Battery low, cloudy day, no grid

[Spizz]

So I’ve woken up and apparently Eskom have been off since before midnight. Our loadshedding was from 10pm to 2.30am, and then 4am to 6.30am. My SOC is set to 45% and batteries were at 45% entering the 10pm loadshedding thanks to a cloudy rainy day and loadshedding in the afternoon from 2pm to 6.30pm. I was obviously hoping for a charge from the grid at 2.30 to get me though the early morning load shedding.

But it never came.

So now I’m sitting on a rainy cloudy morning, cursing Eskom and the weather in Hermanus and wondering if the sun will come out or will I let my batteries run to zero?

TL;DR we have no grid and my 2 x 5.1kWh LiFPo4 batteries are about to die. Should I switch them off now to save them going to zero or pray the sun comes out?

 

[richjdavies]

So I’ve woken up and apparently Eskom have been off since before midnight. Our loadshedding was from 10pm to 2.30am, and then 4am to 6.30am. My SOC is set to 45% and batteries were at 45% entering the 10pm loadshedding thanks to a cloudy rainy day and loadshedding in the afternoon from 2pm to 6.30pm. I was obviously hoping for a charge from the grid at 2.30 to get me though the early morning load shedding.

But it never came.

So now I’m sitting on a rainy cloudy morning, cursing Eskom and the weather in Hermanus and wondering if the sun will come out or will I let my batteries run to zero?

TL;DR we have no grid and my 2 x 5.1kWh LiFPo4 batteries are about to die. Should I switch them off now to save them going to zero or pray the sun comes out?

View attachment 1443167

Sun for the win. Let those Lithiums scrape the barrel!

(This is not engineering advice and I take no responsibility for the impact )

 

[richjdavies]

Sun for the win. Let those Lithiums scrape the barrel!

(This is not engineering advice and I take no responsibility for the impact )

Ps... Maybe reduce your "critical loads"... 300W? Close the fridge and turn off some lights

 

[Spizz]

Ps... Maybe reduce your "critical loads"... 300W? Close the fridge and turn off some lights

Critical loads are at 330w, everything is off except fridges and the cctv stuff.

 

[aleksandar]

Had similar problem the other day (batteries were at 30%, with incoming load shedding) I switched everything, fridges, lights until sun started to charge bit by bit.

 

[Spizz]

Sun for the win. Let those Lithiums scrape the barrel!

(This is not engineering advice and I take no responsibility for the impact )

Haha, I don’t know if it will damage the batteries hitting zero. Rain is coming down harder, sky is as grey as granite but PV is coming up a little and sitting at 170w at the moment.

Batteries have been at 6% since I woke up 30 minutes ago so I might just get away with this.

 

[Spizz]

Had similar problem the other day (batteries were at 30%, with incoming load shedding) I switched everything, fridges, lights until sun started to charge bit by bit.

Fridges were the next move is it drops below 5, but PV has a picking up a bit and hit 270w a second ago.

Checked again, now at 280w, battery still at 6%. Still pissing down.

 

[richjdavies]

The whole point of lithium is to use serious depth of discharge... Yes you shouldn't do it lots as it will start to impact cycles (not like lead acid where you can do it once or twice before they never work again) -- but once in a while is why you have them!

(It's actually charging them to full that hurts Lithiums... Or getting hot)

 

[Spizz]

The whole point of lithium is to use serious depth of discharge... Yes you shouldn't do it lots as it will start to impact cycles (not like lead acid where you can do it once or twice before they never work again) -- but once in a while is why you have them!

(It's actually charging them to full that hurts Lithiums... Or getting hot)

Good to know. I was worried about hitting zero and with the PV being so low and intermittent, had planned to switch to grid, i.e. zero power and let the pv charge the battery as slow as it will be. At least then I’d remove them from a start stop cycle and try and get a decent charge in them to switch in later.

 

[Kosmik]

Bit off topic but its for this type of scenario I would still want at least a small generator, like a 2.5KV etc, so you can in emergency use that to feed your system in a reduced state. Considering how much a solar system costs, small generators is a really minor addition, especially if no grid.

 

[Spizz]

I reckon I might just get away with it. Battery starting to show “idle” now and again instead of discharging. Might have turned the corner here with the sun getting higher in the sky (still grey cloudy sky though) and almost hitting the panels head on (north facing).

 

[richjdavies]

Good to know. I was worried about hitting zero and with the PV being so low and intermittent, had planned to switch to grid, i.e. zero power and let the pv charge the battery as slow as it will be. At least then I’d remove them from a start stop cycle and try and get a decent charge in them to switch in later.

So... Again, I don't know your batteries /BMS and if they will be damaged by going to zero... Probably not, they have protection for this kind of thing (maybe even your victron shows 0% at 20% left...)

The problem as you said, is more likely the rest of the day (and what you do before your next load shedding slot!!) if the sun doesn't come out. If you have a long enough slot later of power being on in the day, then wait until then... I.e. decide at the point of "you have X hours of grid" left and you know the sun will be going down...

It depends on lots of things:
- load shedding schedule and speed of charging
- weather forecast / size of your panels
- how much you use during the day and night...

 

[grok]

Hermanus by the sea. Should've diversified and put in wind too, a mix of renewables is where you have true freedom from Eksdom.

 

[richjdavies]

Bit off topic but its for this type of scenario I would still want at least a small generator, like a 2.5KV etc, so you can in emergency use that to feed your system in a reduced state. Considering how much a solar system costs, small generators is a really minor addition, especially if no grid.

But he can just use the grid? In this situation at least. Hermanus (I think) has a pretty reliable grid...

Agreed though, if you live in an area which goes off for 12 hours regularly, it would be generator all the way!

 

[Spizz]

But he can just use the grid? In this situation at least. Hermanus (I think) has a pretty reliable grid...

Agreed though, if you live in an area which goes off for 12 hours regularly, it would be generator all the way!

This is the first time this has happened I can recall, seems like something has tripped with all of the start stop and recently increased loadshedding. So yes, we’re usually pretty reliable.

 

[Spizz]

Turned a corner?

 

[Sinbad]

I took mine to zero a couple of times. But they were rated for it (BYD)

 

[chrisc]

Have the same problem in Cape Town

I allow the inverter to charge from the mains in the absence of solar. The battery's float charge is 52.4V so I set it to 52.1V and it never gets to 100%. The SOC indicator shows 75% - 100%

Deep discharge and 100% charge both shorten the lifespan of lithium-ion batteries

 

[RedViking]

You not alone. Woke up to no power as well. Never came back on after early morning shedding. There was a massive surge last night as well and people complained of stuff that got fried. Only couple of houses in our complex with no power. I checked all trip switches and everything is on. So something must have popped. Argh, Eskom! Now to get an electrician.....

Only thing is I don't have panels. Although it's been clouds for weeks now, and today would not have been different.

 

[itareanlnotani]

This is a key example of size your system appropriately. Ideally you'd have more battery, but we know what costs are like for that, so your real options are:

More panels. Or a generator. Or go without. I'd add more panels, always size system for winter/worst weather.

I also have 10kw/hr of battery, but I have 14kw of panels now, so even in the worst weather (like yesterday), my system charges at higher rates than i use, and I end up fully charged at the end of the day regardless of what the weather is doing.

Back to your case - I'd probably lean towards turn off the system if it gets any lower than 5%, 5% is fine for Lithium, but I wouldn't go lower.

Longer term - add more panels for additional generation.