Alooma

I had 2 x 48V 2000AH LiFePO4 batteries connected to 2 x Growatt SPF5000ES. Some of the cells of the batteries were not performing well resulting in ALARM being raised when the batteries are about 43% and 25% SOC despite the Inverter 'Low DC cut-off SOC' set at 20%. The issues was reported to the manufacturers in China and since the batteries were under warrantty, I was offered a replacement for the one that was worse. However, I was advised that I could not mix an old battery of 3 years with a new one, so I had to purchase two new 48V 2000AH batteries. The new batteries have arrived but I would like to explore the possibility of using one of the old batteries that was not performing too poorly with the new set. The cost of the batteries does not encourage just scrapping them. Besides the solar system would be enhanced with 3 x 10kW batteries. The new batteries have latest PACE BMS but no idea about the BMS of the old batteries. I have read a number of articles and watched videos indicating that old and new batteries having different BMSs could be connected in parallel. I would like advice on the following 2 options: Option 1 - Connect the three batteries in parallel with the new set as MASTER and SLAVE 1, and the old one as SLAVE 2. I am assuming that the BMS of the old batteries would communicate with the BMS of the new batteries. Option2 - Use the battery banks separately - Bank A for the 2 new batteries and Bank B for the old battery. This entails connecting only Bank A to the Inverter while Bank B is diconnected. And disconnect Bank A when Bank B is connected. Your advice would be much appreciated including pros and cons as well as simplicity of the options.

UPDATE. I am yet to get the installer to review the earthing of the SPD. However, I got someone to get to the roof and shoot the video of the panels. I found out that they are very dusty - installed about 3 months ago. I wanted to get someone to help clean them with water, but fortunately, it rained last night. This morning, my Solar Power generation went up to 23kWH for the day, and was able to get the Amperes unto 9A midday fro the previous maximum of 2.3A. I will continue monitoring and hope that the installer will check the earthing. Meanwhile, I think that if the panels are properly cleaned, I could get nearer to the expected 31kWH per day at this time of the year.

Thanks. I will check on the earth connection with the installer. The use of right image files is noted. I again wish to state that I do appreciate your time and effort in helping to resolve my issues.

Thanks. I am are-checking the spec of the Combiner Box. I think that there are wo SPDs, but will confirm with the installer.

All the panels are facing South and the roof is at an angle around 7 degrees. The photograph of the Combiner Box is attached. Combiner Box.HEIC

Thanks. The suppliers in China suggested two inputs and two outputs combiner box. The spec is attached. I also notice that the panels are dusty, I am planning to get these cleaned as they are on the roof, and then try to measure each panel's output into the combiner box and out of it. The issue now is getting the local installer. Since the two strings give almost the same Amperes, it could be the combiner or even the wiring. I will update you as I progress. I do appreciate your help.

Thanks for your response and contributions. I totally agree with you that it does not make sense. I will have to invest in checking the entire wiring of the panels, it is possible that there is a mistake somewhere and the two inverters are reporting similar Amperes. And if I can add, there is no shading.

Thanks.

I have tried to put loads on the system, but the batteries were used to support the solar power. The solar power is just not being harvested enough with a maximum of about 2.8A. The voltage has been good at about 280V. The 16 panels are connected in series of 8 to each Growatt SPF 5000 ES Inverter. The two inverters are connected in parallel. The cables from each series are wired to the Combiner Box and then to the Inverters.

Thanks for your response. The panels have Vmp of 31.6V and Imp of 17.4A. The distance from the panels to the Inverters is about 10 metres. But could the use of the 10mm reduce the Amperes by almost a third? I am getting about 10kWH daily and the expected power from 16 x 550W at this time in Lagos, Nigeria is about 31kWH.

What is the recommended wire specification for connecting solar panels? The local engineer suggested 10mm instead of 4mm, and I am experiencing really low Amperes from the panels. Could the wires be the cause?

Hi @zsde, do you know the latest firmware of the Growatt SPF 5000 ES?