Solar PV Hints, Tips & Troubleshooting

Exactly which is why I give such a wide range of 5-10c and qualify my statement with probably. If you are Unkel you probably got your battery for free do you can use and abuse it all you want! But if you paid list price for the battery and want the capacity to not deteriorate significantly for 10 years you may want to go easy on the night charging. But as always do your sums and know there is a wide range of outcomes in terms of battery life.

I think a main consideration not many people make is that even with an SEAI installed system, the inverter costs more than the battery. Batteries are relatively cheap these days. Hybrid inverters are still horribly expensive. And they will fail.

Hybrid inverter about EUR1300 + VAT retail
2.4kWh Pylontech battery EUR900 + VAT retail

And you can replace the latter yourself with one made from similar cells for less than half that. People worry too much about batteries! If you went to the expense of getting one, bloody use it and let it pay for itself before the rest of the system fails LOL!

WhoamI2022

From other thread

Looking for some advice, have a GivEnergy system. I have tried to change the mode but it keeps going back to Mode 1 by default, no matter what I do, does everyone else have the same issue? have logged a call

unkel wrote: »

I think a main consideration not many people make is that even with an SEAI installed system, the inverter costs more than the battery. Batteries are relatively cheap these days. Hybrid inverters are still horribly expensive. And they will fail.

Hybrid inverter about EUR1300 + VAT retail
2.4kWh Pylontech battery EUR900 + VAT retail

And you can replace the latter yourself with one made from similar cells for less than half that. People worry too much about batteries! If you went to the expense of getting one, bloody use it and let it pay for itself before the rest of the system fails LOL!

Damn it! I took your advice and charged it to 90% last night and this morning in the bright sunshine ended up exporting. Will have to cap the charge at 70% for now. But it worked beautifully - can do it from the phone app - and had the added advantage of charging my battery at the full rate and not the current-limiting on charge that I had started seeing on my battery due to low temps and low charge levels.

WhoamI2022 wrote: »

From other thread

Looking for some advice, have a GivEnergy system. I have tried to change the mode but it keeps going back to Mode 1 by default, no matter what I do, does everyone else have the same issue? have logged a call

There's a dedicated Givenergy thread. You'll probably get a better response there.

garo wrote: »

The battery has a finite number of cycles (6k-10k) s

I'd love to see some real evidence to back that up.

https://uwspace.uwaterloo.ca/bitstream/handle/10012/12177/Catton_John.pdf?sequence=3&isAllowed=y

Sir Liamalot wrote: »

I'd love to see some real evidence to back that up.

"Thus, lifetime prediction models are developed in order to better understand the design and operational consequences on performance degradation of Li-ion batteries."

That's conjecture not evidence.

Thought you might say that. This is a bit better:
https://iopscience.iop.org/article/10.1149/1945-7111/abae37

DrPhilG

garo wrote: »

Damn it! I took your advice and charged it to 90% last night and this morning in the bright sunshine ended up exporting. Will have to cap the charge at 70% for now. But it worked beautifully - can do it from the phone app - and had the added advantage of charging my battery at the full rate and not the current-limiting on charge that I had started seeing on my battery due to low temps and low charge levels.

Which inverter/battery do you have?

I'm going to set it to not discharge overnight, and start night time charging for the next few months.

garo wrote: »

Thought you might say that. This is a bit better:
https://iopscience.iop.org/article/10.1149/1945-7111/abae37

That's closer to the mark...

"A round of cycling for each cell varied from 125 to 1000 cycles, depending on the rate of degradation at the specific test conditions. .....the study was considered complete once a cell reached 80% of its initial capacity."

6k was it?

"Therefore, for each cell, the total capacity throughput was divided by the nominal capacity to get the total equivalent full cycle count."

Still modelling, not comprehensive testing. Besides a lab doesn't factor age, temperature variations or real world use.

" EFC is extrapolated based on the present degradation rate for those cells." .....yawn.

PS I can do the same with traction lead.

garo wrote: »

Damn it! I took your advice and charged it to 90% last night and this morning in the bright sunshine ended up exporting. Will have to cap the charge at 70% for now. But it worked beautifully - can do it from the phone app - and had the added advantage of charging my battery at the full rate and not the current-limiting on charge that I had started seeing on my battery due to low temps and low charge levels.

If you have a substantial East facing array and your consumption is not as high as mine, then I certainly wouldn't charge it to 90%. In my case there is no chance of exporting to the grid in the morning unfortunately

DrPhilG wrote: »

Which inverter/battery do you have?

I'm going to set it to not discharge overnight, and start night time charging for the next few months.

