Stumped - Sol-Ark 2x 15x setup uses battery when it shouldn't

[BMEP]

I have a new Sol-Ark whole home backup setup and a really strange problem that, so far, neither myself nor Sol-Ark has not been able to figure out.

Problem: Charge the battery to 100%, once reached, the inverters immediately start using battery power. The inverters will discharge the battery to 96% and then immediately begin charging back to 100%. This cycle continues all day, as long as there's a source to charge. If there is no source (e.g. no PV after sunset), the battery sits at whatever percentage (like 96% for example) it was when charging stopped. I've never seen it below 96% and it's never stayed at 100%

I just got permission to operate from my utility this week so I've had the PV on for a few days and this cycle happens throughout the day. I've had the system operational for 2 months and noticed that the battery would always stay at 96%. I didn't think anything of it because without PV, there was no source of charging (unless I explicitly turned on "grid charge" or forced Gen Charge, both of which I tested but did not leave on). So I believe this behavior has been present all along but because I didn't have a charging source in use, I never noticed it until I finally turned my PV on.

The BMS display agrees with the displays in the inverters as far as state of charge and charge or discharge. i.e. When the BMS display says "97% SOC" so do the Sol-Arks. When the BMS display says "charging 2,000W", so do the Sol-Ark displays.

I reviewed all config settings with Sol-Ark and they see nothing wrong, yet they can't explain why this is happening or how to stop it. There has to either be something I'm missing or a problem with the inverters.
Here's an example of the charge/discharge cycle



One really odd thing I noticed... when the inverters are discharging, one of them discharges at various rates, like you'd expect but the other seems to limit itself to about -3A. In the graph below, blue is one inverter, yellow is the other.



Anybody experienced anything like this before?

Setup details

• New install - been in service w/o NEM for 2 months, just got NEM permission to operate this week.
• 400A service
• 2x 15k-2p in parallel - install is just like Page 54 in the current 15k-2P manual
• 17.5kW PV, 5 strings (inv1 has 3 strings, inv2 has 2)
• 10kW HomeGrid Stack'd battery. All settings in Sol-Ark setup reflect the recommended settings from HomeGrid The batter is wired in parallel to both inverters with 4/0 (i.e. oversized) cable. Also, the connections to the inverter "batt" terminals are using bus-bars so both +/- inputs on each inverter are utilized.
• 100% of load on "load" terminals (i.e. no "critical loads panel/setup)
• 26kW generator, on "Gen" terminals, setup for 2 wire start from master inverter

Config:

• Battery: All settings match HomeGrid's recommendations. Nothing checked on Smart Load tab.
• Limiter
  • Grid Sell checked - limit set to 9,000 (on each inverter)
  • Limited Power to Home - unchecked
  • Limited Power to Load - checked
  • Time of Use - unchecked
• Limiter/Other
  • Gen connected to Grid input - unchecked
  • Zero Export power 20W
  • Batt First - checked
  • Load First - unchecked

 

[DIYrich]

I assume you are NEM3.
Try this:

Uncheck Limit to Load. Export whatever you can't use.
Check Load First. You want to power loads as much as you can.
Enable Time Of Use.
Power to 15,000.
Battery to 20%, or whatever reserve level you want. Make this number above the grid charge level on the battery screen, so you don't charge from grid.
Ucheck charge and sell boxes.
Put time periods in order.

The above should maximize self consumption.

 

[BMEP]

Thanks @DIYrich - I'll give it a try. FWIW, I'm NEM2 - long story but I managed to get grandfathered because my service (new construction) hadn't yet been installed on the 4/15/23 deadline. It's taken me this long to finally get the house done and the solar setup together.

I also posted this on the "Sol-Ark Owners Information Network" FB group. Questions people asked pointed out some interesting things. I noticed that the float/absorption/equalization voltage settings are changing during the day - and roughly coincide with my charge/discharge cycles. Fortunately, I have Solar Assistant integrated with Home Assistant do I have some data collection happening. Here's what those 3 voltages are doing during the day. I assume the BMS is changing them. This kind of makes me want to set them manually and try open-loop to see what happens. Dunno, maybe it's normal for the HomeGrid BMS to dynamically change those? I will definitely share this with Sol-Ark tech support.

 

[DIYrich]

If homegrid is changing your settings, it may be a homegrid problem. Try voltage mode / open loop.

If you buy/sell at the same price, then uncheck limit to load, and uncheck time of use.

My SA has a constant draw of around 100w off the battery. Annoying because PV has to recharge it before exporting.

 

[Oldphile]

I had a few issues including 200 watt idle current on a single 15K. I did a factory reset and all problems vanished.

 

[2TrevorJ]

Glad i could help on FB. I've never seen it on my setup but if the voltage request is changing on the battery info screen then it's squarely a HomeGrid problem and I would expect them to work the issue.

You paid a premium for what should be bulletproof closed loop operation. Light em up.

 

[BMEP]

Glad i could help on FB. I've never seen it on my setup but if the voltage request is changing on the battery info screen then it's squarely a HomeGrid problem and I would expect them to work the issue.

You paid a premium for what should be bulletproof closed loop operation. Light em up.

You definitely got me pointed in a new (good) direction - thanks! For fun, this morning, I waited until the battery was at 100%, unplugged the CANbus connection, unchecked "lithium battery" and set the charge voltages to the HomeGrid spec of 53.2V (which is crazy low to me, but whatever). It is not flip/flopping any more. The inverters see the SOC as only 45%, which interestingly has not triggered my generator, but oh well. I'm unable to create an account with HomeGrid, despite them saying they "set it up on their end" so I'll have to wait until Monday when I can talk to their tech support.

 

[PulseSolar]

Run the battery SOC down to your lowest point then charge back to 100% this will help get the SOC reading correctly on the inverters. Also make sure the resistance battery setting is correct.

The number of milliohms depends on how many batteries you have in parallel. Each battery has internal resistance which you need to know, then use a simple resistance calculator to find the total milliohms. I can tell you with 12 EG4 ll 48v batts the setting is about 8milliohms. Keep in mind these numbers are milliohms not ohms as some people think. The EG4 48v batteries are about 100milliohms each. 100 mΩ = 0.1 Ω

You can ask google something like this "12 .1ohm resistors in parallel equal what ohms"

 

[Chris72]

Did you get this fixed because I had a similar problem but I was discharging the battery when I had a heavy load on the inverters. Even though it was supposed to ignore the battery. It turned out to be grid Peak shaving. Even though I had my time slot battery percentage for time of use at 100% state of charge it would still use the battery to help with loads.