I have a solar panel/battery system and wondered if anyone can recommend a website or forum for asking basic questions and getting useful answers ?


My question are ...
If the minimum battery capacity (on grid) is set to 20% and minimum battery capacity (off grid) is set to 10%.
I'd have thought the battery would stop discharging at 20% and stay near 20% until the PV can recharge it.

My 9.5Kwh battery appears to drop down to 16% SOC and then use the grid to charge back up to 20% when the PV is insufficient to meet the domestic load.
Is this to be expected ?

Are 20% and 10% SOC settings sensible ?

I have also asked the installer the same questions. Jules

Surely charging the battery from the grid defeats the object of the battery, unless you can get an extremely low rate which makes it worthwhile to charge the battery for use in a high tariff hours. from what I remember from the UK electricity tariffs there's only 2, off peak and standard, unlike here where the tariff changes quite a few times during the day and week.
9.5 KW may be a problem in winter to fully charge the battery alongside normal use. my PC is slightly to the right of Genghis
2012 HSE SD4 In Orkney Grey now gone, best car ever.

Let's see if I can remember this right.
(My head is a bit mashed after talking with the sales people for a system I'm looking at having put in.)

If your system has been sized correctly then your panels should cover your usage.
Any surplus will charge your battery, to be used after dark.
If your batteries are low they will receive a charge during the overnight off peak hours from the grid.
Any further surplus can then be sold to the grid.

Unfortunately Jules I can't answer your original question reguarding a forum or %'s .

One would assume though, from trying to understand the question is that, the idea is to preserve some power in the batteries for any emergency usage due to a power outage.

Dartman the one wrote:

Surely charging the battery from the grid defeats the object of the battery,

DEG5Y wrote:

Let's see if I can remember this right.
(My head is a bit mashed after talking with the sales people for a system I'm looking at having put in.)

If your system has been sized correctly then your panels should cover your usage. It does
Any surplus will charge your battery, to be used after dark.
If your batteries are low they will receive a charge during the overnight off peak hours from the grid. Not if youre on a fixed incoming tarrif (not changed anything yet - wanted to see how thing span out - there are pros and cons
Any further surplus can then be sold to the grid. Yes - but only worth while if charging from PV or a low off-peak tarrif

Unfortunately Jules I can't answer your original question reguarding a forum or %'s .

One would assume though, from trying to understand the question is that, the idea is to preserve some power in the batteries for any emergency usage due to a power outage. Yes, hence the lower "off grid" SOC limit of 10%

Sounds like a settings issue
It's possible that you may have an imbalance too

So if it all works right yhe battery while grid connected will discharge to 20% and then stop to protect the battery

In a power outage situation it will go lower as keeping the lights on is a priority over battery life it's quite a small trade off every now and again to discharge a bit lower but done regularly will effect the battery life

If in an ongrid situation you get down to 16% and then it switches off and recharges from the grid then that sounds like an imbalance or bms issue
But if you are off grid and it goes down to 16% and then starts to recharge from the grid to 20% then that is normal expected behaviour

@Pinhead - thanks for that

"If in an ongrid situation you get down to 16% and then it switches off and recharges from the grid then that sounds like an imbalance or bms issue"

Thats what it has started doing now- it didnt do it to start with (stopped at 20%) , only started doing it (going down to 15%) in the last 2 weeks.

System was installed mid- November.

Im in communicatiuon with the installers and awaiting them to get back to me. Jules

@ pinhead

Could you expand on what you mean by an "imbalance" please.

This is all new technology to me and I dont know much about the software doing the BMS.
The ability of the owner/user to change settings is limited from what Ive read eg can change grid charging times and SOC minimums.

FWIW
I have a 15 x Tiger Neo 440W panels (6.6kw) , FoxESS hybrid inverter 6kW and 2x FoxESS Batteries 4.74 kWh

FoxESS have a community forum but not much posted it seems. Jules

Unfortunately my dear friend and neighbour, Andy Neaves, - long time Landrover nut and guru about all things electrical sadly died earlier this year and its times like this I really miss his advice.

https://alrc.co.uk/andrew-neaves/ Jules

An imbalance is as it sounds
Different states of charge between the cells
The bms will monitor individual cell voltage and pack voltage as a whole
State of charge is dictated by voltage with different chemistry having a different curve
Some chemistry is very difficult to know the exact soc as it has a very flat discharge curve in the middle part of the charge range and the bms will need to see the top and the bottom every now and then to calibrate itself
Remember what is 0% and what is 100% is decided by the manufacturer and how much of that you can use
Different manufacturers approach things differently with this regard
With some allowing 0-100% use and another 10-90% use but they may have the same top and bottom voltage if that makes sense

Click image to enlarge

Jules
I think that the BMS may be taking other factors into account when it decides when to react to State of Charge, and it also is trying to 'learn and adjust' to your needs.

This is what my Computer AI returns about Solar BMS Systems -

A battery management system (BMS) for solar panels monitors and controls a system's various aspects to ensure safety and optimal performance. Here are some ways a BMS works:
Balancing
A BMS keeps all the battery cells at the same voltage or state of charge. It does this by redistributing energy between cells, such as by connecting the most charged cells to a load or shuffling energy to the least charged cells.
Monitoring
A BMS monitors the battery's voltage, current, temperature, and other parameters. This helps prevent overcharging or over-discharging.
Fault detection
A BMS detects abnormalities, such as excessive heat or abnormal voltage fluctuations, and triggers alerts or takes action to mitigate risks.
Temperature protection
A BMS uses sensors to monitor the battery's temperature and can raise the temperature before charging if it's too low. This helps prevent lithium plating, a chemical reaction that occurs when lithium ions move too quickly.
Remote monitoring
Many modern BMSs can be monitored remotely using a smartphone app or cloud-based platform.
A BMS is especially important for lithium-ion batteries, which are commonly used in solar systems. Temperature readings can affect whether a lithium-ion battery should be charged or discharged FL2 XS SD4 Auto 2010 2012-2017 (21k - 91k miles) (MY2011)
FL2 Metropolis SD4 Auto 2014 2017- (16k - 79k+ miles) (MY2015)
Metro in its 11th Year of (Extended) LR Warranty / Full LR Service History
(Expensive, but Trouble/Worry free - hopefully?)

Yes - thanks all.
Ive been reading all the blurb that about the system and have rechecked the setup - all seems as it should be and there are no errors logged.

I think what Im seeing is probably the BMS "learning" and in combination with very few sunny days in the last week or so the battery has had little chance to get charged up above 60%.

My intention is to change Octopus tarrif once I could see my usage in relation to the PV power production. Jules

Dartman the one wrote:

Surely charging the battery from the grid defeats the object of the battery, unless you can get an extremely low rate which makes it worthwhile to charge the battery for use in a high tariff hours. from what I remember from the UK electricity tariffs there's only 2, off peak and standard, unlike here where the tariff changes quite a few times during the day and week.
9.5 KW may be a problem in winter to fully charge the battery alongside normal use.