Wondering about generator use with Solar Roof and Powerwalls

[GregBallantyne]

I've got a fairly simple system, Solar Roof feeding single Gateway thru two inverters, with Powerwalls. Grid power, inverters, and Powerwalls connect to Gateway, and the Gateway feeds the load center thru the 200A main breaker. It's been in operation since mid June of 2023. Grid power outages are common here, so before getting the solar system I used a generator during outages. The generator puts out a 30A 240V circuit, which feeds my load center bus thru a sub panel from the barn. I was in the habit of manually isolating from the grid to do this.

Yesterday, wind took out our power once more via downed trees interrupting the supply. The initial estimate from BGE was about 3 days for restoration, they had many outages from the large storm. I'm only generation about 12-16 kwh on a good day this time of year, so even tho I had charged my batteries to 100% before the montages I was not certain about how long an outage I could weather. It only ended up a 17 hour outage, and we didn't run the heat pump, just ran backup propane heat. Got decent sun today, and might have made 3 days or more with low use and decent generation.

But.... I began to think about running the generator. I thought of two possible ways of doing this:
1. Wait until the powerwalls go low, throw the main to isolate from the Gateway, and use generator power as before, or
2. Run the generator at night, depending on the Gateway for grid isolation, to power low-level demand and charge Powerwalls

I don't know if that second method is actually feasible. Does anyone have any suggestions or opinions?

 

[jhn_]

I've got a fairly simple system, Solar Roof feeding single Gateway thru two inverters, with Powerwalls. Grid power, inverters, and Powerwalls connect to Gateway, and the Gateway feeds the load center thru the 200A main breaker. It's been in operation since mid June of 2023. Grid power outages are common here, so before getting the solar system I used a generator during outages. The generator puts out a 30A 240V circuit, which feeds my load center bus thru a sub panel from the barn. I was in the habit of manually isolating from the grid to do this.

Yesterday, wind took out our power once more via downed trees interrupting the supply. The initial estimate from BGE was about 3 days for restoration, they had many outages from the large storm. I'm only generation about 12-16 kwh on a good day this time of year, so even tho I had charged my batteries to 100% before the montages I was not certain about how long an outage I could weather. It only ended up a 17 hour outage, and we didn't run the heat pump, just ran backup propane heat. Got decent sun today, and might have made 3 days or more with low use and decent generation.

But.... I began to think about running the generator. I thought of two possible ways of doing this:
1. Wait until the powerwalls go low, throw the main to isolate from the Gateway, and use generator power as before, or
2. Run the generator at night, depending on the Gateway for grid isolation, to power low-level demand and charge Powerwalls

I don't know if that second method is actually feasible. Does anyone have any suggestions or opinions?

If your 200A main panel is is now fully backed up from the gateways (ie - main panel from before Powerwall install was turned into backup loads panel after install). And the sub panel and generator isolation switch are wired into the 200A panel, then yes you can run your generator just like before Powerwalls, just isolate the 200A panel by throwing its main breaker for extra grid safety, or if your transfers switch supports, just do the loads there.

 

[Marktm250]

Possibly I'm off-base on this, but seems that use of the generator (with solar that is DC coupled) would be a function of the inverters - in an off-grid mode. Does it have a "generator" input as most hybrid inverters provide? If AC coupled (my limited Powerwall knowledge),I'm sure you'll get some good advice from this forum.

 

[nyprepper]

I've got a fairly simple system, Solar Roof feeding single Gateway thru two inverters, with Powerwalls. Grid power, inverters, and Powerwalls connect to Gateway, and the Gateway feeds the load center thru the 200A main breaker. It's been in operation since mid June of 2023. Grid power outages are common here, so before getting the solar system I used a generator during outages. The generator puts out a 30A 240V circuit, which feeds my load center bus thru a sub panel from the barn. I was in the habit of manually isolating from the grid to do this.

Yesterday, wind took out our power once more via downed trees interrupting the supply. The initial estimate from BGE was about 3 days for restoration, they had many outages from the large storm. I'm only generation about 12-16 kwh on a good day this time of year, so even tho I had charged my batteries to 100% before the montages I was not certain about how long an outage I could weather. It only ended up a 17 hour outage, and we didn't run the heat pump, just ran backup propane heat. Got decent sun today, and might have made 3 days or more with low use and decent generation.

But.... I began to think about running the generator. I thought of two possible ways of doing this:
1. Wait until the powerwalls go low, throw the main to isolate from the Gateway, and use generator power as before, or
2. Run the generator at night, depending on the Gateway for grid isolation, to power low-level demand and charge Powerwalls

I don't know if that second method is actually feasible. Does anyone have any suggestions or opinions?

