Today was bright, though somewhat hazy for much of the day. However, it was still our best day so far from the point of view of collecting solar electricity. The peak output of our 2.3kWp system was 397 W, and the total power generated was 1106 Wh.
I mentally batted around some figures, to see if I could calculate from this whether the estimates made by the installing company were reasonable. We are at 50° north (near enough), and since we are at the winter solstice (near enough) the Sun was at 22° south. That means the highest it gets into the sky (at noon) would be to an elevation of about 18°. In the summer, with the sun at 22° north, it will reach an elevation of 62°. Assuming the relative amount of incident radiation varies with the sine of the angle of elevation (from zero at 0° to 1 at 90°), the sun will be (0.883/0.309), 2.85 times more intense on the basis of its angle of elevation in the summer. With the sun flatter in the sky, its radiation will also be attenuated to a greater extent by the depth of atmosphere through which the light has to travel. The modelled estimate of a 1600-1700 W or thereabouts peak in the summer - around 4 times the level we saw today - seems to be a sensible ballpark. We shall see.