PGE requirement, what does this mean? Meaning, if you put in batteries with no solar, Tesla does grid charging and I assume PGE has no issues. So why would adding solar make any difference?
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For folks with 2 Gateways, do things cross charge?
- Thread starter h2ofun
- Start date
RKCRLR
Active Member
It's the whole charging from the grid thing when you have solar. Tesla said PG&E wouldn't allow charging from the grid when you have solar. However, PG&E has told me it is OK with them. I haven't gone back to Tesla to tell them that.
Bottom line is if Tesla doesn't want to allow charging from the grid when you have solar, they don't have to.
Yep, I get the feeling they just point the finger back and forth, for whatever reason. But we do have the person I believe in Arizona who did get Tesla to enable grid charging when he has solar. So not impossible. And technically, it does not look that hard to do, but that is a different topic
I assume the automatic transfer switch has a delay for the generator to start up?
If your load calc is under 200A, then you could do the following if the AHJ will allow the use of 2020 NEC 705.13 (not yet adopted in CA):
Put 1 Gateway, 6 Powerwalls and solar behind one 200A service disconnect (I'm assuming that 1 Gateway is limited to 6 Powerwalls, if not you could use 7). This is more than 200A of inverters on a 200A service, hence the requirement for 2020 705.13, which recognizes that the Powerwalls can be programmed to ensure the total export never exceeds 200A.
Put the Gateway CTs around the joint service conductors, so the Powerwalls can offset usage from both sides during grid operation. As the other side is only 200A, that will never entail exporting more than 200A through the Gateway.
- Add an automatic transfer switch, so that when the grid is down, the service without the Gateway switches its power source from the grid to a feeder from behind the Gateway.
This in effect gives you a 400A service when on the grid, and an up to 200A Powerwall based supply when the grid is out. But it depends on the total load calc being under 200A. If it is over, you could presumably do the same thing you have with the generator, which is put some modules on some of the load to drop out before the automatic transfer switch operates, so those loads would never be backed up.
Heck, if your load calc is under 200A, you could just switch to a 200A service, i.e. put the Gateway with a 200A main breaker between the meter and your two 200A feeders.
Cheers, Wayne
Wayne, thanks for the inputs, got the wheels rolling. Just finished a few emails, and a long phone call.
I got a new wrinkle to my design. One cannot share SGIP and non SGIP batteries. The SGIP batteries must report on their own
Gateway(s). They cannot have any other batteries tied into them as the standard setup.. So, we are having to rethink the design based on this, plus I added your idea.
So, what do you think about this. I connected the 5 sgip batteries to a generation panel with all my existing solar and it drives a gateway connected to my subpanel with all my heat/.air mini splits. This clearly is my largest load so this allows me to meet the cycling sgip requirements.
I then buy 2 more batteries, and install them into my second gateway that is connected to my house. Since I would not drive any solar into these batteries, the gateway would set these for grid charging. I could just leave them for power outage only mode.
But, Could I then put in a automatic transfer switch between the garage generation panel and gateway, so that when power goes out,
that panel with the 5 batteries and solar also connect into the house generation panel? Then those 2 batteries will be charged from solar also? Is this technically possible?
Glad we found this sgip requirement now before we had things installed and sgip failed the system.
So, by me asking questions, we have avoided one huge system redesign and having to tear it apart.Have you considered just having the 5 SGIP Powerwalls? That would be much simpler. I haven't heard of this need to segregate, I wasn't aware that I would be prohibited from adding non-SGIP Powerwalls to my SGIP Powerwalls.
As to the question of the transfer switch with two different sets of Powerwalls operating in off grid mode, that exceeds my knowledge of the product. I'm guessing that in off grid mode, multiple Powerwalls need to be connected via the communications cable in order to coordinate their behavior. [E.g. 1 Powerwall, no problem, it just charges if there is excess power from PV, and discharges otherwise. But for 2 or more Powerwalls, how do they split the charging behavior when there is excess PV? Or split the discharge required when there is net demand?]
