when to stop filling up the battery at night?

Does anyone have an idea for how to decide when to turn off the automatic importing electricity at night so there is room for the panels to charge it during the summer sun?

thanks
Nick

Never if you have IOG and export?

Jackman Welcome to the forum.

i should think it depends on relative sizes battery and solar array... And also daily consumption and tariff, to some extent. If you can be bothered, you can use solar forecasting to judge how much you need. But that is subject to quite large errors.

I currently charge 9.5kWh battery to 40% overnight - on even an overcast summer day, I get enough solar during the day to power the house, and 40% more than enough to cover evening use. But my tariff is such that I basically want to export all solar, and I only let enough into the battery to avoid clipping. Your circumstances are probably different.

I choose not to churn the battery every morning to make a few extra pennies, but that's certainly an option.

I have a bit of a different strategy - again it strongly relies on the tariff that I'm on. Currently on intelligent go with a 15p export.

1. fully charge the battery overnight
2. force export 6am-9am -> this usually leaves me with around 40% SOC
3. force export 9pm-11pm

The 40% I'm left with at 9am each day is enough to get me through a day if there is no / minimal sunshine but also low enough of a SOC so that I will not clip the inverter and take advantage of the 7.5kw sun power in case of clear skies.
Again, this setup is used as a default for all year long and it suited me well; on days that are predicted to be very sunny I extend the morning export do dive the SOC as low as it can go.
I'll post some charts for a non sunny day vs a sunny day below:

dragos.balaban It would be a bit more efficient to export the solar directly, rather than charging the battery during the day, then exporting it to the grid in the evening. On the less sunny day, for example, battery charged from about 40% to about 80%, which would be about 3.8kW on a 9kWh battery. But there's probably say 10% losses from charging/discharging the battery. So you could possibly have exported 4.2kWh directly, which also avoids a bit of battery cycling.

But obviously you need to allow charge into the battery on the sunny day to avoid clipping. If you have a 5kW inverter, then limiting charging rate to 2kW may be enough to avoid clipping. (7.5kW max input, but then probably around 500W inverter losses.)

What I now have is an external agent which monitors the inverter, and tweaks the battery charging rate to try to keep AC generation close to 5kW, in order to export as much as possible directly without clipping.

I’m charging to 100% so at 5.30am the battery starts running things but this time of the year the sun ( or bright clouds like today) soon puts it back to 100%. IBoost is heating the water because I’m being mean about buying oil - getting ASHP quotes - then cook breakfast, make coffee tea etc run washing machine maybe, cook tea about 17.30/18.00 then do a timed discharge 18.30-20.30 (probably about 4 kw) and usually get to between 25 and 5 % by 23.30 and charge again. Export for example on 20th was 21.86kw including the timed discharge. In the winter we pretty much managed on the 9.5 battery most days with the heavy consumption things running at night on IOG.

DD
I do understand there are more efficient ways of doing this out there, you give a brilliant example
What I was looking for was a solution that could be left alone most of the time and still do a good job most of the days.
With my strategy there is minimal user action needed. If there is a very sunny forecast, somewhere around 9 am I go into the app and press one button to force export. Later I need to go in again and stop the force export (again, one button)

Is there an easy way of changing the charging rate?

dragos.balaban I’m not doing anything it’s automated via the portal with charging reduced to under 2kw mostly to keep the temperature a bit lower (inverter and battery in a cupboard.)

@SimonClarke , @DD mentioned a strategy to reduce charging rate automatically on sunny days only and I was asking how can that be achieved without logging into the portal and manually adjusting it to 2kw and then at the end of the day adjust it back to 3.6

dragos.balaban why not just leave it at 2kw?

Because I want to charge as much as possible during the night in the 6 hours cheap period.
But now that I stop and think, I might get away getting rid of the first discharge session and adjust the charging rate to a 2.5 for starters...

dragos.balaban I easily charge the battery to full in the six hours from empty at under 2kw I’m not sure why you can’t?

Sorry I forgot to mention, I have 2 x 9.5 installed

dragos.balaban that would explain it!

Jackman

One simple answer won’t fit all scenarios unfortunately.

