PV Oversizing

[philorden]

HI everyone, I have a H1-3.7-E inverter and a 4kW PV array which is set due South on an average roof pitch but I rarely get the 3.7kW output from the PV or the inverter. I was thinking of adding another string of panels but on a West facing garage roof which is directly above my inverter and battery installation, to keep cable runs simple. I realise that I will never get more than 3.7kW during peak conditions but reckon I will gain in cloudy conditions and especially in the late afternoons when my South facing roof is sheltered.

Appreciate your thoughts here..?

Kind Regards,
Phil.

[Dave Foster]

Quite a few if's on that, the inverter can handle 2 strings, each string has a voltage limit, and a current limit so the answer will depend on how many panels and what size are on currently each string.

As a rule the H1 3.7kw doesn't like to be oversized and often has problems with overcurrent alarms at peak power (usually a bright clear day when it is cool) - tbh 4kw sounds about right for this inverter.

[Ched]

We have a H1 3.7 inverter with 4 x 410 watt panels facing southish and 8 x 410 watt panels facing westish. So a total of 4,920 watts of panels. It was installed in Feb and, touch wood we haven't had a single error or alarm. Our max output has been 3.9Kw which I assume is the inverters max output - I was expecting a max of 3.68Kw.

From, my very limited experience, our arrays peak at different times thus flattening the input to the inverter.

I would say as your garage is west facing you should be OK with some extra panels (not many though) - I think you need a minimum on a string (check specs). Technically you might also need to inform the DNO although your inverter is limited so you might e OK - I don't know the legal regs.

[pdw]

Our max output has been 3.9Kw which I assume is the inverters max output - I was expecting a max of 3.68Kw.

3.68kW is the inverter's maximum output (i.e. the amount of AC it can produce from PV/battery). The maximum PV input is 4.68kW, which is the limit on both battery charging and inverter usage. Your 3.9kW was presumably when your battery was not fully charged.

One trick that you can do is to limit the maximum battery charge until after the midday peak has passed. I do this using home assistant to switch to feed-in priority if the battery hits 95% before 2:30pm. This means that if the PV output exceeds the inverter's limit, the surplus can be used to charge the battery rather than wasted. Without this, on a day when I'm likely to see PV output in excess of the inverter's capacity, the battery will usually be fully charged before it happens. With this in place, I fairly regularly see output above the inverter's limit on a good day.

[Ched]

Our max output has been 3.9Kw which I assume is the inverters max output - I was expecting a max of 3.68Kw.

3.68kW is the inverter's maximum output (i.e. the amount of AC it can produce from PV/battery). The maximum PV input is 4.68kW, which is the limit on both battery charging and inverter usage. Your 3.9kW was presumably when your battery was not fully charged.

One trick that you can do is to limit the maximum battery charge until after the midday peak has passed. I do this using home assistant to switch to feed-in priority if the battery hits 95% before 2:30pm. This means that if the PV output exceeds the inverter's limit, the surplus can be used to charge the battery rather than wasted. Without this, on a day when I'm likely to see PV output in excess of the inverter's capacity, the battery will usually be fully charged before it happens. With this in place, I fairly regularly see output above the inverter's limit on a good day.

The 3.9kW is when batteries are full, that's the regular high I see on nice sunny days. I have just had a look at Hone Assistant for the value of PV Now and over the last 2 weeks it peaked at 4.37kW. Maybe I'm looking at the wrong parameter?

How do you limit the max battery charge?

[pdw]

The 3.9kW is when batteries are full, that's the regular high I see on nice sunny days. I have just had a look at Hone Assistant for the value of PV Now and over the last 2 weeks it peaked at 4.37kW. Maybe I'm looking at the wrong parameter?

That's strange. I don't have a "PV Now" entity, but I look at "PV Power", and it maxes out at pretty much exactly 6kW when the battery is full (I have a 6kW inverter) and at around 7.5kW otherwise.