I have a Growatt SPH3000 and a Pylontech US2000plus.

unkel wrote: »

If you have a substantial East facing array and your consumption is not as high as mine, then I certainly wouldn't charge it to 90%. In my case there is no chance of exporting to the grid in the morning unfortunately

Right I forgot you are W facing. I'm 50/50 E/W. I've set it to 70 for now but looking at tomorrow's forecast 50 might be better. It's promising to be a good one here in Dublin.

Sir Liamalot wrote: »

6k was it?

Was on my lunch break so couldn't respond properly.

Sir Liamalot wrote: »

"Therefore, for each cell, the total capacity throughput was divided by the nominal capacity to get the total equivalent full cycle count."

Still modelling, not comprehensive testing. Besides a lab doesn't factor age, temperature variations or real world use.

I think you misunderstand this as they discharge to different DoD and convert to Equivalent Full Cycle to compare like for like. So a 100->50 cycle is worth hald a 100->0 cycle.

As regards age and temperature, the paper linked first has real world number at 25 and 60C for storage from 1 to 6 months.

Sir Liamalot wrote: »

" EFC is extrapolated based on the present degradation rate for those cells." .....yawn.

Yeah I agree that's not a full test. But which side are you on? Do you think 6k-10k is an overestimate or underestimate?

I'm going to go dig for some more research papers.

garo wrote: »

But which side are you on? Do you think 6k-10k is an overestimate or underestimate?

I'm going to go dig for some more research papers.

Vastly over. Unproven. Marketing figure.
And OPzS Lead can generate the same on paper figures. They're about 8-10 times cheaper.

Keep digging I've been looking since before Elon Musk launched Neo-Tesla.

Now Sir Liam I don't thin you are being very fair. Read that second paper carefully. It's a good one. For EFC:

In this work, one EFC is based on the nominal capacity of the cell. Therefore, for each cell, the total capacity throughput was divided by the nominal capacity to get the total equivalent full cycle count.

For LFP they say:

The LFP cells exhibit substantially longer cycle life spans under the examined conditions: 2500 to 9000 EFC vs 250 to 1500 EFC for NCA cells and 200 to 2500 EFC for NMC cells. Most of the LFP cells had not reached 80% capacity by the conclusion of this study for the NCA and NMC cells, and their longer-term degradation will be reported in a later work

However, they did test LFP cells to 3000 full cycle equivalent and most of them retained 90% capacity. Those that didn't were operating at higher temperatures or 3C discharge rates. Look at figure 3 in particular. I would say that extrapolating from 3000 full cycles is not a terrible reach. A "round" of cycling was 125-1000 cycles but they did multiple rounds. So some of their tests went to 4000 effective full cycles.

Just for arguments sake these are ~8 times cheaper.

1500 cycles to 80% DOD to 80% rated capacity.

A lot depends on how you use them. Phone batteries last a year generally for instance.

Mine has lasted four and is still at 82% health.

You are changing the topic though. Reading that paper we see real life experiments which show > 90% capacity after 3k cycles. 6k for 80% DoD isn't likely to be a vast overestimate like you claimed.

And remember all those "facts" on spec sheets are the number of full cycles to 80% capacity. This could be 7000 (which is about 25 years) but the battery will still be fine, just degrading further. You could very well get 50 years and still be at 50% capacity

Per spec sheet cycle / per kWh LiFePo4 have been cheaper than lead acids for several years now and of course they are getting cheaper. Lead acid isn't

That said, I wouldn't buy either at market values but if you get them dirt cheap or free, you are laughing

garo wrote: »

You are changing the topic though. Reading that paper we see real life experiments which show > 90% capacity after 3k cycles. 6k for 80% DoD isn't likely to be a vast overestimate like you claimed.

Sure I was. Same as I've no idea how you made that leap of faith.

unkel wrote: »

Per spec sheet cycle / per kWh LiFePo4 have been cheaper than lead acids for several years now and of course they are getting cheaper. Lead acid isn't

Per spec sheet it's not because cost per kWh extracted ought outlast the lifetime of a lottov installations so the on paper figures of LiFePO4 if they are true are redundant (lead's still looots cheaper) because we'll never see the end of them.

However; my tool, laptop and phone batteries don't last, If I wasn't such a cynic I'd wonder why.

Sir Liamalot wrote: »

Per spec sheet it's not because cost per kWh extracted ought outlast the lifetime of a lottov installations

Haha, yes this is true. I can imagine the people having had "cheap" battery installs done courtesy of the very generous tax payer and then a few years in (just outside of warranty) their ridiculously expensive hybrid inverter fails and they get a quote of €2k to get it replaced :eek: