Decision time: series vs parallel

bstory

I realize this may be tiring to the experts, but I still am not sure how to wire my two new Kyocera 135 watt 12 volt panels on my camper: series or parallel.

I understand how wiring in series will lead to problems with shading, but since the Kyocera panels have bypass diodes - I've checked several times and yes they do have them - doesn't this mean that partial shading in one place will NOT mean the whole string will drop out? Perhaps I don't fully understand what bypass diodes do but I thought this is what they are intended to do.

If the presence of the bypass diodes mean I don't need to worry about the downside of wiring the two panels in series I'd be crazy not to do it, right? I am going to be using the Rogue 30 amp MPPT controller so I'd much prefer the input to be 24 volts.

Advice much appreciated.

Cariboocoot

Re: Decision time: series vs parallel

Panels in series: nominal input Voltage to controller = 24 Volts.
Shadow falls on one panel, its output drops (possibly to zero): nominal input Voltage to controller =12 Volts (half what is "expected" or "needed"). Supplied Voltage not above requirement for charging = no charging.

Panels in parallel, one panel shaded, Amperage drops; Voltage remains the same. Charging continues, albeit at a lesser rate.

(Travel day = terse answers from 'Coot. )

BB.

Re: Decision time: series vs parallel

Assuming this is a 12 volt bank--I would mount the panels in series... If one is blocked (or partially blocked) the second panel will still charge the battery bank with because the dark panel will bypass through the diodes.

Problem is, most times, shadows are variable (season, time of day, etc.)--and it is difficult to say how the panel will be blocked. So, it is difficult to say if series or parallel would be slightly better or not. Best bet is to remove the amount of shading as much as possible--panels just do not work well under shadowing at all.

The 2xVmp is just much nicer (smaller wire gauge, less losses in wire run from panels to charge controller, etc.). And is the only answer if this was a 24 volt battery bank (Vmp-array > Vbatt-charging).

-Bill

niel

Re: Decision time: series vs parallel

i agree with bill, but if you aren't convinced it may be easy for you to just try it both ways and see what works best for you.

RCinFLA

Re: Decision time: series vs parallel

It is hard to know how many of cells in a panel are covered by a single bypass diode. Most companies do not state bypass diode arrangement in their specs.

I did see one description that says the Kyocera 135 watt panel has one bypass diode in the junction box. That would say the whole panel is taken out with partial shading.

Maybe someone else on the forum knows for sure.

Look for bumps in the plastic in the back of the panel.

If all you have is two panels and shadowing takes out one whole panel you would be better off in a parallel configuration. You would save the voltage drop of the whole panel bypass diode. This assumes you are using large enough wire gauge to avoid too much voltage drop for twice the current of two panels in parallel. The MPPT controller may also have slightly higher efficiency running with 18 vdc input then 36 volts.

BB.

Re: Decision time: series vs parallel

If I recall correctly, there should be at least one bypass diode per 12 volts of vmp. Over that, the high voltage across dark cells can damage them (solar cells are just giant diodes themselves with their own maximum ratings that blocking and bypass diodes are there to protect.

-Bill

bstory

Re: Decision time: series vs parallel

Here is the installation manual where the bypass diodes are described - in item #10. If I fully understood what this says I would probably not have to ask you guys, but as is, I need an interpreter.

Thanks again for everyone's help!

niel

Re: Decision time: series vs parallel

by the kyocera specs the module has 2 bypass diodes in it.