Solar PV battery options

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