So - what if I want to get a bigger inverter?

[calum]

As always, experience is something you get just after you need it

We have x14 panels on the roof, we could have fitted 17 but we'd have needed a bigger inverter, and our installer advised it wasn't worth doing a DNO application for the sake of 3 additional panels worth of output - and as such, it wasn't worth getting an inverter bigger than the 3.7kW H1. What I didn't realise at the time is how this would limit how much AC power we could consume in the house at any given time, including how fast we can potentially charge our six HV2600s.

So - what if want to put say, an H1-5 or -6 in there? From what I can see the connections are all identical, it would appear to be literally be a straight swap?

Assuming this is correct, I'm wondering about the DNO side of things - looking at my DNO's webpage for this topic (https://www.enwl.co.uk/get-connected/ap ... nnections/), it would seem that this is straightforward if you have a device that is type approved for G100:

Working in partnership with the ENA, a relaxation was written into G99. This relaxation has primarily been developed where a customer is wishing to combine a G83/G98 generator with an Energy Storage Device. This is also known as a fast track process.

To qualify, the following conditions must be met:-

• All generation and/or storage is located at a single installation
• All generating units (including battery storage) are type tested to G83, G59, G98 or G99
• The basic design capacity of each device is up to 32A/7.36 kW
• The sum of the rating of all equipment is no more than 60A/13.8 kW per phase
• Export to the network is limited to 32A/7.36 kW by a G100 scheme

However as far as I can see, the H1 family of devices are not G100 certified eg

As such, if I want to upgrade my inverter I assume I need to do the G99 I would have had to do last year, had I known what I know now? (with the possibility of getting told "no", of course)

[calum]

Hmmm, here is a G100 declaration for the H1 and AC: https://cdn.shopify.com/s/files/1/0257/ ... 1675684985

[Dave Foster]

The G100 would make sense, although 'technically' you could upgrade your inverter, leave it's safety set as G98 and make sure an export limit is set to 3680W but some DNO's don't seem to like that, some prefer to see a meter installed rather than a CT, and others agree - in that scenario all in-house use is 5 or 6kw (depending on inverter), export is limited to G98 (16A).

Personally I would go with the 6kw H1 then you've got lots of capacity and capability to fast charge your batteries, it's only a few pounds difference and you'll likely need to uprate the cables anyway. The decision around the G100 / G99 I think will depend on a conversation with your DNO - G100 if you consume a lot more than you export (and the DNO agrees), G99 if you want to add a few more panels and export more power.

The DNO's are often quite helpful and will point you in the right direction, and you could ask whether they would accept an upgrade to bigger unit if the G98 safety and export limit was set - in which case you don't need to do anything other than get your installer to change the inverter.

I would imagine if they installed the H1 3.7 as standard, your main MCB will have to be changed for a 32A breaker, the wiring between that, the generation meter and the inverter uprated to 6mm and the AC isolator would need the rotary switch replacing with the 32A version.

[calum]

Hi Dave

Thanks for the thoughts. Sounds like I do need to call the DNO at some point then, see how they "like" to do it. Do you have any idea why there is a G100 "declaration" for the FoxESS inverters but no evidence of them having being tested to that - seems odd!

We don't export much as a rule - most of our spare generation ends up in the car. It's really about pinch points - as you say, charging batteries more quickly depending on what tariffs come along in the future, potentially adding a few panels to the current array. Even potentially if we end up getting aircon installed, leaving headroom for other things while that's running on a sunny day - as it stands we could end up having to draw from the grid even though we'd have enough between the batteries and panels to power everything on site. . I know it's been a pretty cool and grey summer this year, but we're clearly going to get a repeat of 40C (and worse) in years to come.

I hadn't thought about the wiring but of course that needs to be looked at. I'm thinking about it now because I'm thinking about getting the installers back to move some of our circuits onto EPS, get an earth rod put in, etc, so we have some backup capability in the case of power cuts - and the thought occurred, would I make different decisions about which circuits I'd put on the EPS if I had a bigger inverter? And of course then, would it make sense to upgrade for other reasons.

[Dave Foster]

Yes it's an odd one, for G100 there is no accreditation, it's more like a set of guidelines that are 'in addition to' G98 or G99 - so in effect it's like a G98/9 'plus' as long as the DNO accepts the principle.

I'm with Scottish Power and this is their take on what it is acceptable https://www.spenergynetworks.co.uk/page ... _grid.aspx but sadly every DNO seems to have their own take on it.

I'm a lot like you, mostly a consumer rather than a big exporter, my extra solar goes in the car as well - but for me the thing about having a bigger inverter is just being able to put the kettle and toaster on with the normal house load all together without worrying about the extra pull being taken from the grid - it's not a lot of extra power probably no more than 0.5kwh a day, but much less stress - that coupled with the ability to fast charge the batteries in 4 hours (i've got 20kwh), that really helps.

To be fair it's difficult to justify the cost to replace unless you are thinking of extending, or going to EPS etc.. the physical hardware doesn't cost that much ~£1k the labour cost to do it all is where its all at.

[calum]

So - this has progressed (slowly!) since I last posted. The installer was eventually able to get someone out to assess things and has confirmed the basics as expected, we'd need an earth spike and a manual changeover switch. Our DNO has also given us the nod to increase our export up to 6kW, without additional charge. So the choice really comes down to the H1-6.0, or the KH-7kW; they differ by a relatively small amount in purchase price, and the H1-6.0 would be a G2 by now but essentially the same as what we have now.

