Exporting to grid before batteries are full

[Mhys1016]

Hi all
Thanks in advance for any advice.
I have a split phase system . 33 panels split in half feeding two inverters and two 5kw battery (on each phase).
Recently the system has been exporting to the grid before the batteries are full. Also sometimes the batteries are actually discharging rather than charging when there is power being sent to the grid.
Also I have an iboost to heat the water and this has been coming on when the batteries are nowhere near full ( like 34%). The system was working fine in the summer months but something has happened recently which has caused an issue. I have just today built an insulated box around the batteries as I read that they don't recharge in freezing weather but the system still seems to have a problem. Any ideas anyone ? As far as I can see the system is on self use. One battery is set so it force charges from grid from 2-5am .

1 phase

2 phase

[MaterialBarracuda48]

You can get the battery temperature and post these values, that would give evidence to back your probably cause of low temperatures. If your batteries are outside exposed, then they will be very cold, which will stop charge/discharging.

You can also post up the graphs (swipe right on your home screen, and scroll down to find this) of the system during the night time charge.

Your first picture is quite telling, it is barely charging the battery, which is highly likely to be caused by cold.
Look at the video posted by @Will to see how the temperature will limit charge

[Mhys1016]

Hi.
Thanks for the reply. Since building some insulation around the batteries they are now sitting around 10 degrees. They were around or just below zero. So annoying that installers didn't warn me about this as I asked them whether it was better to have the batteries inside the house.
See attached screenshots of graphs requested

[MaterialBarracuda48]

Well it's good to see from your graphs that they did charge up, just limited.
I bet if you go back a few months, you will see a higher charging amount.

Anyhow, what batteries do you have installed? Some do have heaters, but might need firmware updates to work.
Hopefully your enclosure keeps them in the Goldilocks zone, and tomorrow you will be able to post SoC/Temp/Graphs accordingly.

[Mhys1016]

My batteries definitely don't have heaters . Thanks for the video recommendation. I didn't realise batteries needed to be above 10 degrees to work efficiently. The co I bought the gear off really were a joke to be honest.
Anyway . After looking at the temp now it's already dropped below 10 degrees so I reckon I'll put a little low watt heater in tomorrow and see what difference that makes. I wonder if the temperature issue would explain my iboost coming on when batteries weren't at 100 % ?
Thanks again for your advice on this .

[MaterialBarracuda48]

Seems like installers were muppets then.

I guess you may need to put a little heater as you say, or beef up the insulation a little more.

I would be tempted to see how your overnight charge performs, and what temperature you have in the morning/afternoon/evening before installing heater.

[Mhys1016]

OK. Will do thanks. Do you think this issue may have been the cause of the iboost acting up ?

[MaterialBarracuda48]

OK. Will do thanks. Do you think this issue may have been the cause of the iboost acting up ?

I presume iboost is some solar energy diverter... and I wouldn't think so. It probably took what was to it "spare" energy, because the battery wouldn't take it. I presume that is what the iboost is programmed to take/use?

[Mhys1016]

Ah yes. OK that makes sense. Iboost diverts power to immersion heater for hot water when batt is full but like you say - if batt isn't taking the charge it may well go to the iboost instead. That makes a lot of sense. Thank you ! So pleased to have found this forum !

[Mhys1016]

Hi.
OK so insulating around the batteries with some 50mm celotex seems to have worked well. Batteries charged very quickly from off peak grid 2-5am so that's all good -

But something else which im slightly confused about . The batteries have just reached 100% and now rather than just sitting full have (according to app) started discharging even though there is excess power now being exported

. Is this anything to worry about or does the battery not have the ability to stay full and always has to be doing something ?
Thanks again for any advice !

[MaterialBarracuda48]

That's perfectly normal!

The cells don't like being stuck at 100% for extended periods, so they will start to send energy back to the home.
If you next time watch it when charging from 95% to 100%, it will hit 100% and begin to discharge immediately, which is what you see in your picture.

Once it drops say to around 95% iirc, it will then begin to charge back to 100% (depending on your settings) and stay in this charge/discharge loop.

ETA: If I am correct, it has 3 states, Charging/Discharging and Idle
Picture of mine taking a siesta earlier
viewtopic.php?p=11757#p11757

[Mhys1016]

Thank you so much for this advice which has really helped.
So annoying the co that sold me the set up didn't mention about the need for a min temperature ! Complete Muppets they were. I have to say the industry is still pretty chaotic from my first impressions
One last thing - my battery reserve capacity is set to 20% and system min SOC 10 % . Is this about right in your opinion ?

[MaterialBarracuda48]

I would set both at 10%, the reserves can be useful if you live in an area where you get often power cuts... but that only helps if you actually have setup and EPS circuit.

So set to 10% if you don't have an EPS circuit/frequent power cuts.

[Mhys1016]

We do have an eps system.

[MaterialBarracuda48]

We do have an eps system.

Then you need to weigh up the chances of a grid fail, I have also got EPS, but leave mine on 10% unless some big storm rolls in, in which case you can increase value if you suspect there could be a power cut.

[Mhys1016]

I can't really see that the 10% either way would make that much difference ? Maybe I'm wrong.

[MaterialBarracuda48]

10-20% of a small battery is minimal difference, but I presume you got a battery to store energy for evenings or something like that. So by locking off that additional 10% only comes in handy if you get a power cut.

Ultimately, it's your system and your choice. I am happy with setting my mins at 10% and would only change if a really bad storm was forecast, I am thinking of Michael Fish levels of wind

[Mhys1016]

Yep. I hear you. Great advice. Thanks so much. You ought to get paid by Fox ! .
Thanks a lot. Happy New Year !

[Mhys1016]

Sorry.
One more thing .
When might you use the ' charge from grid disabled ' option ?

[MaterialBarracuda48]

Sorry.
One more thing .
When might you use the ' charge from grid disabled ' option ?

I think that is for when you don't want it to use peak price electric I presume?
I am not 100% certain on that, as I have never used that before.

Give it a few hours and hopefully someone can confirm it's function/use.


And Happy New Year also

[Mhys1016]

I thought I would share the analysis graphs of a cold battery compared to a properly insulated and heated one .
The first graph shows the batteries state when they are just outside hung on the back of our house (where the installers said they'd be fine ?!?) . Here they were getting to freezing point which meant they were not working properly. Not charging and actually discharging when they should be charging.

This next shot is showing how much better the battery is performing after i insulated around it with 50mm celotex and added a low watt heater into the compartment.

Bearing in mind the weather outside has stayed pretty constant (very cold) as you can see - the battery is working so much better. Charging quickly , holding charge and discharging correctly.
I'm going to purchase a thermostat plug adaptor with a 2m probe cable which can sit inside the insulated battery compartment and automatically turn on the heater when inside the compartment gets below 10 degrees. If I was to purchase the system again (using knowledgeable installers) I'd buy the batteries with the heaters built in. Lesson learnt ! . Thanks to BM for all your great advice.

[MaterialBarracuda48]

Thank you for posting up some extra information, it actually helps others that are affected by the same issue (as you can see there are many posts currently on same theme)

Good shout on a little thermostat, then it is fire and forget.

As for installers that say you can fit outside, they are just thinking about the water/dust IP ratings and not using an ounce of noodle power.