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diy solar

Parallel panel wiring not recommended.

JOVO

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May 11, 2023
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germany
I recently saw a valuation parallel vs seriell. So to make it short i guess its not recommend. There a backward diodes in most of the available panels to prevent backwar current thats fine. But if one of your parallel string get shadowed thats when problems may occur. Since its parallel the panel in the string that gets no light is suddenly turned into a load. That means this panel draws actually current from your system. Any one has more insight?
 
I use micros which are wired in parallel. Most string inverters use serial strings although it is possible to put two panels in buddy pairs and then put the buddy paired panels in series. Where I see more panels in parallel is classic off grid installs where solar contollers can handle the higher current which comes from panels in parallel. I think the title probably refers to some very narrow circumstances only involving shading. If no shading it depends on the install.
 
Can you point to the source? I have not heard of this, and cannot think of how/why current could be drawn from the system into a shaded panel. That doesn't sound right. The way I see PV, it via light and heat it generates power, when put into parallel, the output amperage is added together. When shading occurs, there just isn't current added, and the overall production is lower. For example: If you have 5a in each string and 3 in parallel you have potential of 15a, if 1 is shaded you might get less, but I don't see it sucking out more from the system.
 
The slightest amount of ambient light makes Voc of a shaded panel about same as Vmp of a panel in full sun. Approximately zero current will backfeed. If system isn't drawing any current and voltage rises towards Voc of illuminated panels, then a small amount of current can backfeed the shaded one.

Test it yourself, with two panels individually using volt meter. Then if wired in parallel you can test with ammeter.
 
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There a backward diodes in most of the available panels to prevent backwar current thats fine.

That is a bypass diode, so if series connected and this panel shaded, there is not a large voltage (Voc of string) applied across reverse-biased PV cells, damaging them.

If you have several panels or strings in parallel and one gets shorted (failed diodes or damaged wires), current from all the others can be excessive, burn the panel or melt the wire. So fuses recommended.
 
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