Powerwall 2 install.

[JSchnee21]

Sorry, I'm still not getting it. If the PowerWall's are wired such that they could see the entire load of the house (including the air conditioner(s)) I just don't see how such a system could pass engineering design review / inspection. It's not good enough to just say that you'll turn them off (been there, tried that).

You must demonstrate that the reasonably anticipated diversity of the load is not likely to exceed the current carrying capacity of the UPS/generator WITHOUT human intervention to shed loads. If load shedding is required (because the UPS/generator) is sized smaller than would be necessary, load shedding must be automatic. Hence separate UPS protected and non-UPS protected panels.

Two PowerWall's can provide 48.3 amps continuous and 60 amps peak (for 10s) at 240 VAC per spec's available (granted if one had access to the Tesla partner portal, more detailed specs are available). Any normally sized air conditioner (3-5 tons) will draw roughly 25-40 amps. Larger homes, say ~3000 square feet an up, often have two HVAC units here on the East Coast -- where its not that hot -- typically with a 3-4 ton for the first floor and a 2-3 ton for the second floor.

Here's a top of the line 20 SEER York, older, and less efficient units will draw even more when running.

http://www.upgnet.com/PdfFileRedirect/5331838-YTG-B-0517.PDF

The Condenser alone draws (all 240VAC):
3 ton 25.7 amps continuous (30 amp breaker), starting inrush will be at least 2x to 3x granted only for a second or two
4 ton 28.6 amps continuous (40 amp breaker), starting inrush will be at least 2x to 3x granted only for a second or two
5 ton 33.9 amps continuous (50 amp breaker), starting inrush will be at least 2x to 3x granted only for a second or two

Plus the blower fan in the air handler will use another 3 to 4 amps @240VAC, plus any other loads that might happen to be active in the house at the time the Poco power goes out.

All will be well until you're away at work one day, for example, and the compressor tries to cycle on automatically and stalls due to insufficient voltage/current from the inverter causing 1) a brownout in your home, 2) damage to your electronics / compressor while it tries to start with insufficient voltage, and 3) the PowerWall inverters sense the overload and shutdown abruptly dropping all of the other loads in your home (fish tank, security system, Solar PV, etc.)

Many such UPS systems will try to automatically restart when this happens and the system goes through these start, fail, stop cycles for hours until something fails -- compressor motor, starting capacitor, inverters, etc.

But, obviously, its not up to me. If your AHJ is willing to sign off on your engineering design AS IS covering the whole house mains panel, then that's up to them and you. But, it doesn't mean its going to work (well). Regardless, I suggest you find this out sooner rather than later as it could potentially cause a lot of re-work in your wiring design.

I agree it's close. But IMHO, either three PowerWalls or separate UPS/non-UPS panels is what would be needed from my perspective, Especially given little or no current consumption info. Unless the house is particularly small and we're talking room or mini split AC systems.

[sriram97]

Here's a description of the new app that's basically an update to the stock Tesla app. It seems to show the entire source and flow of power to the home and also apparently gives you alerts so in case of extended outages manual load shedding can be supported

https://www.google.com/amp/s/electrek.co/2017/04/20/tesla-powerwall-solar-app/amp/

[adoublee]

It doesn't. I talked to a Tesla rep about it and there is no regulation. Powerwall accepts energy until it can't any more; voltage rises and the microinverters (hopefully) trip off-line due to voltage out of range.

So Powerwall(s) have to be provided such that maximum solar current (inverter AC rated current) does not exceed battery current limits (assuming no load is present)? Other than that (and battery shutting itself and therefore the whole system down on low voltage when discharged) - no coordination between battery, solar, and load? I do like the idea of a whole whole house grid isolation switch (gateway) instead of a critical loads panel - then I can just manage the energy implications myself. That is a major benefit of the high power rating.

[sriram97]

Sorry I was not aware that solar edge also made microinverters and assumed that you were asking about their central inverters. If you meant the microinverter, fwiw I was not aware of and did not evaluate solar edge microinverters as an option.

