Battery Isn't Tied to All Roof Panels

[Jomby]

I had solar installed and a BYD battery backup with sunny boy storage installed but learned that only half my solar panels are wired to the battery, the other half aren't. I would think you would want all panels wired to charge the battery so that when power goes down there is sufficient solar production to not only charge the battery but also to power the critical load during the day. Is this not possible? I have 2 inverters, half the solar panels go to each inverter and battery is only hooked to one of these inverters is my understanding. Effectively when power goes down half of my system is doing nothing? Seems silly not to have all panels running to battery to ensure critical load is powered by solar during day and by battery at night?

[Ampster]

Tell us more about the specifics of your inverters and the other parts of your system? Two thirds of my solar panels are not connected to my batteries. That is because they are connected to Grid Tie inverters but the GT inverters are AC coupled to the battery inverter so I can charge batteries from all my solar. In my case is was cost effective to do it that way. It is a system that is best analyzed by looking at all the parts instead of just one piece.

[SunEagle]

The panel wattage can be a factor as to how many panels are connected to the battery system. You can't always connect all of them because it might be too much for the Ah rating of the battery system.

As Ampster asks, please provide us with some info on your system.

[Jomby]

There are 30 panels and 2 inverters; 15 panels to each inverter. Panels are 340 watt.10 kwh BYD battery storage. I'm new to all of this so I aplogize. Let me know if there is other info you would need to provide insight. Thanks for your time. Sub panel is 125 amp. Main panel is 200 amp. One of the two inverters runs to the battery and that same inverter goes to the sub panel is my understanding. The other inverter goes
to grid.

I'm just thinking if both inverters went to battery and battery was fully charged it would then feedback through sub panel to the grid?

[oregon_phil]

There are 30 panels and 2 inverters; 15 panels to each inverter. Panels are 340 watt.10 kwh BYD battery storage.

I think you should get an electrical diagram from your installer. Please have them explain your installation to you. I do not think your installation is built as you described it.

I am guessing the installer installed ONE SMA 7.7 -41 SOLAR inverter for your 10.2kW of solar panels. This inverter converts the solar panel DC to split phase 240VAC.

Your BYD battery is connected to ONE SMA SUNNY BOY STORAGE 6.0 US BATTERY inverter. This inverter converts the battery DC to split phase 240VAC.

The two inverters are electrically connected on the AC side hence Sunny boy storage 6.0 AC coupled architecture. Look up the data sheet on the SMA america website. I believe your set up is configured for "energy management" not "backup system" because you didn't mention a transfer switch.

I could be wrong with my assumptions, but I bet I am close because SMA doesn't make a hybrid inverter.

It sounds like the battery inverter is connected to the sub panel as a critical loads panel, but until you look at the schematic you won't know for sure. I think you have the correct number of inverters.

What was your goal for the entire system? Energy management or backup per SMA brochure?

[Jomby]

I think you should get an electrical diagram from your installer. Please have them explain your installation to you. I do not think your installation is built as you described it.

I am guessing the installer installed ONE SMA 7.7 -41 SOLAR inverter for your 10.2kW of solar panels. This inverter converts the solar panel DC to split phase 240VAC.

Your BYD battery is connected to ONE SMA SUNNY BOY STORAGE 6.0 US BATTERY inverter. This inverter converts the battery DC to split phase 240VAC.

The two inverters are electrically connected on the AC side hence Sunny boy storage 6.0 AC coupled architecture. Look up the data sheet on the SMA america website. I believe your set up is configured for "energy management" not "backup system" because you didn't mention a transfer switch.

I could be wrong with my assumptions, but I bet I am close because SMA doesn't make a hybrid inverter.

It sounds like the battery inverter is connected to the sub panel as a critical loads panel, but until you look at the schematic you won't know for sure. I think you have the correct number of inverters.

What was your goal for the entire system? Energy management or backup per SMA brochure?

I should have explained further. There are two inverters 15 panels to each inverter and a separare battery inverter; 3 inverters total. Also I'll look further in the morning but I can see the SMA battery management unit appears to only have one of the solar inverters feeding it while the other goes straight out to main panel. I'll see if I can locate the plan diagram. Is there a limit on how much can go to the sma battery management unit? It looks like 50 is allowed based on sticker and the amps from each inverter appears to be just under 25 amp.

[chrisski]

Is there a max amperage your BYD bank can charge at?

My 4 12 volt Trojan batteries totaling 458 AH and a little over 5 KW can only be charged with 60 amps. I can put in 13% of total battery power at the 20 hour rate. In theory, I should be able to reach that limit with 800 watts of panels, but because these panels are never in perfect sunlight, it takes me around 1300 watts to reach 60 amps.

Other batteries have different charge rates, and I'm sure for a battery bank twice my size even with a charging chemistry of something that can be charged closer to the full 20 hour rate nine times the panels would come close to exceeding that max charge rate. Don't quote me on this, but lithiums might be charged at up to 100% the 20 hour rate, and AGMs close to 20% the 20 hour rate.

