Second AC3 or wait for AC5?

Good morning

So I thought I would throw this one out to all you clever people as you have clearly put huge amounts of time and thought into your systems.

Query, I currently have 1x AC3 and 1x 8.2 battery and I am adding a 9.5 battery next month (my installer says next month) now I am wondering if I should have a second AC3 added with the 9.5 battery to give me 6kw charge/discharge speed. Or wait and have a AC5 fitted next year to give me 8kw max. I am going to assume the AC3 and AC5 will work together as a plant.

Basicaly AC3 now or wait for AC5? This will be the last item I can add, no more wall space after this. The idea is during sunnier days I can store more solar while I am at work then dump a chunk of battery into my car and use less from the grid. So a AC3 + AC5 combo covers the 7kw car charger. Plus obviously the other benefits of having more devices on at home using the batteries, Oven and ASHP etc.

Many thanks

One question would be will the DNO via G99 accept an additional 3kw or 5kw export potential? Likely this will be out of G99 Fast trace scope 16A>Pexp<32A, so will need funding for a full application.

I may look to swap my AC3 for an AC5 if its out next year, or also look at an 2nd AC3

It would be down to personal preference, charge time window and expected load, if the additional expense of the AC5 warrants it

THALL For some reason, I thought you were planning on adding PV. Anyway, personally, I'd not wait for an AC5 if you can get an AC3 sooner.

Points to ponder - you want to store more solar? How often does your existing/planned PV output more than 6kW above your house load, bearing in mind that if your EV is at home, you can/will be able to charge that from PV output at 7kW? If the PV array is sufficient, you would also be able to charge your battery at 3kW, or 6kW with your new AC3.

It won't matter to the EV charger whether it charges at 6kW for 3 hours or 7kW for less than 3 hours, you will be fully depleting your batteries to the EV.

Normally, I'd plump for the biggest and best but "a bird in the hand" might get you something that works now rather than wait for something that may take some time to be available.

TheDragon (GivEnergy) I already have a G99 which they capped me to 3.68kw. So I expect a G98 will be fine declaring the new configuration but state it will be export capped to 3.68kw

@Tim Yes I am adding more pv too. But that will be going on a solis inverter. Currently I have a 4.62kw system on a 5kw solis inverter and 2.4kw on a 2kw solis inverter. The 2.kw inverter is coming out an a 6kw going on, the current 2.4kw panels are going on 1 string and 6x 545w panels going on the second string. Hense the AC3 bring both systems together.

First point, depending on the time of year. But my ASHP draws between 1200 and 3400w, so if someone has used hot water then someone cooks I can be sucking 5 - 6 kw for a period. Then in winter the heating is on. Worse use case will be winter, heating on, cooking, car charging at which point I might draw 14kw? As I work Monday to Friday 8 til 4 my car gets very little solar directly. But over the Summer I was able to dump 4kw ish from the battery into the car which was using about 13kw per day. So a second battery and second AC3 would mean I could put around 9 - 10kw into the car.

It all makes sense, and the big one at the moment is I know AC3's work together as a plant, while I would expect a AC3 and AC5 to work together there is the chance that they wont, or that a AC5 will not appear for another 12 - 18 months. So 6kw max output vs 8kw.....

To be clear my final home pv will be 1x 4.62kw system West facing and 5.63kw system East facing. A AC3 charging 1x 8.2 and 1x 9.5 battery. BUT as mentioned I can add another AC inverter. There is just enough space on the wall.

It is likely you will need a fresh G99 application.

THALL I know AC3's work together as a plant

Hmmm. I'd say they were designed to work well together but nobody has yet shouted out to say that their AC3s work well together; only folks who say the opposite.

Presumably you've got FIT on your original PV which you don't want to change and you're adding new PV. Why not pull out the 2kW Solis and replace with a Givenergy gen2 HY5 with 9.5kWh battery attached? Your total PV on that inverter would be 2.4+3.3=5.7kWp. We've got 8x390W panels on each string of our gen1 HY5, giving a total of 6.2kWp, all south-facing. It does clip occasionally in summer but the added panels gives us a longer harvest period in the day and in the year. A gen2 HY5 would give you 3.6kW from battery, not the 5kW you're looking for but it would surely reduce the cost of the installation, and it would potentially give you the opportunity to add another AC3 later if you wanted. Having an HY5 would mean that you don't have to worry about AC3s playing nicely, at least until they get the firmware sorted.

I think that a fast track G99 might be in order too as you're already limited, but you need to inform them.

ispookie666 My installer for my extra 3.3kw pv did a G98 which has come back and the DNO have not asked for a new G99. They said I should only need another G99 if I wanted to challange the 3.68kw cap. They sent that to the DNO months ago and have not come back to me saying there is an issue, I would hope the same would happen if I add another AC3. Hope :-)

@Tim No fit on the orignal PV, the house is only 2 and a bit years old. That is because in my AC3 setup I can use both solar arrays which is 4 strings in total. 1x Solis 5kw and the new Solis 6kw inverter then an AC3 feeds of those. With my new panel setup I will have 4.62kw West facing and a 5.63kw East giving me 10.25kw total though in the East West setup I expect I will see 5.5 - 6kw max at any one time. But with the AC3 my zappi also works exactly how I want, ECO+ mode all the time apart from scheduled boosts. My id3 is set to 80% max charge and my zappi schedule is set for my go period. My GivEnergy timed charge currently keeps 40% minimum in my 8.2 battery for my home and all I do is move the slider to 100% nearer the dead of winter. It all works perfectly well. Also my givenergy gear is installed on the outside of my house so having the HY5 inverter in the loft would mean moving the batteries up there too? How far away can the battery be from the inverter?

THALL How far away can the battery be from the inverter?

There's no limit but the further away, the greater the losses. Losses with AC are less of an issue (higher voltage and therefore lower current). Sounds like you've worked out your answer, given your circumstances.

The obvious descision point is whether you will have enough batteries connected to the new inverter to use the extra capacity of an AC5.

As to distance between the inverter and the batteries, there is no electrical reason why you couldn't use larger cross section cables to get the same voltage drop in a longer run, but I guess that negotiations would be needed with GE for them to accept the concept.

I think a second AC3 will be fine. I have contacted GE to ask for a list of "plant" issues which might put me off. I also have my installer coming out 1 more time this weekend and will discuss placement of a second AC3. But it sounds like my setup from the end of October will be

4.62kw on a Solis Inverter West facing (280 degree)
5.63kw on 2nd Solis Inverter East facing (110 degree)
2x AC3 1x 8.2 batt 1x 9.5 batt
Total solar 10.25kw
Total batt charge/discharge 6kw
Total batt capacity 17.7Kwh
Zappi v2
Daikin ASHP

Hopefully. As mentioned above at least the AC3 is available now.

@THALL
These are the exact words from DNO when I had my G99
"For the avoidance of doubt, any future low carbon technology installation, whether or not of a similar nature to this application, must be dealt with on their own merits and you must therefore apply for consent from UK Power Networks before such installations are carried out."