If so, then the transfer switch idea wouldn't allow all 7 Powerwalls to charge and discharge during a protracted outage. You could put a transfer switch between Gateway 2/Powerwalls 6-7 and their loads. Then in a power failure, Powerwalls 6-7 would power the Gateway 2 loads until depleted; after that the transfer switch would eliminate the extra equipment from the system, and everything would run from Gateway 1 and Powerwalls 1-5. So your storage capacity at that point would be reduced by 2/7, but depending on your daily solar production and daily usage that might not matter.
Cheers, Wayne
As to the question of the transfer switch with two different sets of Powerwalls operating in off grid mode, that exceeds my knowledge of the product. I'm guessing that in off grid mode, multiple Powerwalls need to be connected via the communications cable in order to coordinate their behavior. [E.g. 1 Powerwall, no problem, it just charges if there is excess power from PV, and discharges otherwise. But for 2 or more Powerwalls, how do they split the charging behavior when there is excess PV? Or split the discharge required when there is net demand?]
If so, then the transfer switch idea wouldn't allow all 7 Powerwalls to charge and discharge during a protracted outage. You could put a transfer switch between Gateway 2/Powerwalls 6-7 and their loads. Then in a power failure, Powerwalls 6-7 would power the Gateway 2 loads until depleted; after that the transfer switch would eliminate the extra equipment from the system, and everything would run from Gateway 1 and Powerwalls 1-5. So your storage capacity at that point would be reduced by 2/7, but depending on your daily solar production and daily usage that might not matter.
Cheers, Wayne
This sounds like the right answer. If PW 6-7 don't have any solar, just have a transfer switch power their loads from PW 1-5 after the 6-7 batteries are depleted and leave the dead PWs and GW alone until the grid comes back. After the grid comes back the transfer switch would switch the loads back to their original Gateway.
Yep, we just found out about the sgip requirement, so having to rethink.
when you say just use 5 pw's. I still have to backup 2 homes. so if I split, I still have the issue of reporting, and we do not know if SGIP will allow them to be split and having to report from 2 gateways.
Yep, you cannot have non SGIP, and it maybe ER batteries, to share with sgip. (I did not ask about non ER since that is was we are designing for).
I have no idea about cross sharing batteries with communications cables, over me head also.
Interesting idea about the 2 batteries. If we assume they just get depleted, would not kill me since I could use the generator for that leg then if needed.
2 homes? Do you mean (2) 200A feeders from your meter? With 5 Powerwalls behind one Gateway on one 200A feeder, you could still use the transfer switch idea (my post from this morning) to back up the other 200A feeder in the event of a power failure.
Cheers, Wayne
Another piece of data I did not know?
Unfortunately we cannot have the batteries or solar hooked up to more than one Gateway. I understand what you're thinking for the physical setup, but Tesla does not allow for the batteries or solar to be shared between multiple Gateways.
I am also asking can SGIP ER batteries be even split between 2 gateways. So many details in this darn configuration since I have 2 must load panels I cannot rewire
Yea, just trying to make the point I am basically doing two homes kinda since I have 2 200 amp panels with must things to power, that
cannot be rewired.
Your first transfer switch idea engineer did not like.
I just passed along your second transfer idea.
Another is I just use the 5 batteries, split into 2 GW's, split the solar, assuming the SGIP ER batteries can go between 2 gates.
Details, details. Stupid house
I haven't proposed that.
I'm not sure why, it's the idea I like best so far (if load calc works out).