[Ampster]

.....I can see the SMA battery management unit appears to only have one of the solar inverters feeding it while the other goes straight out to main panel. I'll see if I can locate the plan diagram.......

Is your observation based on a diagram that you can share or based on reports that you are seeing when the system is operating? Could it be that you are using less than the system is producing and the excess is being sold? Have you tried to put more load on system and observed if the sell back to grid is reduced?

[Jomby]

In diagram below (red arrow) I'm wondering why the 15 panels can't also go to the sma automatic battery backup unit so that if I have substantial draw in daytime with sun up I can power something like my heat pump. Longer term I may add an additional 10 KWH battery for heating during night as my energy during night my usage with no rationing is 1.5 to 2 kwh per hour so I figure cutting out something like the water heater reducing light usage etc. but at least during the day I figure I could either heat up or cool down the house. I don't really have space near my service panel to put generac generator and propane tank. Also at 1.5 kwh my heat pump is more effective than space heaters would be I would think. sketch.JPG

[Ampster]

Okay, I understand your diagram. Yes during a power outage you can only use half your solar panels. During normal operation the solar connected to the main panel shoul also feed your house loads first before going to the grid. You can test that by turning on more loads.
I think this issue turns on the earlier question by @oregon_phil about the system design goal.

[Jomby]

My goal is to not just charge the battery but be able to power off all 30 panels when grid is down. Currently 15 panels on a cloudy day looks like it would only support charging the battery; no usage.

[Ampster]

Your goal and the system design goal may not line up on a cloudy day depending on your usage and how much you used the batteries the prior day. It would be easy to test by turning off your main breaker one day. You could do that on a cloudy day or sunny day. Do you have good data from your system to give you meaningful data?

Currently we only have a hypothesis. I did a test like that six months ago and concluded I did not have enough batteries, especially if the skies were blocked by clouds or smoke.

[Jomby]

Could it simply be rewired to have all 30 panels flow through the sma automatic backup unit? I must be missing something. Why wouldn't you have all 30 panels wired/available during the day with grid being down?

[oregon_phil]

My goal is to not just charge the battery but be able to power off all 30 panels when grid is down. Currently 15 panels on a cloudy day looks like it would only support charging the battery; no usage

BTW, thanks for the schematic. That saves so much trouble and guessing. I am not an electrical engineer, but am a retired engineering that is researching whole house backup solutions for wildfires. So take my advice with a grain of salt and review all and anything with your electrician/inspectors.

What exactly did you tell that to your installer? Did the installer make you sign off on the technical design before buying materials?

**You want full house backup powered by the battery inverter and ALL solar panels.

As you stated, the current configuration doesn't work this way. A transfer switch needs to be on the "line" side main panel to isolate your entire house. But I think I know why your system is configured the way that it is. The SB 5.0 solar inverter generates 21 amps max at 240VAC. 2 X 21 amps = 42 amps for two inverters. Minimum breaker size is 1.25 x 42 amps = 52.5amps. The internal breaker in the SMA transfer switch is only rated for 50amps; this would be a violation.

The SMA transfer is not service rated, but this can have a work around.

The other thing that sticks out in my mind is that you have 125 + 30 = 155amps of PV/Battery generation breakers in your main panel. That leaves you 240- 155 = 85 amps left in your main panel. In other words, your main panel should have an 85amp max breaker on the top of the main panel.

Like I said, I'm not an electrician, so please check my math.

[oregon_phil]

Now that I think about it, the 125amp breaker in the main panel may or may not be considered PV/battery generation if the transfer switch is set for zero export. So forget my statement above about the main panel breaker size.

If you look at the SMA transfer switch manual, it says 9.6kW AC max for the solar inverter. So my assumptions about your two inverters being greater than 50amp max was correct.

You also didn't say what kind of rapid shutdown and/or power optimizers you have installed. In other words, are all the panels facing in the same direction and is there shadowing at all?

Depending on your roof situation, you could get one larger inverter for all the panels in three strings using a SMA 7.7 -41 at 32amps/240 AC out to hook up to the transfer switch. This will work with the 50amp breaker. But then the entire transfer switch and additional shutoffs will have to be moved between the meter and main panel. The SMA has a lot of solar/battery functionality built in, but it is relatively brand new. I bet nobody has too much experience with it here.

Like I said, I was researching backup solutions for my house during wildfire seasons and have looked extensively at 200 amp transfer switches. These transfer switches are monsters compared to the SMA transfer switch. In other words, I doubt that the wire from your electric meter to your main panel will fit in the SMA transfer switch. Your existing wiring is probably aluminum.

Re-reading the SMA transfer switch installation manual, it says 3/0 to 300 kcmil copper wire will fit in the transfer switch. You push the power wire into the terminal block then slide a lever down to secure it. I'm used to seeing a massive bolt securing this connection, but it probably works.

I am not an electrician. You should have everything verified by and electrician and/or inspector.