Grid usage when battery is full

I wonder if a newer firmware revision adjusts this behaviour a little, as I have Octopus Go (and am looking at Flux soon) I would like to keep grid import to a minimum in peak hours, especially if I have plenty of battery.

The problem is that sometimes the inverter prefers grid import over using the battery, even if the battery is full.

Take today for example between 16:00 - 17:00. The load demand was higher than the solar generation, but the inverter spent 15 minutes or so importing from the grid with the battery sat at 100%.

right click open in a new window to make bigger

This typically works pretty well, but I find it gets confused when the solar generation isn't quite covering the load, the BMS doesn't react instantly, but you'd think that it would realise that the battery should be used to cover the shortfall instead of the grid in this kind of situation.

Anyone else see this kind of behaviour?

Eco mode is on 🙂

LordHippos Yes. Although when first installed it didn't. Enclosed pic shows the system importing from the grid even though the battery has the capacity. In the graph it's the periods about 15:30, between 18:00-19-00 and about 21:00 where the inverter isn't taking enough from the battery.

Your battery stepping is a little strange there, very quickly shot from 70% to 100%!

In general mine does work pretty well, but it's sad to see it wants to use the grid sometimes more than it has to, when the battery has a lot of power available.

I know it can't charge and discharge the battery at the same time, but if the demand is higher than the generation, the battery should be topping it up rather than grid importing.

It feels like it's a bug in the way the inverter is balancing the load.

Similar picture today.
Battery firmware is 3009. Portal says it was 0.76kwh from the grid today. Don't know what version the firmware was when i first had it installed and the system was supporting the house more from the battery. Is this using the grid part of some recent firmware changes ? Does it depend on what the logic is trying to do, using the battery to its max to eliminate grid import when it can vs maximising the life of the battery whilst reducing the amount of grid import ?

Maxwell , on that same Power Graph, click the text where is says (+3 others), then select the Grid Voltage option.

You need to be checking that your grid voltage is not exceeding 253 Volts during the period when the solar output is reduced.

Simon_C Thanks, for the heads up. But that doesn't appear to be the issue. Grid voltage is not exceeding 253. I have trimmed down the data feeds to make it easier to see. So, are you saying that the spiky downturn in solar output means i have some other issue with my set up ?

Maxwell , potentially yes.

Grid Voltage exceeding 253V, or a low allowed Grid Export Power can both cause the inverter to throttle back the solar generation.

The allowed Grid Export Power is authorised by your local DNO following an application by your installer. You should have a copy of the DNO response to the application. It can be 0 kW for some people, or 3.68 kW or more, and it is a setting applied to the inverter only by installers and GivEnergy under user account and password protection.

LordHippos Yes. Mine has just done it today.
Battery at 100% all afternoon, house running on solar + export. In the Flux peak period and house load increased to 2kW, there is some solar but instead of using the battery to top up, the inverter imports from the grid for about 20 minutes before the battery takes over. 🙁

alan_johnston I think this is a behaviour bug myself as it makes no sense, it's as if the inverter has the battery on standby for charging, even if the solar is fairly consistent or dropping later in the day as the sun goes down.

I suspect you'd avoid this if you force exported the battery to dump the energy, this would mean it would use the battery power + solar first, and then export any additional.

When/If I get onto Flux (probably later this month) I would like to configure it like this:

02:00 - 05:00 - Charge to 100% regardless of SOC %
05:00 - 16:00 - Charge to 80% **
16:00 - 19:00 - Discharge battery to grid
19:00 - 02:00 - Battery should be low or empty, use grid

** Alternative option for charge slot 2 would be to do the same sort of thing but in the 3 hours preceding the 16:00 - 19:00 window instead, gives more free reign to solar discharge/charge into the battery.

The above isn't possible out of the box but I heard that GE are adding a second charge slot or maybe even multiple charge slots. Home Assistant can do it, but this does rely on the flaky WiFi dongle working at the right moment in time.

My plan above makes sense to some degree if you think about it. Flux import pricing is about 20p/kWh. if I over-charge the battery and the day is sunny, it will export at 24p/kWh in the day so no real loss there. In the day it can hold at min 80% charge but if it's sunny will get to 100% and be exporting. If not then there is plenty of power for the 16:00 - 19:00 window to discharge and use/export it.

Will mean some grid usage but should be counter-acted by decent solar generation, as each kWh exported will make imported units cheaper or subsidy them. My 8.2kWh battery charges/discharges to grid at about 2.4kW so 80% will typically be about what I can charge or discharge in a 3 hour window.

