Building my own pseudo(Powerwall)

[400bird]

This is super cool. Great job! I like reusing the original battery frame.

You sound confident that other than the inverter you are up to code. I am working on designing my system and am hung up on the batteries. I believe the batteries need to have specific UL listing. Do you know anything about this one way other the other?

Also, my AHJ said my only option was to up the batteries in a box 5' from any buildings and the property line. I was just going to buy a fire box and bolt it all up to the wall.

 

[400bird]

Does the forum not allow editing posts?

Just adding that I am also in California.

 

[L-P-G]

This is super cool. Great job! I like reusing the original battery frame.

You sound confident that other than the inverter you are up to code. I am working on designing my system and am hung up on the batteries. I believe the batteries need to have specific UL listing. Do you know anything about this one way other the other?

Also, my AHJ said my only option was to up the batteries in a box 5' from any buildings and the property line. I was just going to buy a fire box and bolt it all up to the wall.

Hey I have no idea about UL listing requirements for batteries, My AHJ doesn't seem to care about that. I also didn't seem to see anything about it in NEC 2014 which is what my system needed to comply to.

Maybe CA is more strict about these things since you guys are more serious about renewables and adopted them earlier. If you do end up building a separate structure to your home put the inverter there as well. AC will require less AWG over distances since it runs at a higher voltage than the high amperage DC that the batteries will use.

 

[brur]

This is super cool. Great job! I like reusing the original battery frame.

You sound confident that other than the inverter you are up to code. I am working on designing my system and am hung up on the batteries. I believe the batteries need to have specific UL listing. Do you know anything about this one way other the other?

Also, my AHJ said my only option was to up the batteries in a box 5' from any buildings and the property line. I was just going to buy a fire box and bolt it all up to the wall.

About putting the batteries outside. Is your climate freeze proof? Freezing is why I wasn't planing an outdoor structure.

 

[Ampster]

............
Also, my AHJ said my only option was to up the batteries in a box 5' from any buildings and the property line. I was just going to buy a fire box and bolt it all up to the wall.

There is a new fire code that limits the amount to 20 kWh in a structure. Then as you suggested there needs to be a separation for any additional capacity. That is the general rule that I have heard about. Any jurisdiction can change or vary the rules as they see fit. I won't know for another few months when I pull my permit.

 

[400bird]

About putting the batteries outside. Is your climate freeze proof? Freezing is why I wasn't planing an outdoor structure.

Freeze proof, no. But, this is California 99% of the time, where I live, we are 33-105f
Only a handful of nights per year do we freeze. I will probably need to use the original coolant passages the OE used when these packs were in a car. I'll have to add both a heater and cooler to the loop. I'll end up wasting energy (lots!), but a peltier is about the only thing I could think to use to cool the pack when it smoking hot outside.
Heating the coolant loop should be easier.

But, both of these are not immediate concerns and real world results will tell if either of theses are needed. I might get away just running the packs as is inside the insulated box I get to build.

 

[400bird]

Hey I have no idea about UL listing requirements for batteries, My AHJ doesn't seem to care about that. I also didn't seem to see anything about it in NEC 2014 which is what my system needed to comply to.

Maybe CA is more strict about these things since you guys are more serious about renewables and adopted them earlier. If you do end up building a separate structure to your home put the inverter there as well. AC will require less AWG over distances since it runs at a higher voltage than the high amperage DC that the batteries will use.

Yeah, my AHJ uses something newer than NEC 14, it was 16 in 2018 when I did the solar.

Very good point on the wiring. I am currently planning to leave the inverter in the garage near the breaker panels and solar inverter.

My two reasons for this:
The transfer switch is integrated into the inverter, so I would have to run the AC wiring to the inverter and back, double lap. That probably negates some of the difference in copper
The inverter is only nema 1 and the height/clearance requirements will require the battery house to be significantly larger that the roughly 3'x3'x6' box I currently plan to build.

