Good Day,

As the title above states, I am struggling to answer this question, about 5 months ago I started my home solar project. the goal was to lower the monthly spend on electricity.

thus far I would say that the goal has been achieved I went from about +- R2600 to about +- R700 per month. with the system in its current form and changing other things like adding solar tubes to an existing geyser, replacing the electrical stove/oven with a comply gas one, and changing all lights to low-watt LEDs and some other smaller things

Currently, I have 8 x 12V 100Ah batteries that are cabled up so that the system sees 1x 48v 200ah battery. as mentioned these batteries are about 5 months old. I want to increase my battery bank so that I can cope with the number of times we have load shedding in the evening specifically, and also hopefully bring electricity costs down a bit more

so in the end, the question that I am struggling with is, do I get rid of the 8 100ah batteries and go Lithium or do I just add another 8 100ah batteries

looking forward too all your input

More informed people will have to add their view, but common understanding is that you cannot just add newer lead-acid batteries to older batteries. Even if it were technically possible, I'd think that more lead-acid batteries would be throwing good money after bad. If the inverter allows it, I'd go lithium for the cycle life as a next step, but first goal would be to get maximum value for money out of the current batteries, cycle them for all they're worth while they're still good, and hope that a few months down the line the demand and supply situation has stabilised such that battery prices come down.

 

1 hour ago, grahamkhan89 said:

Currently, I have 8 x 12V 100Ah batteries that are cabled up so that the system sees 1x 48v 200ah battery. as mentioned these batteries are about 5 months old. I want to increase my battery bank so that I can cope with the number of times we have load shedding in the evening specifically, and also hopefully bring electricity costs down a bit more

That's already a decent sized battery (to talk in the singular). How fast can you charge it? And how deep can you discharge it?

Long term lithium is the winner. The life you get from them will outweigh the upfront spend. You'll be changing SLAs every 2 or 3 years (more likely 2, given the now constant load shedding). Also you'll probably be able to charge the lithium batteries more quickly, which comes in handy when we're defending against load shedding. They generally can be discharged way past 50% depth of discharge, and in most cases they will take a greater load, which extends the scope of what you can back up. Most lithium batteries on the market right now will be at least 0.5C, which means you'll be able to draw 100a from a 200aH battery.

It's more money up front, but in the long term there are advantages.  

Edited November 7, 20223 yr by Bobster.
clarification

3 hours ago, GreenFields said:

More informed people will have to add their view, but common understanding is that you cannot just add newer lead-acid batteries to older batteries. Even if it were technically possible, I'd think that more lead-acid batteries would be throwing good money after bad. If the inverter allows it, I'd go lithium for the cycle life as a next step, but first goal would be to get maximum value for money out of the current batteries, cycle them for all they're worth while they're still good, and hope that a few months down the line the demand and supply situation has stabilised such that battery prices come down.

 

Noted!

Buying more lead acid would be similar to giving more money to Eskom to fix their power stations.Throwing more good money after bad money.

 

My dad was also stubborn, he wanted to save money so he was running lead calcium batteries, and 2 years down the line they gave up. After a lot of convincing he spent R23K on a 5.2KWh LiFePO4 battery and now 2+ years down the line he still gets the full capacity. If you ask him he just says he is very happy with their performance. He does not want to spend money on a smart shunt so some days the battery runs till the bms shuts it down. Also using voltages on his voltronic inverter. Sigh, tried to convince him but I lost that one. Luckily lithium does not mind the occasional abuse and they still perform like new

Battery Prices are pretty inflated and Eskom is doing a great job making sure that demand continues to outstrip supply

Edited November 7, 20223 yr by iiznh

Adding (repeating) to some of the points already made.

 

Starting a project from fresh I would say go lithium. But, it depends  a lot on your setup and that you already have a sunken cost. Mixing old and new batteries would have it's own challenges - and isn't really suggested. At best connect the old and new in parallel.

Without the particulars it's difficult but I would lean towards abusing the current batteries and save up for lithium.

With a 48v system you would do best to look at a single lithium battery - most recent inverters support lithium batteries.

There are a couple disadvantages (& advantages) with lead acid batteries:

1. Their capacity is rated at a discharge rate over a 20 hour period. With a higher discharge rate, the internal resistance increases resulting in a drop in their capacity. The same doesn't really occur with lithium batteries - their capacity is (largely) constant regardless of the discharge rate. At discharge of 1C you would lose about 40% of the capacity.
2. A lead acid battery can handle a (brief) high discharge rate - above 1C. However, as noted above, lithium batteries will restrict the discharge rate to 0.5C or 1C for the better lithium batteries.
3. The depth of discharge (DOD) influences the lifespan of a battery. You should only discharge lead acid batteries to 50% DOD. Comparatively you can discharge most lithium batteries to a 70% (or more) DOD. Simplistically a 100ah lead acid give you less than 50ah whilst a lithium battery will give you 70ah - 40% more capacity.
4. Lithium batteries can charge a lot quicker than lead acid batteries - important when there are multiple blackouts daily.
5. You can really cycle lithium batteries - 5k plus cycles. Your lead acid will depend on a lot of factors but somewhere between 200 & 1.2k cycles. To take full advantage of the solar power available during the day you can afford to discharge your lithium batteries (aggressively) on a daily basis. This will give better savings.
6. Lithium take up a lot less space.

Make sure your inverter is compatible with your battery and/or BMS. This will prevent very crude approximation of DOB through battery voltage. Your current setup has  4.8kwh useable at best - likely lower. Crudely you can run 1.5kw for 2 hours or 800w for 4 hours - smarter people than me can do those equations.

On 2022/11/07 at 12:08 PM, GreenFields said:

More informed people will have to add their view, but common understanding is that you cannot just add newer lead-acid batteries to older batteries. Even if it were technically possible, I'd think that more lead-acid batteries would be throwing good money after bad. If the inverter allows it, I'd go lithium for the cycle life as a next step, but first goal would be to get maximum value for money out of the current batteries, cycle them for all they're worth while they're still good, and hope that a few months down the line the demand and supply situation has stabilised such that battery prices come down.

 

You really think Eskom will help us out with lowering demand for batteries in a few months? 

I certainly hope so. 

22 minutes ago, Chris_S said:

You really think Eskom will help us out with lowering demand for batteries in a few months? 

I certainly hope so. 

After the CEO indicated we will have lots of LS for the next 5 years I would rather have my system as is in place than hoping for better times and less demand for PV equipment.

16 hours ago, Scorp007 said:

After the CEO indicated we will have lots of LS for the next 5 years I would rather have my system as is in place than hoping for better times and less demand for PV equipment.

Any help is needed. Even if it comes from a stronger rand. I'll start purchasing in a few months so I'm praying

17 hours ago, Chris_S said:

You really think Eskom will help us out with lowering demand for batteries in a few months? 

I certainly hope so. 

I don't think Eskom's troubles are going away, and I don't think the demand is going to subside anytime soon. The hope is rather that the higher prices will be a signal to manufacturers and the supply chain to bring more product to the market so we're not faced with the shortages we have right now. I mean, how long should it take for the good folks at NingboDeye/Voltronics/Luxpower/Victron/etc to send a few more container ships of stock to SA?