I don't see any mention of what equipment you both have installed. AC, Hybrid, Gen 1 or 2, 3.68kw or 5kw

All of these can impact how your system responds to load and where that power is drawn from.

dragon2905 4kW solar PV, Hybrid 3.6 gen 1 inverter, 8.2kWh battery.

alan_johnston sorry alan was referring to the OP originally.

With regards to your Flux config. Your only option is likely to be HA. There just isn't the granularity within the GE settings to, currently do this.

I am still massively on the fence about the benefits of Flux as a proposal and it's hard to compare against Go or some version of E7 without having those forward rates to carry out some calculations on.

If I look at my history I used the following:

13 Feb to 13 March (Octopus Go @ 7.5p / 39.35p inc VAT)
Trying to reduce the numbers to the most basic values.
Night Rate (0:30 to 04:30) Load Shifting : 251.8kwh
Day: 43.9kwh
Total: 295.7kwh @ £36.16
Gives an Average Unit Rate = 12.23pkwh
Grid Export SEG (British Gas): 59.39kwh @ 6pkwh = -£3.56
New Average Unit Rate = 11.02pkwh

I decided to do some simple spreadsheet work to see how the numbers stack up.

My Flux Rates (East Midlands) would be:
Import (inc VAT)

• Day: 32.4
• Flux 02-05:00: 19.44
• Peak Rate: 45.36

Export (inc VAT??)

• Day: 21.4
• Flux 02-05:00: 8.44
• Peak Rate: 34.36

So the numbers work out to:

• Day: Consumption 159.36 @ 32.4 = £51.63
• Flux: Consumption 130.01 @ 19.44 = £25.27
• Peak: Consumption 6.26 @ 45.36 = £2.84

Total Bill Consumption would be £79.74
I use British Gas for my SEG so don't have 30min amounts.

Lets look at each of the 3 possible Export scenarios:
Current SEG Export: 59.39kwh

• @ Day Rate 21.4p = -£12.71
• @ Flux Rate 8.44p = -£5.01
• @ Peak Rate 34.36p = -£20.41

So my Net Bill would be

• @ Best £59.33 (average rate of 20.07pkwh)
• @ Median £67.03 (average rate of 22.67pkwh)
• @ Worst £74.73 (average rate of 25.28pkwh)

Anyone have the latest Go values for East Midlands as if you were to sign up for it today?

Hope that helps someone

dragon2905 I think the OP was wondering why the system would prefer to import from the grid when the battery SOC was 100% and consumption was easily within what the battery could supply.
Which was also what I was wondering having just seen it happen with my system.

Today, I have seen the same behavior as the OP with the Inverter choosing to import from the grid rather than use a fully charged battery. It is a new system only a week old and up to now has behaved as expected covering demand from house that cannot be covered from the panels from the battery.

I tried restarting the inverter but it did not make any difference.

alan_johnston Yes sorry with so many people responding/semi/hijacking threads its difficult to keep a consistent response train.

I think everyone should be encouraged to provide the specs of their equipment ie. Number of Solar Panels, Peak Output of Panels, Inverter Type and Gen and Battery information as responding to random queries without this is beyond speculation.

Not sure why but there doesn't seem to be a lot of thread etiquette on here. People are all to happy to either partially or completely hijack threads.

The reply re potentially changing to Octopus Flux was in reply to your comment about Flux @alan_johnston and also to @LordHippos

as I have Octopus Go (and am looking at Flux soon)

Was only intended to provide some actual historical data that if we (personally) had been on Octopus Flux versus Octopus Go we would have been worse off.

Managed to find a link to current East Mids Go Rates so can provide an update on "Go versus Flux";
https://octopus.energy/blog/go-faqs/#:~:text=This%20is%2012p%2FkWh%2C%20no%20matter%20where%20you%20are.

Unit rate (04:30 - 00:30): 42.46p/ kWh
Unit rate (00:30 - 04:30): 12.00p/ kWh

So can update
Night Rate (0:30 to 04:30) Load Shifting : 251.8kwh
Day: 43.9kwh
Total: 295.7kwh @ £48.86
Gives an Average Unit Rate = 16.52pkwh
Grid Export SEG (British Gas): 59.39kwh @ 6pkwh = -£3.56
New Average Unit Rate = 15.32pkwh

So still would have been worse off using Flux v Go (current rates) by £14.03 to £29.43 during Feb to March 2023.

Going back to the OP and query about the data.

Yes something looks off but again without knowing your specs its very hard to comment.

Here are mine from the same time and day (Gen 1 5kw Hybrid + 9.2 Battery + 5.6kwP PV + Software Version
D0.450-A0.451)

First thing that comes to mind have you messed with your Inverter Settings?
ECO Mode, Timed Charge, Timed Discharge, Timed Export, Battery Options

These are the standard things to check. Also go into My Inverter (on the left) then into Remote Control (Cog in top Right) and see if those settings are the same.

dragon2905 think everyone should be encouraged to provide the specs of their equipment ie. Number of Solar Panels, Peak Output of Panels, Inverter Type and Gen and Battery information as responding to random queries without this is beyond speculation.

