Dual battery setup for off grid solar

Author	Message
Godoh Guru Joined: 26/09/2020 Location: Australia Posts: 712	Posted: 08:22am 20 Jun 2026       We have a 24 volt off grid solar system. At the moment if the cloud cover is heavy and no solar energy is generated we have 3 days max of power in the batteries before they drop to 70% charge. Our batteries are BAE valve regulated lead acid batteries at 24 volts and 660 amp hour. We are thinking of getting another bank and using a switching system to change over banks when we have cloudy weather. ( in winter we are in the clouds a bit). It is rare that we have no power input at all but it does happen, recently I had to resort to a small petrol motor and car alternator to top the batteries up. The spec sheets for the batteries say that if we only use the top 30% of the capacity they should last around 15 years. That would be nice. So I have ordered two 500 amp kilovacs to do the switching, but I need both banks to be kept charged when the solar input is enough. I was thinking of using a voltage controlled relay to switch the kilovacs, so that when one bank is fully charged then the other would be switched on to supply power and also be charged up. I am just wondering if anyone here has ideas on the best way to run the system. Our original bank of batteries are now about 8 years old and still in good condition, obviously I don't just want to parallel a new bank to them. Thanks Pete