Set maximum battery charge level

Richard60

I'd like to be able to set the maximum level the battery will be charged to. I want to preserve the battery by not charging above 90% irrespective of solar prediction or solar generation.

Richard60

Currently wonderwatt charges to 100% on low solar prediction days

SilverArt

Richard60 From everything I've seen 'charging to 100%' in itself is not a problem as the GiveEnergy BMS manages it. It appears that the 100% that we see is the operational 100% not the physical 100% if that makes sense.
The bigger challenge as I see it is the rate of charge, as the higher the charge rate the hotter the battery gets. This means it is kinder to the battery if it can be charged over longer periods. In my case I reduce the 'Battery Charge Power' to a sub 65% level over-night, how low depends on the next day solar forecast and the battery state in the evening. (Our 20:00 to 07:00 usage is very consistent so easy to do). Then I reset it to 100% in the morning to maximise solar gain during the day..

felmer

I think this is probably correct as my battery capacity is around 13.5kWh, but its stated as 11.5kWh usable, so seems there is some headroom at both ends of the capacity "built-in".
EVs also have sophisticated BMS, but most manufacturers recommend around 20-80% charge window.
So I think it would still be useful to be able to set ones own max charge level and be comfortable with that.

SilverArt

felmer I think this depends on the exact battery technology however what is true across all of the technologies is that charge rate is equally important as that is a heat generator, both to the batteries but also to the inverters.
I'm keeping my fingers crossed that it won't be too much longer before WW manage to provide a 'Charge Rate' based solution for the GivEnergy users (I think they manage it on Growatt). This time of year a 'Charge to 100%' is working fine for me in terms of following day cover, but it would be even better if I could use WW to back off the 'Charge rate' based on battery charge % at midnight to just meet the 100% target at end of E7 period and reset the 'Charge rate' to Daytime % for the daytime.
Any progress... please @admin

admin

SilverArt Hi - we're aiming to get this rolled out next week sometime.🎅

Let me know if you or anyone else is happy to test this out, if so, please DM your associated Google account e-mail, and we can test this out prior to wider rollout.

Cheers!

SilverArt

admin Brilliant, looking forward to trying it out. Just DM'd from the gmail account.

admin

Rolled out now for @JMA and @SilverArt in version v0.3.143 and higher.

SilverArt

admin Thank you, I've set the battery 'Charge Rate' to maximum in Giv. and set WW to 100% so will see what happens tonight and tomorrow morning.

JMA

Reporting back on the first results of the reducing of the charging power.
My charging window was set from 2-5 am and my inverter did receive a command to reduce power to 2666W (whereas the command coming from WW indicated 2700 (W not % - small issue to be solved in what appears on the log).

This spread the charging and I reached 95% SOC, not 100% (probably due to difference between 2666 and 2700 W ?)

Just before the end of the charging window the charging power was then reset to 3047 W. This is something I do not really understand, since the max. charging power is 3600 W for my inverter. Does that make sense ?

I'll keep monitoring over the next few days. It will be interesting to see what happens if we have a day with some sun predicted where the desired SOC is not 100% but some much smaller value.

Overall seems to be doing well.

SilverArt

Brilliant 😀😀😀... you've done me out of a job! Just what I've been pestering you for and I suspect will meet my needs for the next few weeks until we start getting some meaningful solar and the charge % can be reduced to below 100%

OK I see the same minor discrepancies as @JMA but from my own manual automation simulation I've been getting the same 'problem'. I 'think' it's a watts v % thing and I'm not sure I understand the correlation especially as Giv.'s steps on the slider are 5% except for the last one which is 8% . I've not experimented with using the app and entering watts there.

Charged to 98% when 100% is asked for: The charge pattern in general is not linear, it does get odd 'steps' in it where it has a little rest, also in my case the charge rate from 95% full onwards steadily reduces to 0. I suspect that this is due to the the way the 9.5 & the 5.2 batteries charge and it has appeared to be a little more apparent as the temperature has dropped. (My batteries are in an unheated garage.). I get one at 100% and the other at 98%

I also think that the the 'Charge Power' was very promptly reset - at 6:57 I guess in preparation for my 06:59 charge end time. I would have expected it later but can see the logic.

