Pre-emptive battery charging overnight in case of rolling cuts

Would appreciate an indication of how best to configure my system if I want to charge the battery from grid overnight and ensure that I always retain at least 2 hrs charge to cover my essential household items.

My system - 8.2 battery and installed (but not tested) with EPS, an additional breaker box with critical circuits (fridge/router). I have seen mutterings about possible rolling cuts at some point - I'm not panicking but equally I bought a system which ought to be able to mitigate so why not.

Basically - I want to charge battery from grid overnight - then draw back down during the day if required but stop discharging normally at (say) 25% which ought to support my critical base-load, call it 500w for several hours.

So - 2 questions:

1. How should I set the charging parameters to configure to manage the charge/discharge/retain cycle I outlined?
2. If I stop discharging at 25% and the power drops - will the grid disappearing override that programmed "stop" and allow the battery to feed the house.
   I'm conscious I should be asking my installers for #2 but they (on your advanced list) went into radio silence as soon as the final payment was made. The EPS wiring "looks" reasonable but I'm unsure how the invertor/battery is supposed to work.

Thanks
Mike

MikeBakke You don't say which inverter you have, but that shouldn't make much difference to what you are trying to achieve. My recommendation would be to test your EPS circuits sooner rather than later as if there's a problem, it'd be good to address it before you need it in earnest. I assume you have a manual maintenance changeover switch so you can feed the EPS breaker box from grid? If not, I'd plan to fit one so that you can feed those circuits if your inverter is ever faulty.

To test the EPS, simply open the AC isolator between the inverter and the main house consumer unit. Ideally this should be done when the inverter is feeding no load and a simple way of shutting down the output is to go to Inverter Remote Control (in the web portal), go to Inverter control and reduce Inverter max output % to 0 and press send. You can then open the AC isolator next to the inverter or trip the MCB in the consumer unit to isolate the inverter from the house load. As log as everything is tickety boo, the inverter should trip (on loss of grid supply) and after a few seconds, the EPS should reconnect and start to feed those circuits from PV and/or battery. If that all looks good, close the isolator/MCB. The inverter should resynchronise to grid and you should be able to reset the Inverter max output % to 100% again.

To reserve battery for EPS, my recommendation would be to run the system as normal with no special settings until you know there will be a planned grid disconnection. For the day when there is a planned interruption to supply, simply set the battery reserve to 25% or whatever you want in the web portal. The battery will discharge to meet house load until 25% at which time house load will be met from grid. When grid is lost, the EPS supply should come from battery. In fact this would be a good thing to check when you carry out your EPS test - set the reserve higher than the battery charge when you are about to do the test. Check that EPS is being fed from grid (via the inverter internal connections), disconnect the inverter from the consumer unit, and the EPS load should start being fed from battery even though the reserve is higher than the battery SoC. If not, you'd have to change the reserve level once your planned disconnection took place, but that's all part of the testing; to understand what needs doing in what circumstances.

Hi Tim, thanks for the reply.
It's a Hybrid inverter system...

I'm really nervous about doing a test myself because as I say my level of trust in the installers plummeted (disappeared) when they stopped talking after I paid them. I now actively discourage anyone from using them as the mark of a company is how they deliver service.

Funnily enough - that's why I originally insisted on a GE solution as when I engaged them on webchat before buying anything, the engineers were really, really good. Now having read a lot of the posts on here, particularly about the SOC/BMS firmware and a general lack of responsiveness I'm more nervous. Not panicking about GE yet but certainly watching. To balance on the plus side - the two times I've engaged with them directly post install with actual issues, they have responded well - once on chat and once on phone.

I know the demand on solar companies is insane and they suffer from the same financial stresses we all are but it's so frustrating. Not just renewable companies either - for the past 18 months I've found it actually impossible to engage an electrician to do a minor piece of work for me. Seems to me they are all either taking major extension type works or they're sub-contracted out doing solar installs. This is a key reason I'm loathe to do the test as if something goes pears I have little confidence I can get someone to resolve on the ground.

With the EPS I will take your advice on the threshold setting when I know a cut is potentially occurring and I guess the test will be in live, just like all software :-)