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Several months ago I installed a 10 panel 4kWp array on my garage roof, tied into a 3.6kW Solis inverter.
Performance has been good, but now that we're firmly on the way towards the winter the 5 degree pitch is rapidly losing ground.
Normally I'd shrug and just accept the drop off in performance, but that would be far too easy!

Instead, thoughts turned to the front wall of my house....
Facing almost directly south with extremely low shading, it could be a great winter PV addition.
Measurements indicate I can fit 3 panels in landscape between the ground floor and upstairs windows, spanning the full width of the house. I did consider the upper gable wall, but structural concerns and access issues have put me off.

So, I put in an order for 3 Longi 405w panels from ITS, ready to experiment further. These arrived yesterday with no damage and ready to go.
Of course, nothing is always quite as simple as it might appear...


The main issue I needed to check was how well this would work with the Solis inverter.
The garage array used 1 MPPT, leaving the second for the front wall which is great. Unfortunately, the datasheet indicates that the start-up voltage is 120v, above the 90v or so the new array will produce. Additionally, it's only just at the very edge of the MPPT range.

I'm expecting this to be ok though, as I've seen the Solis start the main array at 75v every morning.

I set the panels up temporarily, leaning against a wall and facing the house on an incredibly cloudy day - basically worst case scenario.


Connected them to MPPT 2, turned the PV isolator back on and... it's alive!


The graph shows how the new array settled at about 90v, only dropping down when I used the PV isolator to kill the main array


It looks like the Solis can indeed work with just 90v of panels, I assume the higher start-up voltage on the datasheet is to cover situations where the inverter has no DC input power from batteries, and is 100% solar powered.
As you can see, the performance of both arrays is dire today but that's entirely down to the weather.

The next step is to finalise the mounting design on the front wall and get them up there!

Many inverters will "start up" when one string is above the threshold and the 2nd string doesn't need to meet the threshold so long as it is within the MPPT range.

Stinsy wrote: ↑Wed Nov 16, 2022 12:53 pm Many inverters will "start up" when one string is above the threshold and the 2nd string doesn't need to meet the threshold so long as it is within the MPPT range.

That was my thought as well, but after disconnecting both arrays but only reconnecting the three panels at 90v, there was no issue.
Bodes well for days where the rear array may be fully shaded and only the front wall is getting sun.

The open circuit voltage of those panels may well be around 120V so would still likely kick the inverter into gear as long as the operating voltage remains high enough to fit within the MPPT range.

My SMA inverters even work well below the bottom of their spec'd MPPT range.

And your project is part of what this website is about.

More photos as it progresses, please.

Some progress made today in between the heavy rain.
I've run the 2 core 6mm SWA from the front corner of the house, along the side, down to under the rear decking and into the garage.
The wiska box at the front is ready to accept the MC4 extensions, plus the garage has been fitted with a DC isolator.

The solar mount framework should be finished this week, then I should be able to enjoy some extra generation.
Pictures to follow once I have better lighting.

Finally, it's up!


The mounting system is a bit of a different approach, simply because I wanted to bring the panels away from the wall to avoid any shading from the 20cm deep eaves when the sun is at an angle to the wall.
I used some hangers and truss clips that were left over from another project to bolt 4x2s to the wall, then mounted a wooden cleat along the length at the top.


The panels have a corresponding cleat bolted to the back, so simply drop down into place. I used some glass suction lifters to manhandle the panels up, but I'm glad I shelved the upper gable idea...


There's another wooden rail bolted to the bottom of the panel which is fixed to the uprights. Screws through the cleat also lock the panels in place, giving me secure fixings top and bottom.

Alas, I only got it wired up and turned the DC isolator about 10 minutes before the sun starts to drop behind neighbouring houses, but I did see a peak of 500w in that time. Fingers crossed I'll get some meaningful winter generation and can reduce the grid charging of the batteries.

Looking good.

Looks very nice and secure.

Very nice!