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?

 

[miimura]

PS I was wrong about 1 item:

1) The bi-directional inverter does 400V and 800V DC fast changing, not 200V and 400V

I didn't understand this post until I saw the thread it was intended for:

First Powershare home installation

So far just a teaser.

teslamotorsclub.com

 

[CrazyRabbit]

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?

New solution. Buy a cybertruck and charge it with the generator and then connect truck to house!

 

[CrazyRabbit]

It would be cool if Tesla made a separate box with a generator disconnect switch that could be connected to your generation panel. Probably require a few chips to connect to canbus and check for stable voltage and have CT’s to monitor load be applied to generator.

 

[BGbreeder]

It would be cool if Tesla made a separate box with a generator disconnect switch that could be connected to your generation panel. Probably require a few chips to connect to canbus and check for stable voltage and have CT’s to monitor load be applied to generator.

This has been covered in other threads, but the electrical challenge is how to taper and shutoff the generator well before the batteries are full so there is never power pushed into the generator, something generators aren't designed to handle. Then there is the renewable energy component.

As that sort of control requires special programming, it would require solid buy in from Tesla, and Tesla gave up support for generators in off grid deployments some time ago. So, I don't expect it to happen. I would love it, for winter outages. (Our generator runs on 95-99% renewable fuel.)

YMMV...

All the best,

BG

 

[miimura]

Conceptually, it seems so simple to just rectify a generator's output to DC and run it through a solar string inverter. Add an automatic start relay and you're done, right? I really don't understand why Tesla hasn't made this a product to add to their micro-grid solution.

 

[BGbreeder]

Conceptually, it seems so simple to just rectify a generator's output to DC and run it through a solar string inverter. Add an automatic start relay and you're done, right? I really don't understand why Tesla hasn't made this a product to add to their micro-grid solution.

Yes, that is certainly one way to do it. Or just use one of the available relays in the gateway to drop the generator. It was previously supported for off grid, after all.

I think that there is a strong belief at Tesla to promote sustainable or renewable solutions, and I can see how support for generators would run counter to that philosophy. But I certainly don't have an inside line to the Chief's thinking.

Things could always change.

All the best,

BG

 

[GregBallantyne]

New solution. Buy a cybertruck and charge it with the generator and then connect truck to house!

I've thought about that one already.... but well after reserving the CT. When I reserved the CT, I had no solar and no concrete plans to get it. All that came about during the CT production delays.... and I spent a likely top trim CT's price on it. Then Elon went on his brand destruction crusade, and my CT plans went the same direction as my TSLA holdings value......

 

[CrazyRabbit]

This has been covered in other threads, but the electrical challenge is how to taper and shutoff the generator well before the batteries are full so there is never power pushed into the generator, something generators aren't designed to handle. Then there is the renewable energy component.

As that sort of control requires special programming, it would require solid buy in from Tesla, and Tesla gave up support for generators in off grid deployments some time ago. So, I don't expect it to happen. I would love it, for winter outages. (Our generator runs on 95-99% renewable fuel.)

YMMV...

All the best,

BG

That is why I said “It would be cool if Tesla made a separate box”; and that is why it would have a disconnect switch.
It could even check the THD to protect Tesla’s hardware.
Would probably need some sort of circuit to help synchronize generator.
I would probably fork over 2K for said box plus installation.
Enphase has it, so does Franklin (add in module).

 

[GregBallantyne]

That is why I said “It would be cool if Tesla made a separate box”; and that is why it would have a disconnect switch.
It could even check the THD to protect Tesla’s hardware.
Would probably need some sort of circuit to help synchronize generator.
I would probably fork over 2K for said box plus installation.
Enphase has it, so does Franklin (add in module).

IF I had a CT..... I believe I could use the following approach with my current setup: I could isolate the building where I park and charge, by throwing the subpanel isolation switch by the main load center, and then charge that building's panel with the generator. My "prior to solar system" generator supply path already in place for this. The charger would use the gen power to charge the CT battery. Then, shut down the gen and open the building subpanel to the main load center, to allow sharing the CT battery with the system. Of course all untried at this point, and manual manipulation dependent.
Of course, I don't have a CT, and what you describe above would be a much better method.