Anyone knows what happens if the incoming grid shorts?

[Shygar]

My dad is thinking of getting a powerwall. He already has solar. But he was wondering today what would happen if a tree fell on the grid line coming into the house and it fell in such a way that the wires shorted itself out? If it matters his solar grid tie in is directly in the line, not as a breaker.

Would the backup gateway be smart enough to cut off the grid? Or could his equipment get damaged?

 

[Tam]

...grid...

I think if the shorts / lightnings / damages / tree falling on live wires... are from the grid side, your solar-PowerWall system would isolate itself and continue to work independently from the grid.

 

[ewoodrick]

In reality, if a tree falls on a line outside of your neighborhood, the line will always show a short, because the transfer near your house is a short. Only if the tree falls on the lines between your transformer and the box will an open occur.

One of the issues, and the reason why a whole house disconnect is required, is that if you try to power your house, you will attempt to power all of the houses on your circuit and the generator will not have enough power, and it will represent a electrocution hazard to anyone working on the line.

 

[Tam]

...it will represent a electrocution hazard to anyone working on the line.

Traditional solar panel system will be down whenever the grid is down to protect electrical linemen and women.

That is not the case with solar panel + PowerWall system. When the grid is down, the system would isolate itself from the grid and it continues to work (solar charges the PowerWall on daylight and PowerWall powers the house at night.)

If you have a small PowerWall system, you can choose to have "Essential Load Backup".

If you have a bigger capacity PowerWall system, you can choose "Whole Home Backup."

 

[Shygar]

Thanks @Tam! I knew it would in a normal scenario but wasn't sure about this specific scenario.

Separately I wonder if my dad's solar going straight into the line (not breaker fed) will have to change when a backup gateway is installed. I'm guessing so to keep the system isolated behind the meter.

 

[Tam]

...change...

Tesla will make an evaluation and design your project to incorporate with your existing solar panels.

Their basic setups are listed in:

Tesla

Your solar power and solar powerwall are behind Tesla "Backup Gateway" so they can be isolated themselves from the grid (Utility Meter) when the grid is down.

 

[Ampster]

Separately I wonder if my dad's solar going straight into the line (not breaker fed) will have to change when a backup gateway is installed. I'm guessing so to keep the system isolated behind the meter.

I am guessing you are correct. When you say, "straight into the line" are you talking about a side tap? My understanding is that is used to reduce calculated load on the buss. A friend has that situation and the installer told him there was an inline fuse in that setup.

 

[Shygar]

I am guessing you are correct. When you say, "straight into the line" are you talking about a side tap? My understanding is that is used to reduce calculated load on the buss. A friend has that situation and the installer told him there was an inline fuse in that setup.

Yes I believe that's the same thing and that makes sense. I'm not sure why they did it that way but he does have a 12kW ground mount solar system so that might be why also. Just thinking that will have to come inside the "system" in order for this to work with a powerwall.

Thanks @Tam, I am aware of the site survey and engineering process before it gets installed, as that's what I went through with mine. But my dad is in SC and Tesla doesn't serve that area, so likely he will be dependent on a third party installer, and I hope they are as thorough as Tesla themselves.

 

[coleAK]

Are you all sure the power wall will function if the grid is down? Looks to me like you also need the backup gateway, a secondary breaker panel and various other disconnects. Most of the systems are tied to the grid so if the grid goes down you go down.

I built and installed my own hybrid system 2 years ago for our house, did 80-90% myself. I had to hire an electrician to wire into and out of the meter and breaker panels. I have been looking into adding additional batteries which is why I’m reasearching Powerwall. For batteries I currently I have 12 - 12v 234 AH@20hr AGM batteries. I did a minimal battery bank as I felt batteries were going to get better on the next 5-10 years. I had to register with the city and the power company as I can back feed to the grid. I have manual disconnects and also a rapid disconnect between my house and the grid that trips if the grid goes down and I have to manually throw back when the grid comes back online. When I’m “off grid” I have a 2nd breaker panel that runs the essentials: well pump, heat recirculating pumps, fridge, freezers,... I have 27 - 295w panels. Then I have a generator as a backup to the backup in case I had to charge my batteries and my panels were snow covered.

I’m set up exactly like the partial home backup version of the Powerwall.

Also the function to store produced solar power and use it at night would currently be useless here in AK. Our grid isn’t that high tech, we only have one rate for power and my bill is a net for the month. So if I make X kWh durring the day then use X kWh at night my net is 0 kWh. X-X=0

 

[cwied]

Are you all sure the power wall will function if the grid is down? Looks to me like you also need the backup gateway, a secondary breaker panel and various other disconnects. Most of the systems are tied to the grid so if the grid goes down you go down.

I don't think there's any way to get a Powerwall 2 to work without a Gateway. In the US, I think they're all backup Gateways (unlike the UK, where backup functionality is not available yet). When Tesla installed my Powerwalls, they added a generation panel, a load panel and the Gateway. Since my whole house is backed up, the load panel contains all of the circuits that used to be in my main panel.

 

[Tam]

...manually throw back...

