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.
I'm not sure if the 7k has it but here;s the official SMA doc with models that support it, page 7 has info on curtailment
https://files.sma.de/dl/7910/SB-OffGrid-TI-US-en-20.pdf
Here's the tech specs on Enphase (although only the IQ line can curtail) page 6
https://enphase.com/sites/default/f...Considerations-AC-Coupling-Micros-Battery.pdf
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.
Wait, your inverters output single phase 240? are you sure it's not split phase 240? I don't know anywhere in the US where single phase 240 is used, that's mostly overseas.
Page 38 in the link below shows the 2 configurations for the 7k, you have the bottom on with only N, L1 and Ground(PE)?
https://www.cedgreentecheast.com/files/SB5678 INSTALLATION(3).pdf
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.
The inverter I'm using is made by Sigineer
12000 Watt Inverter | Pure Sine Wave 48V 12KW Inverter Charger
It's an inverter charger so it has a charger built in that lets you charge the batteries off the grid. However, in an AC coupled system the built in charger isn't used as much, the reason for this is because the grid tied inverters are connected on the output side of the battery inverter. When the battery inverter switches its internal ATS from grid to battery backup it controls the frequency since its internals are generating the sinewave. After 300 seconds (per UL) the grid tie inverters will have synced to the sinewave of the battery inverter and will start to produce power. This power will start to power the loads and start to lighten the load on the battery based inverter, if you are producing more power than the loads require the power will flow backwards through the H bridge on the inverter, will be converted to 48v and it'll be stored in the batteries, if the batteries are nearing full the battery inverter will start to increase the frequency causing the grid tied inverters (which at this point are synced to the battery inverter not the grid) to start to lower their output, when the batteries fill the battery inverter will simply shut off the GT inverters by rising the frequency to 62.5hz or above. The GT inverters will stay off until the frequency drops again.
On my inverter (Sigineer) where there is no gradual shift of frequency only trip, I have my controller configured to listen to the EVTV controller which is sending out messages on the battery state, when a cell reaches 4.1v I tell the Sigineer to trip and turn off the GT inverters. Every 2.5 minutes it continues to trip for 200ms (UL requires a 5 minute timeout between trips before GT inverters can continue to output) this ensures that the GT stay off until the battery drops by 10% (threshold configured by me) at which point my controller stops triping the frequency and the GT inverters start to produce, when a cell reaches 4.1v again the cycle repeats, in reality the time window depending on what loads I have running is about 1.5-2 hours.
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.
The EVTV BMS controller has contactors built into it. It also communicates with the BMB boards inside each module, it gets voltages of every cell plus the temperature for each thermistor. I can configure OV, UV, OT all within the EVTV controller. When one of those limits is reached the contactors inside the controller open.
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.
You're partially correct on the charging side of things, if you remember the table I posted on my last post it had my calculations on it, broken down to this:
14,500kW of solar / 240v = 60.41A, that's the amperage that will be sent to the inverter at no load and full solar (worst case scenario), if we step that down to the 48v side of things (14,500kW / 48) 302.08A will be sent to the pack to charge the batteries. Each module can take a peak of 8kW (360A) and a continuous 5kW (225A) of charging amps. If i had a single module that would present an issue as a spike in solar productiong lasting longer than 10 min (8kW peak) would cause damage, but I have 14 modules, this means that the 302A is actually 320/14 = 21.57A, or in other words, I'm charging each module 52% below the max charging amps. In other words the battery output/input capacity is a lot higher than what my solar can produce so I don't need any kind of charge controlers to lower the amperage being sent to the battery.
Now that being said, near the top end 4v+ side of things throwing that much power will not get you a nicely balanced pack, this is why I have my controller set to disable the GT inverters when a cell reaches 4.1v so the pack can balance itself without reaching its limits.
The second part, you don't always have to match your battery size to your dialy avg output. For around spring I have days when I produce +100kWh but my pack is only 60kWh. when that occurs my controller knows if the grid is available or not if it is, instead of triping the frequency and stopping solar production it tells the sigineer inverter to switch to grid mode (essentially stand by mode in a traditional ATS) this directly ties my GT inverters to my power company grid and sells any excess back after the pack is full.
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.
Yes, having a good idea of power usage is a must here. Oversizing is always fine, under is a bad idea.
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.
That's correct, otherwise AC coupling would be impossible. You could even use the same Siemens panel I used that has an ATS built into it.
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.
You could always de-rate your main to get around 705.12(D)(2) (120% rule), just be careful that you don't de-rate below what you would normally use when no solar is available.
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.
I'll take a look at it in a few, my GF is telling me I need to get off the computer and spend time with her, so ...
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.
Just FYI, when nearing full charge even the PWs use the same shut off and resume method.
Take a look at this video, He logged the status of the PW using the API
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?
I believe I answered some of the charging questions in a couple questions above, as for how to charge in a power our scenario, if you look at the diagram you'll see that the ATS upstream of the house and the sigineer defines what source is powering the home (grid or inverter) the backfeed breaker is on the same side as the house loads so solar will also move back and forth with the house.
Gotta go, I was just told a second time to get off the PC. let me know if that clarifies things.