The regulation is 5' from the house. So the box will be 5.01' from the house to keep the DC wiring as short as possible. But I do still have to run up the wall to the inverter. So probably 10' each way.

 

[L-P-G]

About putting the batteries outside. Is your climate freeze proof? Freezing is why I wasn't planing an outdoor structure.

Nope, 36F-115F.

Freeze proof, no. But, this is California 99% of the time, where I live, we are 33-105f
Only a handful of nights per year do we freeze. I will probably need to use the original coolant passages the OE used when these packs were in a car. I'll have to add both a heater and cooler to the loop. I'll end up wasting energy (lots!), but a peltier is about the only thing I could think to use to cool the pack when it smoking hot outside.
Heating the coolant loop should be easier.

But, both of these are not immediate concerns and real world results will tell if either of theses are needed. I might get away just running the packs as is inside the insulated box I get to build.

You'd be surprised, Tesla modules have a high point of 66C (150F). Remember that in an EV they pull a lot more amps, so cooling when using them as backup for solar isn't as big of a deal. For example when supercharging they can see anywhere from 20-150kW, in my setup the most they see is 14kW. I actually did the math and when charging at the max output of my solar which doesn't stay at that very high I don't even reach 50% of 1C. When discharging that's even less since the inverter is limited to 12kW so overheating due to usage never happens for me.

Heating on the other hand is definitely necessary if you're in an area that reaches freezing temps. That's easily accomplished using the OEM coolant lines as all the modules already have that built in. Hell you can simply use a small water heater and a water pump to cycle the coolant through existing lines only when temps fall to freezing.

Yeah, my AHJ uses something newer than NEC 14, it was 16 in 2018 when I did the solar.

Very good point on the wiring. I am currently planning to leave the inverter in the garage near the breaker panels and solar inverter.

My two reasons for this:
The transfer switch is integrated into the inverter, so I would have to run the AC wiring to the inverter and back, double lap. That probably negates some of the difference in copper
The inverter is only nema 1 and the height/clearance requirements will require the battery house to be significantly larger that the roughly 3'x3'x6' box I currently plan to build.

The regulation is 5' from the house. So the box will be 5.01' from the house to keep the DC wiring as short as possible. But I do still have to run up the wall to the inverter. So probably 10' each way.

Fair enough, just remember at 48V the amperage is way higher, I see over 300A sometimes which calls for 0000 AWG cabling and my run is less than 10ft, when going further you'll have to account for voltage drop and either double up conductors (which I'm not sure is code compliant) or fall into the K ranges wire gauge.

 

[400bird]

There is a new fire code that limits the amount to 20 kWh in a structure. Then as you suggested there needs to be a separation for any additional capacity. That is the general rule that I have heard about. Any jurisdiction can change or vary the rules as they see fit. I won't know for another few months when I pull my permit.

Interesting, do you know the code number on that?
I didn't mention my intended storage capacity when talking to the city, but they may have assumed it would be over 20kw.

I wonder if the rule is for 20kw of unknown (not ul listed) batteries?
You can stack as many powerwalls as you want in your garage (up to 10) at least per the Tesla certified installer that just stopped by. BTW, they want $15k/ for the first powerwall, plus another $10k for each additional. And he didn't even look at anything electrical, just started spewing numbers.

 

[400bird]

Fair enough, just remember at 48V the amperage is way higher, I see over 300A sometimes which calls for 0000 AWG cabling and my run is less than 10ft, when going further you'll have to account for voltage drop and either double up conductors (which I'm not sure is code compliant) or fall into the K ranges wire gauge.

The max current listed on my planned inverter is 180 amps. I believe that puts me at 000. Roughly $3/foot I believe. So it's not too bad to run 10' each way.

 

[BrettS]

The max current listed on my planned inverter is 180 amps. I believe that puts me at 000. Roughly $3/foot I believe. So it's not too bad to run 10' each way.