Why do it manually when Tesla can do it seamlessly. It's so smooth that your home computers and other appliances don't even notice the switching between off-grid when the grid is down and on-grid when the grid is back on.

 

[coleAK]

Why do it manually when Tesla can do it seamlessly. It's so smooth that your home computers and other appliances don't even notice the switching between off-grid when the grid is down and on-grid when the grid is back on.

As I said built it myself and did it before the Powerwall was widely available. I switch from on grid to off grid seamlessly to my partial (2nd breaker) panel that is. If I put in a toggle style breaker it would switch back seamlessly as well.

However Anchorage muni requires any power source able to function off grid that is in a grid tied structure to be manual reconnect to the grid if disconnected. So even if I had 2-3 of the the newest Latest and greatest Powerwall to run my entire house it would need to have a one way toggle with a physically operated throw to go back on grid. I guess It’s a redundancy to make sure my house dosnt put power to down lines. I even tried to get using a WiFi switch that I could manually active remotely approved with no luck. It had to be a Good old fashion button (picture).

We are behind in terms of solar regulations and I was the first hybrid on/off grid system to be installed within the muni. There are many homes up here with the big Kohler generators and the muni considers my solar to be the same thing.

We face many unique situations in Alaska and geographical isolation is the biggest. Tesla/solar city don’t do work up here and when I started mine there was only one solar company in state and they were only doing off grid cabin systems. It took me a year to do my own system and 8 months of that was waiting for (fighting with) muni approval.

 

[Shygar]

As I said built it myself and did it before the Powerwall was widely available. I switch from on grid to off grid seamlessly to my partial (2nd breaker) panel that is. If I put in a toggle style breaker it would switch back seamlessly as well.

However Anchorage muni requires any power source able to function off grid that is in a grid tied structure to be manual reconnect to the grid if disconnected. So even if I had 2-3 of the the newest Latest and greatest Powerwall to run my entire house it would need to have a one way toggle with a physically operated throw to go back on grid. I guess It’s a redundancy to make sure my house dosnt put power to down lines. I even tried to get using a WiFi switch that I could manually active remotely approved with no luck. It had to be a Good old fashion button (picture).

We are behind in terms of solar regulations and I was the first hybrid on/off grid system to be installed within the muni. There are many homes up here with the big Kohler generators and the muni considers my solar to be the same thing.

We face many unique situations in Alaska and geographical isolation is the biggest. Tesla/solar city don’t do work up here and when I started mine there was only one solar company in state and they were only doing off grid cabin systems. It took me a year to do my own system and 8 months of that was waiting for (fighting with) muni approval.

So if your grid goes out even for a minute, you have to manually reconnect back to the grid (presumably with that green button)?

 

[coleAK]

Yes it’s a pain. But all of our essentials that need power are on the back up panel so: heat, fridge, freezers, security, WiFi,... function off the solar/battery. But the rest of the house dosnt come back on power until someone pushes the button and re connects to grid. So if I had the entire house wired to battery back up it would run off grid until the button was pushed to re connect to the grid... Thank you Anchorage Muni

 

[Ampster]

Also the function to store produced solar power and use it at night would currently be useless here in AK

The physics are the same regardless of how high tech your grid is. Your meter may not be able to account for sending power to the grid but that is the only physical limitation I know of. Economically the price may not be favorable.

 

[coleAK]

The physics are the same regardless of how high tech your grid is. Your meter may not be able to account for sending power to the grid but that is the only physical limitation I know of. Economically the price may not be favorable.

Sorry instead of “useless” I should have said something like: is no advantage given our current meter and grid constraints where I live.

 

[Yinn]

My dad is thinking of getting a powerwall. He already has solar. But he was wondering today what would happen if a tree fell on the grid line coming into the house and it fell in such a way that the wires shorted itself out? If it matters his solar grid tie in is directly in the line, not as a breaker.

Are you sure it's wired directly in line? This doesn't seem up to code; so unless he did it himself without a permit I would think it's not wired directly into the grid. They do this specifically to protect the utility workers as they generally do not enjoy working with wires that could be suprisingly live or not live.

Would the backup gateway be smart enough to cut off the grid? Or could his equipment get damaged?

My guess is that it's a typical grid tied system with netmetering. He has the solar hooked up w/o the use of a critical loads/backup panel. Somewhere in that system should be an automatic disconnect switch. It can be a breaker on the panel or it could be a service disconnect or even built into the inverter he's using. Installating a battery backup to the system wouldn't change it much. It would still disconnect itself in the event of an outage. The difference would be in how the micro grid stands up.

In that case, everything works as it would with a generator. So when there's a short or an outage; the home is pulled off the grid and isolated - just like he probably is today. The difference would be that instead of a generator kicking on, the powerwall would supply power to the home. If configured correctly; the solar would not turn off in the event of a large grid outage and instead continue generating power to charge the batteries when possible.

*I don't have a powerwall...yet. But I have a battery backup system from another manufacturer and have experienced multiple outages since installation - including a tree falling on an incoming grid line. It's uneventful. My largest issue right now is needing more battery power and needing more amp capacity/support to my panel.