I have a quick question on the external ATS Setup. On Amazon, the ATS Switch seems to come with 125A breakers for the switched legs. Did you downgrade the breaker on the leg connected to the Out of the 12kW inverter to 80A ? (19kW of PassThru power) Did you add a 80A breaker in the Main section of the ATS for the In of the Inverter ? Thank you.
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No, let me explain it a different way. The panel ATS is only used to bypass the battery inverter for when I need to do maintenance, as such I don't have to downgrade the breaker since the panel has a a 200A main and 125A breakers above the ATS and below the ATS (left side of the picture attached.
When the panel ATS is not in bypass mode (switched to the right side of the pic attached) an 80A breaker on the grid only side of the panel gives power to the inverter, the inverter in turn (depending on the configured mode) will either pass the grid through its internal ATS giving the house 80A of grid power (also giving me the choice to grid charge the batteries) through the backfeed 80A breaker attached to the right side of the panel ATS.
In this way I can keep the panel ATS always switched to the right and the inverter ATS will act as a whole house UPS, when the grid goes out it'll switch its internal ATS to island the house and give power to the whole house and the AC coupled solar.
If i switch it to the left, all the batteries and the inverter is bypassed and the house/solar is just grid tied.
Attachments
Sorry for asking more questions but in the inverter manual, it states:
PreventingParalleling of the AC Output
The AC output of the unit should never be connected to the utilitypower / generator.
Such a connection may result in parallel operation of the differentpower sources and AC power from the utility / generator will be fed backinto the unit which will instantly damage the inverter and may also pose a fire and safety hazard.
So if Solar power is backfed through AC Out of the inverter, isn't this going to create a problem ?
PreventingParalleling of the AC Output
The AC output of the unit should never be connected to the utilitypower / generator.
Such a connection may result in parallel operation of the differentpower sources and AC power from the utility / generator will be fed backinto the unit which will instantly damage the inverter and may also pose a fire and safety hazard.
So if Solar power is backfed through AC Out of the inverter, isn't this going to create a problem ?
My solar is connected using grid tied inverters, said inverters work by listening to the grid, matching the grid frequency then outputting synced to the existing grid. In my setup the solar is tricked into thinking that the grid is on by the battery inverter. The sigineer uses battery power to energize the circuit which gives the solar a grid frequency to sync to from there as solar starts to produce more than the loads of the house the power is sent backwards through the battery inverter, inverted to 48v DC and stored in the batteries (not all inverters can do this).
That's why it's called AC coupling because the charging is being done from the AC side instead of the DC side. There is about a 10% loss in the conversion but my batteries came after solar and rewiring the whole system for DC was not happening for me.
Let me know if that clears it up.
Hello, A quick question. I am doing the load calculation for the ATS panel.
How many watts did you allocate for the 12KWh Battery Charger ? Or how many amps at 240v will the charger use to charge the batteries ? I am assuming that it is limited to 19kW which would mean around 80amps which is quite a lot with other loads going. (The manual state 120Amps. Is that on the DC side at 48v ?)
How many watts did you allocate for the 12KWh Battery Charger ? Or how many amps at 240v will the charger use to charge the batteries ? I am assuming that it is limited to 19kW which would mean around 80amps which is quite a lot with other loads going. (The manual state 120Amps. Is that on the DC side at 48v ?)
That's correct, the built in charger can be adjust from a few amps to 120a on the 48v side. It comes out to around 5kW.
Keep in mind if you're ac coupling the system very rarely will you grid charge as the excess solar will charge the system instead.
I only have the grid charger enabled to top off the batteries after they've drained from not being used so I don't have to go off grid for it.
No, I keep my inverter in grid priority. This essentially makes it a whole house UPS. The modules have almost no self drain, the only constant load on them is the BMS and the RPi controller which are so low they don't even register on the current sensor. I can go a few months the pack will drop maybe 10%, to prevent getting caught on a power out scenario with a low battery in the middle of the nigh my controller has an option to define when to turn on and off the grid controller.
This lets me keep the pack between 75%-85% regardless of the power going out or not. I think I can go 4-5 months of the BMS/RPi consuming power from the battery before the 75% is reached which enables the grid charger to top off the pack back to 85%.
