interesting video. JA 280W panels are bit low spec these days but a good panel none the less. As for the inverter, I'm not a fan of Solaredge where you don't have shading issues, it costs more than 1-2% higher output is worth on non-shaded roofs. I will now try to explain the inverter under sizing.
8 years ago, when I first started installing solar systems, many inverters were still transformer types. The efficiency of these could drop to as low as 70%, so to compromise for loss of performance in lower light level weather conditions, it was advised on all the training courses, to under-size the inverter by up to 20%. You lose some of the perfect weather performance but gain at all other times to give a higher annual yireld. However, since then inverters have improved an awful lot, and the current Transformerless designs maintain efficiencies as high as around 94%. This makes the advice previously given a non-sense, but most companies still do it, because smaller inverters are cheaper, and I don't think anyone has changed the training courses? I now prefer to size inverters on a like for like basis, ie 6 kW for 6 Kw of panels, or perhaps slightly larger, say a 6kW inverter on a 5.8kW set of panels. The panels are +ve tolerance, so in reality they can output up to 3% more than expected anyway, and I've also found Japanese panels will go higher than the max tolerance stated. Panel outputs are interesting, German do exactly what they say they will, Chinese do what they should, just, Japanese outperform the stated figures. It's a cultural thing, the **** would rather you be happy with a better than expected output so slightly understate the performance.
