Dynamic adjustment of battery charge level?

Our system was completed last week and we are busy learning the basics. Eco mode plus a time charged to match Octopus Go Faster seem to handle most of it, plus periodic car charging via the Zappi. So all good so far.

Up to now we've been selecting 100% for the battery charge and an end time to coincide with the end of the Octopus window. However today is supposed to be sunny so I figured I'd leave some battery headroom to take advantage. I started by setting 70% on the battery and left the end charge time the same but noticed the battery discharging and then topping back to 70% from the grid. I don't really want this behaviour as it's not ideal for the battery I'm told. Then I set an earlier end time which worked but seems a bit clunky as you have to guess what the battery may have charged to.

Is there a slicker way of setting the max charge for the battery when you are expecting some solar generation please? Cheers.

sponev Weclome to the club!

FIrstly, be clear about what you're trying to achieve and why. There are multiple use cases for batteries and your situation will not be the same as others. Consider it as risk and reward: the risk of not charging enough overnight and having to buy in at day rates vs the savings you could make. For example, my solar PV is old enough to have deemed export so I don't get paid for any exports and I'm still on an old version of Octopus Go (off-peak 5p, peak 13p). If I save 1kWh, it is 5p, if I need to buy, it is 13p so as long as I save about 3x as much as I have to buy the world is good. If you are paid for export at 10p/kWh, with 7.5p off-peak and 40p peak, the sums won't make sense.

As for slicker ways to set the overnight SoC, the answer is yes! Several of us have developed free software to do this; there's an add-on for Home Assistant and I've produced a stand-alone Python program which takes the forecast generation and historical usage to modulate SoC each night. www.github.com/salewis38/palm

@sponev I have noticed the same behaviour. It has something to do with visualisation of the SOC. What I mean is that at 100% the battery doesn't seem to go through this cycle of "charge-discharge" and is stable at displayed 100%.

But if you set a lower SOC, for example 70%, the battery will charge upto the set limit. While charging it is all good. But once it is at 70%, the battery will disable "charge mode" and go in and start supplying power to any load from the house. It takes a couple of % points for the batter to trigger the "charge mode", and so on and on.

I have not yet found a way to get around this....

Try setting the battery charge rate lower - it then takes longer to get to the % charge you have set in the available time without cycling around the % chosen. I think 70% could be a bit optimistic for this time of year, as you will also be supplying your routine base load using the solar. You may find 80% a bit more realistic?

My AC 3.0 acts a bit odd too. Set a lower level of overnight charge of say 70% and that is where it gets to. But, when teh sun comes out, the solar stops adding to battery at 70%, then exports. Not what I expected. I have reported this, and its not what GE expected either. Currently, my overnight rate is 12.7p and I get 15p to export each unit. So, really simple, charge to 100% and just export the excess.

Thanks folks. I'm simply trying to be as economical as possible by charging thr batteries (19kwh) as much as possible on cheap Octopus rate whilst still leaving headroom to charge via solar when sun is expected.

I was looking for the easiest way to achieve this without needing to adjust the battery charging end-time and avoiding the recurring charge/discharge event when you just set the battery charge % to a lower figure. I thought that the battery would simply charge to the set % and sit there without discharging until the end charge time is reached. But seems mine starts to discharge as soon as the set % is reached and takes lots of incremental top-ups from the grid until the charging end point is reached. Is that the expected behaviour?

sponev yes, you can expect some top-ups and sometimes a small amount of discharging as the battery stabilises and the temperature changes.

stevelewis OK thank you. I also like the suggestion above about moderating the charge rate to better utilise the available Octopus window. Lots to learn!

Roberto

Roberto Currently, my overnight rate is 12.7p and I get 15p to export each unit. So, really simple, charge to 100% and just export the excess.

What tariff is that? I'd love to have a supplier that sells me energy at a lower price that I can then sell back to them! They'll be bankrupt soon.

With Octopus Go you are limited to SEG, which is 4.1 pence per kWh exported.

sponev OK thank you. I also like the suggestion above about moderating the charge rate to better utilise the available Octopus window. Lots to learn!

