It's a fascinating idea. Great for endurance sports, especially when oxygen is a limiting factor (swimming, cycling in the mountains).

But wouldn't it require being naked outside? And you'd probably feel unwell if you weren't in the sun. Maybe you wouldn't need to be naked if you had branches with leaves growing out of your shoulders.

Biohacking will be necessary to survive in desert climates after a few degrees of global warming. Photosynthesis might help; plants use water so inefficiently that it's a form of sweating.

We don't have to become green, by the way. Any pigment can be used to capture light. There are red, brown, olive-green and even neon-blue algae.