Measuring performance is very difficult to quantify as I have no monitoring facility set up so I can only go on infrequent observations of the differential controller temperature read outs for the upper and lower tank temperatures, the Solar pump is on/off or the boiler is on/off. I will at some stage install a low power consumption monitoring device so that more accurate information can be obtained.
Since installing in late July and during August and mid September I would say that the boiler rarely kicked in so the panels were supplying 95% of my domestic hot water, this tailed off to the winter months. During the winter months it is fair to say that on a clear day, i.e. no clouds the panels could get up to 60 degrees C even when the outside temperature was at freezing 0 degrees C however this would only be for a few hours but it was sufficient to heat the lower tank from 10 to 35 degrees C.
So far I am very pleased with the results and am keen to see what happens in the coming months especially June as historically this is a hot month.