RV rooftop panel connections-Does even wire lengths matter ?

[Spleeft]

Ill be wiring 4 HQST 100 Watt 12 Volt Polycrystalline on my RV roof. Two groups of series to parallel. Each is 18.2v 5.5A so I will end up with 36.4v 11A at the MPPT, correct?
Depending on how I configure the panels on the roof , does it matter if my 10AWG solar wire extensions are all the same length? For example one 2 panel series could end up much closer to the roof gland than the other series.
PS - I just ordered and received the panels and am getting amped for my first solar project !!!!! I immediately unboxed all 4 and put the volt meter on them !

 

[cass3825]

Ill be wiring 4 HQST 100 Watt 12 Volt Polycrystalline on my RV roof. Two groups of series to parallel. Each is 18.2v 5.5A so I will end up with 36.4v 11A at the MPPT, correct?

Correct.

Depending on how I configure the panels on the roof , does it matter if my 10AWG solar wire extensions are all the same length? For example one 2 panel series could end up much closer to the roof gland than the other series.

Technically, yes, but 11A on 10AWG wire the voltage drop will be negligible.

PS - I just ordered and received the panels and am getting amped for my first solar project !!!!! I immediately unboxed all 4 and put the volt meter on them !

Welcome to the addiction!

 

[tictag]

Two groups of series to parallel. Each is 18.2v 5.5A so I will end up with 36.4v 11A at the MPPT, correct?

Yes and no, but mostly yes! There are two PV panel specs to consider, particularly when connecting PV panels in series and matching to a SCC, they are Voc and Vmp (the parameter you quoted above). Solar charge controllers are usually specified with Maximum PV Voltage and PV Power limits, sometime they also specify operating range, which is where Vmp comes in.

The Maximum Voltage a SCC might see is the sum of all series-connected Voc's (i.e. Voltage Open Circuit). Your panel has a Voc of 21.4V. Most MPPTs these days have a Maximum PV Voltage of around 150V, so you can connect up to 7 such panels in series and be within spec (150V / 21.4V = 7)

The Maximum Power a SCC might see is the sum of all Pmax (Power Maximum). For example, 1,000W, which means you can connect up to 10 such panels in total i.e. irrespective of connection method.

So all that aside, you are dead right ... in normal operating conditions (i.e. maximum power point, I mean this is what you buy an MPPT for!) you will have 36.4V at 11A (i.e. 400W) at the input to your MPPT.

does it matter if my 10AWG solar wire extensions are all the same length? For example one 2 panel series could end up much closer to the roof gland than the other series.

Really great question because length really does matter when it comes to the battery side, but because the voltage will be bucked down to a suitable charging voltage by your MPPT, it doesn't matter, save to say that shorter overall lengths (i.e. there and back cable runs) reduce resistive losses.


As a side note, it's really nice to see somebody using the PV side specs to properly specify their PV cable runs. I see a lot of people take a 40A or 50A SCC controller and, therefore, assume 40A or 50A cable is required on the PV side. Some would say that overspecifying their cable isn't going to harm, and that's true, but it also adds additional weight and cost to a project for no appreciable benefit (imho).

Edit: Clarified series-connected
Edit: Corrected no of panels

 

[Spleeft]

Thanks for the great replies. I will mount my panels then buy the crimping tool and connectors and make extensions that fit best and not worry that one series may have shorter/ longer extensions than the other.