A little research says that if he has this thing (UVB sensitivity) then it can lead to carcinomas or cancers on his ears. Could mean amputation. But there's basically no treatment besides "keep them away from sunlight".
It seems to be the best suggestion though... Everything else is...
4 years ago my kitten went to the vet with a sunburn-cum-ear infection. He was deemed to have no mange, no ringworm, no mites. We treated him, and for the next two years he was fine, although he got crusty every spring/summer.
There's never anything wrong with him. He's going for his yearly...