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Optimisers for solar panel shading

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rthorntn:
Hi,

My setup is 20 normal DC panels in two equal strings going to normal inverters, no microinverters or anything like that.

Coming into March in Sydney I've noticed bad shading coming from the council's eucalyptus in the street up till 11am. It's badly obscuring 3 panels on the string of 10 nearest the street.

I can see my 10 panel string furthest from the street putting out 1800w at 10:20am and the shaded string of 10 only doing 270w.

Now I assume as the sun gets lower in the coming months that this shading is going to get worse until like September..

I'd like to mitigate this somewhat, I don't believe council would take metres of healthy branches off the top of the tree.

So I'm thinking optimisers, the installer uses Tigo but says "what optimisers can do is to bypass those shaded panels and let the rest in one string produce normal current. So the improvement with optimisers is very limited"

Is it really as simple as just bypassing panels, for some reason I thought it was more complex?

Any thoughts, experience?

Thanks
Richard

thm_w:

https://diysolarforum.com/threads/do-bypass-diodes-in-solar-panels-eliminate-need-for-micro-inverters-or-dc-optimizers.48241/
https://help.aurorasolar.com/hc/en-us/articles/115001339907-Global-MPPT-and-Bypass-Diodes

bdunham7:
Optimizers should do a bit better than simple panel bypass, so if 3 out of 10 panels are shaded and the others have full sun, then you will see better than 70% output.  How much better depends on how much of the panel is shaded and how many bypass diodes it has. 

Properly configured modern string inverters should also do a lot better than the results you are seeing.  Find out if your inverters have a global MPPT function and if it is turned on.  The panels should have bypass diodes (typically 3) so that partial shading results in less power reduction.

Siwastaja:
This is not normal; if 70% of your panels are not shaded at all, you should see just 30% drop, not 85%. Something's wrong with your inverter. Maybe you have a seriously misdimensioned inverter with too high minimum MPPT voltage, or an inverter with broken MPPT algorithm.

I have kinda similar situation myself because someone thought it's a good idea to use a 5kW inverter designed for ~16 panels and only buy 10 panels. Normal string inverters can deal with ~half shaded panels just fine (and if more than half are shaded, chainsaw is better solution anyway). But in my case, 4 shaded panels means I have only 6 panels producing, which is below the minimum MPPT voltage of the designed-for-16-panels inverter.

But you need to check the inverter specs to be sure (minimum MPPT voltage).

rthorntn:
I have it from a reliable source that the MPPT algorithm in these Voltronic inverters (with the high PV array voltage) is rubbish, and often gets stuck in a local maximum that is not the global maximum, under shading...

Georg594 in Germany has been patching his MPPT code to address shading in this thread https://powerforum.co.za/topic/15621-axpert-max-8-kw-shadow-management-firmware-upgrade-beta-still-based-on-stable-9006/. I think he ported it to at least one other machine.

So I'm a bit stuck.  I've attached a picture (taken today at 10:36am) of the panel shading as visible from my neighbours wall, at least three panels look shaded to me, one is off to the left behind the tree.

I can see that this string performing at about 25% of the string on the right, the panels and inverters are all the same.  The good string is putting out 160w per panel

As the sun gets round the tree and more directly to the panels I get pretty amazing performance in summer, like over 9KW on 7.4KW of panels.

A thought...could the panel orientation affect the bypass diodes with the shade coming in this way, my panels have 3 bypass diodes?

Cheers
Richard

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