Assuming I need a 2nd inverter? Another expansion post

hick

Hi all,

would appreciate thoughts please, it’s kind of similar to the other recent thread on adding more PV

we have a 6kW solis hybrid, 14 panels on 2 strings ( 8 on front and 6 on mid part of a double pitch roof) facing SW 230 deg, so roughly about 5.4kW Array, I can squeeze 2 more panels on this array at the front. This set up has 10kW battery too which is about to go to 15kW

what I’d like to do is add another 6 panels at the back (circa 2.4kW). We get the sun all morning till lunchtime face on there and even the as the pitch of the roof is so shallow, I’d expect to pick up something through the day, especially in the summer, but anything would help during winter. As it is even though the panels are on the wrong side, I was picking up 440W at 0600 this morning! Lastly I’m determined to throw a few DIY panels up on the shed, as I have mains power and a small CU there.

A few questions please:

1) do the panels have to be the same (similar) W when adding to a string

2) if I did all this I’d max out the Solis as it would be over 8kW… but my installer told me I couldn’t mix different orientations on the same string. So given I’m on a second string as it is, does that mean the 6 panels at the back will need a new inverter (or micro inverters) I’m not against it but would like to keep this as simple as possible

3) am I mad putting a few on the shed? They’d have to be small units, about 200W or so but reckon I’d get 4-5 up there and they could export away.

all advice guidance and question gratefully received! 👍 We reached our 1 year anniversary last week 🎉(29 June) so clearly we are well into the wish we’d installed more camp!🤷

hick

17 hours 36 views 🤞

ColemanY2K

I can't answer 2 but re 1 the panel with the lowest wattage brings down the whole string to that panels level. So say you had 5 panels at 410 watts each and added a sixth which was 400 watts, the 5 panels would each reduce to 400 watts losing a total of 50 watts in the the process.

As for point 3, absolutely not. Fire them up. I was today driving through the rural Sussex countryside near the south coast of England. Every Tom, Dick and Harry has not only their houses covered in panels but the out houses and garages/sheds as well. It was noticeable how every square inch was covered. Now they've had FIT for a decade or so which is probably the reason in addition to the awesome weather this part of the country gets. EV's are everywhere as a result.

bullit_dodger

It makes it easier for people to visualize if you rotate the image with North at the top.....have I got this right below? You mentioned facing 230 or so?!

So basically on the main house you'd be reconfiguring the arrays. Adding 2x panels to the SW array, and then 6-7 panels to a new NE facing array.

Some answers for you.

• You can have different orientated panels on the same string, but you'll have to have optimizers on all the panels on that string.
• I dunno about the shed. Yeah it's easy to slap them up there, but t looks like you might have some shading on the SE facing roof on the shed and you have a NW on the other side. Sure you'll get something out of it, but it won't be super.
• If you could do something on the wall to the NW side of the garden that might be a good one. Vertically mount the panels and perhaps have a bracket to angle them out from the wall 30-40 degrees. Just a thought.

hick

https://www.boards.ie/discussion/comment/120823322#Comment_120823322

@ColemanY2K

Thanks for the guidance on mixing panels, that makes and I thought that might be the case. So the summary is get as close to the panels you have already on the same string.

Big Lar

I think in the shed you should put a 2mptt micro inverter to cover that end.

12 panels would be kind of the max per string for a the inverter and without having to put in a second inverter you could perhaps relocate as many panels as you can from area 2 below to area 1 for one string, then move the rest to area 3 and add additional panels there for the second string? I think that perhaps the winter sun may be troublesome for you with with the chimney and the first roof causing shading on area no2.

Or, leave the 8 panels on area 1, change the panel layout on area 2 so that you put 4 panels horizontally close to the ridge to avoid shading (You may still need optimizer for those 4 panels - winter sun you see) so that 12 panels on one string and then everything else plus the new panels on area 3 (Suspect you could max out to 12 there)

hick

https://www.boards.ie/discussion/comment/120824177#Comment_120824177

@bullit_dodger appreciate the detailed reply! yep that’s the right orientation and assumptions on panels is correct.

Between this and the other thread I think I understand the following

1. I need to interrogate the solis and check the voltage on each string to make sure I’m not breaching 600V
2. I can expand the 6 panel string on the mid section or PV2 by up to 6 or 7 panels, assuming 375/380W at about 45V each. Probably best to keep at 6 to stop over voltage errors.
3. I will need optimisers on the 6 panels on the rear NE ( I am assumingz a just those and not the original 6 facing SW)
4. i can add 2 panels on PV1 to bring up to 10 with no problem
5. the Shed is a go! But completely separate, that might be a winter projec filled with AliExpress goodies. Or at the very least some 2nd hand panels
6. Finally my assumption in the title on needing another Inverter in this instance is wrong!