Depends on;
A) import and export tariff
B) your battery capacity
C) your charge/ discharge rate)
D) your DNO export limit
E) if you have an electric car and can get on IOG.
F) if you have other “ideas” about trying to be even ‘more green’ or cycling your battery less or concern about equipment temperatures or eeking out every last penny.

Maybe describe your system and tariffs to us and someone in a similar position can help better.

For example;
I’m on IOG, and 15p fixed export, 36kWh battery storage and 2x 5.0 hybrid inverters. Also on the inverter balancer beta trial (to avoid cross charging). I’ve got 27x 420w panels: 5x South, 8x North, 14x East facing. 11.34kW peak, although I won’t see anywhere near that most of the time and certainly not all panels will be producing their max at the same time due to orientation. (Maybe the east ones, might occasionally clip 880w in perfect conditions if the batteries are full but they are split on a lower and upper roof with partial shading from next door)
I’ve got a 10kW DNO export limit.

For my set up and today’s tariffs I’d say charge them to full every night at 7.5p, (and the car) all year round.
Let the solar export all day at 15p, then export what battery is left in the evening at 15p to be close to empty at 23:30.
Then repeat.

In summer it’s easy. My “timed discharge” is automated to start at 7pm. My discharge rate is ₂₁% battery capacity per hour at 8kW.
In winter I just adjust the discharge start time. ie if I have 50% battery I set it to automatically discharge at 9:15pm.
If I have little or no battery power left in Dec/Jan: no timed discharge!

I wouldn’t personally be discharging in the morning, because I’ve not seen major clipping issues (yet?). Others may need to. (As may I, if I see clipping later on). I’ve only had my system less than a year and my export wasn’t signed off until September 2023. Also, export was only 4p so the strategy was different back then, until it became 15p.

If you discharge the batteries to then top them up with solar, that’s inefficient because you’re introducing unnecessary battery cycles and round trip losses of say “5-15%” which also depends if your system is AC or a DC hybrid system.
All the extra round trip losses might outweigh the occasional chance of clipping, which might be minimal. Or not. Again it depends. There is a lot to calculate!

I’m achieving 99-100% off peak energy usage all year which I’m really happy with at 7.5p. And hopefully cost wise with the savings sessions as well, it’s looking like I might achieve a net zero electricity bill for the complete year but still got a month or so left to go until I know for sure.

dragos.balaban Is there an easy way of changing the charging rate?

On the app, you can access it from the cog in the top-right - it's 'charge power' at the bottom of the charging section.

For automating it, you'd need some sort of computer, ideally always-on. I just had a quick look at wonderwatt.com but unfortunately it doesn't appear to offer a mechanism where you can simply adjust the power level on a schedule, without requiring active charging or exporting. @Wonder Watt possible enhancement ? (But I think it could be used to do your morning routine: at 0900, if there's a certain amount of solar forecast, force an additional export for an hour or so.)

Similarly, octopus r&d offer access to a scheduler, but again it doesn't seem to offer a way to simply adjust power level on a schedule.

The premium version of https://givenergymonitor.wixsite.com/tutorials offers scheduling of some form, but I don't know if it can just adjust power levels.

Failing all that, either something like a rpi locally (which is what I use), or a cloud service (of which I think there are some free ones ?) can run trivial api scripts to do it.

I'm manually intervening at the moment, using IOG to top to 100% unless there is a fair bit of sunshine due. We have a 10.1kwp array (E/W) and so clipping can be a feature if we're not careful, not dangerous but a bit wasteful. I'll export in the morning to avoid it if necessary. We managed over 60kwh a few days ago and even with some careful management, we still clipped a little in early afternoon. Spoiled a lovely curve! I guess it's a balance between what you lose from clipping vs the bit you pay to top up on IOG, but you can still export that and make a bit.

My main "dilemma" at the moment is whether to switch back to Flux, very lucrative last year but not so much this year. We could probably make a few hundred quid extra but not sure that's worth the hassle and wear on the batteries with prolonged export. I'll probably stick with IOG and 15p fixed export this year.

dragos.balaban force export 6am-9am -> this usually leaves me with around 40% SOC

A possible risk with this is that the car could still be charging at this time - bit of an own-goal to try to export only to find the car consuming it. I'm quite regularly seeing car still charging after 9am on a Saturday morning (despite there having been plenty of time overnight to have done so - I rarely need to charge more than 9kWh in a night).