I'm not sure if the 7k has it but here;s the official SMA doc with models that support it, page 7 has info on curtailment
https://files.sma.de/dl/7910/SB-OffGrid-TI-US-en-20.pdf
Here's the tech specs on Enphase (although only the IQ line can curtail) page 6
https://enphase.com/sites/default/f...Considerations-AC-Coupling-Micros-Battery.pdf
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.
Wait, your inverters output single phase 240? are you sure it's not split phase 240? I don't know anywhere in the US where single phase 240 is used, that's mostly overseas.
Page 38 in the link below shows the 2 configurations for the 7k, you have the bottom on with only N, L1 and Ground(PE)?
https://www.cedgreentecheast.com/files/SB5678 INSTALLATION(3).pdf
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.
The inverter I'm using is made by Sigineer
12000 Watt Inverter | Pure Sine Wave 48V 12KW Inverter Charger
It's an inverter charger so it has a charger built in that lets you charge the batteries off the grid. However, in an AC coupled system the built in charger isn't used as much, the reason for this is because the grid tied inverters are connected on the output side of the battery inverter. When the battery inverter switches its internal ATS from grid to battery backup it controls the frequency since its internals are generating the sinewave. After 300 seconds (per UL) the grid tie inverters will have synced to the sinewave of the battery inverter and will start to produce power. This power will start to power the loads and start to lighten the load on the battery based inverter, if you are producing more power than the loads require the power will flow backwards through the H bridge on the inverter, will be converted to 48v and it'll be stored in the batteries, if the batteries are nearing full the battery inverter will start to increase the frequency causing the grid tied inverters (which at this point are synced to the battery inverter not the grid) to start to lower their output, when the batteries fill the battery inverter will simply shut off the GT inverters by rising the frequency to 62.5hz or above. The GT inverters will stay off until the frequency drops again.
On my inverter (Sigineer) where there is no gradual shift of frequency only trip, I have my controller configured to listen to the EVTV controller which is sending out messages on the battery state, when a cell reaches 4.1v I tell the Sigineer to trip and turn off the GT inverters. Every 2.5 minutes it continues to trip for 200ms (UL requires a 5 minute timeout between trips before GT inverters can continue to output) this ensures that the GT stay off until the battery drops by 10% (threshold configured by me) at which point my controller stops triping the frequency and the GT inverters start to produce, when a cell reaches 4.1v again the cycle repeats, in reality the time window depending on what loads I have running is about 1.5-2 hours.
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.
The EVTV BMS controller has contactors built into it. It also communicates with the BMB boards inside each module, it gets voltages of every cell plus the temperature for each thermistor. I can configure OV, UV, OT all within the EVTV controller. When one of those limits is reached the contactors inside the controller open.
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.
You're partially correct on the charging side of things, if you remember the table I posted on my last post it had my calculations on it, broken down to this:
14,500kW of solar / 240v = 60.41A, that's the amperage that will be sent to the inverter at no load and full solar (worst case scenario), if we step that down to the 48v side of things (14,500kW / 48) 302.08A will be sent to the pack to charge the batteries. Each module can take a peak of 8kW (360A) and a continuous 5kW (225A) of charging amps. If i had a single module that would present an issue as a spike in solar productiong lasting longer than 10 min (8kW peak) would cause damage, but I have 14 modules, this means that the 302A is actually 320/14 = 21.57A, or in other words, I'm charging each module 52% below the max charging amps. In other words the battery output/input capacity is a lot higher than what my solar can produce so I don't need any kind of charge controlers to lower the amperage being sent to the battery.
Now that being said, near the top end 4v+ side of things throwing that much power will not get you a nicely balanced pack, this is why I have my controller set to disable the GT inverters when a cell reaches 4.1v so the pack can balance itself without reaching its limits.
The second part, you don't always have to match your battery size to your dialy avg output. For around spring I have days when I produce +100kWh but my pack is only 60kWh. when that occurs my controller knows if the grid is available or not if it is, instead of triping the frequency and stopping solar production it tells the sigineer inverter to switch to grid mode (essentially stand by mode in a traditional ATS) this directly ties my GT inverters to my power company grid and sells any excess back after the pack is full.
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.
Yes, having a good idea of power usage is a must here. Oversizing is always fine, under is a bad idea.
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.
That's correct, otherwise AC coupling would be impossible. You could even use the same Siemens panel I used that has an ATS built into it.
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.
You could always de-rate your main to get around 705.12(D)(2) (120% rule), just be careful that you don't de-rate below what you would normally use when no solar is available.
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.
I'll take a look at it in a few, my GF is telling me I need to get off the computer and spend time with her, so ...
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.
Just FYI, when nearing full charge even the PWs use the same shut off and resume method.
Take a look at this video, He logged the status of the PW using the API
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?
I believe I answered some of the charging questions in a couple questions above, as for how to charge in a power our scenario, if you look at the diagram you'll see that the ATS upstream of the house and the sigineer defines what source is powering the home (grid or inverter) the backfeed breaker is on the same side as the house loads so solar will also move back and forth with the house.
Gotta go, I was just told a second time to get off the PC. let me know if that clarifies things.