This thread is a great reference for others

https://www.boards.ie/discussion/2058220669/choosing-which-string-to-add-additional-panels-to#latest

hick

https://www.boards.ie/discussion/comment/120824517#Comment_120824517

A great shout @Big Lar

like the thinking on mixing area 2 with area 1. Though I’d still like to add 2 panels to area 1 as it’s the largest space with zero obstructions. If I add 4 from zone 2 I can’t add my 2 additional and it seems to me I’d be better maxing out Area 1.

I suppose I could move 2 panels from Zone 2 to Zone 1, it’s only a matter of running a cable.

I never thought about the chimney causing shading on the west side of Zone2 and the installer never mentioned it. There is a gully between the 2 roofs with a decent gap. I know the winter sun is notorious for long shadows though. (Been watching the off grid garage recently and the fun Andy has been having with shading!! https://youtu.be/vn81y5vg3B4

but I’ll check out the PV stats over the winter to see if PV2 stats drop to 0 much during the day, if so I can add optimisers there as part of the expansion project.

Im loving the learning and resources coming together! 👍👍

Big Lar

@hick On the shading, you could look back on the app to see how you got on last year and see how Area 2 performed

bullit_dodger

https://www.boards.ie/discussion/comment/120824524#Comment_120824524

Couple of follow on thoughts. The 600v limit is dependent on the inverter make/model. Most of them are 600v, but I've seen some of them with 500v being mentioned on the spec sheet. I wouldn't push it right to 600v. I'd leave yourself 10% margin off the specifications. The reason being is that the voltage varies with temperature (or more specifically the resistance on the panels varies with temp). So the Voc is defined as something like 41v @ 25C. As the panels get cooler, the Voc rises, so you could have a 41v reaching 45v (speculating). That said if your inverter was to go to 601v, it won't blow up....they have a little safety margin built in I would think on the far side, but it's not good for it to be operating out of design parameters.

No unfortunately I think you need optimisers on all panels in the array if your panels are differently orientated. I could be wrong on that, but I'd be pretty sure. People mention "internal bypass diodes", but in my own testing.....I wasn't able to see them work. Could be that my panels didn't have them, or they weren't operating the way I thought, but yeah.....I think you'll need optimizers on all the panels (on that string). They are about €60 each.

Did the shed myself last summer including 2x vertical ones like this. It's what i was suggesting about your wall NW of the garden.

https://www.dropbox.com/scl/fi/f70lf74z6h0vzfjrpgugs/2023-05-27-17.40.46.jpg?rlkey=96afptifle25o5bme88s1ux5v&dl=0

hick

So in the first instance the open circuit voltage on my panels is 41.45

https://www.enfsolar.com/pv/panel-datasheet/crystalline/47440

so I’m guessing in that case I can add 14 similar panels to the same string (14.475).

if that’s the case it give me a lot more flex on how I link all the panels.

now comes on to the practical aspect. thinking of buying all the gear myself (from midsummer or similar) and getting. Roofer to put the panels up and a sparks to commission. But I wonder (and I know!) if the sparks is necessary if it’s a matter of cabling everything up when the roofers get the cables into the attic?

the quest continues!

bullit_dodger

https://www.boards.ie/discussion/comment/120825407#Comment_120825407

Generally 12 (max 13) is the limit for the reason that 12x41 = 497v, but if it was a cold day and the sun came out from behind a cloud and the panels were cold with the sun beating on it, you could be looking at 12x45(ish) = 540v. If you had 13 panels, you'd be looking at 13x45 = 585v, so you can see that 14 would be a bridge too far. You need to have a little bit of a safety margin. I know that isn't the answer you want, but I think if you went to 14 you'd have over voltage alarms tripping your production fairly regularly.

Looking at your main roof, I'd probably just add 2x panels to your SW facing ones on #1 above, bringing that to 10, and then add 6 panels to #2 so you would have 12 there. Or to restate.

• 10 panels all facing SW on arrary 1
• 12 panels split 6 (facing SW) and 6 (facing NE) all with optimizers as array 2.

That said, I'd probably do the shed first. Get some panels and micro-inverters and you can do that yourself relatively easy. You don't need ladders/scaffold, and you'll probably get 1Kwp there and you can see how you get on.