When the weather improves enough and for long enough that you can run from solar and battery safely.... oh wait, thats it, summer has been and gone now...

I agree with everyone above, it depends on each individual situation.

Last year I was on Flux and charged at night slot, discharged at peak slot 4-7, this was an easy set up.

This year I am on Agile and fixed export rate 15p, so at moment I am charging at cheapest rate over night, letting solar export all day (at moment that is up to about 7pm most days) then discharge battery for 2 to 3 hrs. All done via Wonder Watt.

There is also a cheap slot around 2 pm to top the battery up if needed to cover the 4-7 slot, but recently these have auto cancelled as battery above setting.

Jackman Our smart charging option takes into account solar forecast and your battery size, SOC etc. and calculates a dynamic SOC target to charge to overnight.

Some more info here: https://www.wonderwatt.com/multiple-schedules-smart-charging-with-growatt-and-givenergy/

DD I just had a quick look at wonderwatt.com but unfortunately it doesn't appear to offer a mechanism where you can simply adjust the power level on a schedule, without requiring active charging or exporting. @Wonder Watt possible enhancement ?

But surely the OP's reason to adjust the charge rate was to not fully fill up the battery at the end of the off peak window, when expecting a sunny day, right?

Which effectively is achieved by using our smart charge schedules, which takes solar forecast into consideration, and calculates a target SOC to reach by end of the offpeak window, and optionally adjust the charge rate to achieve just that.

I only have a small system (8.2kw battery and 3.2kw panels) but I am currently operating "the lazy man's charging controls". Usually on a moderately clear (not especially sunny day in May). I will go from 100% battery charge at dusk the night before, down to about 70% by sunrise the following morning. So I set my battery % charge to 70%. This usually mean during the cheap period the grid supports my house load if needs be, and the battery is at 70% at the end. If we have a horrible day there is enough in the battery to see me through to the next charging period regardless of what appliances I use during the day. If it is really sunny day the solar will fill the battery by about 11.00am then export to the grid, and will still be exporting during the peak period. Because my system is small I don't have to worry about clipping (3.6kw Solis inverter and AC3.0)). Some days I don't actually use any grid electricity at all, but I always know there will be enough in the battery to run the house whatever the weather. I haven't had to change any settings for about a month. It may cost me a few pennies overnight now and then and I know I'm not "making" as much money from the system as I could by forcing exporting, but it is so much easier than constantly juggling settings.

@Wonder Watt
My goal is to charge the batteries as much as possible during off peak (i.e. every night)

Next day, IF it is really sunny, I want to be able to use the full 7.5kw power that my array and inverter can do for as long as possible but that means there should be a constant flow of 2.5kw towards battery and 5kw towards export. In my mind this can be achieved successfully only if you discharge before sun is up but also limit charge rate to about 2.5kw.
In the evening I will need another discharge window so that I am prepared to buy as much as possible during off peak

If sun forecast is below 5kw, there is no point to discharge in the morning, so just keep the evening discharge window

Is this something your product can do?

dragos.balaban

Is this something your product can do?

Not at the moment, but that's an interesting use case though. Do you manage all of this manually at the moment?

Our system can do parts of what you want to do, apart from this: 'but also limit charge rate to about 2.5kw.' - and doing that on a schedule based on solar forecast.

So effectively we would need to introduce another 'schedule type' (alongside charge and discharge options), called 'charge rate adjustment'.

And the setting would basically take two inputs, as well as a start time and end time.

Adjust charge rate to X % when solar forecast for today is greater than Y kWh.

Am I understanding this correctly?

Wonder Watt But surely the OP's reason to adjust the charge rate was to not fully fill up the battery at the end of the off peak window, when expecting a sunny day, right?

That may have been the starting point, but there are other reasons for wanting to adjust the charging power independently of actively charging from grid. In particular, here, for limiting how much solar power goes into the battery, with the aim of exporting as much directly, but without solar clipping.

I used to run very simple scheduling from a rpi which simply tweaked charging power from 0 at 8am to 500W at around 11am, then 1500W at noon, that kind of thing. Very crude, but did what I wanted

I was just looking around to see if any existing cloud tools could do anything similar, since not everyone wants to set up a rpi.

