Just to inform any of you willing to build a thermal solar collector with simple materials, controlled by Arduino.
Project ARETHA http://www.meteoenergia.it/aretha/index_aretha.htm
intends to provide instruction and sharing experiences on this subjects.
We have also launched a funding campaign to build one ARETHA with recycled material in Sicily, see:https://www.indiegogo.com/projects/aretha-project#home
I can provide any other information about this project. It is an open one.