Adding another solar array

I thought I'd post something a bit different to all of the firmware update posts going on at the moment 🤣

I have 2 PV arrays, 6 panels on each array. Both are south facing, although very slightly off due south towards the east. 1 of the arrays has tigo optimisers on each panel. There are all connected to a gen 2 5kw hybrid inverter, and a 9.5kwh battery.

I've noticed that we get a lot of sun later on in the day but the panels aren't very well oriented for the later sun so don't generate all that much after about 4.3-5pm at this time of year.

I was wondering if I'd be able to add some panels to the west facing roof of the house, I think I'd fit maybe 2/3 panels. If so how would this be done? As far as I'm aware the gen 2 inverter only supports 2 strings. Would I need another inverter or can this be done with the existing inverter somehow? I've seen some info about modern panels not actually being anywhere near as sensitive to panels generating different amounts of solar so I was wondering if the extra panels could be added to the string with the tigo optimisers and if they would be sufficient to handle panels being on different aspects? Or if there is some other solution utilising the existing inverter?

The other option would be putting 6 panels on the garage roof with is also west facing, the garage is detached from the house, about 15 meters away. We already have a spare 3 core cable running between the house and the main board as well as 2 cat6 cables, but I'm not able to run any extra cables than. There is also a 3 phase cable running between the house and a separate box next to the main board. We don't have a 3 phase supply but this was just to future proof when we laid cables for an EV charger and if things ever for 3 phase as standard. Our inverter and battery are in the loft of the main house. I'm not sure if we have any options available to us with the garage using the existing infrastructure?

I'm not an expert... but what you suggest sounds fair enough... except that if I understand correctly you will need to recertify your system (i.e. not just install panels and go), and there is also the issue of where to connect the new panels "to".

Solar panels are electrically very odd, and to get the most out of them the panel needs to be illuminated to the same degree all over, or the higher-insolation parts will be dragged down to the power rating of the lower-insolation parts. Put simply: if part of a panel is shaded, the panel treats that shading as being over the whole area.

Now, if you connect two panels together you can do so either in series or parallel; in series you get a higher voltage but the same current, in parallel the same voltage but more current. In series the shading issue is mitigated between panels, but you also get a higher peak voltage, possibly higher than the inverter can handle. In parallel the panels behave as one, so make sure all panels are equally illuminated (because of power reduction). There is also a max current limit on the inverter, and parallel'd panels may need new cables (higher power capacity).

All the GE inverters seem to have 2 inputs, for two series-connected 'strings'. If you haven't reached the limit for the string, you can add more panels up to that (peak voltage) limit. If you have reached the limit, you could change some (e.g. pairs of) panels to parallel (I think, pls check!) and accept the shading issue, or you can add another inverter, which kind-of sidesteps the issue. However, the GE inverters aren't currently specified to run in pairs, although people have had success doing so.

I have heard tell of 'micro-mppt' units which fit beside the panels (i.e. outside) and electrically 'fix' the shading issue. The units are not cheap, but it may be worth using. However I don't know if they can be used with the GE inverters.

Regarding cable runs, you need to check with an electrician: there are specific rules about what you can do with an MCS-certified system and it would be a bad idea to break them! Fundamentally, though, you should only need one power cable from a group of panels to an inverter -- I don't think anything else is needed. Note, though, that the longer the cable the higher the resistance, so a chunkier cable (=lower per-length resistance) is good.

Finally, beware of maximum export limits (often around 3.6KW, sometimes as much as 10KW, you will have documentation for this) and power ratings of the other cables in the house!

Why Tigo optimisers only on 1 string? Potential shading issue?

Sad to say Tigo optimisers are likely not making much difference.
https://www.youtube.com/watch?v=9GvhDhCSJgo&t=779s
https://www.youtube.com/watch?v=ESpsdMFEFZo
Much of this video is built on the back of investigations carried out by a very large installer in Australia.

But moving on.

As rivimey said you can wire panels in Series, Parallel or a combination of the two.

You can potentially look at using a PV combiner box

You could under that particular situation look at using a micro inverter which converts the DC from the panels into AC which can be fed into the house directly. Its just a solar power generator in that case. This would definitely be the simplest route forward rather than trying to balance panels.

There are a LOT of technical considerations to be made though. In all honesty best off having a chat with an installer

dragon2905 Why Tigo optimisers only on 1 string? Potential shading issue?

Yes, we have a /\/\ shaped roof, the outer part has no shading but the inner can be shaded by a chimney or other parts of the roof at certain times.

rivimey thanks for all the info, that's a lot to digest too! We aren't looking at replacing the inverter as it's only just been installed so would only be looking at options that could be added to what we have.

To be honest it may not even be worth it, it just feels like we are wasting perfectly good sunshine in the early evening when, for instance it's almost 6pm now and there is loads of sun from the west but our panels are only at 330w of generation total. If there was a way to fairly cheaply and simply add some west facing panels we could utilise the later sun.

I wonder if adding more battery capacity would be the more cost effective option. It's hard to know as I don't know how much solar we would be generating due to the Gen 2 inverter bugs when the battery is full.