PV string configeration?

[Kiddell]

Hi All.
Looking for a bit of advise.
Having purchased some second hand kit very cheap, I am cosidering putting some panels on my Garage roof - 3Kw in total, split equally East/West.
I thought i had done a bit of research after seeing an inverter for sale locally and worked out that all Solis S5 inverters over 2.5Kw were duel MPPT. which would have made the wiring easy.
However when I went to collect said inverter, I instantly noted that it had only one pair of MC4 connectors and therefor only the one MPPT. Seeing as the iverter is new and unused, at the price, it was still a no brainer and at a push, I could probably sell it at a profit so its sitting beside me now.

Obviously , I can fit one side of the garage with six panels in series and leave it at that but was looking for advise to see if I can do anything else.
I could fit both sides, all in series but with one half not getting the sun during morning and evening, I assume this would not be very efficient.

What I was wondering was could I wire in 2 strings of 6 panels (one on each slope) and then connect the 2 strings in Parallel? . The problem as I see it with this idea is I would then have a current of around 17amps at about 180v and the inverter max input current is around 14 amps but with voltage up to 600v
My question is would this be an issue with the inverter - would it clip and only use the 14 amps or would it destroy the inverter?
If it was able to accept the current, would it confuse the MPP tracking?
My thinking is with the sun not on both sides except for a short period in the middle of the day, and even then there may be a little shading from a lamp post, with warm panels, I am unlikely to get the full 8.6 amps from both sides.
Any thoughts.
Thanks.

 

[SeaGal]

Hi All.
Looking for a bit of advise.
Having purchased some second hand kit very cheap, I am cosidering putting some panels on my Garage roof - 3Kw in total, split equally East/West.
I thought i had done a bit of research after seeing an inverter for sale locally and worked out that all Solis S5 inverters over 2.5Kw were duel MPPT. which would have made the wiring easy.
However when I went to collect said inverter, I instantly noted that it had only one pair of MC4 connectors and therefor only the one MPPT. Seeing as the iverter is new and unused, at the price, it was still a no brainer and at a push, I could probably sell it at a profit so its sitting beside me now.

My S5 hybrids are both dual MPPT - which model is yours?

Obviously , I can fit one side of the garage with six panels in series and leave it at that but was looking for advise to see if I can do anything else.
I could fit both sides, all in series but with one half not getting the sun during morning and evening, I assume this would not be very efficient.

Correct.

What I was wondering was could I wire in 2 strings of 6 panels (one on each slope) and then connect the 2 strings in series? .

Did you mean in parallel?

The problem as I see it with this idea is I would then have a current of around 17amps at about 180v and the inverter max input current is around 14 amps but with voltage up to 600v
My question is would this be an issue with the inverter - would it clip and only use the 14 amps or would it destroy the inverter?

Should just clip, but another user on here had an issues with the RHI model with panels of too much current - it generated errors, so was upgraded to the EH1P version to resolve the over current issue.

If it was able to accept the current, would it confuse the MPP tracking?
My thinking is with the sun not on both sides except for a short period in the middle of the day, and even then there may be a little shading from a lamp post, with warm panels, I am unlikely to get the full 8.6 amps from both sides.
Any thoughts.
Thanks.

Off the top of my head, I would assume MPPT would not work with parallel strings of panels with different exposure. The point of MPPT is to maximise power output which will be a factor of voltage vs current. I can't see how the inverter would be able to do that with different facing strings, but maybe others on here have more experience / knowledge of attempting that.

My 2p worth would be to upgrade to a dual MPPT Solis - very happy with mine

 

[Kiddell]

Kiddell said:
What I was wondering was could I wire in 2 strings of 6 panels (one on each slope) and then connect the 2 strings in series? .

Sorry, yes- was being chased up for tea so didn't re-read.

 

[Kiddell]

My S5 hybrids are both dual MPPT - which model is yours?


Correct.


Did you mean in parallel?


Should just clip, but another user on here had an issues with the RHI model with panels of too much current - it generated errors, so was upgraded to the EH1P version to resolve the over current issue.


Off the top of my head, I would assume MPPT would not work with parallel strings of panels with different exposure. The point of MPPT is to maximise power output which will be a factor of voltage vs current. I can't see how the inverter would be able to do that with different facing strings, but maybe others on here have more experience / knowledge of attempting that.

My 2p worth would be to upgrade to a dual MPPT Solis - very happy with mine

model no. is S5-GR1P2.5K-M

Could get another duel MPPT inverter but might be cheaper to get a smaller second hand one for the other side?
The new inverter only cost £120 and it would only cost about the same to complete one side as I have the panels already.