I should also mention I'm not following the standard empty and full voltages for lithium as I want to get as many cycles out of the pack as I can. my 0% is 3.1v (.1v above lithium 0%) and my 100% is 4.1v (.1v below lithium 100%), so that 85% is 3.85v per cell
pgrovetom1
Member
This is a fabulous post. I've been debating building my own Powerwall versus buying a duel PW2 system from Tesla. Below is a post I made looking for ideas. And someone sent me here. It would be great if you could document your final design with a design description, line diagram, choice of components, summary of settings, summary of controller functions, specs, issues etc... Its a fantastic design effort and it would be shame not to show off your final design and describe how its operating. I may try and document what you describe in the running posts but it would be much cleaner and complete if you could document it and provide a PDF. I suspect you would get lots of interest since its no trivial task and their is plenty of interest.
"Is anyone aware of any working DIY efforts to build a Powerwall for backup purposes now that PG&E will be shutting off power in California in the Autumn fire season regularly. It would be difficult to duplicate the fancy Powerwall software APP but it should be reasonable to build a straightforward power loss backup system controller using Python on a Raspberry Pi, a few Tesla $1000 5.2KWh batteries on Ebay, a commercial automatic transfer switch, a large frequency adjustable sine wave inverter and a battery BMS and solar charge controller. The tricky part is whether it can be done code compliant.
I have a Telecom Engineering background but the part that is daunting is whether it can be done code compliant. It would seem that duplicating Tesla's architecture with a commercial automatic transfer switch based disconnect gateway run by the Raspberry Pi communicating with battery modules built around the available 5.4KWh Tesla batteries on Ebay would make sense. The battery modules could be run by Raspberry Pi's all networked. Each battery module would require a commercial BMS, charge controller appropriate for the Tesla battery and frequency agile pure sine wave inverter. The frequency control over the inverters allows for shutting off the solar inverters when the batteries are fully charged. The UL1741 has a requirement that solar grid tie inverters shut down when the "grid" frequency drops below 59.3Hz. This can be used by the software to shut down the solar grid tie inverters once the batteries are charged and turn them back on when charging is needed.
I haven't given this much thought and was wondering if anyone had actually done a workable code compliant system. It seems feasible. It should be possible to build it cheaper than the $1100 gateway plus $6700 per 14KWh PW2 plus expensive installation. I see a 4 module 85KWh Tesla battery for $1250 on EBAY. If its accurate, just one of those 4 modules should exceed a 14KWh PW. Otherwise one could utilize 2-3 of the $1000 5.4KWh modules. I'm curious if anyone has actually built one or investigated the code issues and components. Hopefully a code compliant commercial automatic transfer switch would go a long way to meeting code requirements. It would disconnect the home and alert the software to bring up a battery powered master inverter in the 5-7KW range. It would bring up the house and prime the solar inverters to begin startup. The charge controller could be run off grid power or off backup mode solar power. The home would be powered by all the inverters slaved off the main frequency agile master inverter. When the software detected the batteries were fully charged, the frequency output of the voltage mode master inverter would be dropped to 59 Hz. That would cause the UL1741 current mode solar inverters to drop off. The Raspberry Pi's provide easy to use WiFi which could be used to monitor the system via a simple Web interface in the home on a PC. When the power came back on, the ATS would alert the software and the master and any slave system inverters would shut off till next time.
Thoughts? Ideas? Problems? Code issues?"
"Is anyone aware of any working DIY efforts to build a Powerwall for backup purposes now that PG&E will be shutting off power in California in the Autumn fire season regularly. It would be difficult to duplicate the fancy Powerwall software APP but it should be reasonable to build a straightforward power loss backup system controller using Python on a Raspberry Pi, a few Tesla $1000 5.2KWh batteries on Ebay, a commercial automatic transfer switch, a large frequency adjustable sine wave inverter and a battery BMS and solar charge controller. The tricky part is whether it can be done code compliant.
