15 panel Sanyo N235W vs 16 panel Sanyo N240

[TrickyDicky101]

Hi

I have agreed a PV installation on my South facing roof with a local installer. They listened to my requirements (I have limited roof space) and designed a system I was very happy with. The pertinent facts are:

South facing roof approx 8.3m wide with 2.90m usable space from bottom of the roof to a dormer window which is slightly offset to the West from central, there is probably approx 2.7m of roof from the Eastern edge of the Dormer to the Eastern edge of the roof.

This has permitted an array below dormer of 15 N235 panels in a bank of 3 X 5 panels arranged in a landscape pattern (total system size 3.525kWP). There are no shading issues with this arrangement.

This is with a Fronius IG TL 3.0 which I understand is ideally sized for the 15 N235s on 1 string.

I was very happy with this array size and agreed to the quote.

I am now informed that there is a stock issue with the N235s (just can't get 'em) but there are N240s available, and these are the same size.

However, 15 panel array using N240s doesn't work on the Fronius inverter.

Hence i asked if it would be possible to place a 16th panel in landscape orientation on the Eastern edge of the roof alongside the dormer (technically approx 1m away from it).

This would require use of another inverter (Fronius IG TL 3.6) which would allow 8 panels on each string (2 in total) and giving a total array size of 3.84 kWP (bearing in mind I have had several installers - who are each tied to a specific panle please note - offer no more than a 2.20 kWP array, the potential size of this is very tasty).

Placing the panel next to the dormer does introduce a potential shading issue but this is limited to last few hours in the day (and probably not in summer when the sun is higher in the sky - it is an October to March problem).

My installer didn't seem wholly convinced this was a good idea - can anyone confirm this 16 x N240s does sound reasonable? Is the Fronius 3.6 still ideally suited to this new array size? This isn't a cost question - I am wondering from a maximum efficiency pov.

Thanks for any replies.

Richard

 

[SolarCity]

However, 15 panel array using N240s doesn't work on the Fronius inverter.

Who told you this? It would work but it is perhaps a little undersized. Simply upgrade to the IG TL 36 (shouldn't cost much more) and the system is fine.

 

[SolarCity]

It sounds like you'll be struggling for space with that array also. Be very careful that your installer doesn't try and fit the panels too close to the edge of the roof or near the eaves. If he does do so, make sure you ask him about his wind calculations.

Is there any reason why your installer is using Fronius and not another manufacturer?

If you go for the 15no. N240 panels then I'd suggest the Fronius IG TL 36 or the Power One 3.0

If you go for the 16no. N240 panels, and therefore introduce a shading issue, then I'd definitely go for the Power One 3.6

One last bit of advice. Don't underestimate shading.

 

[TrickyDicky101]

Thanks for the replies Biggs.

You are correct in that as far as I can determine, the panels will be darn close to being flush with the edge to the roof. i will ask my installer about the wind. Because they are landscape does this present less of an issue given there is less edge of each panel exposed to the wind?

I went with the Fronius due in the main to the 20 year warranty I can get with it at the moment. The installer also recommended it (several of his previus installations use a Fronius).

Excuse my ignorance, but what benefit would the Power One have over the Fronius were I to plump for the 16 panels?

I believe it is a minor shading issue (in terms of when the panel will/might be shaded) - does inclusion of the 16th panel which may have some shading issues really reduce the viability of the system?

Regarding the 15 N240 on the 3.0 not working, I am just going by what the installer told me.

Assuming relatively close in costs, which would you have: 15 N240 & Fronius 3.6 or 15 N235 & Fronius 3.0?

 

[SolarCity]

If the panels are flush with the edge of the roof then just ensure that the installer has checked to make sure that he has the correct calculations carried out to ensure that it is ok. Good practice is at least 300mm, perhaps as much as 500mm gap from the edge of the panel and the edge of the roof.

The Fronius inverters are indeed excellent but I was just wondering if the installer was limiting his options by purely using that range of inverters.

The Power One would give you a benefit over the Fronius inverter if you were to add the extra panel because it has two MPP trackers. As the Fronius inverter has just one MPP tracker, the extra shaded panel would effect the output of the whole system. With a Power One inverter, the shaded panel could be put on a small string on one of the MPP trackers - this would ensure that when the extra panel became shaded it would only affect the panels which are connected on the same string.

It would be difficult to predict how much the extra panel would affect the system. What I do know is that generally customers underestimate just how much shading their roof receives and that installers generally seem to underestimate how much effect the shading is going to have.

