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Can someone please advise on what the maximum amount of solar panels I'm able to connect to a mppt 75/10. The only actual limitation (not considering the 10A maximum charging capability) it seems is the 75V Voc rating if I'm correct?
If a 100W panel with a 22.3v Voc is to be used...
It's my understanding: 75/22.3 = 3.36
Meaning a maximum of ×3 of the above mentioned panels
You also have to calculate the string voltage in the lowest possible temperature for that place (in cold weather, panel voltage can be higher than Voc). This must remain under 75V (for that 75/10 charger).
Regarding the total power of your PV array, it depends on the battery voltage (higher is better). You can oversize the array (for cloudy weather/winter production), but do not exaggerate.
Thank you for the quick response
Considering I only have a limited amount of the actual solar panel specifications available, how does one go about doing this?
22.3V x 3 = 66.9V
That is relatively close to 75V.
How cold can it be in your area (during the day)?
Did you already bought the panels and the 75/10 charger?
But I recently haven't had the opportunity to actually travel a lot..
Was planning on using the system to power a bunch of 12v downlights in my house (to keep the lights on during power failures)
But the only spot I can temporarily place my solar panels doesn't exactly get the best sun during the day.. hence the additional panels..Temperatures normal vary between 20°c - 28°c (average maximum winter and summer temp.)
I need minimum winter temperature (lowest ever recorded), not average, nor maximum.
If you only have that single 100W panel, don't be stuck on that model (if you can even get the same model).
For a house, better look at 60 cell PV panels instead. A single such panel can have 300W (or more). Price / W should be better.
Considering this still needs to be a fairly temporary/mobile setup (and there isn't a lot of space for big-surface-size objects while on the move) a 300w panel wouldn't be the best option....
Voc temperature coefficient for most PV panels/modules is around -0.3%/°C.
Assuming yours is not very different:
The panel Voc is given for Standard Test Conditions (STC), which, among other things, mean 25°C PV panel (PV cell) temperature.
You say your minimum temperature is 5°C.
5 - 25 = -20
(so you have -20°C difference from STC in the coolest weather)
Now that we have the temperature difference, we go back to that -0.3%/°C temperature coefficient for Voc:
-0.3/100 x -20 = -0.003 x -20 = 0.06
You said that for your 100W panel the Voc = 22.3V
=>
0.06 x 22.3V = 1.338V
This is the voltage (Voc) increase (compared with Voc at STC) when the panel is at 5°C.
So the panel voltage (Voc) at 5°C is:
22.3V + 1.338V = 23.638V
For a string of 3 panels (3 panels in series), the string voltage (Voc) at 5°C would be:
23.638V x 3 = 70.914V
This is lower than maximum allowed for your 75/10, but if the actual temperature coefficient of your panel is very different or if the actual panel temperature can go even lower than 5°C, then the actual voltage will be higher and you will damage the MPPT.
In other words, too close for comfort (in my opinion).
For your 75/10 charger, it would be safer to make strings with only 2 such panels (only 2 panels in series).
Also keep in mind that all panels from a PV array connected to a single MPPT must be the same.
