I remember some old threads about fitters forgetting to connect a string etc on PV installs and didn't fancy waiting year/few months to check performance.

So using pvgis (thanks Damon) I calculated the clear sky irradiance of the two 45 degree inclination arrays 1.75kW SSE(-11) and 2.25kW WSW (-79) for May.

The pvgis fixed plane clear sky irradiance is multiplied by panel efficiency (15.4%) x panel area (1.6m2) x no of panels (16) x non-panel system efficiency (90%). The the two aspects summed for each time interval.

This only holds for a perfect cloud free days so I was rather chuffed when day 1 was the start of our mini heat wave!

The only fudge factor is the non-panel system efficiency (inverter + wires + panels getting hot + etc) which pvgis suggests as 86% but I got a better fit at 90%.

So it seems at a first (and arguably second) order pvgis is a very good predictor of clear sky irradiance and that my array(s) 'does what it said on the tin'.

Now it just 'weather' to investigate - I think I should hold off for a bit before making any impressive claims for annual yield based on the 5 days since install..

No idea where you are, but I would expect 95% of the time your output will be between Red and the Green lines.

Could be allowance for horizon effects.

I get some very early morning shading even now from a tree a considerable distance to the north east of us.

Rgds

Damon

Diffused light can be quite deceptive. Sometimes it is possible to get more power by pointing a panel directly upwards (how solar data is collected) as then, regardless of the time of year, as soon as the sun is up, some light is being collected.
Keep wanting to test this more to find out how much difference it makes over a year.