Discuss Global optitrac, on or off for east/west split?? in the Solar PV Forum | Solar Panels Forum area at ElectriciansForums.net

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matt25

Hi, im after some advice on an east/west split with a 4000tl please. I would assume it wise to turn on the optitrac feature due to the consistant shading issues an e/w system on a pitched roof would have? Has anyone ever compared yields with it on/off? All advice most welcome as this will be my first e/w installation! Many thanks in advance
 
East/West is a good option - especially if the home is occupied for most of the day.

I would recommend enabling optitrac. I'm still not sure exactly how it works but if you have shading issues then it's a winner.
 
Thanks. The east side will deinitly be shaded pm as will the west am. I had previously been told to enable during winter months and not for summer, although i think this may not be the best scenario for an e/w split though?
 
I'm still not sure exactly how it works but if you have shading issues then it's a winner.

Ordiinary MPP trackers climb to the top of the nearest hill in the power output curve. IIRC OtpiTrac Global Peak checks there isn't a higher hill somewhere else. The downside is a slight loss of output while the tracker is checking for this. Shouldn't make any difference with a simple shading problem as in the sun moving round the sky, more useful where there are multiple/odd-shaped shadows passing over the array. More here OptiTrac Global Peak. SMA Solar Technology AG. [Grateful if someone could tell me how to post abbreviated links, maybe not possible with Quick Reply.]
 
There are 4 or 5 different approaches to MPPT algorithms - discussed here: http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.119.6513&rep=rep1&type=pdf

Useful reference paper, thanks TedM.

(i) The results for the two methods with the best results (Perturb & Observe and Incremental Conductance) are very much the same, and so much better than Constant Voltage that no one would use that (and it requires prior knowledge of the panels).
(ii) none of the algorithms described are capable of dealing with more than one "hill" in the characteristic.
(iii) the cost of implementing the more complicated algorithms e.g. DSP or Fuzzy Logic in software is much lower now than when the paper was written so I expect in practice inverter manufacturers have their own proprietary algorithms which may use a combination of methods.

See also http://files.sma.de/dl/7418/GlobalPeak-UEN101210.pdf which has more details of OptiTrac. In particular it says the penalty for using it when there is no shading can be up to 0.2%. So this would seem to imply that for a simple E-W system where all the panels will go into shadow simultaneously you would be be slightly better off without it, presumably this is why you can turn it off.
 
Sma's response was "Probably best to enable it. Worst case scenario is you might lose 1-2% yield as the MPP trackers search for the best power curve. Without it enabled you could lose ten times more from shading"
 
The figure of 1 - 2 % is not consistent with their own data sheet, which says

"with this procedure, losses during searching are unavoidable. However, OptiTrac Global Peak is a search procedure specialized in keeping losses in times without shade at a maximum of 0.2 % when searching for a possible second power maximum. To keep these search losses even lower, it may be useful to adapt and reduce the frequency of searches (cycle time), individually for PV plants with slowly appearing shadows [2]."​

With an E+W design the shading due to time of day will affect all panels or none in each array and there will not be more than one peak on the power curve. So provided the E and W arrays each have their own MPP tracker the Optitrac Global Peak algorithm can't improve the yield. If it is really true that "it might lose 1 - 2%" then you would be better with it off. At least make the cycle time as long as possible if this is programmable.​
 
hmmmm must admit i did cringe when i looked at the weather report, not looking good. So if it was your house Powervan & Sharpener (this is mine in question!) would you enable or leave it off??
 

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