And crucially heat decreases their efficiency although not normally by
factors of two. You should measure peak output when the sun is aligned
with the axis of your collectors (roughly same time each day).

Then you have a comparable number. It is possible you have a dodgy panel
that is misbehaving under thermal stress or they are covered in pollen
and dust at the moment.

Any partial shading of the array severely compromises output.



Must post up a pix somewhere. A neighbour has had his roof adorned with
panels and a nearby tree casts a large shadow across them, be
interesting to see just how much that reduces the output..

Must ask the council if they would be permitted to take it down as it is
in a public road...

--
Tony Sayer