is possibile to fork the bitcoin blockchain and change it checking if the pow is created from a clean energy?
It isn’t possible because there’s no way for other nodes to check the source of energy used by an anonymous member of an anonymous mining pool.
A connected clamp meter maybe to check if it’s clean energy?
A clamp meter measures current, it can’t tell you anything about the power source of the generators that provide that current.
Other nodes have no access to that clamp meter and cannot tell if it is accurate.
Remember that a fundamental part of a peer to peer cryptocurrency that is like Bitcoin is that nobody has to trust what miners tell them.
At the very least, it is an immense job to make anything of this sort bulletproof enough to be usable.