Whole home generator backup with Tesla Powerwalls

[Tank11]

I'm working on a large residential home (1000-amp service) and the owner is requesting full generator backup. There will also be a 20 kW PV system and (4) Tesla Powerwalls. I'm looking for the best solution to integrate these two systems. The owner does not want a manual transfer switch to turn the Powerwalls on and off, they are looking for a hands-off solution.

Would a relay work to disconnect the solar PV from the Powerwalls while in generator mode? Would the Gateway still work? I'm thinking it would be the same as if it were nighttime.

Any help is much appreciated.

 

[gadfly56]

I'm working on a large residential home (1000-amp service) and the owner is requesting full generator backup. There will also be a 20 kW PV system and (4) Tesla Powerwalls. I'm looking for the best solution to integrate these two systems. The owner does not want a manual transfer switch to turn the Powerwalls on and off, they are looking for a hands-off solution.

Would a relay work to disconnect the solar PV from the Powerwalls while in generator mode? Would the Gateway still work? I'm thinking it would be the same as if it were nighttime.

Any help is much appreciated.

Four Powerwalls don't sound like enough to carry a home with a 1,000 amp service through a winter night, let alone for a couple of cloudy winter days. What is the exact scenario they are trying to cover?

 

[Tank11]

Very good point and I should have been more clear. The Powerwalls will only power a fraction of the overall electrical system via a backup loads panel.

 

[gadfly56]

Very good point and I should have been more clear. The Powerwalls will only power a fraction of the overall electrical system via a backup loads panel.

Is the generator going to feed the same, and only the same backup loads?

 

[jaggedben]

My Powerwall training might be a little out of date but to my knowledge there is no true way to integrate the systems. The best you could do is regular automatic transfer switches either ahead of the gateway or downstream of the Powerwalls and solar and ahead of the backup loads panel. Unlike with some other systems, it is not possible to my knowledge to have the Powerwalls sync with the generator or to have the generator charge the batteries.

You have completely confused me by stating 'whole home' in the subject, then saying the Powerwalls will only power a fraction of system, i.e. partial home.

If it is truly just partial home backup, then your oversimplified line diagram could be essentially:

service ---> non backed up panel ---> Gateway ---> Powerwall and Solar connections ---> ATS for generator ---> backed up loads panel.

This arrangement makes the generator a secondary backup system for the Powerwalls and solar if the batteries run out. Getting this to operate smoothly when the solar is ready to recharge the Powerwalls could be a challenge.

If it is intended that the generator power loads that are not backed up by the Powerwall system, I have more questions, beginning with: what is the point?

 

[Tank11]

Great questions jaggedben. By 'whole home' I mean that the generator backs up the entire system, not just critical or selected loads. In addition, the powerwalls will only power a 'backed up loads' panel.

If there were an extended outage, where the generator is on via natural gas, the PV and powerwalls do not play together well with the generator. Without having to manually or monitor the situation, would the system work by shutting down the PV and just running the home from the generator? Including the 'backed up loads' panel, through the gateway from the generator?

 

[wwhitney]

So you'd like all the generator to backup everything, but the PWs for only partial backup. What is the point of the PWs, to provide additional backup power when the grid is down and the generator dies? Or to allow the PV to continue functioning while the grid is down, and thereby to reduce the load on the generator/extend the generator's run time? The latter is hard to do with PWs, to my understanding, assuming you still want the generator to power those loads if the PWs run out of energy.

Cheers, Wayne

 

[synchro]

There might be an advantage having the Powerwalls if they can handle the essential loads overnight and therefore avoid noise from the generator while people are sleeping.

 

[jaggedben]

Yes the goals of having the Powerwalls here are still unclear. To save generator time? To save fuel? As a secondary backup?

... Without having to manually or monitor the situation, would the system work by shutting down the PV and just running the home from the generator? Including the 'backed up loads' panel, through the gateway from the generator?

No, it would not. Not in any simple way.

Enphase Ensemble will support generator integration soon. So do some others. There are limits to the size of the generator though. One wonders how many of the 1000 amps are truly necessary or will be used in an outage.