I have a Telecom Engineering background but the part that is daunting is whether it can be done code compliant. It would seem that duplicating Tesla's architecture with a commercial automatic transfer switch based disconnect gateway run by the Raspberry Pi communicating with battery modules built around the available 5.4KWh Tesla batteries on Ebay would make sense. The battery modules could be run by Raspberry Pi's all networked. Each battery module would require a commercial BMS, charge controller appropriate for the Tesla battery and frequency agile pure sine wave inverter. The frequency control over the inverters allows for shutting off the solar inverters when the batteries are fully charged. The UL1741 has a requirement that solar grid tie inverters shut down when the "grid" frequency drops below 59.3Hz. This can be used by the software to shut down the solar grid tie inverters once the batteries are charged and turn them back on when charging is needed.
I haven't given this much thought and was wondering if anyone had actually done a workable code compliant system. It seems feasible. It should be possible to build it cheaper than the $1100 gateway plus $6700 per 14KWh PW2 plus expensive installation. I see a 4 module 85KWh Tesla battery for $1250 on EBAY. If its accurate, just one of those 4 modules should exceed a 14KWh PW. Otherwise one could utilize 2-3 of the $1000 5.4KWh modules. I'm curious if anyone has actually built one or investigated the code issues and components. Hopefully a code compliant commercial automatic transfer switch would go a long way to meeting code requirements. It would disconnect the home and alert the software to bring up a battery powered master inverter in the 5-7KW range. It would bring up the house and prime the solar inverters to begin startup. The charge controller could be run off grid power or off backup mode solar power. The home would be powered by all the inverters slaved off the main frequency agile master inverter. When the software detected the batteries were fully charged, the frequency output of the voltage mode master inverter would be dropped to 59 Hz. That would cause the UL1741 current mode solar inverters to drop off. The Raspberry Pi's provide easy to use WiFi which could be used to monitor the system via a simple Web interface in the home on a PC. When the power came back on, the ATS would alert the software and the master and any slave system inverters would shut off till next time.
Thoughts? Ideas? Problems? Code issues?"
mspohr
Well-Known Member
You'll need a commercial inverter which usually has built in control circuitry.
EVTV has done a lot with inverters, batteries, and Raspberry Pi, Arduino
(Check out his YouTube channel)
EVTV Motor Verks - Custom Electric Car Conversion Instructional Videos
Here's another source for batteries.
My Blog – My WordPress Blog
What you're looking to do is totally doable. My system already does a lot of the things you listed, the main difference is that I'm AC coupled and you described DC coupling, meaning that my battery based inverter will take the over production off the grid tied micro inverters and use it to charge the batteries.
My system is 99% code compliant, everything from the DC to the AC wiring is within NEC rules. The last 1% is the UL listing on my inverter. The inverter is built to UL specs but the manufacturer didn't pay for the listing. If you want to be 100% compliant you'll have to get something like an Outback Radian / Magnum MS / Schneider Conext. The problem with those is the kW to price ratio is pretty bad. For example the highest output Outback is 8kW peak of 16kW (100ms) / 12kW (5 seconds) / 9kW (30 min) at a price of around $3k-$5k without any of the accessories like the Mate3 you'll need to do advanced programming like Li profiles / freq shift/ etc.
In comparison my inverter was $1900 with a continuous 12kW output and a surge of 36kW (20 seconds), it already has Li profile built in, AC coupling, freq shift, ATS, out of the box.
The one benefit of the Outback Radian / Magnum MS / Schneider Conext. Is that they can be stacked for parallel operation, so you could have 2 GS8088 for a continuous 16kW output but that doubles your pricing on the inverters.
If you provide some more details on your solar system I can probably throw some ideas your way.
pgrovetom1
Member
Thanks for responding. I've been looking around and there seem to be many claims of DIY Powerwall systems but yours is the only one that is done properly and is well thought out. I am interested in an AC coupled system.
My PV system is composed of 2 separate systems built a few years apart. My original 2008 system was both designed and constructed by me. Its built around 2 Sunny Boy 7000 inverters each with 2 strings of 15 210 watt panels. So there are a total of 60 210 watt panels = 12,600 watts. The outputs of the 2 Sunny Boy inverters are summed via 40A breakers in a small panel and the combined power exits to a 100A disconnect via a 80A breaker. The power level exceeded the 120% rule for my 200A panel for backfeed so is line fed into a spare lugs on the back of the meter socket. They currently still produce over 11,000 real watts on a summer day.
