Adding extra Solar Panel to system (advice needed)

[Widdzuk]

Hi.

Im looking at adding an extra Solar panel to our current system. Currently we have a PV logic 100W low profile flexi panel, which has an external Diode box going to a Victron MPPT 75/15.
Id just like to know if my plan attached is correct for a series connection.

I got a little confused as to whether the diode should be on each panel, then wired in series or just one diode and the series wired before it. - From what i have read it should use both diodes as my attached plan suggests - Just need confirmation from someone who actually knows what they are doing




thanks

Martin

 

[Raul a/3]

Your panel should have reverse flow diode built in. If it doesn’t, I wouldn't touch those panels. Series for 24v is a must. But if your batt. Is 12v not worth it because the shade. Unless you have a long run to the controller I would stick to parallel.

 

[Widdzuk]

Hmmm, ok. Regarding Series (more V) vs Parallel (More A), im sure i read on here that Series would be better to make sure the battery was charging more often. As the chances the voltage been over the minimum to charge would be greater. Hope that made sense in how i wrote it. I might email PV logic too. The reason the diode box is separate is because its a low profile flexi panel and only has a wire coming out vs the classic lump on the end of the panel

thanks for your reply

 

[Littleblackflash]

That logic makes sense, but I think you'll need a new 24v MPPT. Someone in the know will confirm.

 

[Widdzuk]

Happy to go parallel if that’s the better way. Just need to figure out my cable run lengths

 

[RoadJumper]

If your panels are new or in good condition, then you will not gain anything by a Series connection, as in Series, you will only increase the Voltage, which is mostly beneficial if you have very long runs from the panels to your MPPT.
As you only have short runs, a Parallel connection is better, as the necessary Voltage (For the Victron 75/15 12/24 to function correctly) only needs to be some 5V higher, then the Battery Voltage, which your Panels will achieve anyway.

You don't show any Fuses and/or any Switch in your diagram, to safeguard against cable issues and/or to disconnect the Solar Panels from your MPPT!
These are both a must!

 

[Raul a/3]

As above, and the parallel will gain you in a situation of a shade or bird droppings. It will take out the shaded one but not all. In series you have higher voltage but without amps, it’s still meaningless. The controller will make power when amps are available as well. Also from 35-40v down to 12v the controller will have more conversion losses compared to 18-20v to 12v. Ideally you will go parallel, unless it’s a long run exceeding 10m, for that kind of power, the loss in cable may be 2-3w.

 

[Widdzuk]

Cheers guys. I’ll look further into my current system and weigh it all up.