I have the same situation/set-up. I have a sub panel with a set of critical circuits that I can isolate and run off my 5kw Yamaha gas generator in a scenario in which my PW's are depleted or malfunction. In 4 years with Solar/PW I have not had to use this contingency, knock on wood. I lose grid power frequently and am a huge fan of redundancy. Unfortunately, in our scenario of running the generator on the isolated sub-panel the PW's will not charge.

 

[GregBallantyne]

If your 200A main panel is is now fully backed up from the gateways (ie - main panel from before Powerwall install was turned into backup loads panel after install). And the sub panel and generator isolation switch are wired into the 200A panel, then yes you can run your generator just like before Powerwalls, just isolate the 200A panel by throwing its main breaker for extra grid safety, or if your transfers switch supports, just do the loads there.

But... if I throw the main, I can't charge Powerwalls, because I'm also isolated from the Gateway and Powerwalls,. I think that method is feasible - but the ability to charge Powerwalls from generator power is a real advantage. I'd rather charge Powerwalls at night via generator, and run the house during the day with Powerwalls. I can get 90A from them, start heat pump, etc...
Or as you suggest connect the generator to the Gateway as another "grid". Too much modification for what I'm thinking about I suppose, but could certainly be an answer. I think there are installers out there who do exactly that sort of thing. I'm hoping to use what's currently in place. My number 2 method may not be feasible.

 

[CrazyRabbit]

There are 56v generators, ecoflow come to mind, that could be connected to the correct amount of micro inverter and if connected to your generation panel could charge your powerwalls…. Waiting for someone to do this.

 

[Matt-FL]

What if you somehow got your 5kw generator to supply power to your panel and charge the powerwalls, how would the PWs know to not charge at full wattage? Seems like it could request more power than the generator could supply which could cause a brown-out or other issue.

I think I would go with leaving the main panel breaker off, and let solar run on its own and charge batteries during the day, and evaluate each evening whether to continue the generator or switch back to solar/powerwalls.

Interesting scenario, curious to hear other thoughts.

 

[GregBallantyne]

I have the same situation/set-up. I have a sub panel with a set of critical circuits that I can isolate and run off my 5kw Yamaha gas generator in a scenario in which my PW's are depleted or malfunction. In 4 years with Solar/PW I have not had to use this contingency, knock on wood. I lose grid power frequently and am a huge fan of redundancy. Unfortunately, in our scenario of running the generator on the isolated sub-panel the PW's will not charge.

Mine generator is a little larger, but I was using it as a whole house backup. Of course with limitations - I couldn't start the heat pump, or anything else with a starting loads greater than the supply of a 30A 240V circuit. I'm certain I could run the same way, but ability to charge the PWs is of great interest. I'd rather get some input rather than just trying it.....

 

[GregBallantyne]

What if you somehow got your 5kw generator to supply power to your panel and charge the powerwalls, how would the PWs know to not charge at full wattage? Seems like it could request more power than the generator could supply which could cause a brown-out or other issue.

I think I would go with leaving the main panel breaker off, and let solar run on its own and charge batteries during the day, and evaluate each evening whether to continue the generator or switch back to solar/powerwalls.

Interesting scenario, curious to hear other thoughts.

My generator is larger than 5kw, it's 7.5kw. Not that it matters to your question tho.... When my PWs charge from the grid, they are limited somehow and draw 5.8kw anyway - that is the same as a 30A 240V circuit. When charging from solar production, they can take 3 times that. Or, when Stormwatch actuates, I've seen them draw 12kw from grid. I'm not sure at all what or where the control of that comes from, must be the Gateway.... But, if I could charge them at night from the generator when house loads are in the 300-600 watt range, I could fill them in about 7 hours or so depending on starting level of charge. Then I could self power indefinitely.

 

[GregBallantyne]

There are 56v generators, ecoflow come to mind, that could be connected to the correct amount of micro inverter and if connected to your generation panel could charge your powerwalls…. Waiting for someone to do this.

I'd be interested in that, but this other method is currently in place, with no new equipment or wiring required. I'm just not sure about feasibility. And maybe a bit chicken to just try it!

 

[GregBallantyne]

Possibly I'm off-base on this, but seems that use of the generator (with solar that is DC coupled) would be a function of the inverters - in an off-grid mode. Does it have a "generator" input as most hybrid inverters provide? If AC coupled (my limited Powerwall knowledge),I'm sure you'll get some good advice from this forum.

My generator circuit sends power directly to my load center bus, by back charging a sub panel. I'm wondering if, without grid power, excess load center power would be routed to Powerwalls by the Gateway. I guess that would have to be how it could happen. The Gateway decides where any power goes. Now that I think about that, the Gateway would need to do something that it's current operation modes that I've seen do not do. Direct power from the load center toward the PWs. Perhaps it cannot....

 

[miimura]

The only safe way to use a generator with the OP’s configuration is to turn off all the breakers for the solar and PowerWalls and Grid. The generator will power the house the same way as before the Tesla equipment was installed. All supported generator configurations require isolation from the solar and PowerWalls. You cannot charge PowerWalls from a generator.

