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How deep do you draw your lithiums?


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I'm new to lithiums after recently replacing my lead acids. I have 2 x 3.5kW Pylontechs.

I'm looking for the sweet spot where I will get good battery life as well as maximum utilisation of the bank at night. I do understand the technology is new so there's no real data out there.

Currently I'm drawing down to 25% before switching to grid, but the Axpert powers itself from the batteries so this causes a further slow drop of a few %. Never goes below 20% which is my personal comfort zone limit. I'll likely modify this strategy for load shedding to leave a little more in should I need to go back to battery at 4am.

What's the feeling on this? Am I cycling too deep, or not maximising ROI?

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1 hour ago, PhilFM said:

I think you are at a good level currently, given that your panels are able to recharge completely during the day and you do not need grid power to do so

Thanks Phil. I usually don't reach 100% in the day but can easily handle all the loads even in poor weather. When it's sunny we do extra loads in the washer and pump water to keep the panels running at max to get the maximum "free" energy, or cook with the oven rather than gas. The batteries run the house to 5am in a best case scenario but more usually around 3am.

I never charge from the grid. In Cape Town we do 2.5 hours of load shedding so a cutoff of around 40% would work for me at those times and only for load shedding in the early hours. This never happens due to grid overload but can happen if they are resting the gas turbines or refilling the top dams at the pumped storage.

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Hagu13, I think you are set up nicely and as you said when there is loadshedding, you can plan for that with the needed SOC

Unfortunately for us here in rural Limpopo, infrastructure maintenance is a huge problem so it's almost always a gamble with how deep you discharge your batteries as one storm, one gust of wind, one fart in the wrong direction can mean anything from 1 to 24 hours without grid, and this happens a lot.

So I run my batteries from 2am (can probably start at midnight rather), then wait for PV to start up after 6am, charge batteries during the day, which is usually done around mid day on a good day, then we add load as needed to maximize PV and switch back to grid around 5pm.

I can extend my night hours on the batteries, but then we have no backup should something go wrong and there is a rainy day or two. Here in the Lowveld it gets seriously overcast some days, we had two weeks now with very little sunshine and lots of rain, but we do not complain as we are coming from a severe drought. Unfortunately it is under these conditions (wet/damp) that we experience most of the grid cable faults, potentially leaving you without grid for a long time.

All this said, it basically just comes down to different circumstances, there is no one correct answer for everyone and it seems you understand your needs and risks well and plan/run your system accordingly

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