Solar PV battery options

big_red · 24-11-2023 10:45am

Hi All,

It took a while but we are up and running with...

· 15.75kwh ground mount array (South facing, 36 degrees tilt)

· 2 x Sofar HYD 6000-EP in parallel

· 45kwh DIY battery configured as 3P16S in parallel (3 x Seplos BMS DIY kits from Fogstar and 280ah EVE grade B cells from NKON)

We are still on the Energia D/N rate so I am charging the battery overnight and between it and the solar production we are mostly avoiding purchasing any daytime units. I say mostly as this is where I’m having some teething issues. I seem to be only able to discharge max 30kwh from a full charge before the SOC drops below 10% (even though pack voltage is still around 51.5v) and the invertor automatically flips to charging the battery when in self use mode. Mostly I make it to 11pm but there has been one or two days when this occurs and I end up charging one battery for an hour or two at day unit rates!

So I think I have two problems and would greatly appreciate any community advice please.

1) I don’t fully understand how the inverter works in self use mode as I expect it should just stop discharging the battery when SOC reaches a certain level rather than actively switching to charging mode? The battery is connected to the master inverter via CAN bus from master battery and is set to ‘General’ battery type.

2) I think I need to recalibrate the pack SOC so the BMS can ‘learn’ the proper total capacity?. The best way to do this a full charge and discharge cycle? A full charge I seem to be able to do via the inverter overnight but I am not sure how to fully discharge the battery i.e. instruct the inverter to ignore the SOC and keep going until the BMS low voltage shutdown kicks in? Each battery has its own BMS and each one is reporting a different SOC, it looks like the average of the 3 is reported to the inverter. All pack voltages are aligned and cell variance is minimal e.g. 10mv max.

As an aside, NC7 is in progress albeit I don’t expect to have a significant excess for export until the summer months.

unkel · 24-11-2023 11:21am

@big_red - You're brave to install that while still applying for your NC7. What if the ESB denied it? Lovely setup BTW.

And to answer your question. Your inverter does as it is told by your batteries. More specifically by the Seplos BMS in your batteries. As you reckoned yourself, let the batteries do a few full to empty cycles, so the Seplos can get a better idea of SOC and hopefully you'll get a bit more than 30kWh available. 51.5V is barely above nominal though for LiFePO4, the SOC is no more than about 30% at that stage

DC999 · 24-11-2023 11:27am

https://www.boards.ie/discussion/comment/121410696#Comment_121410696

Tbh I won't pretend to know but watched an off-grid garage video last night and he talked about trouble if you had multiple Seplos BMS DIY kits linked. Basically the BMS's cant talk to each other, so one BMS can knock all the other banks offline. So if a single cell had an issue, it can shut it all off. But we'd only expect that one 16S to be affected, not the other 2 as well.

23:15 in on this one https://www.youtube.com/watch?v=Kpd_eRyD-wU&ab_channel=Off-GridGarage

Have a look at the comments as he asked people to confirm if that happened - as he's only been told via a comment on a video. Video is 1 year old so would of been the older BMS software. Looks like v3 solves a lot of issues - no idea if it solves that.

graememk · 24-11-2023 11:37am

https://www.boards.ie/discussion/comment/121410696#Comment_121410696

Getting a good 100% is important, once the BMS has that, they work much better.

If you can get all cells at 3.5 or above, that is a good starting point for a 100% charge.

Then its counting the power in and power out. That's how they calculate the Soc while running

big_red · 24-11-2023 11:43am

https://www.boards.ie/discussion/comment/121410879#Comment_121410879

thanks Unkel, my electrician is ex ESB and is confident the NC7 will be ok. I'm taking the view that FIT is the icing on the cake, we've a couple of EVs in the pipe so the system still makes long term sense for us even without it. Worst case I'll add more batteries :-)

When you say "..let the batteries do a few full to empty cycles" .. isn't that my issue that they aren't getting close enough to empty? It's only been about 10 days, I'll give it another while and see how it all settles. I just wish it wouldn't automatically grid charge at expensive day rates.

