[kalium-xyz]

You ever see those projects where they generate biofuel from algae growing ontop / against building using special build tanks? Its really cool.

[bubblewrap]

Cool, but also energy efficient?

[anoncake]

It certainly beats bare roofs. AFAIK photosynthesis is still more efficient than photovoltaic, too. In any case, it's easier to store biofuel than electricity.