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johnsmith avatar image
johnsmith asked

4 x 345W Half cell panels in total, Series or 2 x Parallel config which Smart MPPT with large shading

4 x 345W Half cut cell panels in total, Series or 2 x Parallel config which Smart MPPT with large shading.

Going around in circles for 2 weeks with my OCD.

I have a small building with a 5 degree pitch flat roof facing south. Northern hemisphere.

I have 4 x 345W half cut cell panels.

I have full sun in the morning up until around 2pm then up to 2/3rds of roof will be covered by a shadow from a building around 10meters away.


I am either going to buy the MPPT 250/70 ve.can and run all 4 panels in series knowing that I will have possibly 3 out of the 4 panels slightly shaded after 2pm...

OR

Run 2 series strings in parallel and use an MPPT 150/35 or MPPT 150/45.

I would prefer to run ve.can MPPT but I have the cerbo gx so could run multiple ve.direct if needed.

I fully understand the electronics side of stuff but am hearing 2 different arguments with shading and - series vs parallel.

My MAIN concern is I am running 48V battery with Multiplus ii 48/3000 and worry about my voltage dropping too low as panels are around 34v-39v, plus it does get down to -10 degrees in winter were I live.

This is a part of a bigger project where I will have 3 areas to place x 4 panels but all strings facing in different directions, so I am just figuring out the best solution.

regards

MPPT Controllers
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4 Answers
ejrossouw avatar image
ejrossouw answered ·

@Johnsmith With that level of shading I'd simply go for an all series setup and let the bypass diodes take care of things. Worth searching some real world tests on youtube showing how well it works. I'll post a link later showing how effective they are on my 125W CIGS panels with one diode for every two cells. I manage to cover close to half the panel (28 cells) completely of 56 cells in total before the voltage is too low and the mppts shuts down.

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johnsmith avatar image
johnsmith answered ·

To close this question, running 2 panels in series/parallel with a total voltage of 61V is a bad idea with a 48V battery. So go for 3 or 4 panels per string in series and you will also have to use a MPPT250 as the MPPT150 will be right on the edge when temps drop and possibly damage the controller. This is never taken into consideration as most youtube videos show 3 panels but always in warm climates, were as in northern Europe we can get down to -12 or more in winter and this would possibly damage the MPPT150 controller on a 3 panel series string.

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johnsmith avatar image
johnsmith answered ·

@ejrossouw Thanks for the swift reply.

My panels don't arrive for another 2 days, and like you say it's difficult to make decisions. I am just trying to get my Victron stuff ordered whilst its in stock. I was leaning towards the series setups on their own MPPT. It is more expensive going Multiple 250/70 (series) than the 150/35 (series/parallel) but it gives me daisy-chaining with cat5 and a nice clean setup in the VRM using ve.can.

I also thought that the data would be useless from the MPPT if they are sharing series/parallel strings as opposed to more accurate data from each MPPT per string feeding back into the VRM.

I think like you say these new half cut Qcell G9s more or less take care of themselves.

I was just worried about the current getting slashed. Most of the stuff I have watched and read, points towards series with the new style panels.

regards


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ejrossouw avatar image ejrossouw commented ·

Have a look at some of the actual bypass diode tests and explanations here https://www.youtube.com/watch?v=Nu4nUcBCZ-U Probably the best I found so far. Only things he does not mention however is the voltage that will drop as you lose more output from shaded panels, which may ultimately leave you with less than Vbat+5 to keep the charger going, but with such a series string, this is mitigated to some extent. Final point, if you are interested in remote configuration and viewing of the MPPT via VictronConnect, it will not be possible use VE.Can, but only matters of course if you will have such a requirement.

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johnsmith avatar image johnsmith ejrossouw commented ·
Yeh,


I'm even thinking of using 100/20 on each pair of panels and have 2 x MPPT 100/20 per 4 panel strings, this just means that I will need 6 controllers in order to service all 12 panels and then I have to add another Lynx Distribution block to the chain as they only have 4 inputs and I will need 6 charging inputs and invertor in/out.

Ihe only sure way is to try all these configurations but at $1000 for the 250/70MPPT its an expensive experiment.

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klim8skeptic avatar image klim8skeptic ♦ johnsmith commented ·
You started of with 4 panels?

Now you have 12 panels??

What else have you forgotten to disclose???

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johnsmith avatar image johnsmith klim8skeptic ♦ commented ·

I have 4 for the intial setup and a total of 12, as written above, all 3 strings of 4 panels will be facing in different directions, with shading that I cannot avoid.


So this is why I was asking the question regarding the 4 panels as it will apply to all 3 strings.


1. My cheapest option in 2 x 100/20 per 2 series panels = 68Voc/20a (my main concern is i need 52v+5v to start the controller)

2. 1x150/35 with 2 series panels in parallel connected to the same controller(not ideal) = 68Voc/20a (my main concern is i need 52v+5v to start the controller)

3. 1x250/70 tr ve.can and have all 4 panels in series = 136Voc/10a , but 3 times the price, but does give me ve.can.





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shaneyake avatar image shaneyake johnsmith commented ·
Having a VOC of 68V which you won't get most of the time won't work. You will be below the 52+5 you need too often.

You can go 3 series, 2 parallel on a 150/60, 6 panel per MPPT.

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johnsmith avatar image johnsmith shaneyake commented ·
Yeh,


this doesn't solve my problem, my panels are physically laid in 4 per roof all facing different angles, so it looks like i need the 250/60 or 250/70 and run them all in series.


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johnsmith avatar image johnsmith shaneyake commented ·
Just got rammed in for a MPPT 250/70 MC4 Ve can. Will run all 4 panels in series.
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shaneyake avatar image
shaneyake answered ·

Another option you could consider is installed 4x Enphase micro inverters and AC-Coupling them to your multiplus. Works really well for shading conditions and you don't have to worry about low string voltage. Not saying this is the best option, just something to consider.

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