 

[Tank11]

In this jurisdiction, batteries are required with any PV system over 10 KW. The owners also want full generator backup for extended outages, thus the requirement for both systems. Therefore back to my original question, for both systems to work I see the easiest solution being to shut off the PV and let everything else function as if it were on grid power (but on generator).

 

[gadfly56]

In this jurisdiction, batteries are required with any PV system over 10 KW. The owners also want full generator backup for extended outages, thus the requirement for both systems. Therefore back to my original question, for both systems to work I see the easiest solution being to shut off the PV and let everything else function as if it were on grid power (but on generator).

OK, that was important information regarding the batteries. I think you have the correct solution, dump the PV and let the generator handle everything. In which case, you can also lose the emergency panel for selected loads.

 

[Terminator5047]

Main tie main. Tie switch gear

 

[jaggedben]

In this jurisdiction, batteries are required with any PV system over 10 KW. The owners also want full generator backup for extended outages, thus the requirement for both systems. Therefore back to my original question, for both systems to work I see the easiest solution being to shut off the PV and let everything else function as if it were on grid power (but on generator).

You seem to think that the PV cannot work with the generator but the Powerwall can. This is wrong. The PV and Powerwall can work with each other. Neither can work with the generator.

You could do something a little Rube Goldberg and two ATSs on site, and use the Powerwall+PV as either a separately system that is backed up by the generator, or as a partial backup to the generator if it fails or runs out of fuel.

Or you could waste the backup capability of the Powerwalls and connect them and the PV on the line side one whole home ATS. What gadfly suggested.

Or you could use a solution other than Powerwall.

 

[texie]

In this jurisdiction, batteries are required with any PV system over 10 KW.

A jurisdiction requires storage? That's a first for me. I find it amazing that the public accepts some of these government edicts.

 

[wwhitney]

A jurisdiction requires storage? That's a first for me. I find it amazing that the public accepts some of these government edicts.

Seems more likely to be a POCO requirement, for a POCO that doesn't want too much solar exported.

Cheers, Wayne

 

[wwhitney]

You could do something a little Rube Goldberg and two ATSs on site, and use the Powerwall+PV as either a separate system that is backed up by the generator

I don't see a second ATS as "Rube Goldberg," and it could be worthwhile, depending on the owner's desires. Namely:

Select up to 200A of loads and up to 200A of inverters (after the 125% factor). Those loads are connected as Grid -- GW --Inverters -- 2nd ATS -- Loads. Everything else is connected separately as Grid -- Other Inverters -- 1st ATS -- Other Loads.

Cheers, Wayne

 

[jaggedben]

I don't see a second ATS as "Rube Goldberg," ...

Yeah, I said 'a little' Rube Goldberg.

 

[thekwhour]

to many manufacturers all trying to play nice with each other. Doubt it will happen. Your gonna be doing service calls for years chasing down communication issues and troubles hooting who isn't working with who. Tell these homeowners to go with a Ensemble System by Enphase. Better system, better product, better results. just saying

 

[iustacould]

Was there ever a solution to this problem? I have a similar situation using Enphase with a custom home coming up in a few months. I'm meeting with the Greentech guys tomorrow but if anyone had a solution to present other than "scrap the PV" or "you don't need it" I'd love to hear (read) it. It seems the issue is communication between the generator ATS and the PV system pertaining to the schedule of events, should an issue occur (aka ITTT). If I get a good answer from the meeting tomorrow I will post it as well. Thanks

 

[thekwhour]

Was there ever a solution to this problem? I have a similar situation using Enphase with a custom home coming up in a few months. I'm meeting with the Greentech guys tomorrow but if anyone had a solution to present other than "scrap the PV" or "you don't need it" I'd love to hear (read) it. It seems the issue is communication between the generator ATS and the PV system pertaining to the schedule of events, should an issue occur (aka ITTT). If I get a good answer from the meeting tomorrow I will post it as well. Thanks

Yes Enphase has the Enpower that allows for PV shedding and load control.