Global optitrac, on or off for east/west split??

[matt25]

sma's response to sharpeners last post is below! what does changing the cycle time achieve? I’d already assumed that you’d be using both strings (A+B) of the SB4000TL to get the best out of the E/W scenario using both MPP trackers.
Cycle time can be changed from 6min to 30min using Sunny Explorer.
The following link will show you how shading can affect your daily yields. The video is pretty good at explanation.
http://www.sma.de/en/products/knowledge-base/optitrac-global-peak.html
Best advice is to monitor your systems’ performance (Sunny Explorer is free). If you encounter yield curves that suggest shading issues, then Optitrac is worth trying. You could then compare the yields with/without Optitrac and then make a decision.
It may be that Optitrac really helps at the transition stage between E -> W as the sun tracks across your panels.

 

[sharpener]

AFAIK at the end of each "cycle" the Optitrac will check if there is another, better peak than the one it has been using. To do this it has to vary the current drawn from the panels from zero to maximum, measure the voltage at each step and calculate what is the best power output (power = voltage x current). While this is going on the array will by definition not be producing at its peak capability. So if the shading is only changing slowly then you want it to check relatively infrequently to minimise the lost power.

The SMA video is impressive but it illustrates severe shadowing over only part of an array caused by a dormer roof, this is quite a different scenario.

If it were my system I would turn it off. If you want it on I suggest setting the cycle time at 15-20 min, IMHO this would be a good compromise between lost power and following the sun round the sky (1/4 degree per minute). If the arrays are not perfectly flat there will be some irregularity of the illumination when the sun is due S but as it will be at glancing incidence to the panels at that point anyway you will not lose any significant power from that cause.

All this assumes that there is no other shading (from trees, pipes etc) and the E and W arrays are connected to separate MPP trackers, this will mean that as the sun moves from one to the other each array is continuously optimised in any case.

HTH

 

[matt25]

I have spoken to 4 guys at Sma on this and 2 of them say turn it on whilst another 2 say leave it off! I'll have to run my own tests i guess to see what happens, thanks again for your advice.

 

[solarsparkie]

mmm 0.2% potential loss of earnings is still alot less than a hair transplant , flip a coin and live with it

 

[sharpener]

Yes if it is only 0.2%. But the OP reports that at least one person at SMA thinks it might be as much as 1 - 2% which would be more worrying

 

[powervan]

off!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

 

[matt25]

Hi, after alternate week on week off recording throughout dec & january the winner is .............. global optitrac ON! by a magin of 7.1kWh (58.078 on, 50.942 off, courtesy of sunny explorer). Might do the same in the summer if the novelty hasnt worn off by then!!

 

[sharpener]

I think it is too weather dependent for this to work over such a short period, unfortunately.

By comparison, my figures for alternate weeks starting on 5 December are: odd weeks total 79.876, even weeks 113.253kWh.

If I change the sampling period to be alternate weeks starting on 7 Dec, then the differences are even more extreme, 72.537 and 121.393 respectively. So my figures show more variability from week to week than yours even with no changes at all to the system!

 

[matt25]

Wow, very interesting and many thanks. I appreciate its all dependant on the weather and particular system but i had to base it on something. Im going to leave in on, as in my case it appears more than coincidence, hopefully this will prove the correct decision. After speaking to SMA again it was mentioned that they are hoping to implement a physical switch on their inverters to opperate "optitrac", apparently this is down to its continual success and making more customers aware of it.