Manual Transfer Switch Solar from Main to Backed Up Load Center?

[Kbra]

Anyone have their solar installed outside their backed up load center with a manual transfer switch that allows the inverter to come back online during a grid loss to run house loads and recharge PWs?

Why do i want this?
By installing my solar to my main panel, outside my gateway and backed up loads, i send much more of my power to the grid during peak hours. Meanwhile my Powerwalls continue to run as they do right now by powering the house for 16 hours a day, and recharging themselves at night during off peak.

The downside to this install is that the solar will go down when the grid goes down. So ideally id have a transfer switch which isolates me from the grid and re-energizes the inverter so that the solar can produce energy with the PWs as they sync.

This is a non-conventional configuration. This would disqualify you from the SGIP program too. For me though i already don't qualify for SGIP so it doesn't matter there.

Doing some usage analysis i save about $1500/year by installing my Solar + PW the "normal" conventional way. However, if I do it as described above, I save an additional $600/year and can install a smaller system to offset my usage.

 

[miimura]

So, let me get this straight - you have existing Powerwalls without solar today. You want to add solar without integrating it into the Powerwall system. Is that right?

If you don't care about SGIP and the ITC tax credit, you should be able to do it like you propose. You just have to get PG&E to allow you to interconnect the system that way.

As far as the transfer switch goes, you would just have a A/B double throw switch that has one pole connected to breakers in your main panel and the other pole connected to breakers in your backup panel and the solar inverters in the middle. Presumably, your Powerwalls already have the Tesla Backup Gateway that allows your Powerwalls to power the house when the grid is down. I don't see why you can't do the transfer switch as long as you convince the building inspector it's OK. The only open question is what the Powerwalls will do with solar generation when it's configured without solar.

 

[power.saver]

I do, but only part of the solar is outside. When the grid fails, the outside part is automatically switched inside and can assist covering loads and charging the PWs. Otherwise, the outside solar would just shut down.

 

[cwied]

Why do i want this?
By installing my solar to my main panel, outside my gateway and backed up loads, i send much more of my power to the grid during peak hours. Meanwhile my Powerwalls continue to run as they do right now by powering the house for 16 hours a day, and recharging themselves at night during off peak.

If I understand what you're saying correctly, there's no need to do a funky installation to make this happen. In time-based control mode, the Powerwalls do exactly this - they handle the house load and your entire solar production gets exported during the peak rate period.

 

[Kbra]

If I understand what you're saying correctly, there's no need to do a funky installation to make this happen. In time-based control mode, the Powerwalls do exactly this - they handle the house load and your entire solar production gets exported during the peak rate period.

Once the gateway knows the Powerwalls are tied to Solar it prohibites the PWs from charging off the grid. Which I prefer them to charge from when in off peak.

 

[Kbra]

I do, but only part of the solar is outside. When the grid fails, the outside part is automatically switched inside and can assist covering loads and charging the PWs. Otherwise, the outside solar would just shut down.

Did Tesla do this Install? Also does your setup allow for the PWs to recharge with grid power at night when there's no solar?

 

[Kbra]

So, let me get this straight - you have existing Powerwalls without solar today. You want to add solar without integrating it into the Powerwall system. Is that right?

If you don't care about SGIP and the ITC tax credit, you should be able to do it like you propose. You just have to get PG&E to allow you to interconnect the system that way.

As far as the transfer switch goes, you would just have a A/B double throw switch that has one pole connected to breakers in your main panel and the other pole connected to breakers in your backup panel and the solar inverters in the middle. Presumably, your Powerwalls already have the Tesla Backup Gateway that allows your Powerwalls to power the house when the grid is down. I don't see why you can't do the transfer switch as long as you convince the building inspector it's OK. The only open question is what the Powerwalls will do with solar generation when it's configured without solar.

The initial feedback from Tesla engineering is that the PWs wouldn't understand the incoming load correctly if the system isn't configured for Solar input. But I agree with you that it's physically possible. Really comes down to can the gateway and PWs be configured to run as load shift using grid and not know that solar even exists day to day. Then if the grid goes out. The manual transfer switch just makes the PWs see an inflow of current, not knowing it's solar vs grid.

 

[power.saver]

No, and no. Because I have solar, there is no grid charging.

 

[cwied]

Once the gateway knows the Powerwalls are tied to Solar it prohibites the PWs from charging off the grid. Which I prefer them to charge from when in off peak.

I see. I think the main issue is going to be that the Powerwall would not know to charge from solar when off-grid if it isn't configured for the solar. I don't know where the power would go, but I can't imagine it would be a good thing. If you want to preserve your grid-charging, you'd probably have to also forgo using your solar panels during a power outage.

 

[wwhitney]

I see. I think the main issue is going to be that the Powerwall would not know to charge from solar when off-grid if it isn't configured for the solar. I don't know where the power would go, but I can't imagine it would be a good thing.

I don't believe that's correct. The CTs and the software configuration of the Powerwalls just govern their behavior while in grid-tie mode. When operating in island mode, that layer is not involved (it would be too slow to respond, I believe), and the inverters manage charging/discharging at a lower level. I'm not clear on the details, but in island mode the inverters simply try to provide a constant voltage source--providing more power if it finds the voltage is dipping due to load, and charging if it is finds that the voltage is rising due to another generator on the microgrid.

Cheers, Wayne

 

[cwied]

I don't believe that's correct. The CTs and the software configuration of the Powerwalls just govern their behavior while in grid-tie mode. When operating in island mode, that layer is not involved (it would be too slow to respond, I believe), and the inverters manage charging/discharging at a lower level. I'm not clear on the details, but in island mode the inverters simply try to provide a constant voltage source--providing more power if it finds the voltage is dipping due to load, and charging if it is finds that the voltage is rising due to another generator on the microgrid.

Cheers, Wayne

I stand corrected. I suppose given that it has to be able to charge with solar anyway, there's no reason non-solar can't do it. Even so, I wonder if a non-solar configuration does the frequency shifting to curtail solar production when it can't handle the power.

 

[wwhitney]

I stand corrected. I suppose given that it has to be able to charge with solar anyway, there's no reason non-solar can't do it. Even so, I wonder if a non-solar configuration does the frequency shifting to curtail solar production when it can't handle the power.

In my last post, when I said "generator" I meant any power source, not necessarily an engine-based one. In a microgrid you can only have one island-type inverter/power source, the others would need to be grid-tied, and would need to curtail production in response to frequency shifting. I don't know if grid-tied small engine generators are readily available.

Cheers, Wayne