Remember it’s more than just the cost. 000 wire is getting close to half an inch in diameter and about half a pound a foot. Physically wrestling with that wire, especially if you need to get it through a conduit, is a lot easier said than done.

 

[400bird]

I appreciate the words of caution.

I think I'll be ok on handling the cables. The service drop was 2x 0000 plus ground. But, that was straight conduit. The pull from the main panel to sub panel had 180° of bend and the conduit was something like 0.05" under the fill spec. That was my fault, I didn't read how close to full the conduit was going to be or I would have planned differently. It went fine, but was more effort than necessary.

 

[Ampster]

Interesting, do you know the code number on that?

This is from a Google search and there may be more as well as your local jurisdiction implementation.
Searchable platform for building codes
the 20 kWh is in section 1206.2

 

[Ampster]

You can stack as many powerwalls as you want in your garage (up to 10) at least per the Tesla certified installer that just stopped by.

Yes, you can stack as many as you want, but you might not pass the inspection.

 

[400bird]

This is from a Google search and there may be more as well as your local jurisdiction implementation.
Searchable platform for building codes
the 20 kWh is in section 1206.2

That is amazing. Thank you for the link!

 

[Xianrecords]

I have a few questions related to the Sigineer inverter:

- Are you still happy with it ? I am planning on buying the 15kW 48V. Wanted to check if that is still a good buy or if there are better option for a split phase 120/240v system

- The documentation recommend 10 to 5AWG wire to the AC terminal block. With 80A breaker, I am planning on using a 2AWG Aluminium (Will put the battery in a shed away from the house so need a more flexible cable that copper). Will I get into an issue trying to get this wire in the AC Terminal block ?

- The max Battery charging is 120A for the 15kWh and I am assuming that the max discharge would be 15000/48 = 312A.
What size battery cable would you need for this ?

- Were you able to find a way to switch mode (Battery to AC Priority) through the RS232 ? I would like to put a scheduler that would only allow Battery Priority during the PG&E peak hours and switch to AC after 9pm (After peak hours) to maximize the battery life. If I understand correctly, you are using Relay Contractors to emulate that functionality. I was wondering if I could control this from a Raspberry PI.

- I have a doubt about the Max ByPass current through the Inverter. I read through the doc that for the 12kW it is 63A and for the 15kw it is 100A. Am I reading this correctly ? Should I then put 100A breakers on my ATS Subpanels ? (I recall we talked about 80A before.... getting confused.)

Thanks in advance, and Thanks for the post. I did build my solar system with the same Siemens ATS than yours. Your post was tremendously helpful.

Christian

 

[L-P-G]

- Are you still happy with it ? I am planning on buying the 15kW 48V. Wanted to check if that is still a good buy or if there are better option for a split phase 120/240v system

• Yea I'm still happy with the inverter, I wish it curtailed but that isn't too big of a deal. SMA now makes the Sunny Island if you really want an inverter that can curtail, however it's only a 6kW and the peak isn't anywhere near the Sigineer, you'd have to parallel 3 units to get 15kW and triple the cost. SMA now also makes a 350v Sunny Boy Storage inverter which would allow you to hook up a whole pack without having to rewire it to 48v like I did.

- The documentation recommend 10 to 5AWG wire to the AC terminal block. With 80A breaker, I am planning on using a 2AWG Aluminium (Will put the battery in a shed away from the house so need a more flexible cable that copper). Will I get into an issue trying to get this wire in the AC Terminal block ?

• Yea, you'll never get 2 AWG into the crappy plastic block the inverter Comes with. Take a look at some of my pictures, I skipped the block and connected directly to the breakers inside the unit.

- The max Battery charging is 120A for the 15kWh and I am assuming that the max discharge would be 15000/48 = 312A.
What size battery cable would you need for this ?