My second 4500 watt system is built from 18 Enphase M215 inverters and 230 watt panels and which are routed to a small 60A disconnect and backfed via a 30A breaker into my 200A main panel and with meter and service entrance.
My service entrance and Sunny Boy inverters are about 50 feet outside my home in Sonoma and my solar panels are ground mounted between 70 and 120 feet further north west from my service entrance. My garage is at the opposite side of my rather long house and fed by a 100A panel inside my home with only a 50A panel. Its physically impossible to run and new wiring to my garage from my service entrance area making it impossible to install either Tesla Powerwalls or a DIY powerwall inside my garage. I would need to build a small shed or out building to house a DIY system just to make it practical. A real Tesla PW2 could be installed adjacent to my Sunny Boy 7000s which are on a structure I built.
So my idea before seeing your post was something like this:
Build a small building or shed so I could work on my system inside and protect the batteries and equipment from the occasional sub freezing temperatures, occasional >100, rain, falling tree limbs and leaves from the oak tree above my service entrance. I haven't given it lots of thought but I assumed I would separate my non-essential power needs including 30A well breaker, 50A pool breaker, and 20A irrigation pump breaker. I would leave those in my main service entrance and install a Automatic Transfer Switch between that existing 200A panel and a new 200A essential service panel containing the underground feeds for a 200A and 100A panel inside my house and a 20A home water jet pump. This means my well, irrigation pump and pool would go down with my PG&E power. I would need to decide if all three sections of my solar ( 2 Sunny Boy 7000s = 5500 watts each and one Enphase based system = 4000 watts ) would be used by my powerwall battery storage. That decision would be based on my battery capacity and whether it would take all three to charge on a good winter day. Everything would be AC coupled.
From there, my system would be similar in structure to yours. I would assume I would manually limit my power use when running on backup power to be sure I didn't exceed the inverter limit peak and be able to survive cloudy days if necessary. Fortunately the PG&E shutdown due to fire risk will occur in the fall from August till November when we only rarely have rain or cloudy days. So I would typically have decent solar so I would want a typical November day solar production to fully charge the batteries. Then I would want to easily go through the night on battery power. If it was cloudy, I would tighten my belt and try and limit my power usage to stretch the batteries as long as possible if I knew it was needed. I would probably use a Raspberry Pi and Python to perform the control over the system and allow reporting via WiFi to my PC inside my house. It would monitor and control the various components including the ATS, Inverter, charge controller, batteries, environmental, misc etc.. I would probably use used Tesla batteries as can be found on EBAY and add a commercial BMS rather than the Tesla custom BMS.
That should be enough to get your initial thoughts. Could you list your final components and any you discovered later that you thought you might have used. I'm not worried about UL as my main concern is figuring out how to get the main electrical approved by the building department without them digging into everything. Hopefully the commercial ATS would go a long way to meeting the building codes if it all was done to support a generator backup rather than a PW battery system. If most of this was in my garage, it would be subject to less scrutiny. That is my concern.
My PV system is composed of 2 separate systems built a few years apart. My original 2008 system was both designed and constructed by me. Its built around 2 Sunny Boy 7000 inverters each with 2 strings of 15 210 watt panels. So there are a total of 60 210 watt panels = 12,600 watts. The outputs of the 2 Sunny Boy inverters are summed via 40A breakers in a small panel and the combined power exits to a 100A disconnect via a 80A breaker. The power level exceeded the 120% rule for my 200A panel for backfeed so is line fed into a spare lugs on the back of the meter socket. They currently still produce over 11,000 real watts on a summer day.
My second 4500 watt system is built from 18 Enphase M215 inverters and 230 watt panels and which are routed to a small 60A disconnect and backfed via a 30A breaker into my 200A main panel and with meter and service entrance.
My service entrance and Sunny Boy inverters are about 50 feet outside my home in Sonoma and my solar panels are ground mounted between 70 and 120 feet further north west from my service entrance. My garage is at the opposite side of my rather long house and fed by a 100A panel inside my home with only a 50A panel. Its physically impossible to run and new wiring to my garage from my service entrance area making it impossible to install either Tesla Powerwalls or a DIY powerwall inside my garage. I would need to build a small shed or out building to house a DIY system just to make it practical. A real Tesla PW2 could be installed adjacent to my Sunny Boy 7000s which are on a structure I built.