Not sure why but there doesn't seem to be a lot of thread etiquette on here. People are all to happy to either partially or completely hijack threads.

Yes there are some off-topic replies to my original post but the Flux stuff I was interested in so hijacked my own thread there! March was incredibly poor for generation compared with expectations, so I think Flux will come into it's own once you start exporting more.

@alan_johnston is having the same problem as me so no issue with their posts, as they are on topic and it's good to get more confirmation of the issue as well.

My equipment is similar to theirs:

alan_johnson: 4kW solar PV, Hybrid 3.6kW gen 1 inverter, 8.2kWh battery.
mine: 4.8kW solar PV, Hybrid 5kW gen 1 inverter, 8.2kWh battery.

So same inverter but mine is larger, same battery, slightly more PV on my end.

My software version is D0.450-A0.451 which is same as yours, and battery firmware of 3007.

In regards to settings on the inverter I've enabled Eco mode, and have a timed charge set for Go (00:30 - 04:30).

LordHippos My software is D0.450-A0.451, battery 3007.
Default settings, ECO mode on, plus charge battery from 2am to 5am (to 100% if possible).

I have only seen the system import from the grid (for a long period) when it should be using battery the once, which is the one I reported on this thread. Hasn't happened again so far.

alan_johnston It's not that common I agree, but it's not totally isolated here either. Seen it at least a couple of times, can sort of detect it by seeing the grid import spikes.

Have another example here on 17/03, where the battery was being charged by the solar 15:10 - 15:15 whilst also importing from the grid to cover the house consumption. Solar generation was a little in and out, and was not covering that window by itself.

This whole time frame is a bit wonky as shown, even if it's 5 min snapshots, it was taking more from the grid that it needed to considering solar wasn't zero, and the battery had a good amount of charge.

This seems to be a symptom of this in between state where it doesn't quite know what to do with the solar generation with regards to charging the battery, exporting, or covering base load. My preference would always be base load > charge battery > export in that order.

@LordHippos ofc everyone has to make their own decisions based on their own use case scenarios.

I forgot to mention we also have an Eddi. That doesn't mean we don't export but it does reduce it.

For our personal use I don't think Flux is worth it, Cozy neither, Agile or perhaps Wholesale Tracker maybe now that prices are coming down.

I think the biggest issue with Flux is that Flux rate just isn't low enough. @ 15p Import it probably starts to make sense.

dragon2905
I agree , it is surprising that flux import should be more than eco7. On the other hand even with an eddi i am seeing plenty of energy being exported at rubbish agile rates so even though the 22p is not good it may be the best option now.

dragon2905 I ran some numbers based on my own calculations, and taking some worst case scenarios into account as well. This is based on 8.2kWh battery, 2.4kW charge/discharge rate (2.6 from inverter translates to around 2.4 in reality to/from battery via grid), and 0.7kW constant load (my average usage per day is 16-17kWh so seemed fair to start here).

The calculations I ran also assumed 0 solar generation for the whole day, though I've also added some calculations at 5/10/15/20 kWh generation for a day. Go can get very cheap no matter how inefficiently you use it by virtue of allowing cheap import rates, but export payments are awful.

Eco7 was surprisingly good on the whole, though tracker or agile may be able to win out in general depending on how you use it.

Where Flux started to shine was as the generation starts to tick up. If I assume no solar as a baseline, then any generation is valid for export, or can be offset against usage at the prevailing export rate. I don't think it's an entirely unfair comparison anyway.

For the purposes of comparing apples with apples, I've set my rates at the current Go/Eco7/Flux values when I ran this, rather than back-dating legacy ones. I am on the same 7.5/40p rate you are, so my actual numbers on Go will be slightly better, but this rate runs out end of August for me.

Flux values across any given day, where it's charged and held until discharge time, this isn't 100% efficient, just a baseline. Having a 2nd charge slot that tops up battery just ahead of peak rate should improve this a little.

Go values where the battery is charged and then discharged in the day, at my usage this would run out with 0 solar and have a deficit of around 5 kWh in the day. This means I need at least 5 kWh of generation to really make Go as reasonably cheap as possible, or to avoid most peak usage.

Summary for all 3 options, can see that at lower values of say 5 kWh generation in a day, Go is cheapest for me, but it just doesn't really scale much beyond this value. At 10 kWH generation, Flux starts to take the lead, and is the best one for negative relative unit pricing for my input parameters beyond this point.