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We have been looking at a job with considerable shading on what would be the main location of panels. It is a big late Victorian Semi where we can probably get ten panels on one side and a further 6 on the flat roof above. Nearly all the shading comes from a chimney stack located on the outside wall with a dormer type arrangement behind it which bisects the side where we could get 10 panels.

I have run numerous permutations through PVSol, including using 14 LG 285W panels in an attempt to mitigate the effects of shading rather than 16 high output 250W panels. Have Permed this with Solar Edge and also with Enphase. The panels on the flat roof are virtually unshaded.

Here's the rub. Using LG 285 panels is simply not worth it due to the additional cost, which leaves using a greater number of 250W panels. 14LGs do not perform as well as 16 Renasolar or REC.

PVSol shows a negligible improvement using Enphase micro-inverters and only a 5% improvement using Solar Edge compared to a Power One 3.6. Shading with the Power One configuration is 16.4% in total, 13.6% with Solar Edge.

It would appear the additional cost is not worth it, as it pulls down the ROI and increases the payback period.

People bang on about the benefits of Solar Edge or Micro Inverters (I have used the latter), but do they really make a bigger difference than predicted by PVSol? If they do how do you substantiate this and show the benefit to a customer?
 
Its a tough one to call, but in my view I would look at two options.

1 x SMA SunnyBoy 3600TL, split into two strings and with OptiTrack enabled.

or

Use PowerOne 250W Micro Inverters.

The simplest is the SMA route. Enabling OptiTrac gives much better performance with shading conditions. Similar effect of adding Solar Edge optimizers, but without having to install them. The OptiTrac function just needs enabled (via bluetooth with Sunny Explorer)

The other option is micro inverters. I would recommend the PowerOne micros as they are 250W (or 300W) so not going to clip nearly as much as the 215W Enphase.

Ken
 
This doesn't answer the question, all it does is provide another two permutations that reflect your own preferences or the equipment you sell at CCL. There is no guarantee that either of these are any better than those already considered and no indication that they will perform any better. The issue is if micro-inverters or optimisers are the best option, how do you show this to a customer when you have no way of substantiating a gain greater than that shown by simulation software.

Why should a customer pay substantially more if you cannot quantify a gain and demonstrate it is cost effective? If you make claims you are unable to substantiate, you are at serious risk of mis-selling.

Both technology's selling proposition is that they increase output over the use of a string inverter, especially where there are shading issues. Solar Edge appear to have worked quite closely with the developers of PVSol, so one would expect the performance predictions to be reasonably accurate, but as stated, in this case the gain is marginal and nowhere near enough to justify the extra cost.

Unless anyone can prove otherwise, we will live with the reduction due to shading, but allow the customer to benefit from the increased return and shorter payback period.
 
Micro-inverters aren't all they are cracked up to be when it comes to shading - they are not all the same and hence sometimes power optimisers can be better, or not even nescessary...

Here's the biggest rub with micro-inverters, - look at the minimum voltage that they need (same as a normal inverter - lowest mppt voltage) - it's worse with micro's - if one part of a panel goes into shade, that could easily trigger the bypasse diode, all of a sudden you've lost (in most cases) 33% of your output voltage, and hence maybe the 100% of that panel output.

With the excpetion of the new Power-one micro inverter that will usually mean that effectively you've lost the whole panel, whereas a string inveter will still be happily providing the new mpp voltage to the string.

There are three areas that micros help with -
1) Mixed orientation / elevation (value - 2% - 7%)
2) Panel mis-match / multiple panel types / sizes (value - 0.5% - 2%)
3) Shading (value - 4% - 8%)

and also of course Small systems (< 6 panels)

above figures are from fromal testing done as a comparison with a well designed string system, so for shading only, the value may be only 4% (maybe more :) ) Seems like your result are right for the enphase system.

Because of the mpp issue I would expect slightly better performance from the Power-one Micro inverters than enphase or enecsys.
 

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