Have recently installed a solar panel, 30 evacuated tubes, to heat the domestic hot water. Since the thing has been up and running we've had some quite good suuny days and I have felt some heat, very slight heat at that, running through the pipes. I was thinking of attaching some type of temperature probe onto the inlet of the hot water cylinder and monitor the temperature by just taking a glance at the reading whenever I think of it.
BUT, this is where you come in. If you can think of another way for me to monitor the efficiency or point me in the right direction I would appreciate it.

I would also like to say that I am not that impressed with the solar panel so far!!