MPP Solar 5048MG PV array help...

[Batonage]

Hi All,

We're battling through a very wet winter here, but making some progress. The roof is on and I'm getting ready to order PV panels and battery.



We're looking at

aasolar.co.nz/product/400w-perc-mono-half-cell-pv-solar-panel and pylontech us3000 lithium battery to combine with a previously purchased MPPSolar PIP-5048GK .

Initially I'd like to get the system powered up with just 4 panels in series, and 1 pylontech, so we can operate the waste water system. I'd like to later add another 1 or 2 strings (in parallel) , and more pylontechs. My question is...the 5048GK lists max voltage as 500Voc, and start up voltage as 150V. Panels have Voc of 47.91V (4 x 47.91V = 191.64V, OK for start up). However looking at the details of the panel I see at Normal Cell Operating Temperature the Vmpp is rated at 37.29V (4 x 37.29V = 149.16V, not enough for start up). Am I over thinking this?

Also the panels have 4mm2 Anderson fittings. Are 4 panels in series OK for this size wire? I've been checking DC wire calculators (looking at max 10m/30ft from PV to inverter) and some calculators seem to be saying I should be using 6mm2 wiring. Again, am I making it more complicated than it needs to be? It'd be great to use off-the-shelf 10m cable with MC4 connectors if possible.

We're hoping to have the panels angled at 35 degrees from horizontal, directly North, but on their sides for lower profile. Plenty of roof space, but they'll need short MC4 joiners between each one, a small cost only. Any other downsides?

Sorry for all the questions, and I hope I've not made things too complicated, or completely confused myself. Really excited to get started after nearly a year of planning.

Cheers from (mostly) sunny New Zealand!

Andi

 

[tictag]

My question is...the 5048GK lists max voltage as 500Voc, and start up voltage as 150V ... Am I over thinking this?

I am not able to find this "150V start-up" specification anywhere. The datasheet does however specify "MPPT Range: 120 - 450VDC", which would leave me to believe that 4 panels in series should be fine. And even if the unit does test the array for a minimum 'start-up' voltage, it would be doing this without a load so it would 'see' Voc from the array, not Vmp. I think you'll be fine.

Also the panels have 4mm2 Anderson fittings. Are 4 panels in series OK for this size wire?

If 4mm² is good for one, then it'll be good for four or a million* if your panels are connected in series - remember it's the current that determines the safe cable/connector size and all panels in series have the same current flowing through them, that is the Imp of a single panel. But a safe cable might not necessarily be the most efficient cable.

You generally want to keep the voltage drop along your PV cable runs to <3% and, whilst I appreciate you are only fitting four panels now, it is best to do this as-if this were your final installation. So how many panels will you be getting and how do you plan to connect them?

Let's say you want to take advantage of the maximum charging capability of your MPP, that is 80A. In order to generate 80A at 58.4V you'd need a minimum PV array 4,627W (ignoring losses). Most people will over-panel their array by 30% or 6,074W, but this is above the unit's maximum PV power, so let's restrict ourselves to 5,000W.

5,000W made up from 400W panels is 12 panels. With a panel Voc/Vmp of 48V/40V, Isc of 11A, connecting all 12 in series (12S1P) would produce an array Voc of 576V, which would exceed this unit's maximum PV voltage specification of 500V. So the next optimal array configuration would be 6S2P, which would give a string Voc/Vmp of 288V/240V and string Isc of 11A.

Assuming you'll want to connect these two strings into a fused combiner box, in order to safely carry 11A x 1.56 = 17A and avoid a >3% voltage drop along a 10m cable run, you'd need to use a minimum of 2.1mm² cable (according to here).

If instead you intend to combine the array at the array, in order to safely carry 22A x 1.56 = 34A and avoid a >3% voltage drop along a 10m cable run, you'd need to use a minimum of 3.3mm² cable.

If you're planning to use 4mm² cable, this will easily support both configurations, be over-specified in fact for this example.

It'd be great to use off-the-shelf 10m cable with MC4 connectors if possible.

Sounds like a good plan. Just be sure that this 'off the shelf' cable is specified for PV installations, usually this means UV resistant insulation and tinned conductors. For the MC4 connectors, try to get the ones with the easy-release lever on them, and rated for 30A, not 20A (because these would generally be of better quality). Don't forget to pickup a proper MC4 crimping tool - crimping with pliers will only cause you problems in the long run (trust me!).

We're hoping to have the panels angled at 35 degrees from horizontal, directly North, but on their sides for lower profile. Any other downsides?

Try to get the racking that enables the panels to be properly bonded together (WEEB) so you don't have to run an earthing cable between them all. There are online tools for determining your best positioning angle for where you are.


*ignoring voltage!

 

[Batonage]

Hi tictag,

Thanks for your amazing reply, very helpful.

The start up voltage is in the manual that came with the inverter. It actually says 150V +/- 10V, so really good with the 4 panel array if we go that way.

Based on your help I'm now thinking of starting with one string of 6 panels, with the option to add another string in a combiner box later.

Thanks for the reminder about current dictating wire size, and the good advice about mc4 connectors.

Cheers

 

[tictag]

@Batonage, you're welcome. Don't forget to 'like' the reply if you got any value from from it. Not that I follow the forum statistics or anything!