• You'll have to reference a couple things, first is the NEC allowed ampacity for that amperage which you can find in the table below,
  
• Then you have to take into account voltage drop based on the distance of the cable run, you're most likely going to get into the kcmil numbers since 4/0 AWG isn't big enough for 312A even for short distances.
• Here's a good links with the math you'll have to do Wire Sizing Tool for 12, 24 and 48 Volt DC Systems

- Were you able to find a way to switch mode (Battery to AC Priority) through the RS232 ? I would like to put a scheduler that would only allow Battery Priority during the PG&E peak hours and switch to AC after 9pm (After peak hours) to maximize the battery life. If I understand correctly, you are using Relay Contractors to emulate that functionality. I was wondering if I could control this from a Raspberry PI.

• I think you're misunderstanding battery priority mode. On that mode the inverter will start on the grid, and stay on the grid until the power fails then it will switch over to battery and stay on battery until the battery gets low then it'll switch back to the grid and wait for another power outage. You can easily switch over the inverter to battery mode using a relay on the pi by soldering to the small board where the dip switches are BUT that won't give you the functionality you're looking for, you're better off leaving the inverter on grid mode and using a contactor to drop the grid during peak hours. Then when you want to go back on the grid close the contactor and after 15 seconds the inverter will go back to the grid.

- I have a doubt about the Max ByPass current through the Inverter. I read through the doc that for the 12kW it is 63A and for the 15kw it is 100A. Am I reading this correctly ? Should I then put 100A breakers on my ATS Subpanels ? (I recall we talked about 80A before.... getting confused.)

• Yep, you're correct. I couldn't find any 70A breakers so I had to use 80A breakers and size my cabling accordingly.

 

[Xianrecords]

Thanks for the response. I indeed misunderstood the battery priority. I wonder why people would want to use that mode then.

I think I will go with the Relay scheme you suggested.

For your 12kW inverter, did you use Copper 250kcmil/75 deg wire ? Is it ok to use THHN ?

I am not sure what you meant by "curtailed" for the inverter. Can you explain ?

Thanks a lot

 

[L-P-G]

I wonder why people would want to use that mode then.

• The only scenario I can think of is to prevent repetitive power drops during a storm

I think I will go with the Relay scheme you suggested.

• You mean contactor? The relay would be more for the dip switches

For your 12kW inverter, did you use Copper 250kcmil/75 deg wire ? Is it ok to use THHN ?

• I used 4/0 EV thin stranded cable that has a jacket rated to a higher temp so a smaller cable can handle the increased temps. Will THHN work? sure it will, it'll be very rigid and hard to work with but it'll pass power the same. Do keep in mind if you're trying to stay within code you'll have to check with your AHJ, sometimes they have rules as to the type of cable you can use on batteries.

I am not sure what you meant by "curtailed" for the inverter. Can you explain ?

• Curtailing is when the inverter that the grid tied inverters are synced to increases the frequency to lower the power produced by the grid tied inverters (per UL1741). This allows the battery based inverter to taper off the power coming to it when the batteries are almost full. With my current setup the batteries get 100% of the power produced by my micros until any one cell reaches 4.1v then the micros are turned off, when the average of all the cells falls to 3.8v then the micros are turned back on. That cycle repeats until the grid power comes back on or the sun goes down.

Thanks a lot[/QUOTE]

 

[Xianrecords]

Indeed, I meant Contactor. Thanks for the explanation on Curtailing. I have the same setup as yours with MicroInverters that will go off when reaching overcharged. I have added 2 additional safety relay on the battery side along with my BMS for overcharge and undercharged. Probably overkill but better be on the safe side.

I am struggling a bit on the Battery side. If the inverter is 15kW, then it would mean that the max discharge current at 48v would be 312.5A. And that the max current on the AC side when inverting would be 62.5A. My batteries are 280Ah, 1C, LifePo4. I also have 100A breakers on the In/Out as the internal ATS of the inverter is also 100A rated. So is there a way to limit the current drawn by the battery to 280A ? I do not expect the Critical loads to draw that much current but I want to put some safety net.

Thanks.

Christian