PV systems with modules on south facing & South west facing aspects of roof

[bigsparks]

Hi

I am drawing up a quote for a PV system. The property is a double bay semi detached property with a small dormer rafter pitch at the front, which is the south facing aspect of the roof. Due to the dormer pitch, we can only fit 5 x 195w panels, in a staggered formation, onto this south facing aspect. I would like to use 250w panels but the width dimension of the panel would be too big and would protrude over the ridge tiles, a big no no. So we have to have 5 x 195w panels to the front (south facing). There is a larger roof space to the side of the property that is south west facing that we can fit 8 x 250w panels onto.
When calculating kwp, I will add both strings together, and use one sma inverter to generate.
Can you advise best way to calculate SAP performance. Will it be just a case of calculating produced kwh of south & south west strings separately and then adding together. Or as im using one SMA inverter with 2 strings connected will I have to take anything else into consideration as the roof aspects face different positions??
Any help appreciated.

Cheers

 

[optician]

Where in the Country is the Roof?

 

[bigsparks]

It is in Suffolk, East Anglia.

 

[optician]

Sorry, also should have asked pitch of each roof?
Also consideration needs giving to how far away from each other the roofs are?

 

[optician]

Assuming 30 degree pitch for each roof, Smallest South facing array may produce 790 kwh and the Largest SW facing array may produce 1680 kwh per year.
Are you connecting in series or parrallel? what is the spec of your inverter?

 

[Worcester]

@Optician

The two arrays cannot be connected in series and certainly not in paralletl as they have different characteristics, they need to go either to seperate inverters, or an inverter with twin MPP Trackers

 

[Worcester]

@bigsparks, -

a)Which PV training course did you go on?
and
b)Which SMA Inverter were you thinking of using?

 

[bigsparks]

@ Worcester

I did 2372 training at MGS in Surrey, the training I recevied was not the best, hence, the question on the forum. Why do you ask?
I am aware there are twin MPPT inverters on market but wanted to see how other installers had overcome the same problem and then maybe decide best course from there on.
I have used SMA inverters various sizes on our existing installs. These installs have been straight forward systems Ie single roof space all facing same orientation and we used SMA inverters with single MPPT's.
I may be an easier solution to use 195w panels throughout to negate the need for a twin MPPT inverter and leave the SMA to invert to its optimum MPPT.

 

[MikeXl426]

This won't work even on a single MPPT inverter. They are different aspects with different string lengths. As Worcester says, dual MMPT or 2 inverters.

Mike

 

[bigsparks]

@ Worcester
Looking into it, the smallest SMA inverter they have with twin MPP is the 4000TL-20 which will be too big for the systems. Will probably look to fit a SMA SB1200 & SB1700 on each orientation.
One last question, when doing this, my assumption is that there will still only need to be one dedicated circuit at the CCU, looping between the AC isolators and one feed in meter???
Thanks for guidance