Can I mix vertically wall mounted panels with 35 degrees mounted panles on one string? How bad? Scotland UK.

[Hedges]

It seemed to me you compared wall with roof angle at one point in time, didn't break down hour by hour throughout the day. There will be times when current is lowered by a large factor.

As for shaded panels in series, if illuminated panels deliver high enough voltage, current will push through bypass diodes of shaded panels. That works fine with sun off-angle, limited current. If it occurs when some panels get max sun, the current may be too much for the diodes, which usually aren't heatsinked well enough. Can melt and crack panels.

 

[zanydroid]

With the level of deep dive I’m willing to do:

Basically you are overpaneling with extra parallel panels with more diversity. This should be a strict increase in output over the year. As to how much it helps, that is hard to say and likely requires simulation.

I don’t think you can say that the overpaneling will always be less stress on the panels, you can construct cases where there are more.

I will be happy to look at evals of the other approaches or constructively criticize why you don’t feel the other approaches are valid.

 

[billvon]

So ATM my installer connected 4 panles from straight East roof with 4 panels from straight south roof.
Power produced seems to drop badly (by factor of 3-4 probably) in the afternoon when E panels are not getting any direct sunshine.

I think you have a few choices here.

1) Switch panels and find panels that will give you the voltage you want.
2) Get two additional MPPT controllers that will give you the 48 volts that your inverter wants.
3) Add additional panels somewhere else at the same orientation (like a ground mount or something) and use them to complete the strings.

If they made "boosting optimizers" that could work but I don't know of anyone who does that.

 

[zanydroid]

If they made "boosting optimizers" that could work but I don't know of anyone who does that.

They’re available on AliExpress , in the form of reprogrammed SolarEdge optimizers with fixed output voltage

 

[Guy from Glasgow]

Thanks everybody for constructive input.
I totally agree that bviously installing 4 additional panels costs more than replacing inverter to have lower working and starting voltage.
Calculations show that at any angle of the sun here in Glasgow (and any time of day as well) the 2 vertical panels in series with 4 roof panels are providing exactly the same power as 5 roof panels.
This would actually work fine if installed all 12 panels together from the very beginning.

2.Anyway my installer was kind enough to replace my growatt sph3600 (120v V min) for another inverter which works from 80V and with working range 100-500V.
And obviously use 2 mppts.
This will hopefully work well with 2 strings of 120V?

3.This obviously avoids most of the problems with automatic shading of the roof panels relative to wall panels when sun is low.
It was an interesting excersize though

4. Now I might also consider simply installing 4 panels on my south vertical wall and get another string inverter for those. My calculation actually show that most of the day and year those are almost as good as roof panels here in Scotland.
Obviously pvwatts site tells me that they will produce about 2/3 of my roof panels. Which would be very useful addition to my small system.

5.And thanks for pointing out that I can use 50 or 70 V panels instead of 30v. I did not actually know this.

 

[zanydroid]

2.Anyway my installer was kind enough to replace my growatt sph3600 (120v V min) for another inverter which works from 80V and with working range 100-500V.
And obviously use 2 mppts.
This will hopefully work well with 2 strings of 120V?

Ok so for this, you want to look at the voltage reduction at high temperature and see if those temps are probable in your climate. The effect of this would be loss of production when it is hot.

I believe it is the temperature in the solar panel that determines the voltage adjustment, so it could actually be hotter than ambient.

Yeah vertical panels on south side seem pretty popular in the north. The slightly annoying part seems to be the need to do more DIY design of the mount since it’s not that common to do globally. Vertical really sucks at a lot of latitudes, outside of winter

 

[Guy from Glasgow]

Thanks very much Z.
For voltage reduction I found this paper:
https://www.researchgate.net
It seems to show that cell voltage drops from 0.64V to 0.58v at 45C.
0.58/0.64=0.906
So I guess for my panels with Vmax power=29.7V
I should expect 29.7*0.906=26.9V per panel
4 panels should give me 107.6V at 45 C.
This is more then min working voltage of 100V.
O guess 45C panel temp can happen in Scotland as we get to about 29C in the shade once in 3 years probably.
----
2.Did not realise vertical mounts are not generally available. I guess need to check with particular panels installation manuals. Thanks.

 

[zanydroid]

Thanks very much Z.
For voltage reduction I found this paper:
https://www.researchgate.net
It seems to show that cell voltage drops from 0.64V to 0.58v at 45C.
0.58/0.64=0.906
So I guess for my panels with Vmax power=29.7V
I should expect 29.7*0.906=26.9V per panel
4 panels should give me 107.6V at 45 C.
This is more then min working voltage of 100V.
O guess 45C panel temp can happen in Scotland as we get to about 29C in the shade once in 3 years

No need to find and read a paper to get started, the coefficients are listed on the solar panel spec sheet.

The part where a paper or experiment is needed is how much buffer to add above ambient. Most of the error will be in that direction which also is the wrong direction for correct functioning (but at least it is safe, it just turns off)

The error from heat generated on the roof is in the favorable direction for cold temp compensation.

 

[zanydroid]

2.Did not realise vertical mounts are not generally available. I guess need to check with particular panels installation manuals. Thanks.

The best thing to do is to search this forum for vertical installs. That will find you DIY vertical mounting techniques. Good luck getting structural permits though , I don’t remember that anyone did that but I could have missed it.

The panel manuals will include strength numbers for installation to certain mounting standards but I don’t know how these translate to vertical

 

[SeaGal]

Good luck getting structural permits though , I don’t remember that anyone did that but I could have missed it.

Permit is not an issue as he's in the UK - have seen quite a few vertical installations over here.

The caveat though is that a PV installation has to meeting planning permission requirements, one of which (IIRC) is not protruding more than 150mm from the surface it is mounted to - hence flat roof mounted tilt or mounted at an angle against a vertical wall _may_ planning permission.