PowerWall 2 Interface with a Generator

[NanoGrid]

If I was in this situation and had a hard deadline to get the system installed, I would plan for a different system that is designed for generator use. Hybrid inverters from Schneider and Outback power can handle generators elegantly, but they need 48VDC nominal battery packs. I have not checked, but the LG battery solution may be good for this application. When your deadline comes, at least you will have a good solution ready to go if Tesla doesn't work out.

Ah, but will the associated batteries allow my solar to operate during grid loss, as the Powerwall 2 would? It seems like, at present, I can't have my cake (off-grid solar) and eat it too (get reliable, full battery recharge) -- at least not for $5500, plus installation.

 

[Saghost]

Ah, but will the associated batteries allow my solar to operate during grid loss, as the Powerwall 2 would? It seems like, at present, I can't have my cake (off-grid solar) and eat it too (get reliable, full battery recharge) -- at least not for $5500, plus installation.

Yes, grid interactive battery based inverter systems with generator inputs will allow solar use during an outage. No, you won't be able to find a 5kW inverter and 13.5 kWh of batteries for $5500 in one of those systems, even with the much more common lead acid batteries.

 

[miimura]

Ah, but will the associated batteries allow my solar to operate during grid loss, as the Powerwall 2 would? It seems like, at present, I can't have my cake (off-grid solar) and eat it too (get reliable, full battery recharge) -- at least not for $5500, plus installation.

The normal way to set up these off-grid capable hybrid inverters is to use solar charge controllers, not grid interactive solar inverters. So, the solar power naturally goes directly into the batteries and the controllers are configured independently so that they don't overcharge the batteries. They just self curtail when the batteries are full. You can do AC coupling with standard grid-tied solar inverters, but the app notes I've seen do not do elegant frequency based curtailment of solar inverters, they just cut off that input with a relay/contactor until the batteries are low enough that they want the energy again.

The key point is that these systems that have the additional flexibility for on-grid and off-grid and generator integration are more expensive than the PowerWall. For example an 8kW Outback Radian is $4,500 without batteries, charge controllers, or any supporting installation hardware or labor.

 

[dhu1]

Just finished the install successfully with the generator link as well. So as the installers say, I have a backup on top of a backup. Will share if I encounter any issues. Tesla said I was the first on customer on the west coast to have this setup and if completed successfully, they will start rolling out to others.

 

[miimura]

Just finished the install successfully with the generator link as well. So as the installers say, I have a backup on top of a backup. Will share if I encounter any issues. Tesla said I was the first on customer on the west coast to have this setup and if completed successfully, they will start rolling out to others.

Just to clarify, you do NOT have solar, correct?

 

[fresnoboy]

With an off grid house, the battery charger is just another power consumer. If the total load exceeds the generators ability to maintain voltage, the system trips off.

The solar inverter matches the frequency of the generator, just as it does with mains power. So at a fundamental level here there is nothing new. Generator output simply replaces main power as and AC source.

That said, controlling all this with the user making choices as to priorities becomes complicated. Tesla starting with simple rules (empty battery first, then run the generator) is understandable. A highly flexible system may take a couple years. I doubt that the current generation of inverters and chargers will allow a fully flexible system. There will probably be edge safety and performance issues that need to be solved with new hardware.

In particular, seamless transition between modes is complicated when a generator is put in the mix.

Agreed. In some ways, it's pretty straightforward. But there are lots of edge cases that you have to be super careful with.

Even so, you can buy this solution today if you want to use DC batteries. See here for one: Hybrid Inverter for Solar Power - Conext XW+ 230V | SE Solar or this one: Outback Power Inc. - Radian Series GS8048A / GS4048A

The cool thing about these is that they can mix in solar power with generator power simultaneously, or kick the genset in when solar and batteries are inadequate, and also charge the battery. They have dual AC inputs to the inverter, one for grid, and another for generator. But it needs a DC battery system - it can't use the powerwall.

 

[dhu1]

Just to clarify, you do NOT have solar, correct?

I do have solar...here is a picture of the setup..relatively complicated

2017-10-18 15.20.33

• dhu1
• Oct 19, 2017

 

[fresnoboy]

Just finished the install successfully with the generator link as well. So as the installers say, I have a backup on top of a backup. Will share if I encounter any issues. Tesla said I was the first on customer on the west coast to have this setup and if completed successfully, they will start rolling out to others.

So can you tell me what happens when the power goes out? The PW kicks in, and when that is exhausted, the genset kicks in, right? The Genset doesn't charge the PW I know, but does Solar charge the PW, and if so, does it shut down the Genset and switch back to the PW when the battery hits a certain point?

 

[dhu1]

So can you tell me what happens when the power goes out? The PW kicks in, and when that is exhausted, the genset kicks in, right?]

Yes, that is the sequence.

Does Solar charge the PW, and if so, does it shut down the Genset and switch back to the PW when the battery hits a certain point?