Some of the more powerful panels output 17amps so as most inverters don't accept that. I assume there must be a way to manage it.

I suppose, I could put an isolator on each string and only turn on the one that is mostly facing the sun but I suspect the isolator may soon wear out due to switching under load

 

[SeaGal]

model no. is S5-GR1P2.5K-M

Could get another duel MPPT inverter but might be cheaper to get a smaller second hand one for the other side?
The new inverter only cost £120 and it would only cost about the same to complete one side as I have the panels already.

That sounds like a good plan if you can get them that cheaply. Will also give you some redundancy too.

The only thought though, is whether you may consider battery storage in the future. In which case a dual MPPT hybrid may be an option, but obviously more expensive.

 

[zanydroid]

If the strings on different orientations are the same nominal voltage they’re generally thought to work fine in parallel, with some minor efficiency loss but always more production than only using one string. They will only fight each other on voltage a few percent, and the MPPT should not draw so much current as to start sagging the power output.

And there are some forum members really into this approach.

 

[SeaGal]

I guess there is no harm in trying parallel strings. If that causes the Solis to trigger any alarms then you could then get another inverter and rewire as two separate strings.

 

[zanydroid]

I guess there is no harm in trying parallel strings. If that causes the Solis to trigger any alarms then you could then get another inverter and rewire as two separate strings.

There should be an overpaneling guide somewhere on this site. Off hand, I remember
- If manufacturer has a clear do-not-exceed input current or ISC, don't exceed it
- Reverse polarity protection can be compromised (IE instant/accelerated death, rather than give you some time to react [I believe manuals say if you leave it reverse polarity even within spec, it's not a good idea] and turn it off) if you exceed the spec in the absence of a do-not-exceed.

 

[Kiddell]

That sounds like a good plan if you can get them that cheaply. Will also give you some redundancy too.

The only thought though, is whether you may consider battery storage in the future. In which case a dual MPPT hybrid may be an option, but obviously more expensive.

I cannot get another Solis at that price as it was the last one he had- apparently he had bought some bankrupt stock and was selling them off.
Can't see me getting batteries - don't thing its worth it on 3Kw but may get a diverter and heat some water.

 

[Kiddell]

I guess there is no harm in trying parallel strings. If that causes the Solis to trigger any alarms then you could then get another inverter and rewire as two separate strings.

This was my thoughts but only if I am not likely to damage the inverter. The MPPT can't influence what power the panel produces - surely it will make the best job possible of using the power added together from the 2 strings as an input. I am unsure why the inverter would be confused by the differing output from the 2 strings as it will be combined into 1 input( but thats why I am asking others with greater knowledge).

 

[SeaGal]

IMHO You will only be able to damage your inverter if the string voltage exceeds the inverter's voltage input. The inverter will only draw the current it needs to maximise the power generation within the limits of the inverter's specification.

The MPPT controls how much current is drawn from the panels so that, for any given luminance, it will attempt to maximise the power that can be extracted. As the current increases, the string voltage will decrease and vice-versa.

 

[Kiddell]

IMHO You will only be able to damage your inverter if the string voltage exceeds the inverter's voltage input. The inverter will only draw the current it needs to maximise the power generation within the limits of the inverter's specification.

The MPPT controls how much current is drawn from the panels so that, for any given luminance, it will attempt to maximise the power that can be extracted. As the current increases, the string voltage will decrease and vice-versa.

Hopefully be OK then as I will only get around 180v off the 6 x 250w panels on each side.

 

[Hedges]

Obviously , I can fit one side of the garage with six panels in series and leave it at that but was looking for advise to see if I can do anything else.
I could fit both sides, all in series but with one half not getting the sun during morning and evening, I assume this would not be very efficient.

Correct. Full voltage but current limited to the lower of two.
Sometimes optimizers are used to adjust this. I would rather address with series/parallel array configuration.

What I was wondering was could I wire in 2 strings of 6 panels (one on each slope) and then connect the 2 strings in Parallel?

I recommend highly.

The problem as I see it with this idea is I would then have a current of around 17amps at about 180v and the inverter max input current is around 14 amps but with voltage up to 600v
My question is would this be an issue with the inverter - would it clip and only use the 14 amps or would it destroy the inverter?

Good inverters protect themselves. MPPT should make excursions to find maximum power point, so concern would be if it did so until current exceed its limits.

Is 17A what the parallel strings would produce if all oriented the same? But they aren't - given there angles, what percentage of (flat) area do they present to the sun as mouted?