big_red · 24-11-2023 11:45am

https://www.boards.ie/discussion/comment/121410924#Comment_121410924

Thanks DC999. I'll check it out 👍️

graememk · 24-11-2023 11:48am

https://www.boards.ie/discussion/comment/121411038#Comment_121411038

Can you set the depth of discharge to 80 or even 85%

It's a "feature" of the sofars they don't like batteries at 10% or below

big_red · 24-11-2023 11:55am

https://www.boards.ie/discussion/comment/121411070#Comment_121411070

Hi Graememk, Yes I have it set at 90% but aligned to Unkle's comments I think the inverter is taking all its orders from the BMS and looking at the SOC charts on the Solarman app I can see SOC discharges to 8% before flipping to charging. Looking at the BMS manual now and I think 8% is the 'Remaining Capacity Protection' setting kicking in.

That's interesting re Sofar and certainly my experience so far.. I'll have do some more digging

slave1 · 24-11-2023 12:27pm

https://www.boards.ie/discussion/comment/121411038#Comment_121411038

Can you force a full discharge, letting it drop 10 or 15% over a day and then recharging is taking too long, have you an immersion or EV, i could be wrong but you literally have to dump a full discharge. I only had to do this once with pre top balanced DIY cells and it's been rock solid since

big_red · 24-11-2023 12:34pm

https://www.boards.ie/discussion/comment/121411327#Comment_121411327

Hi Slave1.. don't have either EV (yet) or immersion but I do have a thirsty GSHP.. I could ramp up the house temp? But just to clarify.. I have been running SOC from 100% at 8am down to 10-20% by 11pm.

To manage my expectations.. what is a reasonable day to day usable capacity from a nominal 45kwh pack? I was thinking I'd be getting close to 40kwh but maybe that's too ambitious?

graememk · 24-11-2023 12:46pm

https://www.boards.ie/discussion/comment/121411371#Comment_121411371

About 38kwh taking the batteries down to 15%.

big_red · 24-11-2023 12:48pm

https://www.boards.ie/discussion/comment/121411456#Comment_121411456

Cool, I'm about 8kwh short in that case. I'll let it cycle for another week or two and see if any improvements

graememk · 24-11-2023 1:07pm

https://www.boards.ie/discussion/comment/121411464#Comment_121411464

Keep an eye on the voltage of the battery when at 95-99% when actively charging you'd want to be seeing it above 3.45 per cell at least (total voltage of greater than 55v

Also you have 280ah cells

280*3.2*16*3 =43kWh

36 useable down to 15%

Mr Q · 24-11-2023 1:40pm

https://www.boards.ie/discussion/comment/121411585#Comment_121411585

I have 32 similar 280Ah cells and the pack is actually 585Ah or 30kWh rounded.

So I would say 45kWh is a possibility.

DublinDilbert · 24-11-2023 2:04pm

https://www.boards.ie/discussion/comment/121222963#Comment_121222963

Are there any good Solis inverter / battery deals out there at the minute? does anyone know where the above offer is from?

championc · 24-11-2023 2:06pm

Just to add / check - have you the battery type on the Sofar set to General Lithium ?

big_red · 24-11-2023 2:07pm

https://www.boards.ie/discussion/comment/121411902#Comment_121411902

yup👍️

SD_DRACULA · 24-11-2023 5:41pm

Has anyone here got those fogstar seplos kits to run at the full capacity and without issues? The 15kwh packs.

HotSwap · 24-11-2023 6:15pm

https://www.boards.ie/discussion/comment/121411888#Comment_121411888

That offer was from FailteSolar on the 11th Oct.

big_red · 29-11-2023 10:18am

https://www.boards.ie/discussion/comment/121411464#Comment_121411464

I figured out that by upping the SOC ah setting in the BMS I was able to inflate the SOC % and attempt a full discharge. It was all going well up to 38kwh discharged when one cell raced ahead dropping to 2.7v (all others still around 3.1v) and triggering a shutdown before the overall low pack voltage got a chance to bottom out and reset the pack SOC to 0%. I think the pack voltage got to about 49.8v at the lowest.

Nevertheless I'll take it as a partial success as I see I now have 714ah usable. I think next time I'll try for a steady discharge current over a longer period as I was hammering it at variable 5 - 10kwh discharge rate and I guess the passive cell balancing couldn't keep up?. Everything seems to have come back into alignment after a full overnight charge.

.. is anyone using / recommend active cell balancing?