So my idea before seeing your post was something like this:
Build a small building or shed so I could work on my system inside and protect the batteries and equipment from the occasional sub freezing temperatures, occasional >100, rain, falling tree limbs and leaves from the oak tree above my service entrance. I haven't given it lots of thought but I assumed I would separate my non-essential power needs including 30A well breaker, 50A pool breaker, and 20A irrigation pump breaker. I would leave those in my main service entrance and install a Automatic Transfer Switch between that existing 200A panel and a new 200A essential service panel containing the underground feeds for a 200A and 100A panel inside my house and a 20A home water jet pump. This means my well, irrigation pump and pool would go down with my PG&E power. I would need to decide if all three sections of my solar ( 2 Sunny Boy 7000s = 5500 watts each and one Enphase based system = 4000 watts ) would be used by my powerwall battery storage. That decision would be based on my battery capacity and whether it would take all three to charge on a good winter day. Everything would be AC coupled.
From there, my system would be similar in structure to yours. I would assume I would manually limit my power use when running on backup power to be sure I didn't exceed the inverter limit peak and be able to survive cloudy days if necessary. Fortunately the PG&E shutdown due to fire risk will occur in the fall from August till November when we only rarely have rain or cloudy days. So I would typically have decent solar so I would want a typical November day solar production to fully charge the batteries. Then I would want to easily go through the night on battery power. If it was cloudy, I would tighten my belt and try and limit my power usage to stretch the batteries as long as possible if I knew it was needed. I would probably use a Raspberry Pi and Python to perform the control over the system and allow reporting via WiFi to my PC inside my house. It would monitor and control the various components including the ATS, Inverter, charge controller, batteries, environmental, misc etc.. I would probably use used Tesla batteries as can be found on EBAY and add a commercial BMS rather than the Tesla custom BMS.
That should be enough to get your initial thoughts. Could you list your final components and any you discovered later that you thought you might have used. I'm not worried about UL as my main concern is figuring out how to get the main electrical approved by the building department without them digging into everything. Hopefully the commercial ATS would go a long way to meeting the building codes if it all was done to support a generator backup rather than a PW battery system. If most of this was in my garage, it would be subject to less scrutiny. That is my concern.
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Alright lots of info there, here's a couple things:
You won't be able to curtail because the M215 don't support it. In other words you can't slowly raise the grid freq 1hz at a time to lower the solar output by x% per hz. You can still however trip using freq shift, meaning that if the freq goes to 62.5hz they'll shut off. This is good to keep in mind while looking at inverters since curtailing is more expensive than just AC freq trip.
is 11kW the max you've ever seen or the average? You'll want to know the max it outputs for the next calculations, for example here are mine
I used the table above to calculate the charging rate for each module and cell to ensure I wasn't charging the cells at a rate higher than they were designed, to figure out if I would need cooling during charging and the size of my fuses (after figuring out the max usage of my loads). You'll also want to know the max solar output to figure out what size inverter you'll need.
Here's my parts list for the major components, I already had things like RPI, contactors, etc.
Interconnect Pannel $206.03 Amazon 6/1/19
ATS $232.68 Amazon 6/1/19
Hose to drain battery coolant $10.50 Lowes 5/22/18
BMS $2,495.00 EVTV 5/17/29
Four Module Harness for BMS $59.95 EVTV 5/17/29
Four Module Extension Harness for BMS $59.95 EVTV 5/17/29
Sigineer 12kW $2,695.00 EVTV 5/17/29
Surge Protector $119.95 EVTV 5/17/29
Surge Protector $119.95 EVTV 5/17/29
60kW Battery Pack $11,200.00 eBay 5/17/19
Pack wall mounting hardware $30.37 Lowes 6/11/19
Hydraulic Crimper $35.95 eBay 6/2/19
Module Level Fuses + Holders $82.54 OnlineComponents 6/11/19
AC Relay for ATS $11.99 Amazon 6/11/19
Bus Bars $133.13 Alro Metals 6/4/19
Insulator, 20mm Hgt, M6 Thread $33.27 Galco 6/6/19
Line Splice $70.24 Amazon 6/11/19
Wire Cutter $17.65 Amazon 6/11/19
Vise Brake $34.95 Amazon 6/11/19
Q280 Breaker (2) $60.00 Amazon 6/11/19
Q250 Breaker $9.91 Amazon 6/11/19
The main issue I see with your current setup is that you have a supply side interconnection, so islanding your home during a power outage will also disconnect your solar since that is on the meter socket itself, Would you happen to have a diagram of your circuit? I want to make sure I'm reading your post correctly, even a hand drawn one will do.
