Questions about strings/shading/inverters etc...

[stan321]

Hi, I'm thinking about installing a 4kw PV system to my house but after looking into it in a bit more detail I'm more confused than ever as to the best way to have it set up. My house/roof is as you can see in the picture and there will be 9 panels to the left and seven on the right.



Questions...

1. Because there will be some shading from the rest of the roof, especially in the winter (on the left side in the morning whilst the right side is in full sunshine and vice-versa), would I be right in thinking that I would be best off with 2 separate strings?

2. Because, due to availabe space, the strings are uneven i.e. 9 and 7, am I right in thinking I will need an inverter with two MPPT's?

3. Or would I be best just going with 1 string?

I'm new to this so any help and advice would be very welcome!

Thanks
Stan

 

[SolarCity]

1. Absolutely, and I'd strongly advise you to install them on two seperate MPP trackers.

2. Definitely. Although installing on two seperate inverters is also an option - as are micro inverters or power optimisers.

3. No.

 

[Earthstore]

From the drawing, your panels are too close to the ridge and too close to the gable ends, ideally you should be 500mm from all the edges of the roof, as to the Inverter, you would need one that has two mppt that will except unequal strings, or have two smaller inverters which sometimes works better (lower start up voltages)
If the S/E roof is yours and you could fit your desired 4KWP system on there, that may be a better bet for performance.

Many people try to install the biggest system possible on their roofs, however, sometimes a slightly smaller system can offer you a better return, if it removes shading issues, which, some companies neglet the fact that shade can be the kiss of death for performance.

Are you designing this yourself or are a company doing this for you?

hope this helps.

 

[BruceB]

The south east facing roof looks large and one to consider putting panels on.

 

[SolarCity]

ideally you should be 500mm from all the edges of the roof.

Personally I go to 300mm.

 

[stan321]

Solar City - Thanks, that's what I was thinking but good to have someone confirm this. Would the 2 smaller inverters be the better option in this case or does that depend on other factors?

Earthstore - Sorry should have mentioned the picture is just an rough illustration of the house orientation etc, the other roof is part of our house but as it is more ESE I was advised it wasn't the best option but I'm open to opinions (See pic below for angle of sun/shadow at noon yesterday).
I'm not designing the system myself but I have had a company suggest a single string which, after some research, I didn't think was the best option. Trying to make sure I don't end up with a system that isn't optimal.

Thanks for the help.

 

[dansk]

i would keep looking for an optimal company if there suggesting one string!

 

[Earthstore]

I would take the advice of Dansk if I were you.
Why they are suggesting fitting to the small roof areas is quite beyond me, if fitted 300-500mm from the gable and ridge, looking at the photo you would be able to fit, maybe, 3 x 250w panels, and due to the pitch you would get shading issues, and to suggest conecting one string is quite unbelievable.
You have a nice, large roof there, OK, it is ESE, so it would perform at around 10-15% less than a south facing, but what you have been suggested would probably perform at 50% less than a perfect south facing.
If you state where you live, I am sure one of the experts on here would visit to advise you.

I hope this helps.

 

[stan321]

Ok looks like the best option would be on the large roof space above the garage door.

The roof faces approximately 120-130 degrees from North and the the pitch is 45 degrees, which should give around 90% of maximum output if I'm reading the graph on the PV Installation guide I found on a 'sticky' correctly.

Does this sound about right?

Stan

p.s. I live in the North East of Scotland between Aberdeen and Inverness if anyone local wants to come and look at the job.

 

[Earthstore]

Too far for me, but I am sure someone will PM you.

The good news for you is if they post on here you should be assured a good job at a fair price or the other wolves on here will tear them apart.