Jump to content

Want an expert to evaluate PV system and advise on batteries


Recommended Posts

I’m learning the expensive way and don’t want to repeat my mistakes. 
2.4 kw panels, 2 x MLT Oasis inverters, bank of 12 Dixon 105Ah batteries.
After 33 months apparently the batteries are shot and need replacing.

Each each inverters serve different parts of the house which have separate distribution boards.

In nearly three years I haven’t noticed any savings on my electricity bill.

I’m looking for someone to properly evaluate the installation of my system and advise on batteries.

I live in Hilton KZN, but the only experts I can find seem to be hack battery salesmen in a hurry.

Any recommendations?

Link to comment
Share on other sites

21 minutes ago, Party Plant said:

After 33 months apparently the batteries are shot and need replacing.

That's not bad considering the fundamentals, three strings being the first issue, and Dixon the second (sorry... I am just not impressed by them anymore).

So, some ideas.

1. If the budget allows, and if the inverter can handle the chemistry, look at LiFePO4 batteries. I think FreedomWon works well with MLT, @Gerlach?

2. If you want to stick with Lead Acid, the look at a single string of Trojan L16-RE (They are 325Ah, similar to your present capacity). They are flooded cells, so they need watering.

Others should be along shortly to provide more opinions.

Link to comment
Share on other sites

@Party Plant Your problem is that 105Ah batteries isn't really made for this sort of work and for that inverters. They will now last long. You need something like Trojan's that Plonkster mention  or go the LifePO4 way. Way better and they will last you longer. @plonkster So far i remember and have seen they can run on FreedomWon yes.

Drop @Stanley a msg. His a pro with this stuff and owns one. 

 

Link to comment
Share on other sites

Just now, Party Plant said:

Thanks for the pointers and advice. Much appreciated.

I have been quoted R147 k for 6 x Pylontech Lithium-ion batteries (is that reasonable?)
 Are these quite distinct from LiFePO4 batteries What kind of lifespan do they have?

Pylontech 3000

Link to comment
Share on other sites

7 minutes ago, Party Plant said:

I have been quoted R147 k for 6 x Pylontech Lithium-ion batteries (is that reasonable?)

 

7 minutes ago, Party Plant said:

Pylontech 3000

That is a bit high. Low stock levels currently, so if you willing to wait a while i can offer better prices. If not i can offer US 2000 much quicker. 

One concern though, you dont have enough panels to fill up 6 x Us3000's in a single day after depleting them. 

 

7 minutes ago, Party Plant said:

 Are these quite distinct from LiFePO4 batteries What kind of lifespan do they have?

10 year warranty and roughly 16 year life expectancy. 

Link to comment
Share on other sites

7 minutes ago, Party Plant said:

 Are these quite distinct from LiFePO4 batteries What kind of lifespan do they have?

The Pylontech batteries are LiFePO4 chemistry. They are advertised as having 6000 cycles, but one has to look at the fine print. This is if you discharge them only to 80% DoD, EOL (end of life) is considered to be when the battery has lost 40% of its original capacity, and the discharge rate is C/2.

The industry standard is 100% DoD, discharged at 1C, and EOL is when the battery has lost 20% capacity. That usually yields around 2000 cycles. So when comparing, keep this in mind.

Link to comment
Share on other sites

29 minutes ago, stoic said:

what does C/2 mean?

C is when a battery is discharged over the span of an hour.
C/2 is when a battery is discharged over the span of 2 hours, etc.

I'm not so sure about "cycle life at C" being an industry standard, a lot of the lead manufacturers seem to use C/12 or C/20 for their numbers.

Link to comment
Share on other sites

54 minutes ago, Party Plant said:

Thanks for the pointers and advice. Much appreciated.

I have been quoted R147 k for 6 x Pylontech Lithium-ion batteries (is that reasonable?)
 Are these quite distinct from LiFePO4 batteries What kind of lifespan do they have?

10 year warranty, and 6000 cycles at 80% depth of discharge. Meaning if you only discharge them to 80% each night they will last you approximately 15 years, give a single discharge cycle every night.

The Pylontech's are of Lithium iron phosphate (LifePO4) chemistry. For the life of me, I cannot find the graph now, but when I did the research an Australian battery testing crowd compared a lot of different batteries in some really interesting graphs regarding cycles, remaining capacity after time etc.

I selected Pylontech's for my recent installation based on days and days of pondering, and research. I'm certainly no expert but these batteries do seem to be great value for money and quality.

It is important that your inverter "understands" the batteries, so most modern batteries come with a communication cable that allows the inverter to determine the exact state/charge of the batteries rather than just relying on the voltage of the batteries. It is of course possible to use them in an inverter system that doesn't have the direct communications cable.
 

Link to comment
Share on other sites

3 hours ago, Party Plant said:

In nearly three years I haven’t noticed any savings on my electricity bill.

Do you have a choice of modes in which to run the Oasis? I can put my Goodwe into "backup" mode which means that it uses solar to charge the batteries and only discharges the batteries when the grid goes down. No savings there. 

Or I can (and have) put it into another mode where it powers the property first from solar (if available) then from battery and finally from grid (with some rules such as don't draw from battery if SOC <= 40% and grid is available). In that mode I save lots of money.

Also analyse your bill, don't just look at the bottom line. EG in Johannesburg you pay about R700 pm in flat charges just to have a connection if you are on the post-paid tariff. If you go to pre-paid, your cost per kw/h goes up, but the flat fees fall away. The flat fees made up just over 50% of my electricity bill, so converting to pre-paid saved me good money.

Link to comment
Share on other sites

5 hours ago, mmacleod said:

C is when a battery is discharged over the span of an hour.
C/2 is when a battery is discharged over the span of 2 hours, etc.

And on the other hand, 2C would be discharging at twice the Ah rate, so full to empty in 30 minutes.

5 hours ago, mmacleod said:

I'm not so sure about "cycle life at C" being an industry standard, a lot of the lead manufacturers seem to use C/12 or C/20 for their numbers.

Oh no, I didn't mean for lead acid. For lead acid the industry standard is pretty much C/20, and sometimes C/10. Occasionally a manufacturer will try to boost their numbers by going higher, eg Omnisolar AGM batteries are 260Ah.... at C/100 🙂

A C/2 rate is more than sufficient for a house battery. BlueNova even uses a C/10 rate for theirs.

Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

 Share

×
×
  • Create New...