If it was able to accept the current, would it confuse the MPP tracking?

No.

My thinking is with the sun not on both sides except for a short period in the middle of the day, and even then there may be a little shading from a lamp post, with warm panels, I am unlikely to get the full 8.6 amps from both sides.

Hope there isn't shading on one panel while others in series get full sun. That can burn up bypass diodes. Not a problem if sun hits at 45 degree angle, less current.

Off the top of my head, I would assume MPPT would not work with parallel strings of panels with different exposure. The point of MPPT is to maximise power output which will be a factor of voltage vs current. I can't see how the inverter would be able to do that with different facing strings, but maybe others on here have more experience / knowledge of attempting that.

It should work great. So long as the parallel strings are identical except for orientation. Or even different brand, voltage per panel & number of panels, so long as close to same Vmp.

A panel receiving indirect light produces Voc about same as its Vmp in direct sun. So it does not pull down the other string.
When sun hits both panels, each contributes current approximately in proportion to the area it presents to sun.

Kiddell said:
What I was wondering was could I wire in 2 strings of 6 panels (one on each slope) and then connect the 2 strings in series?

Don't connect all 12 panels in series.
Some different orientation, will reduce current output to lowest panel's output.
If 12 x Voc exceeds max allowed PV input, will kill the inverter.

If the strings on different orientations are the same nominal voltage they’re generally thought to work fine in parallel, with some minor efficiency loss but always more production than only using one string.

I read a report from SMA, 2% lower yield than having separate MPPT for the differently oriented strings.
Given the relative cost of MPPT and PV panels, I consider it a win to over-panel this way, multiple orientations for more hours production.

And there are some forum members really into this approach.

Me!

 

[Kiddell]

Correct. Full voltage but current limited to the lower of two.
Sometimes optimizers are used to adjust this. I would rather address with series/parallel array configuration.



I recommend highly.



Good inverters protect themselves. MPPT should make excursions to find maximum power point, so concern would be if it did so until current exceed its limits.

Is 17A what the parallel strings would produce if all oriented the same? But they aren't - given there angles, what percentage of (flat) area do they present to the sun as mouted?



No.



Hope there isn't shading on one panel while others in series get full sun. That can burn up bypass diodes. Not a problem if sun hits at 45 degree angle, less current.



It should work great. So long as the parallel strings are identical except for orientation. Or even different brand, voltage per panel & number of panels, so long as close to same Vmp.

A panel receiving indirect light produces Voc about same as its Vmp in direct sun. So it does not pull down the other string.
When sun hits both panels, each contributes current approximately in proportion to the area it presents to sun.



Don't connect all 12 panels in series.
Some different orientation, will reduce current output to lowest panel's output.
If 12 x Voc exceeds max allowed PV input, will kill the inverter.



I read a report from SMA, 2% lower yield than having separate MPPT for the differently oriented strings.
Given the relative cost of MPPT and PV panels, I consider it a win to over-panel this way, multiple orientations for more hours production.




Me!

Thanks for your confirmation that it should work.
All panels the same same -REC 250v
The 2 strings of 6 panels connected in PARALLEL- not series (was a mistake in original post)
A little shading from post but only when sun is lower in sky early and late in year but will be at approx 45 deg to panels anyway so not at full output.

 

[zanydroid]

A little shading from post but only when sun is lower in sky early and late in year but will be at approx 45 deg to panels anyway so not at full output.

If there is shading then the two strings will affect each other more, since the Vmpp will be different. Probably the maximum power point would activate the same number of bypass diodes in both strings.

 

[Kiddell]

If there is shading then the two strings will affect each other more, since the Vmpp will be different. Probably the maximum power point would activate the same number of bypass diodes in both strings.

Will see what happens. The post is almost level with the apex so as the sun moves round, the shading will be on the side that is getting less sun anyway so may not have an effect. Given the low cost, as long as I get more output from doing both sides of the roof, then it will be a win

 

[zanydroid]

Will see what happens. The post is almost level with the apex so as the sun moves round, the shading will be on the side that is getting less sun anyway so may not have an effect. Given the low cost, as long as I get more output from doing both sides of the roof, then it will be a win

Single or half cut? If single cut I expect it to bypass the same number on both sides (namely the ones that the post goes through). If it doesn't do that then the output on that whole side is dragged down by the % that panel is pulled down. The longer the string the bigger the difference between bypass and no-bypass output.

(I'm not sure I have the energy to re-model the effects of half-cut today in my head).