You also mentioned not being worried about UL, keep in mind that a lot of AHJs require UL listing when submitting your plans, if FL requires it I'm sure CA does as well.
You won't be able to curtail because the M215 don't support it. In other words you can't slowly raise the grid freq 1hz at a time to lower the solar output by x% per hz. You can still however trip using freq shift, meaning that if the freq goes to 62.5hz they'll shut off. This is good to keep in mind while looking at inverters since curtailing is more expensive than just AC freq trip.
is 11kW the max you've ever seen or the average? You'll want to know the max it outputs for the next calculations, for example here are mine
I used the table above to calculate the charging rate for each module and cell to ensure I wasn't charging the cells at a rate higher than they were designed, to figure out if I would need cooling during charging and the size of my fuses (after figuring out the max usage of my loads). You'll also want to know the max solar output to figure out what size inverter you'll need.
Here's my parts list for the major components, I already had things like RPI, contactors, etc.
Interconnect Pannel $206.03 Amazon 6/1/19
ATS $232.68 Amazon 6/1/19
Hose to drain battery coolant $10.50 Lowes 5/22/18
BMS $2,495.00 EVTV 5/17/29
Four Module Harness for BMS $59.95 EVTV 5/17/29
Four Module Extension Harness for BMS $59.95 EVTV 5/17/29
Sigineer 12kW $2,695.00 EVTV 5/17/29
Surge Protector $119.95 EVTV 5/17/29
Surge Protector $119.95 EVTV 5/17/29
60kW Battery Pack $11,200.00 eBay 5/17/19
Pack wall mounting hardware $30.37 Lowes 6/11/19
Hydraulic Crimper $35.95 eBay 6/2/19
Module Level Fuses + Holders $82.54 OnlineComponents 6/11/19
AC Relay for ATS $11.99 Amazon 6/11/19
Bus Bars $133.13 Alro Metals 6/4/19
Insulator, 20mm Hgt, M6 Thread $33.27 Galco 6/6/19
Line Splice $70.24 Amazon 6/11/19
Wire Cutter $17.65 Amazon 6/11/19
Vise Brake $34.95 Amazon 6/11/19
Q280 Breaker (2) $60.00 Amazon 6/11/19
Q250 Breaker $9.91 Amazon 6/11/19
The main issue I see with your current setup is that you have a supply side interconnection, so islanding your home during a power outage will also disconnect your solar since that is on the meter socket itself, Would you happen to have a diagram of your circuit? I want to make sure I'm reading your post correctly, even a hand drawn one will do.
You also mentioned not being worried about UL, keep in mind that a lot of AHJs require UL listing when submitting your plans, if FL requires it I'm sure CA does as well.
Good morning, wonderful post and very informative
I'm considering the full pack evtv route can you tell me what I need to worry about? I'm definitely not able to figure the intricacies you have gone through designing your system. I might be able to assemble from drawings. I am about to build a new home with 10k solar panels on the roof.
I'm considering the full pack evtv route can you tell me what I need to worry about? I'm definitely not able to figure the intricacies you have gone through designing your system. I might be able to assemble from drawings. I am about to build a new home with 10k solar panels on the roof.
A DIY Powerwall is not an easy undertaking. If you don't have a strong background in electrical engineering, it's probably best to get a commercial product (like a Powerwall or similar) professionally installed.
pgrovetom1
Member
I wasn't aware of there being an ability to "curtail" solar inverters using the frequency. Where is this specified and does the Sunny Boy 7000 implement this capability? I was aware of the ability to shut off any UL1741 inverter by raising or lowering the frequency above or below the limit. It seems almost abusive to use that capability to cycle the inverters every 5+ minutes plus charge time. I was a system designer and shutting down system power that frequently just seems like a rough way to limit charging.