DD Yep, makes sense.

exactly that @DD
@Wonder Watt, I want to fully charge off peak, irrespective of solar forecast - this is easy to do

But, IF sunny on that day, I need some way to capture the full potential of the sun and my system.

If my battery is full in the morning, I will very quickly get clipped at 5kw
I would love some sort of mechanism to combine dumping some of the battery contents and limit the charging rate to see me through the day nicely, avoiding clipping and finishing the solar day with an almost full battery - ready to export again before the next off peak window

Something like:
IF SUNNY, export in the morning 50%SOC and limit charge to 2kw
IF NOT SUNNY, do not export in the morning, do not limit charge
REGARDLESS OF SUN, export in the evening as much as to not need to import off peak
REGARDLESS OF SUN, charge batteries fully in off peak

In the example below, you can see a good solar day.
I did manually export as much as possible in the morning - ZONE 1
I did not adjust the charge rate so unfortunately, the battery filled and that resulted in clipping in ZONE 2

dragos.balaban Thanks for the details.

Should be straightforward enough for us to add. Keep an eye on our release notes.

https://community.wonderwatt.com/d/96-wonder-watt-release-notes

Are you effectively saying the charge throttling would remain in place for the morning export window only?

It looks like you'd want a separate schedule which extends the charge throttling post your export end, right?

dragos.balaban IF NOT SUNNY, do not export in the morning, do not limit charge

Hmm .. if it's not sunny, I fully pause charging so that all solar is exported directly - no point charging the battery only to discharge it back to grid later anyway

@DD that's actually a great idea
@Wonder Watt hope that's doable too
IF NOT SUNNY, pause charging until off peak

DD

if it's not sunny, I fully pause charging so that all solar is exported directly

Right - any solar yield that you would get on a 'not sunny' day just services house load and any excess goes grid side?

yes, this will spare the battery of some cycles and also avoid efficiency losses charging the battery only to discharge it later

dragos.balaban pause-charging is arguably just an implementation detail - it's what setting charge power to 0 ought to do, but in practise, on my inverter, charge power of 0 actually still charges at just under 300W. But pausing gets it down to close to 0.
I actually have the pause timer set to run from around 7am to 10pm, and my script just toggles the mode between unpaused and pause-charging. That way, the daytime script doesn't have to worry about unpausing overnight to allow battery to charge from grid.

Wonder Watt correct. Though, I don't try to predict the solar, it just monitors the generation and tweaks charge rate to keep it just below 5kW. So it's sunny intervals, rather than sunny days, it's looking out for.

DD The "pause-charge" API call you're talking about is basically setting the Pause Charge value on the Pause-Battery (id:96) setting?

{
            "id": 96,
            "name": "Pause Battery",
            "validation": "Value must be one of: 0, 1, 2, 3 (Not Paused, Pause Charge, Pause Discharge, Pause Charge & Discharge)",
            "validation_rules": [
                "in:0,1,2,3"
            ]
        }

Does that have any other side effects on other settings?

And equally, does setting Pause Discharge work better than setting Discharge power to 0 on Giv inverters where the latter has been a bit unreliable (still discharging at 300W or so too).

Wonder Watt yes, that's the one. It operates during the interval set by id's 155 (pause start) and 156 (pause end)

I'm not aware of any other side effects, though I can't remember if I've ever tested what happens if charging is paused during a timed charging slot. (Can't test it right now.)

Yes, with pause-charge active, the tools report that the actual charging rate is around 28W, whereas merely setting charging power to 0 results in a charging power of about 280W on my system.

Have a look at my energy optimiser. There is a small charge for it.
I use it and for about 95% of the time it is set and forget.
I set a minimum charge level required for the morning and a time for that to be achieved (07:30). It charges to the required level at the cheapest overnight rate (I am on octopus agile) and it does the rest.
It will also manage discharge and export, although I dont use this.
https://myenergyoptimiser.co.uk

I wonder what the OP @Jackman thinks of all the details of all these variables?

I can offer a different equally complicated set of options.
We have no export tariff since the biggest system is on FIT and we are a heavy daytime user in summer.
With a 9.5 battery I fill to 90% even now in May overnight if it is a low sun forecast day and ₅₀% or less if sun forecast.
It’s all done manually so sometime I miss and we export during the day by mistake.
We have no EV so we are on eco 7. The aim is to use no std rate electricity at all.