VinLieger · 29-11-2023 11:12am

Im not able to shell out for the solar system id want right now but im tempted to just get a battery installed to make best use of the smart meter we have, is there any reason this would be a bad idea?

unkel · 29-11-2023 11:30am

@big_red - you are doing pretty ok getting 38kWh from a 45kWh nominal pack with the Seplos BMS when you have done quite some heavy discharging during that. 5-10kW discharge rate at times? What's your inverter?

Passive balancing never keeps up and simply is a waste of time as it is always active, even when it shouldn't be, so just causes unnecessary wear / use on the cells and unnecessarily burns / wastes energy. Both in pretty small measures though

You'll always have cells that are weaker than others, that's what triggered your BMS to stop discharging when the one went below 2.7V. The best ones at the time were 3.1V, which is only about 15% SOC, hence your available capacity. Personally I could live with that percentage of usable capacity and I do, even though I do have active balancing (but my cells have varying capacity). I guess once your battery is big enough, you can live with that

Hope those comments help!

big_red · 29-11-2023 12:27pm

https://www.boards.ie/discussion/comment/121432095#Comment_121432095

@unkel - I have 2 x Sofar HYD EP 6000 in parallel.

I was slowly coming to the same conclusion that 38kwh is good enough for now!.. certainly enough for me to load shift all my day rate usage. I might have another look down the line if / when I start exporting if there is a good arbitrage opportunities to discharge the battery to the grid.

Thanks again, all small learning steps but I am getting there.

unkel · 29-11-2023 1:13pm

Nice inverter combo! And yes, before you know it you would spend many, many hours perfecting your system, top balancing, buying expensive equipment to help you with that. And for what? To give you a bit more usable capacity that you don't particularly need?

I'm more pragmatic. Suboptimal is the new optimal 😁

Scoopsire · 29-11-2023 4:00pm

https://www.boards.ie/discussion/comment/121432529#Comment_121432529

So in theory I could just buy 16 cells, nkon seem to have ok value on these

https://eu.nkon.nl/rechargeable/lifepo4/prismatisch/envision-ess-72173207-305ah-lifepo4-3-2v-b-grade.html

Hook up my existing hybrid inverter to the latest Seplos BMS (which has active balancing) to the cells and away I go without the need top balancing?

Likely need to add a battery fuse into the mix somewhere (time to reread the DIY thread😄, lost track of how many times it's been read at this stage)

Or am I totally oversimplifying it?

unkel · 29-11-2023 5:12pm

https://www.boards.ie/discussion/comment/121433343#Comment_121433343

No that's pretty much it. Indeed have a look on the self build thread again, you don't really want to miss things like fuses

You saw the new batch of NKON 305Ah B grade cells shipping sometime next month? Just over €60 each + VAT and a very reasonable shipping cost. Lot of battery for the money!

big_red · 29-11-2023 5:56pm

https://www.boards.ie/discussion/comment/121433626#Comment_121433626

Incredible value.. Not that I am tempted!.. but just to understand the options - if I were to add another 16 cells in the future to create a 4P16s - is it important to have the same version of the Seplos BMS in all 4 packs? I have the older (non Bluetooth version) and I see all the Seplos kits seem to come with the newer V3 BMS now.

Scoopsire · 29-11-2023 6:03pm

Thanks, must get reading and shopping 😀

They were the ones I was looking at alright

Anyone any recommendations on where to buy the BMS, frogstar stock a few options but then have to deal with customs vat etc

graememk · 29-11-2023 6:06pm

https://www.boards.ie/discussion/comment/121433825#Comment_121433825

I'd have them in a separate pack, separate BMS but connected to a bus bar before the inverter.

big_red · 29-11-2023 6:14pm

https://www.boards.ie/discussion/comment/121433884#Comment_121433884

thanks graememk - I currently have 3 packs in parallel - all with separate BMS. If I add a 4th pack such that I end up with 4 packs in parallel and 4 separate BMS - how important is it that all 4 BMS are identical?

Sniipe · 04-12-2023 4:37pm

My Dyness BX51100 (5.1kw) unit is not starting. On startup it goes straight to red light alarm.

I've called the installer as its only in since Feb. He said to put a heater beside it to allow it to start up. I've been at that for 2 hours now with a space heater and still get the same issue.