Another thing that bothers me is both my solar inverters produce 240V and not true split phase 120V. That suggests that home 120V appliances cannot really use solar inverter power since they draw power between neutral and one 120V phase which my inverters do not support. That suggests solar power cannot be used by the home except real 240V appliances. The home would only be able to use true split phase 120V/120V to neutral and the system inverter must support split phase with flexible loading on either phase. Is my thinking correct? Tesla's PW2 inverters claim to produce flexible split phase with the load on either 120V phase.
The charging problem: I don't see a charger power supply in your list and the one you specified in an earlier post is no longer available. Solar inverters are current sources. They won't naturally provide less than 100% of the available solar power less inefficiencies. They will increase their forcing voltage to try and force current into a grid load. If they cannot Force 100% of their current onto a load, they will increase their voltage until they shut down due to overvoltage. That is not good when one is trying to limit both the maximum charge current into the batteries and stop charging one the battery is full.
So I'm not sure how your actual charging system works. An off the shelf power supply doesn't provide the constant current needed for Lithium batteries plus must be stopped at the maximum voltage and switched to a voltage source and then stopped. What capabilities do the Tesla BMS's offer? Does Tesla provide specs on that? I see "BMS $2,495.00 EVTV 5/17/29" but I don't understand how one goes from raw AC to a proper Lithium charger with the appropriate current limit, overvoltage limiting, undervoltage cutoff, low temp cutoff etc being done by a coordination of a powersupply and the Tesla BMS, EVTV and solar inverter curtail or 60HZ 5 minute shutdown cycles. I need to look at it closer.
Doesn't it mean the maximum power output of my solar inverters at say 11KW must not EVER exceed the maximum charger current of the battery pack ( or there must be a way of throttling the inverters such as the frequency control you mentioned). But my Sunny Boy solar inverters were producing 6.6KW yesterday afternoon which was a sunny day just past the lowest sun day of the year. So wouldn't the battery pack size be set roughly at my 11KW or 11KW+4KW= 15KW per day full output since that's the most KWHRs I can charge in a day. That suggests my battery size is about the size of 60KHWHrs of a full Tesla battery pack since I can produce about 70KWHrs on a sunny summer day.
I need to measure how much power I can get away with over night to see what my lower limit is. The PG&E power shut offs this year were 3 days each and we rarely have cloudy days in August thru November. That would set my lower battery size that will "get me by". Since I can only produce about 6-7KW peak in November, that would suggest a battery size in the 30-40KWHrs size since a larger battery would have little value in November or during winter storms when the power outages are most likely. One can buy 5KW Tesla modules for about $1000 on EBAY which would require about 6 or so for $6000. Two Tesla PW2's would be 28KWHrs with 10KW continuous power output.
The Tesla PW2 design moved my 2 Sunny Boy's that are line side fed to a 200A panel on the house side of the Gateway which acts as an ATS. My thinking was to move it inside my ATS also. That would eliminate your concern. 200A panels are cheap.
The quote I have from Tesla pairs my 2 Sunny Boy systems with each of one a 200A panels and 1 Powerwall 2 each. They said this was done to avoid the 120% panel current limit rule. They left my Enphase M215 system outside the Gateway so that it isn't used for charging the PW2's. It only acts as a Grid Tie system and backfeeds Grid power while PG&E power is present only.
I have separate diagrams for my 2 systems. I have a hand done diagram of my entire system I sent to Tesla, I'll post next. I used to use a SMA RS485 monitor for my system which no longer works after 11 years. I only had one Sunny Boy failure in 11 years. So I stopped watching my system production years ago. Before my solar I had a $900+ per month PG&E bill. Now I get about $500/year check. So my system saved nearly $10k per year over 11 years it paid off during the third year. I occasionally walk out and look at the power production on the Sunny Boy panel. I checked it a few times last summer around 1PM or peak sun and say power in the 5.3-5.5KW range. Its possible it exceeds 11KW on the perfect day after I clean the panels but not by much.
If I choose to not use my Enphase based system and use less batteries such as 30KWHrs, I could use the curtail method if Sunny Boy 7000's support it. That would seem less "gross" than the shut it off for 5 minutes or more approach. I'm getting lost in details and need to get my diagram and go back and study yours.
