Wiring "24" (actually ~45vdc Voc) panels & Ohm's law

[lonewolf2koc]

If I'm not mistaken, wiring for 24vdc solar panels will need a pair of the 12vdc connecting in series. Then from those series parallel them to combine them to keep the same voltage but increase in amperage. It is not possible to wire 3 panels in series because it'll become 36v right?

Another thing about Ohm's law. I have four 165w panels. If I wire 2 of them in a series set then combine that set of two via parallel to get the total Voc voltage within 45vdc, my wattage will not be lost right? The 24vdc (20-50vdc) inverter will also obey Ohm's law and I'll get ~660 W total (minus efficiency losses from panels and inverters) @24vdc but with a smaller amperage. The way I see running 24vdc vs 12vdc is that the amp will be half of 12vdc right? For example: An 10 awg wire can get a max of 30A@12vdc. But at 24vdc, that 30A max load will be double in overall final wattage capacity.

 

[akrvbob]

The key thing to understand about voltage and amperage is that the job of a MPPT controller is to step down the voltage to whatever your battery can take at that moment, and at the same time step up the amperage so the most possible amps goes into the batteries. A good one does that extremely well!!

You don't have to try to figure out how to get the most amps into the battery, the controller does that for you.

Really, the only reason to put them in series is to be able to use a smaller wire--and that is a good reason. Some people say that when you put them in series you make them more susceptible to loss from shadows on the panels. A shadow on one panel means they all lose power. I don't know for sure that is true, but it is a comonly stated thing.
Bob

 

[jimindenver]

I did quite a few test a few years ago and shading on panels in series as well as parallel was some of them. In series the weakest panel rules the roost so to speak. So be it a mismatched panel or a shaded one, having its voltage cut will lower the voltage of the whole array to match it. MPPT relies on excess voltage to do its thing, so any reduction in it is bad. In parallel shading creates a reduction in only the panel being shaded.

Now then, set up correctly most systems do not have shading from the vehicle and I don't park in the shade simply because I do have solar. So the series vs parallel debate as it deals with shading may only be a issue occasionally if you make a poor decision in choosing a parking spot.