Cheers, Wayne
CrazyRabbit
Active Member
@h2ofun
do not install two gateways, DO the alternative loads calc and you will be fine. but move the spa, car charger, shop to a non backup panel.
i have three electric heaters/ac (2x 9.75kw, 1x 15kw), resistance hotwater, electric dryer, oven, 10kw induction stove top, 3hp well and am putting both my 200 amp panels on a single gateway with 8 powerwalls and 16kw solar (400amp generation panel) all on a gutter with bus bars.
my utility is still freaking out that i'm over 200 amps of generation, they are counting the powerwalls and solar! they say transformer can only handle 200 amps of generation, i say i'm protected by software and 200 amp breaker.
do not install two gateways, DO the alternative loads calc and you will be fine. but move the spa, car charger, shop to a non backup panel.
i have three electric heaters/ac (2x 9.75kw, 1x 15kw), resistance hotwater, electric dryer, oven, 10kw induction stove top, 3hp well and am putting both my 200 amp panels on a single gateway with 8 powerwalls and 16kw solar (400amp generation panel) all on a gutter with bus bars.
my utility is still freaking out that i'm over 200 amps of generation, they are counting the powerwalls and solar! they say transformer can only handle 200 amps of generation, i say i'm protected by software and 200 amp breaker.
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Lets just assume the load calcs would not work out.
My latest leaning is to put 5 PW's on one GW connected to my subpanel with all my mini split heating/air, since they clearly take the most
steady state power. Connect all my solar to these
Then if I get 2 more PW's with a second GW, since this would have no power, just have these charged from the grid.
Still would like to put a ATS on the output of the first GW to the output of the second GW. This way if the 2 batteries die, it triggers the ATS to bridge over to the GW with 5 batteries. If they die, then the ATS's for the generator kicks in. But, not sure the engineer likes
this ATS bridge idea. Seems like a great one to me. And, I get 2 batteries with grid charging. If so, only 5 more to go
With an ATS, you need a load calc to show that the connected load does not exceed the available alternate source power. A manual transfer switch does not have that limitation.
Also, the ATS would receive its second source of supply from behind the first GW, and it would be located between the second load panel and the second GW/Powerwalls. Then if you also have an engine generator, its ATS would be between this new ATS and the second load panel.
Cheers, Wayne
I keep wondering how my generator was installed when I do not believe a load calc was done. If it was, never really saw it. I just assume if I try to pull more than 96 amps, the generator breaker blows, and I assume this is okay.
So assuming same thing would happen with the GW. If I tried to pull more than 200 amps from both panels, would the breaker just now blow, but it would be totally safe?
Interesting a manual transfer switch would be okay. What size would I want? A MTS would be better than nothing I think.
Is behind the output? I am assuming the first GW as the solar and 5 batteries. Its output drives my ATS for the generator, which drives my garage subpanel.
I then put the switch on the output of GW2 but before the second ATS for the generator. The input is the GW2 output. The switch in normal position drives the ATS for the generator. In the batteries are dead situation, the becomes the line connected to the output of GW1 which is before the ATS for the generator. Do I have this right?
What a pain!! One option is to put no batteries on my house panel, and if I lose power, just let the generator connect to it like it did today when we lost power.
Will see if I get feedback from engineer today. Maybe I need to draw something up
SoundDaTrumpet
Member
@h2ofun +1 I am also thinking of adding non-SGIP batteries to my 2PW SGIP system. I am currently under small residential category, so deciding to apply/decline incentives to add-on PWs will surely complicate matters.
I was hoping to avoid installing a 2nd Gateway. I have partial backup on a 125A branch breaker on a MLO service panel. The other loads are 2 A/C and 1 Tesla HPWC v1. I could add 2PWs on the 2nd gateway to power the SGIP system downstream. I assume I can charge from grid on the 2nd gateway. Although I am kW constrained, I can still increase overall capacity. I hope what I wrote above check out with you folks.
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My current assumptions. SGIP batteries cannot be shared on same GW are non sgip batteries. SGIP batteries must be 100% solar charged, even though I am asking why but am not assuming I will be successful. I assume if I buy non sgip batteries, put on a second GW with no solar connected, they will enable them to charge from the grid. Are these your assumptions?
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