Methods to force charge in low solar conditions

Hi everyone,
I’m looking for advice on how to force charge my 9.5 kWh battery, as I have read in a few posts that it is recommended to help with the SOC calibration if the battery has not been charged to full capacity for a while. I have the AC 3.0 inverter and my system has been in place for a couple of years or so now.

Obviously, because of the time of year the most charge I’m getting from solar is up to 39% as was the case yesterday however most of the times it’s hitting between 20 to 35%. I expect the amount of charge from solar to be at its lowest points over the next few weeks.

Battery software is version 3017 and inverter is on D0.205-A0.205. I’d say since updating to this software a couple of months ago, the system has generally been performing to my expectations. During this season because there hasn’t been enough solar, I am noticing that the battery charges from grid itself to hit the 4% level of charge in the early morning but this is far better than, the previous issues of the SOC dropping which most of us are very familiar with by now.

I’m not on any smart tariffs, so I can perform the charge at any time. I just like to know the best way on how to tell the battery to charge itself from grid to 100% on a one off basis. I do use home assistant with the ‘GivEnergy Local’ integration.
Thanks in advance for any replies.

Is there any reason you cannot do a timed charge on a one-off basis and then just toggle this off after the event? If you schedule it some time between 22:30 and 05:00hrs overnight tonight there is expected to be lots of green energy on the grid so you will be modestly improving the carbon intensity of the energy you use - even if not the cost.

I’ve never done anything with the timed charge or timed discharge settings as I have been a bit reluctant changing anything in case something goes wrong. I also wasn’t sure how long to put the timed charge on for and because I wasn’t sure how it works I was worried about overcharging the battery.

Thank you for your suggested times, I was conscientious about when would be the optimal time to do it.

The BMS (battery management system) should stop it overcharging. In terms of how long, it depends on your charge rate which depends on your system. I think your system has a maximum charge rate of 3600W (and you should be able to see that under Battery Options -> Charge Power in the app) but if you want to guarantee giving it enough time and you cannot see it in the app then you could assume the lower Gen 1 rate of 2600W just to be safe.
Then you just divide your battery capacity (in Wh) by your charge rate (in W) and you get the time needed to fully charge it.
So if you have a 9.6kWh battery then you divide 9600 by 3600 to get two hours and forty minutes to charge fully. If the charge rate is 2600 then it will be almost three hours and forty five minutes.
If the battery gets to full before that time, perhaps because you have a battery with limited depth of discharge, then the BMS will just stop charging and just run your household demand from the grid until the end of the configured slot. If you have Eco mode switched on then after that your household demand will be met by the batteries until fully discharged.
One last thing - if your batteries are in an unheated garage, loft or outside then they may charge slower than their maximum supported charge rate due to low battery cell temperatures. In that case you might want to assume that around two thirds of the maximum charge rate is available to you until they have warmed up (which they will do through charging).
There is no real reason not to specify the entire window I gave you for charging tonight as it is green throughout and then your batteries will start being used as people get up and start making breakfast when the grid is dirtier. Your batteries will not allow themselves to be overcharged.

It's possibly kinder to the battery to charge slowly, so rather than allowing for a lower rate of 2600W, you could set the charging power to 2600W. I typically limit the charge rate of my 9.5kW battery to around 2kW to charge overnight - I have 6 hours cheap rate, and it easily fills within that time.

pwdst thank you, this is what I needed to know! Really grateful for your reply.

@P3tro How did you get on charging last night?

pwdst Sorry for the late reply, busy couple of days.

I enabled a timed charge through the app and I limited the charge rate to 2090W. The charge started at 23:30 where it was at 5% and finished 04:26 to reach 100%.

Temperature of the battery went from 10C to 18C over the period. Battery discharge seems normal for the usage since that time whilst on 'eco' mode (I didn't change this setting at all so just left it on).

The process seemed to work OK, so thanks for your help and advice. I'm currently wondering how often to do this.

I’m doing this every day at this time of year. My battery is 8.2kWh. I have charge rate set to 1800w or thereabouts. I have a scheduled charge from 23:30 to 05:30 to tie in with my Intelligent Octopus Go 7p tariff. It charges up to 100%. After 05:30 the battery the starts running the house load. Depending how much solar there is during the day (not a lot obviously at this time of year) will determine house much the house load is served by battery and / or solar and therefore how much battery charge there is left by 23:30 and in turn how much charging is done again before 5:30. Not that it ever takes to 05:30 as even if the start point was 4% then the battery is full again by 04:00am. Some nights I also charge the car in the same period.

P3tro I'm currently wondering how often to do this.

There's a video on the official YouTube channel which I think recommends every week or two.

Many of us are on a smart tariff, and charge when power is cheap. Even economy-7 could be beneficial, but it does very much depend on your daily usage pattern, and in particular whether you'd have to import so much power at peak rate that it offsets the benefit. If, however, all your daytime usage can be covered by the battery, you don't need to worry about the daytime price.

pwdst schedule it some time between 22:30 and 05:00hrs overnight tonight there is expected to be lots of green energy on the grid

Just wondered where I can find out when’s best to charge the battery using green energy from the grid like you mentioned before, if I’m going to be doing this more regularly. I’ve seen a couple of websites with the current or past generation mix but not sure where to get predicted energy generation from. Any tips? Thanks

SteveClubley Thanks for the reply, I wondered what happened if the battery was fully charged before the set end time on the schedule.

P3tro Just wondered where I can find out when’s best to charge the battery using green energy

If you're an Octopus customer, they have a "greener days" forecast - https://octopus.energy/smart/greener-days (but you need to log in to access it)

There's also https://www.carbonintensity.org.uk/ but that doesn't look as far ahead.

P3tro

Once the battery reaches 100%, at some point during the charge period that you have defined, the house load will continue to be provided by the grid. At the end of the charge period the battery will then provide.

DD Octopus...have a "greener days" forecast

Also made available from https://agilebuddy.uk/latest/greener-nights