Once the Genset kicks in, the PW will have been shut off. It will take a manual restart of the PW once the grid is back up to reset the entire system. The only way to shut down the genset is when the generator transfer switch senses the grid is back up. Having said that, while PW is operating, it will be working in conjunction with solar to either charge or offset home usage. So in reality, the PW usage will be much longer than the 26kwh storage since it will replenish from solar to the point where I can probably be off grid for a long period of time.

 

[fresnoboy]

Ok, that sounds modestly useful, though requiring a manual reset is really unfriendly. Do they have plans to make that automatic in the future?

What happens if you have more solar being generated than the home or the PW can take? Where does the power go? There would be no grid to send the excess to, and I assume the genset is disconnected in this case...

 

[dhu1]

Ok, that sounds modestly useful, though requiring a manual reset is really unfriendly. Do they have plans to make that automatic in the future?

I don't think so. The extreme use case where I would go through 25+kwh of electricity + solar generation and the generator is kicked in is something I doubt I would ever encounter. In the 6 years I have my generator, it has not run longer than 1-2 hours, so I can handle going on and flipping the switch once in a blue moon.

 

[dhu1]

What happens if you have more solar being generated than the home or the PW can take? Where does the power go? There would be no grid to send the excess to, and I assume the genset is disconnected in this case...

I asked about that scenario as well, they said that in the event that PW is at 100% and the excess electricity has no where to go (i.e. use in the house) or the grid, then that will trigger a shutdown of the inverter in the solar system. This is why I will unlikely ever keep my PW at 100%--most likely keep it around 70%.

 

[fresnoboy]

I asked about that scenario as well, they said that in the event that PW is at 100% and the excess electricity has no where to go (i.e. use in the house) or the grid, then that will trigger a shutdown of the inverter in the solar system. This is why I will unlikely ever keep my PW at 100%--most likely keep it around 70%.

Interesting. If that happens does the solar ever get turned on again, maybe when the PW his a certain level? That implies a control system between the PW and inverter. Do you have only one inverter or multiples?

 

[dhu1]

Interesting. If that happens does the solar ever get turned on again, maybe when the PW his a certain level? That implies a control system between the PW and inverter. Do you have only one inverter or multiples?

As it was explained to me, the solar system will turn back on once it senses that the grid is back on. Those are the only permutations I was able to ask the installers. Any other use cases, we'll see as time progresses.

 

[BobPaul]

Our situation is we have no grid connection at all. The plan is solar and Powerwall with a generator for when solar is not producing enough to charge the PW. We are hoping that an off-grid PW will work with system.

 

[miimura]

Our situation is we have no grid connection at all. The plan is solar and Powerwall with a generator for when solar is not producing enough to charge the PW. We are hoping that an off-grid PW will work with system.

You should ask Tesla about your specific situation because the solution presented in this thread will not work well for you. In a true off-grid situation, you need the generator to charge the batteries and you need the solar+Powerwall to avoid pushing power toward the generator.

 

[Saghost]

Interesting. If that happens does the solar ever get turned on again, maybe when the PW his a certain level? That implies a control system between the PW and inverter. Do you have only one inverter or multiples?

Normally the solar is turned back on as soon as the battery level drops, automatically (most systems use the anti islanding limits on voltage/frequency to enable/disable the solar inverter.)

I don't know for a fact that the Powerwall does this, but I'd be surprised if it doesn't.

 

[NanoGrid]

Normally the solar is turned back on as soon as the battery level drops, automatically (most systems use the anti islanding limits on voltage/frequency to enable/disable the solar inverter.)

I don't know for a fact that the Powerwall does this, but I'd be surprised if it doesn't.

Verifying that is the crux, for my proposed application. I would rather have the capability to restart the solar to meet minimum daytime demands and recharge the Powerwall for night operation than have to depend solely on the LP genset for all use after the first depletion during grid loss.
Our lot is on the Sonoma coast (with service subject winter winds and summer forest fires to the east), and is a mile on the Pacific side of the San Andreas fault, so multiday outages are possible.

 

[Krash]

...here is a picture of the setup...

So can you help us novices understand what you have here?

1. Powerwall
2. Powerwall
3. Solar Panel String Inverter
4. EV Charger
5. Tesla Junction Panel
6. Tesla Gateway
7. Sprinkler Controller
8. Generac Automatic Transfer Switch
9. Telco Junction Box
10. Utility Meter

Are there manual disconnect switches inside any? Or outside?

 

[dhu1]

1. Powerwall
2. Powerwall
3. Solar inverter
4. EV charger
5. Tesla junction panel
6. Tesla gateway
7. Sprinkler controller
8. Generac automatic transfer switch
9. Telco junction box
10.Utliity meter

Here is a photo from the other direction. The Tesla Gateway warehouses the main breaker for the entire house. The Tesla box has breakers specifically for the PW. I also sub panels and load centers inside the house, but none of those are specific to the PW--they were installed when I redid the electrical panels for the house. Hope that helps