I left and looked at your diagram:
I see the inverter charger is connected to grid only power on your service entrance panel. How would the charger get solar power for a power outage longer than one day. It appears not possible for your inverter charger to recharge off solar production each day while in backup mode. Its AC input is grid only and not connected to your house loads panel where the solar power would appear each day while the grid power was down. It would appear the Sigineer Inverter acts as both an inverter with frequency control and as your charger supply. I will look at its capability. I see Sigineer appears to have a number of products that look like possible fits to this problem. How does the"BMS $2,495.00 EVTV 5/17/29" coordinate between the Sigineer Inverter/charger and the Tesla custom BMS's on each module?
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pgrovetom1
Member
This is just a stream of conscious and not a design.
Here is a diagram showing a Tesla PW2 implementation. My thinking was a similar architecture where one of their PW2 systems was replaced by a single 12KW/30KWHr DIY system consisting of about 30KWHrs of 6 Tesla 5.2KW modules and one "Sigineer 12000 Watt 48 Volt to 120/240Vac Whole House Inverter Charger Pure Sine Wave UL 1741 compliant". It charges the modules from AC derived from either the grid ( while up) or solar inverters ( while in backup and daytime with sun shining) and produces 12KW from the batteries. The Tesla PW2 gateway is replaced by a Automatic Transfer Switch as used in a generator backup capability. It disconnects everything on the home side ( not including my pool, well or irrigation pump power) which then runs off Sigineer 12KW inverter which alternately chargers batteries from solar during the day and battery at night. The ATS would provide full home isolation when grid power was off protecting from powering the grid accidentally. That would island everything. The Sigineer ATS capability would be used to shift between night battery power and daytime solar power. This is where the solar inverters not providing 120V split phase would be a problem. So it would need to be arranged that the Sigineer inverter always runs while in backup and the solar inverters run also such that the Sigineer draws both charging current from 240V from Solar Inverters while at the same time providing 120V split phase for in home usage. I'm not sure if this actually works. It may be necessary to use a contactor relay to switch the solar inverter 240V to the Sigineer input and let the Sigineer power the home while in backup. Then the Sigineer is controlled by the Raspberry Pi to switch its power source from AC from solar inverters or the batteries. Needs some further thinking and investigation. I would use a Raspberry Pi I set up and coded. It would be used to control things not properly controlled by existing stuff and monitor for problems and report into my home via a simple Web Interface.
Here is a diagram showing a Tesla PW2 implementation. My thinking was a similar architecture where one of their PW2 systems was replaced by a single 12KW/30KWHr DIY system consisting of about 30KWHrs of 6 Tesla 5.2KW modules and one "Sigineer 12000 Watt 48 Volt to 120/240Vac Whole House Inverter Charger Pure Sine Wave UL 1741 compliant". It charges the modules from AC derived from either the grid ( while up) or solar inverters ( while in backup and daytime with sun shining) and produces 12KW from the batteries. The Tesla PW2 gateway is replaced by a Automatic Transfer Switch as used in a generator backup capability. It disconnects everything on the home side ( not including my pool, well or irrigation pump power) which then runs off Sigineer 12KW inverter which alternately chargers batteries from solar during the day and battery at night. The ATS would provide full home isolation when grid power was off protecting from powering the grid accidentally. That would island everything. The Sigineer ATS capability would be used to shift between night battery power and daytime solar power. This is where the solar inverters not providing 120V split phase would be a problem. So it would need to be arranged that the Sigineer inverter always runs while in backup and the solar inverters run also such that the Sigineer draws both charging current from 240V from Solar Inverters while at the same time providing 120V split phase for in home usage. I'm not sure if this actually works. It may be necessary to use a contactor relay to switch the solar inverter 240V to the Sigineer input and let the Sigineer power the home while in backup. Then the Sigineer is controlled by the Raspberry Pi to switch its power source from AC from solar inverters or the batteries. Needs some further thinking and investigation. I would use a Raspberry Pi I set up and coded. It would be used to control things not properly controlled by existing stuff and monitor for problems and report into my home via a simple Web Interface.
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