Need help sizing a solar array

[leon.davibe]

I have to do a physical check but there is complete shading in the late afternoon on the North facing section as the East-West section of the roof is higher than the north facing as it is a substantially larger roof.

yea noticed the north facing span is less so assumed that would be the case

 

[Speedster]

So say I use 10 x 425W panels on the north facing roof which leaves me with 8 I can split in parallel on east and west as you say. Adding 2 strings of 4 of those 425W 10 amp panels in parallel will give me 20 amps on the 2nd MPPT which is 4 amps above the 16 amp rating of the MPPT. How will that work? Forgive me if my lack of understanding is showing. Being able to safely use 18 panels is compelling for me.

Here's the current for my one north facing string yesterday. The panels are rated for 18.4A (Isc). As you can see, they only get close to that for a small portion of the day. If, for example, you paralleled your strings to 20A any potential losses really would be minimal.

 

[Speedster]

Thanks so much for all the replies. Much appreciated. The reason I chose those 425W panels was because (a) I can get them at a great price (R1600 each if I can get some people to share in buying a pallet) and (b) the physical dimensions (1764mm length as opposed to 2200mm) mean I can get more panels on my north facing section of the roof. Also I want to use 2 of those 425w panels to power the Geyserwise PV solution I intend installing in the near future (Edit: those 2 panels will be mounted on the small section of north facing roof closest to my neighbour on the North side as it comes with it's own MPPT controller).

Almost forgot to mention, adding a separate geyserwise PV to an existing PV system makes no sense

 

[leon.davibe]

Here's the current for my one north facing string yesterday. The panels are rated for 18.4A (Isc). As you can see, they only get close to that for a small portion of the day. If, for example, you paralleled your strings to 20A any potential losses really would be minimal.

View attachment 1595658

You don't need to hit max amps
On an mppt for it the give you all the panels can produce

Amps and volts are just two variable that determines your watts

You want to stay away from inverter max volts to prevent frying the controller

And stay away from the max amps to not have losses


The volts/amps rise as the sun angle rises having higher amps panel doesn't mean you get more out of panels

(and naturally the inverter can choose the volts at which it chooses to extract those amps)

In fact if going too high in the amps you narrow the band in which the inverter can choose from as you need to do lower volts to fit in the max watts

If any shading that band narrows further

The wider the band the better shade can be dealt with before dropping out of mppt range, dropping out of mppt range is way way worse than some shade

Many confuse dropping out of mppt range as shaded panels killing the array amps

This is worse on low voltage mppt , by going higher amps you are turning a high voltage into a low voltage mppt by choice sacrificing all the advantages brought by high voltage mppt because people don't understand this