The question I have is really to do with the KH series, I'm currently making a lot of use of the Foxess Modbus integration for HA, and it's proven excellent for making the tweaks I need to the two charge periods and the Max SoC. However I see on the Wiki that the KH doesn't allow remote updating of charge periods or reading of BMS information.

I just wondered if anyone has any ideas from Fox about forthcoming firmware updates that might enable any of these features? Having the BMS data (particularly the high and low cell temperatures) has been excellent for monitoring the battery health, but it's not essential for day to day operation. As to the charge periods, it looks like I could use the 'force charge' feature of the inverter to achieve the same overnight charging functionality as I have now?

[Dave Foster]

Good to hear you are progressing with this, that’s an interesting choice - I occasionally wonder what decision I would make here as well as i’ve got used to so much information from all the sensors and have the same thoughts as you about the updates.

If you ever need a 3rd string - I think you’ve little choice but to go with the KH over the H1(G2) and set an export limit, but if you don’t think you will ever move to that the H1(G2) is the perfect choice and probably more palatable to your DNO as you won’t have to set and prove you have an export limit of 6kW.

On the firmware, I don’t think anyone knows the answer to that - Will is closest to their product dev team and on the KH they have said ‘that it is what it is’, the dev’s I have spoken to have said there is an ambition for a modbus2 protocol which would extend the same functionality across the range. But an ambition is all it is, they are so busy it’s my guess that unless they have to release a modbus feature that is market critical there won’t be much of a change in the modbus features.

The H1(G2) is closest to the H1(G1) with modbus sensors, the KH has the majority but misses some of the BMS registers and charge periods as you have said, it also doesn’t have a ‘Backup’ work mode - but that’s easy to recreate by setting the max discharge current to 0.

The KH does now support maxSoC correctly, in the interim I wrote a few automations for KH users which used ‘force charge’ and manipulated the minsocs to stop it ‘fast’ charging at the desired set point - but it has been confirmed the latest firmware works as expected.

As part of the app development, it feels like Foxess want people to use the scheduler going forwards so I think the original charge periods will eventually fall off the feature list (it’s really confusing to new users).

The modbus integration supports the force charge and discharge modes and with a few helpers and an automation will do what the old charge periods did - the difference being your HA must remain in control whilst it’s running a period, if it fails a timeout will revert the inverter back to self use.

I’d be inclined to go with the inverter that works best for your circumstances, if you don’t need 3 strings - go with the G2 it’s closer to the modbus spec so will fit straight in. If after this spend you really want the extra string, go with the KH and re-write a few automations - and hope that the BMS cell hi/lo registers are eventually coded again.

The good news is they are both superb inverters… i’m just trying to work out how to convince my wife I need to upgrade

[calum]

I cannot see us ever wanting to add a third string of panels here - the only roof space left is north facing into a small patch of woodland, so pretty hopeless for PV generation purposes!

The main thing that sways me towards the KH is the main spec bump it seems to have over the H series, which I posted about over here for information completeness in that thread, specifically:

one of the very concrete spec bumps the KH7 gets over the H-series is the ability to do 10kW peak AC output (assuming enough battery and / or PV) for up to 60 seconds in EPS mode.

As one of the reasons I'm making the change is to enable EPS for the whole house, the ability for the system to pull hard on the batteries for a short time and avoid tripping the inverter with a momentary overload is quite attractive, and the fact it can do this suggests the overall power conversion circuitry of the KH is more capable (and hence perhaps longer lived) than the H-series.

All that said, if I understand correctly it's not possible to set up the Schedules / Strategy Periods via modbus, you have to use an app or the website - ie the parameters for those functions can only be changed via the internet connection. If so that's definitely pushing me in the other direction, as the attraction of my current setup is even if the Foxess infrastructure is unavailable / down / gone away entirely, I have full control over the hardware via HA or if needs be, the front panel of the inverter. To my my mind, tying control of those features to a service that requires internet access and the presence of specific infrastructure, is a terrible idea. Maybe I am mistaken about how that side of it works.

I do take your point about being able to work around this with HA and automations, but again, that puts a dependency on the HA system which doesn't currently exist. I mean, I like the increased control and insight I get from using HA, but I don't want to become wholly dependent on it for basic operation.

Overall it feels like the H1-6.0 G2 is probably going to be the best option, unless some major firmware changes happen to the KH between now and ordering. It would be somewhat annoying if there are major updates to the KH in a year's time, but
I'm still clarifying some other bits with the installer who is perpetually maxed out with other work (which is why it's taken this long to get to this point!) - they are a small company rather than a solo outfit, but there's only two of them who do the more advanced electrical stuff.

[Dave Foster]

Yes the schedule/strategy periods cannot be set over modbus, only via the web/app (and ironically via the openAPI interface). I asked their UK product manager when the scheduler was released whether they would become available over modbus and he said yes, but couldn’t say when that would be (that was over 6 months ago).
I just think they’ve got too many things on the go at the moment to be doing anything with these - but you never know it could happen in future.

With the latest integration force charge/discharge ‘work modes’ - the integration does the work in balancing the control so if you were to lose your HA it would stop charging but that’s still more in your control and reliable than the foxcloud has been but I understand your reticence to introduce any more dependencies.

If you go with the KH another way to address it, is to reverse the logic and use the apps to set a normal charge period during your low tariff period and leave it set, then use HA to change MaxSoC to suit your changing demands in winter/summer, that way your inverter will be in control and everything stays addressable through the app and inverter panel.