Mine is in the attic. The house is very warm but the attic is very cold. It has been hitting -3 recently. Anyone any other tips on what to try?

graememk · 04-12-2023 5:20pm

https://www.boards.ie/discussion/comment/121453594#Comment_121453594

Patience, if it's shut down because of cold, it will take a while to warm up.

Sniipe · 04-12-2023 5:42pm

Thanks Graememk, you were right - it turned back after I made this 1 min vid (for the supplier) which was only moments ago:

https://photos.app.goo.gl/kcPPwKJD31u129v66

I'd like to mitigate the issue and come up with a solution to the moisture issue. Any further tips?

championc · 04-12-2023 6:57pm

Get yourself some 100mm insulation board to fully enclose the battery

graememk · 04-12-2023 10:31pm

https://www.boards.ie/discussion/comment/121453917#Comment_121453917

the thing thats moist is the fireboard (in my local hardware store its called non asbestos board. or a cement board.)

Its likely damp because all the warm and relatively humid air is coming up from the house hitting the v cold board and condensing.

Ive even seen it on the board behind my inverters in the barn and theres plenty of ventilation there!

Generally it would have been fine if you hadnt been up there but you did want to heat up the battery.

Sniipe · 05-12-2023 10:57am

Thanks graememk and championc, the supplier has come back to me with the same suggestion. Its currently bolted to the fireboard with a 2cm gap. I'll squeeze some slim insulation under it and cover its sides and top with 100mm insulation board. Thanks ever so much. What a great community boards.ie is.

Alkers · 07-12-2023 7:28pm

Do any battery / inverter combos have an option to discharge to grid or are you relying on having something to use the available power?

Charge every night at low rate EV plan and discharge to avail of FIT is very favourable now if you can use the power.

con747 · 07-12-2023 7:32pm

https://www.boards.ie/discussion/comment/121467891#Comment_121467891

That's what a lot here with big batteries are doing with the Pinergy offer of a 5c 3 hour window night rate and selling back for 27c during the day if they have any spare. Most inverters are capable of that.

VinLieger · 08-12-2023 2:29pm

Currently looking like my only option for battery and inverter placement is in the outside shed. Its fully built external structure only about 2 metres from the house however there's no insulation or heating, would I run into issues during cold weather with battery discharge?

con747 · 08-12-2023 3:05pm

https://www.boards.ie/discussion/comment/121470935#Comment_121470935

You can just insulate around the battery well and it should be ok. Something like this https://www.goodwins.ie/products/xtratherm-polyiso-rigid-foam-insulation-50mm-2-4m-x-1-2m.html?filter_set[]=1413,1426 Just make sure you have holes in it for ventilation and remove it in the warmer months.

unkel · 08-12-2023 3:27pm

https://www.boards.ie/discussion/comment/121470935#Comment_121470935

Battery discharge is fine, even below 0C

Battery charging is the problem. You can't do that below 0C or you will damage the cells. You could just use the insulation foam that comes with the cells in the boxes to wrap around the battery in winter. Their own discharging (just before the charging) causes heat losses and will already have warmed them up, just before you charge. And almost all BMS, even cheap ones, will have temp control anyway, so won't let your battery charge below a temp that you set.

So, in summary, no worries about moving your batteries to the outside shed

pale rider · 22-12-2023 5:14am

Thinking of adding 2 Dyness B4850 2.4 kw batteries to an existing system.

Right now it has 1 Dyness B4850 in a cabinet in the attic, adding looks straightforward if a little tight in the space left in that cabinet, my question is can I stack the two new ones on top of the existing battery or do I need shelving.

I could put a slim metal bar between them but the bottom one is still carrying the weight of the other two. ?

championc · 22-12-2023 9:23am

If the existing battery is only a 2.4kW, I'd seriously consider getting shot of it and going down the 5kW unit route

unkel · 22-12-2023 11:17am

I would be very careful adding any pre made batteries to your system @Pale_Rider. Technically it's easy, but if you already have a smart meter or will soon be getting one, the extra cost of the battery might never pay for itself and you could be better off just exporting your excess PV

Depends of course on your use case and how much you would be spending on the batteries. I would try and stick sum sums into excel to see what way it works out for you