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diy solar

Battery advice and ideas wanted

MBgreen

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May 28, 2021
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Hello,

I have an offgrid property with a solar system. The system is about 8 years old and is due for a new battery bank. I am seeking any advice on what the most cost effective way to do this would be. The system comprises of 3kw of panels feeding into a Sunnyboy 3000HF inverter which is connected to a SunnyIsland 6.0H offgrid inverter. This is currently hooked up to 8 cells of 6V 330Ah sonnenschein sealed lead acid batteries connected in series. So it was originally 15.8kwh of capacity at 48V output.

I am looking for a cost effective way of replacing the battery bank and would ideally like to replace it with lithium ion however my main concern is whether or not the system is compatible with lithium batteries? And also how i would even go about configuring the Sunnyisland inverter to be setup with the new batteries.

I have spoken to a local offgrid electrician who was suggesting that sealed lead acid batteries still provide the best value for money and mentioned that lithium ion is not so great at handling the power surge demanded when appliances like the water pump kick in. Just curious if anyone can confirm this to be true.

I don't use a lot of electricity and only really need 3 or 4 kwh per day.

One option is just to replace the battery bank with the same cells as the original bank. So that would be 8 cells of 6v 330 sonnenschien. These sell for about $650 each here in Australia so about $5200 total for a 15.8kwh sealed lead acid battery bank. That is in AU$.

Another option is to buy 4 of these batteries:

12v 200ah Quantium lithium ion batteries. Connecting 4 of these in series should deliver an equivalent 48V output but I am unsure if there will be other issues that may arise due to compatibility issues. This would give around 10kwh of capacity for around $5000 which seems to be the more economical option whilst still providing more usable capacity and greater lifespan.

Anyway, just interested if anyone has any thoughts or ideas they want to share on this topic. And if I was to go with the second option, what else needs to be done to make it all work other than connecting the batteries?

Thanks for your time.
 
I cannot provide advice on most of your questions.

I would tend to replace the lead batteries with lead batteries- important to know if the SCC has LFP parameters but you can usually enter custom parameters and just not equalize.

Do you have an idea why the current batteries only lasted 8 years? I don’t know those batteries per se but similar setups locally to me are usually 12, sometimes 15yrs.
 
My FLA bank got tired and needed a replacement, when I costed it out (8x Rolls Surette S550's) at $490 CAD ea it worked out to $4400 with taxes.
As that was 22kWh GROSS or 11kWh NET (Useable) and only 85% efficient I had a rethink. I originally looked at recovered / recycled EV cells (Tesla Packs & Bolt Packs) and very quickly realized the issues with those, in particular, the Voltage Curves being ODD and the safety factors as well.

LFP is 99% Efficient. FLA/AGM 84-88% efficient (when fresh & new).
I have spoken to a local offgrid electrician who was suggesting that sealed lead acid batteries still provide the best value for money and mentioned that lithium ion is not so great at handling the power surge demanded when appliances like the water pump kick in.
That is MORONIC ! Old school and not understanding what he is yapping about.
I can easily run (and do) my MIG Welder, Big Compressor off the solar system if inclined and it works without a blink at all. Lemme just say that a MIG will STRESS a system far beyond any "appliance" or pump !

Example:
Typical 24V/280AH Battery Pack can output 280A (1C-Rate) for one hour. LFP is Capable of delivering 5C Burst Rate (1400A for 30 seconds)
24X@280A = 6720 Watts ! which is 56A @ 120VAC or 28A @ 240VAC
More Packs (Complete battery with 8 cells, BMS & Fuse) set in Parallel also DIVIDE the Load & Charge evenly so you are distributing the hit across all packs which does NOT stress them.

To build 48 Volt LFP pack, that requires 16 Cells, one 16S LFP BMS, one 250/300A Fuse and box/casing/frame your choice.
16x 280AH cells Matched & Batched Grade-A = $178.14 AU = $2,850.24 AU + S&H
1, Typical 250A capable BMS (JBD/JK/Heltec) approximately $250
1, Fuse $25.00
COST: $3,125.24 (+S&H) for 48V/280AH/14,336Wh/14.3kWh of which 90% is Useable.
No Watering, No Maintenance, last 10 years+

LINK to Cells: LUYUAN is a Known Good Well Trusted reliable supplier, you can find cheaper but Good Luck.
The only way to get an accurate quote with shipping to you is to open a Chat/Messenger session. The auto-shipping quotes are terrible.


Most Inverter Systems can continue to use the FLA settings with minor changes, ie NEVER Equalize LFP and if that cannot be disabled then set it to no higher than Absorb Voltage and for as short a period as possible. LFP can be FLOATED as well, CONTRARY to MISINFORMATION out there and parroted by those who should know better (as they are outdated). FLA/AGM are "Brute Force" batteries whereas all Lithium Based are Gentle Handed meaning that they are Millivot Sensitive & reactive, therefore system configurations & corrections for voltage drops etc must be addressed.

Hope it helps, Good Luck.
 
Your local offgrid electrician has demonstrated that he is an unreliable source of information. You cannot trust what he says.

With regards to your questions about compatibility of your existing equipment, the best source for answers would be the manufacturers of that equipment.
 
Thank you all for your input. I'll contact SMA and ask if the SunnyIsland has any issues with LFP and enquire about configuration settings. I do like Steve_S's idea of building an LFP battery which sounds a good learning experience too. Appreciate all your time and depth of knowledge. Cheers.
 
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