Different voltage between strings

warrenb

Hi there
I have noticed over the last few days that I am geeting a different AMP reading between my strings, I have 14 panels on an ESE facing roof, with one string the left hand 7 (South end of roof) and the other string the right hand 7 (north end of roof).
Now the above maybe the reason, but just wanted to check.

Below are the Amps for the strings String 1 first

5.3 5
5.7 5.3
5.8 5.3
5.6 5.2
6 5.5
6.1 5.6
5.7 5.7
6.5 6
6 6.1
6.1 6.2
6.7 6.1
6 6.2
6.7 6.2
6.5 6.2
6.7 6.2
6.6 6.3
6.7 6.3
7.1 6.6
7 6.2
7 6.3
7 6.5

Problem with good monitoring is you can get paranoid.
Thanks
Warren

ely_ellis

Looks fine to me.

Each panel will have a slightly different output to the next.

These panels are connected in series (a string), so effectively you have 2 independent sets of panels with slightly different outputs.

The trackers will adjust the voltage to the same level for both strings and thus the current flowing in each string will be different.

I have solar edge optimisers and each optimiser will adjust the output voltage to the same (near as) for each panel. Of course if one is in shade, the current from that one will be greatly reduced.

The output voltage of my panels range from around 24volts to 32volts, but the optimiser output (optimum tracking point) is around 23volts with very little change. So if the voltage is held steady by the optimiser then the current from each panel must vary instead.

I believe that your MPPT tracker is the same as an optimiser but operating at a higher voltage as there are 8 (7 in your case) panels per string rather than 1 panel.

At a guess, the output from your MPPT is probably around 240v, (depends on the panels) so as the two trackers will both try to deliver and maintain this 240v into the inverter gubbins, then any variation between each set of panels will be shown by a change in current which you clearly see.

Its all down to Ohms Law, power(w) = voltage(V) X current(I)(amps). If the power changes and you hold the voltage constant then the current has to change instead!
So your MPPT's should find (track) the best voltage to get the best power from your array.

Hope you understood all that.

Of course I may be way off.

In short, it would be strange if the 2 strings had the same current so no worries!

Any comments on my reasoning please?:rotfl:

warrenb

I did get that, thanks
I think I will learn to be an electrician if I ever leave my current job, because it sounds far more interesting than my job.