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Hello All,

looking to stick some extra PV on a flat roof, hopefully around 1.6kw. Short term it is going to be connected to a used Grid tie inverter (single string) its a tight budget at the moment, but in the near future (hopefully late this year) it will be set up as a DC system to charge batteries.

Problem: I will have at least 2 panels in full sun from sun up until sun down without and shading issues, but 2 panels will be shaded by the side of the house until mid-day ish..

How much will this affect output? Will I loose 50% until midday or 90%? Its been a while since looked into shading, etc.



Long term when on DC, I'll probably buy 2 dc inverters one for the unshaded and one for the shaded.

On a side note, how hight off the roof should I have the back of the panels for cooling? I'm around 99% certain I'm going to keep them flat, as a 15° angle only gives around 150kWh more a year against flat (around 10% maybe), and I can keep the install costs down going flat. I will probably install on unistrut (41x41mm section) fixed to concrete roof with stainless threaded rod chem bolted in.

If you put them as a single string you’ll generate little-if-any power until the last edge of the last panels is in sun. This can be avoided by fitting Tigo optimisers (or similar).

Which model of inverter are you intending to use and what voltage range does its MPPT work at?

Have a look at power optimisers such as the TIGO. They should help. They seem to simply bypass any shaded panels preventing them from bringing the string down.

Do you need all the other tigo gear for them to work (TAP and CCU thingys)?

Or will it just work with one on each of the shaded panels.... looks like they are around £40 each...

Looking at any used PV inverter that will work with the sting voltage. Ideally a solax X1 2.0, if I can get it... I don't really want to pay £350 for a new one... its probably only going to be used for 1 years max...

Looking at JA Solar 460watt panels with 42volts each so around 160volts max on the string unless I can shoehorn a 5th panel on the flat roof (I was considering a overhang on one end to act as a sort of port roof above the door anyway).

Solis 2.5 dual mppt - according to the datasheet this should work

https://www.ginlong.com/uploads/file/So ... -4G_za.pdf

martinW wrote: ↑Sat May 14, 2022 11:04 am Do you need all the other tigo gear for them to work (TAP and CCU thingys)?

Or will it just work with one on each of the shaded panels.... looks like they are around £40 each...

You just need an optimiser per shade-prone panel. I paid £50 a pop for mine.

Hmm... they way I read the info on these optimisers is that you 'could' also mix different panels on a string.

Thinking of 2 x 545w panels (without optimisers as they will be in full sun) and 2 or 3 460w panels (with optimisers different panel and partial shade).

545w panel VMPP 41.8v VOC 49.75v
460w panel VMPP 42.13v VOC 50.01v
Both panels JA solar...

Any thoughts?

martinW wrote: ↑Thu May 19, 2022 6:09 am Hmm... they way I read the info on these optimisers is that you 'could' also mix different panels on a string.

Thinking of 2 x 545w panels (without optimisers as they will be in full sun) and 2 or 3 460w panels (with optimisers different panel and partial shade).

545w panel VMPP 41.8v VOC 49.75v
460w panel VMPP 42.13v VOC 50.01v
Both panels JA solar...

Any thoughts?

I struggled to find a domestic inverter happy with the VOC and ISC of large panels. It's worth confirming this before you go too far. That said, I didn't look too hard, and was very reliant on what PVSol Software had to say on the matter.

martinW wrote: ↑Sat May 14, 2022 11:04 am Do you need all the other tigo gear for them to work (TAP and CCU thingys)?

Or will it just work with one on each of the shaded panels.... looks like they are around £40 each...

The model I was looking at, just uses the optimiser, no other jazz. The only issue is that they seem to be rated at 375W.