Hi, my name is Paul and new to the forum. I have been moving over to solar but as it catches me more and more I am increasing my systems. At present I am fitting a second system and want to know if I can describe my design and get advice. Many thanks.

Paul.

Welcome Paul.

By all means, go ahead and ask what you want to know.

Thanks TTT.

I have an Axpert 3Kva 24V inverter. Input range 30-66Vdc and Max 75Vdc.

Panels 4 x 280W. I have joined 1 & 2 in series as well as 3 & 4 and then joined in paralell. I want to place another 4 panels in similar way and have 2 x strings. The ISC is 9.45A and Max 8.92A.

I will get losses and expected between 60 and 72 W readings from the panels. Inverter set to 30A for charging.

I do have a combiner box with 15A fuses. Battery isolater with 2 x 100kA 24V fuses.

I have 4 x 105ah lead acid batteries.

I have noticed on charging that I already get 30A charging and was only expecting under 20A and its a bit concerning being at inverter MPPT max.

I have set the inverter on SBU and have the ultility power come in at 24v on the batteries so as not to discharge them to much. Basicaly the batteries only come into use for a few hours at night but are not required for much pulling during the day.

Am I on the right track here or endangering the setup.

Thanks again.

 

Excellent Paul ... someone will come past here and check it all out. 

Just three comments from my side:
1) If your intention is to connect the system to your DB board, you are aware of the regulations around that?
2) The 105ah batteries, which I assume are "deep cycle maintenance free" ones, are "training" batteries?
3) Adding a BMV to the mix, is a good idea to ensure the best use of your batteries.

1 hour ago, The Terrible Triplett said:

2) The 105ah batteries, which I assume are "deep cycle maintenance free" ones, are "training" batteries?

24V axpert with 105Ah batteries. Essentially the "starter kit" of PV systems :-)

4 hours ago, The Terrible Triplett said:

Excellent Paul ... someone will come past here and check it all out. 

Just three comments from my side:
1) If your intention is to connect the system to your DB board, you are aware of the regulations around that?
2) The 105ah batteries, which I assume are "deep cycle maintenance free" ones, are "training" batteries?
3) Adding a BMV to the mix, is a good idea to ensure the best use of your batteries.

 

4 hours ago, The Terrible Triplett said:

Excellent Paul ... someone will come past here and check it all out. 

Just three comments from my side:
1) If your intention is to connect the system to your DB board, you are aware of the regulations around that?
2) The 105ah batteries, which I assume are "deep cycle maintenance free" ones, are "training" batteries?
3) Adding a BMV to the mix, is a good idea to ensure the best use of your batteries.

Hi Thanks

1/ No connection to DB.

2/ Yes as you assumed.

3/ BMV? Sorry not sure what that is.

3 hours ago, plonkster said:

24V axpert with 105Ah batteries. Essentially the "starter kit" of PV systems :-)

Hi. Yes. Pretty new at this.Can you recommend batteries

1 minute ago, OTG said:

Hi. Yes. Pretty new at this.Can you recommend batteries 

I started pretty much in the same place, small inverter, small batteries. Those 100Ah batteries are usually meant for camping, and they usually die pretty quickly under regular cycling. Think 12-15 months if you are lucky, maybe a bit more if you treat them really nicely. Under regular 2-hour load shedding slots, they're done for by year end.

Generally we recommend that people look at Trojan T105-RE flooded batteries instead, as they present better value for money (but they do cost a bit more, its double the capacity at 225Ah). There are also many sealed batteries that can do 700-1000 cycles to 50% which are all a bit better. Of course, you'll probably look at Lithium at some point in the future too. Those are the best... but they do cost quite a lot.

4 minutes ago, OTG said:

3/ BMV? Sorry not sure what that is.

Here you go: https://www.victronenergy.com/battery-monitors/bmv-712-smart

You want to ensure that you never ever drain the batts below 50% DOD.

Preferably keep them "trainers" at 20% DOD / 80% SOC or even 10% DOD / 90% SOC to last even longer and only go to 50% once in a while when you need to have to.

 

3 minutes ago, OTG said:

Pretty new at this.Can you recommend batteries

Pylontech batteries - but then you are like me 24v, so then look at these: http://www.trojanbattery.com/pdf/J200-RE_Trojan_Data_Sheets.pdf

And if you don't like the venting, Want to look at AGM: https://www.trojanbattery.com/pdf/SAGM_12_205_AGM_DS.pdf

Ok guys thanks. I dont want to muck about so I think straight to Lithium straight off. Can you recommed a good value one for my 24v system and where to obtain. Thanks.

FreedomWon makes a 24V bank on request. BlueNova can also make one.

The FreedomWon battery has no precharge (not on the entry-level one). Not sure about the BlueNova but I am told they do precharge. You may have to call them and ask about it... :-)

Otherwise wou're looking at the Victron Lithium's (12.8V) with a miniBMS.

Hi gents and mainly TTT and Plonkster.

Have heard you loud and clear so what I did was replace the Axpert 3 Kva with a 5 Kva and purchased a Pylon US3000 Li-Iron Phosphate battery. This was the best I could afford. Due to the really low load it will be used on I only got one.

What I am wondering now is if I want to add on in future will it be a problem. Near future or distant future! Will this be good or bad for such a battery.

Any comments will be appreciated.

Many thanks.

3 hours ago, OTG said:

What I am wondering now is if I want to add on in future will it be a problem. Near future or distant future! Will this be good or bad for such a battery.

Technical discussion upcoming. So the issue with putting batteries in parallel, especially with lead acid, is that current takes the shortest path, which means that whatever bank has the lowest internal resistance takes a proportionally higher amount of the charge, which means that one battery always overcharges slightly and the one next to it undercharges slightly. There are ways to deal with it, but that is not important right now, I only need to explain how LFP differs: As an LFP cell becomes full the internal resistance rises sharply, so that if you have two in parallel and you hold them at the same voltage, there is a natural distribution of charge current towards the lower string. It's not perfect, but it is a lot better than for lead acid. This already makes paralleling of strings easier with LFP, but in addition there is also a BMS that ensures the cells are balanced.

For this reason the paralleling of disparate strings is less of an issue with LFP, and that means you can add more capacity later (ie add a new battery next to one that is a year old). So you can extend it later...

However, I feel like there is a limit to this. I am pretty sure that if I tried to add more capacity ten years later, then 1) I will probably have a real hard time finding a similar battery that will work in my old bank, and 2) they will be significantly different that you might still run into some issues. So I feel like there is a expiry date on this capability, but where a lead acid bank has a limit measured in weeks, for LFP it will be measured in years.

So near future... definitely. Distant? Well how distant? 🙂

3 hours ago, plonkster said:

... where a lead acid bank has a limit measured in weeks, for LFP it will be measured in years.

Within 6 months more or less, not weeks.

FWIW, a titbit. I recently asked what if I was to add another T105RE's to my years old bank. Supplier confirmed that mine seldom goes below 80%, after which he said fine, you can add 4 more, only difference being I won't see +-10 years, but maybe +-9.5 years.

If the bank has worked hard, then you cannot do it. 

Obviously, risk is with the client, as you need to KNOW your bank very well that all the batts are still in a very good condition.

Hi. Ok thanks guys. I was thinking about 3 months as distant future. I feel a lot happier to proceed now.