All in all, very well done, I'm looking forward to the next few weeks monitoring.

admin

Thanks both @JMA and @SilverArt for your excellent feedback and for being willing to be guinea pigs!

Right, yeah, there's a display issue in the log. Will be sorted shortly.

In terms of the charge rate for you @JMA - you are correct that the max charge rate we were using for your inverter was 3KW, instead of 3.6KW. This explains why it fell short of 100%. The functionality to dynamically get this from the inverter was not in place when you signed up. So this has now been manually updated for you and should be accurate going forward.

You are both correct in seeing that the charge values that can be set are staggered in some way and controlled by the GivEnergy backend. The GivEnergy API only accepts absolute Wh values for charge rate, not percentages.

We simply calculate percentage charge rate and apply this to the max charge rate in order to get the relevant charge rate required. Sometimes Giv will adjust down, sometimes slightly up.

As for you @SilverArt - and it only reaching 98%, this might also be down to the charge being throttled further close to 100% SOC by your inverter itself. Hopefully it's close enough. We can see how we go and might need to set an additional few % extra charge rate for head room if it keeps falling short consistently.

Wider rollout of this feature will be happening today. Feel free to mention it to fellow Giv users!

Thanks again!

SilverArt

admin Hopefully it's close enough.

Sure is, it's as close as I was getting sometimes and IMHO for me 294w could be down to temperature and isn't worth worrying about,
Question.... is the switch back to normal actually 'Revert to Max' or 'Revert to Previous'?

admin

This has been rolled out now, available for all GivEnergy users, in version v0.3.149.

JMA

admin Fantastic - keep the updates coming !

Avenir

admin Where can I see this setting please?

admin

Avenir Your chargerate will be automatically adjusted based on the required target and the charging window (this helps battery longevity). This is mainly a backend change which you won't see in the front end.

admin

SilverArt It's revert back to Max currently.

We can in theory snapshot values (any setting really) prior to changing charge rate (or any other setting), and revert at end of charge/discharge window, but we would need to bake in support for a mechanism like that and it's an additional API read too.

JMA

admin I'm happy with Max.

Now that this works, could a next step be to potentially do the same with discharge (which I'm now doing through Giv, not WW).

By being able to set:

the bottom limit SOC after which to stop discharge (as now done by Giv)
(optional) the minimum SOC needed before deciding to action a discharge
- limiting the discharge power based on
battery capacity in kW * (starting SOC %- bottom limit SOC as chosen %) / (end time discharge window - start time discharge window hrs) = discharge power

If that's possible you can avoid stopping the discharge abruptly when bottom limit has been reached and leaving time in the discharge window. If there's consumption from the house in the period it will draw from grid (with expensive rates).
Here's an example of that:

SilverArt

admin

admin We can in theory snapshot values (any setting really) prior to changing charge rate (or any other setting), and revert at end of charge/discharge window, but we would need to bake in support for a mechanism like that and it's an additional API read too.

My thought is that this should be the standard (however of course I'm not doing the work or carrying any associated cost). The one thing that we can be sure of is that the supplier offerings will continue to come in many shapes and sizes and, other than failures, the most commonly thing asked for by users is flexibility. Therefore the better that WW can handle it with ease. the better it will be for WW.

Just my ramblings...

admin

JMA Yep - logical next step. We'll aim to get that in and adjust the discharge rate so it evenly spreads out according to the configured export window.

JMA

Today a situation where maximum charge level was not 100% . The lowering of the charge level also worked and the SOC reached the target at the end of the 3 hour period and did not go over:

Inverter max capacity went nicely back to 3600 W at end of period:

Bit of a strange peak at the end, but that's because the charging power went to 3600W a bit too early just before end of period. I don't think that really matters or affects the battery.

Successful test also in this situation. @admin