Is it possible to use solar power to operate my uncle's pacemaker

It's possible but silly.
He would have to have some solar cells on his head. He has to always be in the sun or under a bright light or his heart stops. At night he has to sleep with a bright light shining on the solar cell.

And he has to have wires from the solar cells through his skin to the pacemaker, always a source of infection.

All this to save a battery that costs a few dollars?

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