Someone mentioned legal action...? what the hell you cant sue someone/take them too court for doing you a favor effectivly. (Seen as he hasnt been paid)
Yes, you can when this amount of damage has been caused to around £120 worth of panels by somebody who is being paid to fit them
Its like asking your mate to come and fit a kitchen unit, he sliped and makes a piece too short so you take em to small claims and persist they buy you a new bit!
If a mate came round to help he wouldn't be asking for money to help usually and if it was me i would be buying a replacement if it was me that damaged or rendered the part unusable.
It dosnt happen!
Believe me, it does happen, you'll see when you reach the adult world
And i fully agree that this should be closed for it to be sorted out to the OPs satisfaction, good luck to him.