It's really not worth the hassle, to be honest. The values that you are talking about is literally pennies. Yes, the way that Timed Charge works is that the battery charges/discharges to hit the SoC that you have requested. It then "bounces" around a little to maintain that level, but in the grand scheme of things is is inconsequential.

You can automate the system to charge it to a level that then maximises the PV generation forecast from the next day. There's a couple of different ways to do this via Home Assistant.

Wonder if that bouncing behaviour will change with the forthcoming soc change firmware update...

Finding a good tariff is not easy - it depends on what you've got and what you want to get out of it. With Octopus, if you have an EV then you can get the Octopus Go tariff (around 12p off-peak but for only a limited number of hours, but you are limited to 4.1p SEG export). Or, you can do ECO 7 - 12.30 to 7.30 off peak at around 15p (soon to go up to 16p). I suspect Roberto may be on an older fix to get 12p. You can partner this with one of the Octopus outgoing agile tariffs. You choose between a fixed rate at 15p or the variable rate that goes up and down each half hour with the wholesale price of electricity. With the variable tariff you either take pot luck and just let your solar export pick up the current price at the time, or if you have a battery you can choose to manually set an export period when the rate is higher. I've just pushed the button on my timed export to get around 35p KW for the next hour. But that is done manually and your have to remember to disable it at the end of the charge period and check ECO is working.

Zakalwe haha. Yes my night rate vs my export rate. The buy in rate runs out in June 2023. Does make the decision to charge and sell back all my excess an easy one. But post June, things will be different.
If only the GE software made it easy for me to fully charge my battery 22.30 to
00.30, discharge to grid until 02.30, then fully charge the battery again. Yes, I live in SE England with a split economy 7.

Karen yes, my 12.7p at night is from an octopus June 2021 tarrif. The 15p export is also octopus outgoing fixed. Not got the confidence to go agile yet.

Zakalwe It's really not worth the hassle, to be honest. The values that you are talking about is literally pennies. Yes, the way that Timed Charge works is that the battery charges/discharges to hit the SoC that you have requested. It then "bounces" around a little to maintain that level, but in the grand scheme of things is is inconsequential.

It's not really the cost of that bobbling around the set-point as I know it's pretty trivial. It's more whether the continual incremental charge/discharge does any harm? Last night mine would charge to the set-point, discharge a few watts and then repeat lots of times until the end point of the charge window was reached. If this isn't a problem I won't worry about it, but I'd certainly avoid it if I was charging my car.

sponev Perhaps a silly question, what makes you think it would do any harm to charge and discharge the battery slightly? Isn't it what the battery is designed to do every day?

stevelewis Yes, but it was more the rate of the charge/discharge cycle which just seemed very fast to me, particularly as it was night time and the house load was pretty static. I expected it to reach the charge percentage set point and then deplete for several minutes before recharging from the grid but it was switching every few seconds. I'm very new to this so probably worrying without reason!

If you need automated control, I would suggest using GivTCP and Home Assistant. Then setting up either Solcast or Forecast.Solar to input your solar generation prediction for the day for limit how much you charge.
I used to manually alter how much I charged everyday. Since setting up the automation, I rarely touch it.
Eg: if the prediction is < 5Kwh then I'd charge to 95% , is between 5-10 then 70% etc.. but if the prediction value is unavailable then charge to 85%.

ispookie666 Looks like a Christmas project for me! Thanks for that.

sponev I've produced a stand-alone Python program which takes the forecast generation and historical usage to modulate SoC each night. Easier to set up than a full HA for changing one variable!
www.github.com/salewis38/palm

stevelewis Thanks for that, I'll take a look!

[unknown] you can do ECO 7 - 12.30 to 7.30 off peak at around 15p (soon to go up to 16p)

currently 16.35p and increasing 8% in January.

[unknown] you can do ECO 7 - 12.30 to 7.30 off peak at around 15p (soon to go up to 16p)

currently 16.35p and increasing 8% in January. = 17.733p

[unknown] Or, you can do ECO 7 - 12.30 to 7.30 off peak at around 15p (soon to go up to 16p).

currently 16.35p and increasing 8% in January. = 17.733p

Rates vary depending where you are in the country. I'm in the South and my current rate is 14.835p - going up to 16.047p in January for off-peak