 

[GregBallantyne]

The only safe way to use a generator with the OP’s configuration is to turn off all the breakers for the solar and PowerWalls and Grid. The generator will power the house the same way as before the Tesla equipment was installed. All supported generator configurations require isolation from the solar and PowerWalls. You cannot charge PowerWalls from a generator.

The reason I haven't just tried it. I guess my number 2 method is not feasible. At least the number 1 is, as a last resort.

 

[miimura]

The only feasible way of charging PowerWalls from a generator is to rectify the AC power and run it through a solar inverter and make the PowerWall system think it is solar power. However, I have never seen a description of how to do this in a properly engineered way that considers electrical safety standards.

 

[cali8484]

Is your 7kW generator an inverter generator? And is 7kW rating continuous? If so, if you turn off the solar, all loads and turn on only 1 PW (no export allowed mode) then it may work. The generator would substitute for the grid.

 

[wwu123]

The only feasible way of charging PowerWalls from a generator is to rectify the AC power and run it through a solar inverter and make the PowerWall system think it is solar power. However, I have never seen a description of how to do this in a properly engineered way that considers electrical safety standards.

I've been reading about things called Chargeverter's in the DIY solar forums, they're generally discussed in the context of using a gas/propane generator to provide backup to solar generally in off-grid solar/battery scenarios. They can take modified sine wave output from cheap generators, and are not necessarily that expensive. However, since they're more for off-grid batteries, they're designed more for 12V/24V/48V DC output since that's what DIY battery banks typically use.

So not sure if they provide the proper DC voltage and amps to feed into the OP's solar inverters, which the specs are not specified. And in any case some wiring would need to be modified to decouple the solar roof and couple the generator to the inverter DC inputs.

 

[BGbreeder]

The only feasible way of charging PowerWalls from a generator is to rectify the AC power and run it through a solar inverter and make the PowerWall system think it is solar power. However, I have never seen a description of how to do this in a properly engineered way that considers electrical safety standards.

One would also need to have a signal to shutdown the generator as the supplied power exceeds what the batteries are willing / able to accept. Generators generally don't respond well to upward frequency shifts...

To the OP's (@GregBallantyne's)original questions, the Powerwall installation manual makes it very clear that the only allowed generator configuration is to island the Powerwall and solar away from the house and generator via a transfer switch. Completely off grid Powerwall installations were allowed, but there was a short list of permitted generators. It is not clear to me that completely off grid is still a supported configuration, but regardless, #2 of @GregBallantyne's configurations is a no go.

This has been covered in depth on TMC.

Off Grid

Looking at a house that is totally Off Grid. Has solar and diesel generator. Not sure about batteries. I've heard that Powerwalls are not the best for totally Off Grid. Comments?

teslamotorsclub.com

Charging off whole home Generac generator

Came home to no power. We have a 21 (whatever) whole home Generac Generator. Anyone ever charge off one of these before I plug in and take down the local grid?

teslamotorsclub.com

And others as well...

My personal takeaway is that is not simple, and the potential to damage some expensive electronics comes up, though I guess if a solar array, some Powerwalls, and generator system are pocket change one might have a different viewpoint...

All the best,

BG

 

[RKCRLR]

As mentioned, using a generator to charge the PowerWalls is theoretically possible. But it would need to be connected as a solar generation system with:
1) Its output mimicking the output of a solar generation inverter.
2) Be able to be controlled like a solar inverter and shut down when the batteries are full.

I'm not aware of any generators that can do this. It would be interesting to see if someone comes up with a generator output adapter that can do this.

 

[CrazyRabbit]

As mentioned, using a generator to charge the PowerWalls is theoretically possible. But it would need to be connected as a solar generation system with:
1) Its output mimicking the output of a solar generation inverter.
2) Be able to be controlled like a solar inverter and shut down when the batteries are full.

I'm not aware of any generators that can do this. It would be interesting to see if someone comes up with a generator output adapter that can do this.

It’s what we have all been talking about for years. It be nice if a inverter generator mfg would do this, perhaps with a switch to change mode.. so theoretically I could connect to grid during a $5k per megawatt event and make money

 

[RKCRLR]

It’s what we have all been talking about for years. It be nice if a inverter generator mfg would do this, perhaps with a switch to change mode.. so theoretically I could connect to grid during a $5k per megawatt event and make money

I'm not an EE but I can envision a kludge project for someone with more money than brains (and you would still need a lot of both).

Plug in an AC to DC power transformer to the generator capable of simulating the power output of solar panels and handling the maximum output of the generator.

Connect the transformer output to a solar inverter that "clips" at the maximum generator output.

Connect the inverter output to the Gateway just like any other "solar" generation system.

Not elegant or efficient but it might work. But be prepared to let the magic smoke out of something including the powerwalls, solar, or house.