I’m planning on setting-up a 600AH solar battery bank comprised of LiFePo 12V 100AH batteries, which seem to be the most common (and reasonably priced) type offered by China manufacturers. In order to have a 48v system, it appears that I would have to have 6 parallel strings of 4 batteries connected in series. Is this design feasible? I have seen some solar sites which indicate that max # of battery strings limited to 4 only. Would this set-up need any special balancing circuitry or maintenance?
Your expert advice would be appreciated. Thanks
One for you @Sparky.
I definitely would not do what you have suggested. You do not setup a lithium battery bank setup the same way as lead-acid batteries. Most lithium batteries (depending on the BMS) cannot be used series to increase the voltage as you suggested and this could be dangerous.
Unlike lead-acid batteries which use 2V, 6V or 12V cells in series to get 48V, with lithium you simply purchase a 48V lithium battery module. These are common in Australia and the US and brands like PylonTech and BYD are Chinese so I would recommend these batteries.
Most lithium batteries systems are only designed to be used in parallel, not series.
What inverter are you planning on using? This will determine what lithium battery you can use.
At Most 2 parallel bank more than 2 ( can be a Fire Hazard ) not advisable hard to balanced the charge
Get a pro to design the sys Good luck
Regards Mel Solar Hybrid Solutions
Hi Mel, Martin, Jason;
Thks for your respective replies.
In the Philippines, esp in the provinces outside Manila, you can find only solar equipment ‘installers’ (however not easy to find an experienced one).
Therefore, solar customers (like me) must buy the solar gear (including the inverters) or allow the installer to buy it, but as you might expect, at a (much) higher marked-up price. Warranties are only from the manufacturers.
FYI, the electric utilities do NOT buy any excess power produced from solar set-ups and in some places, off-grid solar systems are not permitted. However, as long as I pay for a back-up grid tie, then I should be able to run off my solar system 95%+ of the time…
One installer who i have contacted recommended installing qty-2 5KW “Axpert MKV” inverters (Taiwan brand I think). However, he was totally unfamiliar with LiFePO batteries or their set-up, which is why I am doing the research myself. Also another system he installed is starting to fail after only 4 years, which I suspect is due to the lack battery balancing circuitry…
How much would it cost to have a ‘professional’ design my solar system?
The most affordable solar/battery inverters are Victron Energy using DC coupled solar controllers. Do you know how to use these?
Can you purchase BYD lithium batteries in the Philippines? These are modular batteries which work with the Victron inverters. Very safe and reliable with 10 year warranty.
If you cannot get Victron or BYD then you need to find ‘self managed’ lithium batteries. This means they have an internal BMS (battery management system) and do not need to be controlled by the inverter with a comms cable.
Axpert MKV inverters are ok but very cheap and you might have some problems with software. They will only work with self-managed 48V lithium battery in parallel.
Thks for your advice. I checked with BYD and they do not yet offer their HV Li B-Box battery in either Singapore or the Phils. Just to help me scope out the economic feasibility, how much would a BYD HV Li battery configured for 600AH capacity and 8KW output cost in Australia? A rough cost would be fine.
Also in researching the battery it raised questions about AC-coupled vs DC coupled designs. My impression from reading various websites is that an AC-coupled design is good for existing PV installation due to the flexibility and simple installation. However does AC-coupled design for a new PV system offer any advantages?
Lastly, the DC-AC inverters used with HV Li batteries seem to top-out at 5KW, which means I would need to install 2 inverters on the same battery bank? Any design limitations or best practice guidelines for doing this?
Appreciate your guidance and advice.
Do not use the BYD HV batteries. Only the BYD LV (48V) batteries will work with the Victron inverter/chargers. The BYD B-Box are some of the lowest cost lithium LFP batteries available and are also modular so you can add more capacity if required.
I would recommend using a DC coupled system using the Victron Multiplus inverter together with the Victron MPPT solar charge controllers and BYD B-Box LV batteries.
Hope this helps,