If the costs were the same, I'd go for the 15no. N240 panels and the IG TL 36.

 

[TrickyDicky101]

Thanks Biggs - really appreciate the time you've taken to reply.

I will ask my installer about the wind and will pursue the 15 N240 & Fronius 3.6 as an option.

Thanks again

Richard

 

[Worcester]

The latest guidelines currently undergoing public consultation suggest that the minimum distance to the edge should be 400mm.

Unless specifically designed to do so, systems should be kept away from the roof perimeter. For a domestic roof, a suitable minimum clearance zone is around 40-50cm.

If your installer is planning to go closer than 400mm then I would insist on seeing the structural and wind load downward pressure as well as uplift calculations and how he has designed the mounting system to cope - especially as these are within the Edge Zone - he must prepare these to be in compliance with Building Regulations anyway.

(Note – on many roofs a 50cm gap from the edge will still mean that PV modules are fitted in the “Edge Zone” as defined in BS EN 1991-1 where higher pressure coefficients need to be implemented due to the higher imposed wind loads.)

 

[TrickyDicky101]

Thanks Worcester!

I am going to pursue these points tomorrow.

Life is never easy is it?

R

 

[TrickyDicky101]

Update: I am being told by the installers that Fronius inverters will only handle an even number of panels on each string (unless it happens to be the Fronius IG TL 3.0 in whichcase 15 N235s are fine). This makes no sense to me.

What possible issue might there be with a Fronius IG TL 3.6 with 15 N240s? Judging by previous replies in this thread I am assuming there are no issues.

 

[SolarCity]

The installer is right. The Fronius inverters have just MPP tracker which means that the different strings must have an equal amount of modules on each string. For example, if you wished to install 15no. 235s on two strings it couldn't be done. Of course, this doesn't stop you from installing these panels on one string.

Issues with IG TL 36 and 15no 240s? None that I can see aside from the fact that a 36 is very slightly oversized.

 

[TrickyDicky101]

Thanks Biggs.

I am told that 15 N240s won't fit on the Fronius 3.0 on a single string - is this because of some sizing restriction? The array size between 15 N235 and 15 N240 is pretty small so i presume it is a reason other than total array size...

 

[SolarCity]

Okay, so I may have dropped a rick. I've just done my calcs again and the voltage on the 15no. N240s would be too high (exactly where I went wrong yesterday, heaven knows).

The Power One 3.6 would be a great match though.

 

[TrickyDicky101]

Thanks Biggs - appreciate your time.

That's a real pain in the backside though as the 20 yr warranty available on the Fronius was a great incentive to me.

So, just so I understand 15 N240s on a Fronius IG TL 3.6 doesn't work due to the voltage, or did you mean 15 N240s on a Fronius IG TL 3.0 doesn't work?

 

[SolarCity]

Okay, it's been a long day

Just checked again (I have a million things on my desk) and I think it will be ok. The 15 N240s are okay on the IG TL 36 or the IG TL 30 - although I would suggest that the IG TL 30 is too small.

As much as I like the Fronius, I'm still keen on the Power One for this install - even with the warranty sweetener ;-)

 

[TrickyDicky101]

Thanks again Biggs. Decisions, decisions...

As an aside, have you had any experience with using SMA's OptiTrak Global Peak system to deal with shading issues?

 

[SolarCity]

If your system is unshaded like you say it is then I wouldn't recommend using OptiTrak. I certainly wouldn't say it was a good way of installing an 'extra' panel in a shaded area but SMA might tell you otherwise.

I'd love to experiment with the system on an array that received mild shading and examine how it performs with OptiTrak enabled and disabled.

 

[TrickyDicky101]

Thanks - you have been very helpful. I'm happy to go with the 15 N235s and Fronius 3.0 and have told my installer this. Problem is the supply issue. If I can get a firm date then I will continue with this system. If no firm date is forthcoming then i will revisit my options.

 

[SolarCity]

I'd recommend waiting. If your installer is getting his panels from where I think he is then I'd have thought they would be restocked before long.

 

[TrickyDicky101]

The panels just came into stock so my installer has placed the order for the N235s! I am happy

 

[whlphil]

Apologies this is bit late but one thing to watch with 15 in a string (on 3.0tl) is your minimum temps experienced in your area, as at default -10deg C you are right on the voltage limit 845v on an 850v max system voltage, not a big issue but has potential to void your warranty if damage is caused to system. That said they would have to find out damage was caused at less than -10 so it's slightly academic, but never the less worth pointing out if your in an area that is subject to particularly cold temps!