question

Hi iostrym, as any electronic device, the mppt can work in a specific range of voltage. Yours is adapted to work UP TO 100VDC input. So the most important is TO NOT provide it OVER 100VDC, as it will destroy the mppt.

Such situation can happen in winter, when the PV are cold, and the sun is shining, as they will produce more power than the rated one. As long as your PV infrastructure provides you 5VDC over the battery bank voltage, and less than 100VDC, you are fine : for a 12VDC battery bank => 17VDC - 100VDC, for a 24VDC battery bank 29VDC - 100VDC.

In my setup, my mppt can get 150/100, and I have made my PV infrastructure providing a maximum of 120VDC, so I remain 20% under the maximum voltage and will not have any issue.

I hope this will help you to clarify and understand better how the mppt can be damaged, and what voltage to provide in order to have it working within its specifications.

Michel

but the seller told me that the 320W solar pannel is a 60 cells and not a 72 one, this is why it has lower voltage to be compared with a 72 cell solar pannel.

Correct.

He explains me that the Vmp =33.4V when sun is maximal (then it will be ok to load my batteries) but when it is cloudy the voltage Vmp would be below 30V and then the regulator wouldn't be able to load the batteries (if they are discharged and need an higher voltage)

True. When cloudy, the voltage will be lower.

That 24V battery voltage is nominal voltage. The actual battery voltage varies inside a range, from discharged to fully charged. The PV array voltage must be higher than the battery voltage. For instance 5V higher. The MPPT can not increase the voltage higher than the PV array voltage. It can only adjust the output voltage lower from that.

For that 100/20 and a 24V battery you can use two 60-cell panels in series.

Thanks a lot for your answer.

I know that for a 12v battery, when it must be charged, battery voltage is up to 14.8v approx.

Does it means that for a 24v battery the mppt must be able to provide up to 30v, right ? This is why the vmp=30v voltage is the minimum one to provide to have a correct charge of the battery (with more or less power) in every kind of weather situation.

I already have one solar panel 72 cells, 185wc. Vmp = 35.8 (1000w/M2) and vmp = 32.8 (100w\m2). Do you think I could put this solar panel serially connected to the new one (350wc) ?

Even if vmp are quite different ? Would it be always better than one solar panel ?

I understand how it works if solar panel are in parallel, voltage is equal for each solar panel and you need to have quite same vmp for the panel. But When serially connected I don't know what will happen for voltage of each solar pannel... Maybe voltage will be different and, by chance, could be at vmp for each? :-)

Ok all, thanks for details, I understand know that the solar pannel I wanted to buy will be a problem with my 24v batteries. Also, I won't be able to mix it serially with my old solar pannel (185wc) because old solar pannel is 5A whereas the new one would be 10A.

Then looking at victron solar pannel, the 360W monocristallin one may fit, right ? Vmp = 38V. but I don't have the information of Vmp when "sun power" is low but I guess that it shouldn't be below 30V, right ?

and I will use my old solar panel with my old stecca (not mppt) regulator...