35kW PV array - best arrangement

[Will 666]

To All,

My first Post to this Forum and hoping someone can help on this.

Recently had installed a 35kW PV system using two Sunny Tripower inverters (17,000 model),

This system is situated on a shallow pitch roof east/west, but on mountings to face south.

The strings of PV panels incorporate panels from both sides of the roof.

Due to the shading issues,especially in the early am and late pm, can you advise if it would have been better to keep east and west sides of the roof separate?

Regards

Will

 

[Will 666]

Thanks for your reply View attachment 4145

Not sure if I've managed to upload a photo or not.

If you are able to view it then:

looking at the photo, East is to the right /West to the left.

The panels are tilted due South.

The strings of 15 panels per string involve either two rows of 5 panels from the west side and one row of 5 panels from the east side.

The next string is the opposite i.e. two rows of 5 -panels from the east side and 1 row of 5 panel from the west side.

My question is whether it would have been more efficient for the customer if it had been set up with all the panels from the east side arranged in strings connected to the same inverter and all panels on the west side connected to the other inverter. This might then allow the eastern side to function more efficiently early in the morning and the western side to function better in the evening. As it is set up now I can invisage that in the morning the panels on the west side are giving the effect of shading for each string.

I hope this is better info for you, and I appreciate your comments.

Regards

Will

 

[Will 666]

Possibly might work now View attachment 4146

File is definitely jpeg and using windows phot viewer

cheers Will

 

[binky]

if panels are tilted due south then East - west bit is irrelevent. However strings should be arranged to minimise shading effects so from what you are describing, possibly not the best string pattern.

 

[Will 666]

Sorry for the delay.

Any good with the photo this time?

Cheers

Will

 

[binky]

Given the generally low profile of the roof, shading won't make that much difference. But would have been better to keep srings on same side of roof to minimise the shading which would have kept strings working earlier / later for longer. If anything I would have said the panels look a bit close together given avaialble space on roof, but that might just be perspective of photo.

 

[Will 666]

Thanks Binky and Canoeboy,

I appreciate everyones help.

The Forum is a great idea and seems to work really well.

For info, the system was originally designed to fill the whole roof but the bespoke mounting system was changed at the last moment for a German manufactured design that set the panels at 25 degrees instead of the 33 specified for this location. This resulted in being able to, (and having to because of the mounting system ) mount the panel rows closer together. I am assured that the distance between the rows is fully calculated for the winter, but I know what you mean- they do seem close together.

Regards

Will

 

[binky]

no probs Will

 

[WorcesterRenew]

We would have kept all the strings connected to one MPPtracker on one side, simply beacsue it makes good, logical design sense. However as they are actually arranged pointing south at the same angle of elevation, so the east west 'tilt' will have an insignificant impact on the performance.

If the 'German Mounting System' is the Wagner Tric one, (it looks like it, howvere I could be wrong) then they could have been mounted further apart - we've installed over 1/2 MW of it on various sites and you are NOT stuck with the default row spacing, however you do need to know just what you can do with it

 

[eternalenergy]

Wiith the Tripowers you have two MPP trackers each and very flexible string configuration. I personally would have put each half of the roof on a single inverter to optimise the output. (Your system isn't optimised because connecting the East strings to the West strings could potentially reduce your ouptut in the morning and in the afternoon during the winter months). However, as the generation in the depths of winter is so small and this is really the only time when this particular E/W string config could give you trouble the resulting losses are probably going to be small. The sun would have to be really low in the sky to create major shading and if it is the output will be minimal anyway.

 

[Jon Walker]

Will, you're quite right about about it being best to arrange inverters separately (or at least MPPT trackers) separately for the east and west roofs. It may be at low radiation levels but the west roof will be shaded by the ridge in the morning and vice versa in the evening. I'd also agree about the comment about spacing, although its hard to tell distances from the photo. The rule of thumb for spacing is that it will be sufficient to ensure that the winter solstice midday sun, at about 15 degrees, will not shade the bottom of the row behind. In practice that the gap between rows should be nearly twice the plan size of the array (1.75 times for 25 degrees). So only just over a third of the roof area is covered with PV, which is which it may be preferable on a shallow pitched roof to mount east/west and cover the whole roof.

But I don't try and do this in my head as it might explode! I use PV-Sol to try and different designs and look at the cost-benefit of each with regards to FIT bands and DNO/supply limits.

 

[stephen1974]

Just out of interest, what would be the maximum permissable angle those panels could be placed at given that the backs of them have no protection from the wind?

 

[WorcesterRenew]

All depends upon location, topography, elevatio, altitude etc etc, there is no rule of thumb, you have to caclulate every site based on it's specific conditions.

 

[stephen1974]

How can you calculate something like that when you are unlikely to know the variables? It's like in one of the other threads where only a fraction of a panel was exposed but that ment it was not compliant. Here, all the panels are expossed, but i'm assuming it is compliant. There must be a regulation that says you are allowed x,w and z in regards to exposure to winds.

 

[binky]

no regs, but manufactures of frames have lots of wind loading scenarios to calculate correct frame sizes.

Have a look at Schuco and Schletter web sites for info