Which HA integration are you using? I'm using the modbus integration now, but was previously using the foxess-ha cloud integration, and they reported different cumulative energy figures, although the power figures were very similar (and maxed out at the expected 6kW when not charging).

There's some information here that explains that the foxess-ha PV power figure is calculated, rather than reported directly from the inverter: https://github.com/macxq/foxess-ha/wiki ... -foxess-ha but I'm not sure why that would have an impact here.

If you're using this integration, do you see different figures for the individual PV strings, as those are apparently reported directly?

How do you limit the max battery charge?

I have an automation that runs every 5 minutes, and if the battery charge is >= 95% and it's before 2:30pm, it sets the work mode to feed-in priority, otherwise it sets it to self-use. You need to use the modbus integration in order to be able to set the work mode from HA.

[Ched]

I'm using this HA integration: https://github.com/StealthChesnut/HA-FoxESS-Modbus - taken from the configuration.yaml file.

Sorry the parameter is PV Power Now.

Looking at PV1-Power (8 x 410watt Sharp panels - westish) on a good time (14th sept 14:14) was 2.73kW and PV2-Power (4 x 410watt sharp panel southish) was 1.21kW so a total of 3.94kW. The PV Power Now reading was 3.94kW - looking at the entities on HA history graphs it is a sum of pv1-power and PV2-Power.

I do keep meaning to have a try with the other integrations to see if they give more options.

I wonder if the reason why my inverter seems to be able to output 3.9kW is that the H 3.7 inverters are software limited to 3.68kW to the grid because of UK DNO rules. It's looking at a max feed in to the grid of 3.68kW but allowing a bit more to charge batteries or supply the house as the inverters design is for more like 4kW?

All interesting stuff...

[Dave Foster]

I wonder if the reason why my inverter seems to be able to output 3.9kW is that the H 3.7 inverters are software limited to 3.68kW to the grid because of UK DNO rules. It's looking at a max feed in to the grid of 3.68kW but allowing a bit more to charge batteries or supply the house as the inverters design is for more like 4kW?

All interesting stuff...

The inverters are limited by their size and will not export more than that, so with a 3.68kw inverter the maximum AC power it can produce is 3.68kw.

Your batteries charge from the PV DC side so they can soak up any extra PV power that is being generated - so keeping your batteries below full when at peak PV is a good way to maximise your solar generation, it's possible on a good day if you are exporting 3.68kwh and the batteries are charging you may get nearer you maximum array output but if the inverter cannot find a consumer for the solar power it generates it will reduce it's output (derates).

As you are looking at 'PV now' you are looking at the DC power being generated by the solar panels, but you have to remember that there are conversion losses in going from DC to AC (between 5-8%) which means you need to generate more PV power than 3.68kw to get the max AC output.

[calum]

I do keep meaning to have a try with the other integrations to see if they give more options.

The FoxESS Modbus integration (see link in my signature) is a much more mature thing than the StealthChesnut one (no slight on anyone when I say that - it's just had a lot more development put into it).

Worth the effort to move, IMO.

[Ched]

I do keep meaning to have a try with the other integrations to see if they give more options.

The FoxESS Modbus integration (see link in my signature) is a much more mature thing than the StealthChesnut one (no slight on anyone when I say that - it's just had a lot more development put into it).

Worth the effort to move, IMO.

Cheers, I will give it a go but I guess there isn't a way to copy the historic data across is there?

[pdw]

Cheers, I will give it a go but I guess there isn't a way to copy the historic data across is there?

I think it's technically possible, but it involves manually editing statistics in the database.

Assuming that it's the Energy Dashboard stats that you're concerned about, what you might be able to do is add the new entities in addition to the old ones, so you effectively have two imports, two exports, and two batteries. The dashboard will show you the sum, which should be what you want, as the old stats will be zero after you switch, and the new ones will be zero before the switch. I'm not certain that this will work, but I think it should.

[calum]

Most of the entities have the same name, so no editing in the database is required. There's one or two changes needed but it all largely just carried on as it were (I made the same change a few months back). There's guidance about the steps to take beforehand here.