Hi All,
I am trying to improve my system, as currently it is not enough to completely go off grid. The main problem is on over cast days I don’t collect enough energy. To counter this problem I thought I will add more solar panels in parallel to my existing panels, so when the sun is shining, I don’t mind that the output from the panels will be too much, and the extra panels do pretty much nothing. But on overcast days it will be higher than before.
The ES450/100 Data Sheet says:
Max. PV operational input current 18 A per tracker
Max. PV short circuit current (2) 20 A per tracker 2) A higher short circuit current may damage the controller if PV array is connected in reverse polarity.
Note especially 2 in parallel is more than the max PC short circuit current.
Currently I have 14 panels, arranged in 2x strings of 7 panels each. It probably gets to about 5 degress celcius minimum where I live when there is light.
Question
Can I put another 14 panels, and have 2 parallel strings of 7 series strings each on each MPPT input? Is the Max. PV operational input current A warning of what not to exceed, or more information telling one the maximum it will ever pull? I feel like it is the later, because even if you connect more than 5.6KW of power to the MPPT, it limits it (due to thermal reasons). Similarly even if one can feed more current to the MPPT, it should draw the max it can and limit due to thermal reasons?
Have a read of the manual
“Connecting PV arrays with a higher short circuit current is possible, up to an absolute maximum of 30A, as long as connected with correct polarity. This outside of specification potential allows for system designers to connect larger arrays, and can be useful to understand in case a certain panel configuration results in a short circuit current just slightly above the maximum of the reverse polarity protection circuit.”
Do be sure to calculate the array Isc at high temps.
Isc goes up with temperature.
Brilliant thank you. So then the next step is to check the current limits.
So I checked the historic data, the max output current has been 12.5A on one of the trackers, double would be 25A. 5A safety margin is not as much as I would have hoped for.
The short Circuit STC conditions is 14.15A, probablyt at 25 degressC,
with:
Temperature coefficients of Isc Nominal 0.046%/℃
It says they can go up to 85 degrees. That would be (85C - 25C) * 0.046 = 2.76% change. So 14.15A + 2.76% = 14,54054, and double that (for 2 in parallel) is *2 = 29.08A.
30A is the max, and we sitting at theoretical max of 29.08A, and practical max of 25A. That safety margin does not make my electronic engineering heart soar. What do you guys think?
See that the overall real life power coefficient is negative, indicating decreased efficiency at higher temperatures, so you may consider that the current is lower or at least the same at higher temperatures.