No A/Cs in calculation. Yes backup is included. The enphase units allow me to monitor per panel performance. A central inverter was definitely less expensive

[sriram97]

One moreninfo clarification. I may have misspoke the gateway is a separate line item charge of 700 included in the overall price.

Thank you, they have interesting component there called 'Energy Gateway' which I assume would be the 'brain' of the whole setup- did you get that installed as well and included in the cost above?

How much did PV part of the system cost for 7.4kW array? I understand the inverter is built in into PowerWall so that must have provided some savings on PV side of things.

[sriram97]

No A/Cs in calculation. Yes backup is included. The enphase units allow me to monitor per panel performance. A central inverter was definitely less expensive

Just to ask, the OP, sriram97, why is he going with an Enphase solution versus SolarEdge? If the PowerWall 2 AC can communicate / coordinate with the StorEdge, wouldn't this be a better solution. The cost and performance should be pretty similar (or better) than an Enphase solution.

Still, we haven't really addressed the question as to whether or not only two PowerWall systems can carry his whole house (including HVAC). Nor have we found out whether he's getting the PowerWall's with or without backup.

[sriram97]

You are right I stand corrected.

Since the CA SGIP is a rebate you need to do the calculation as:
( 17k - 9,400 ) x 0.7 = $5,320

[JSchnee21]

Just to ask, the OP, sriram97, why is he going with an Enphase solution versus SolarEdge? If the PowerWall 2 AC can communicate / coordinate with the StorEdge, wouldn't this be a better solution. The cost and performance should be pretty similar (or better) than an Enphase solution.

Still, we haven't really addressed the question as to whether or not only two PowerWall systems can carry his whole house (including HVAC). Nor have we found out whether he's getting the PowerWall's with or without backup.

[sensij]

It doesn't. I talked to a Tesla rep about it and there is no regulation. Powerwall accepts energy until it can't any more; voltage rises and the microinverters (hopefully) trip off-line due to voltage out of range.

Answers my question!

[jflorey2]

How that is supposed to work without some 'energy governor': how battery AC would know it is supposed to handle house loads if PV is producing but its output is not enough?

It doesn't. I talked to a Tesla rep about it and there is no regulation. Powerwall accepts energy until it can't any more; voltage rises and the microinverters (hopefully) trip off-line due to voltage out of range.

[Sunking]

Now you're scaring me- I thought I left that place for good . That system (socialism) is not economically viable no matter who tried to make it work. Humanity must be insane to keep trying.

That is what Millennials are being taught in school today.

[SWFLA]

I would guess frequency curtailment that's how SMA does it.

[sensij]

How that is supposed to work without some 'energy governor': how battery AC would know it is supposed to handle house loads if PV is producing but its output is not enough? Or the opposite- it would need some current sensor on the grid side to determine direction of the power flow and make decision if it should let excess of PV energy to go to the grid or be consumed for charging battery.

Load shifting doesn't require the energy to come from PV, so the battery doesn't have to care *where* the energy is coming from, just *when* it is coming. The "backup" model requires more control than the load shifting model does, and adds a switch to disconnect from the grid. It looks like both models use CT's on the service panel feed to keep track of what is going on.

One case I don't understand with AC coupling a powerwall 2 to an Enphase PV system is when in backup mode (off grid), the battery is full, and PV potential exceeds the loads. What would force the PV system to throttle?

[max2k]

op used microinverters and AC coupled the battery, so no coordination between PV and the battery is required for load shifting. ...

How that is supposed to work without some 'energy governor': how battery AC would know it is supposed to handle house loads if PV is producing but its output is not enough? Or the opposite- it would need some current sensor on the grid side to determine direction of the power flow and make decision if it should let excess of PV energy to go to the grid or be consumed for charging battery.

[max2k]

You aren't paying for anything. You are contributing your fair share.
From each according to his ability (to be taxed).

Now you're scaring me- I thought I left that place for good . That system (socialism) is not economically viable no matter who tried to make it work. Humanity must be insane to keep trying.