pair. But I'm splitting hairs.