Dual Solar panels - always better than one?

[Scarfaz1]

One for the solar experts!
I half understand there is a difference in connecting 2 panels in parallel or series and under certain circumstances 1 is better than the other. Is there ever a situation when connection of 2 in either way would result in a lower charge than 1 on it's own.
I have a caravan with roof mounted 100w panel but it's not always enough and there are times when the pitch location is far from ideal. I also have a 120w suitcase panel for the van batteries which I could connect to the caravan and site in a nice sunny position. If the caravan panel is producing next to nothing (due to shade etc.) could this ever result in the suitcase panel operating below optimum meaning I would be better to disconnect the caravan panel and rely on the suitcase?

 

[Ads_Essex]

@Dellmassive will probably know the answer to this

 

[lydart]

If shading is an issue, wire in parallel. Then your suitcase panel can be placed in the best position. This ensures that each array is independent. Just make sure your solar charge controller can handle the combined amps from the separate panels.

 

[Dellmassive]

As above if there is a chance of shading on one panel then connect in parallel, say if the van was parked under a tree,

but most modern solar panels have bypass diodes to help out the situation. (that means you can connect either way)

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the main thing is to try and match the panels as close as possible, so no connecting a 10W and 100W panel.

but, try and go for 100W + 100w or 100W + 120W, or even 100W + 150w. (matched panels is always best)

I've connected 200W + 50W and managed to get 230W out with panels that had similar VOC`s. - so mismatched can work.



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The standard recommendation and the advice from "Victron Solar" is to connect your multiple panels in SERIES and use a MPPT controller.

The reason for this is that the series panels will generate a higher voltage (than the battery) for a longer duration (hours in the day) which will equate to more charge over a 24hr period.

most solar controllers wont start charging until the PV voltage is around 2.0v above the battery voltage . . . say 13.2v AGM battery needs 15.2 PV to start.

with 2x 100w(18v VOC) panels the PV voltage are added . . . 18v + 18v = 36V

that means that the series panels will start rising the PV voltage from sunrise and generate more than the required 15.2v for longer in the day.


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having said all that the solar controller is very important, a decent MPPT controller will out perform any PWM controller in all secumstanses


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remember in series the VOC (panel volts max) is added - but the ISC (panel current max) stays the same

remember in parallel the ISC (panel current max) is added - but the VOC (panel volts max) stays the same


make sure your solar controller can handle either of the VOC or ISC max values before connecting



example panel is 100W 18v VOC, 5.5A ISC (w=v*a)

series - 18v + 18v is 36v x*5.5a = 200W

parallel - 5.5a + 5.5a is 11a * 18v = 200W

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more info here:

[Guide] Mobile Solar Panels ? . . . - How I Did It -

Mobile Solar Panels ? . . . - How I Did It - There is loads of background to this . . . . . but for now here is a vid for you all. =] Just remember W = V*A and as a general rule a good 100W panel will give you up to 6A charge with good sun. 25w = 1.5A 50W = 3A 100w = 6A 200w = 12A 300w = 18A...

www.t6forum.com

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