Some years ago, the efficency was at around 1 % vs. 20% with solar panels, meaning you would need 20× the space, meaning only dessert areas and big scale production worth it. And since no one did it big scale yet, means it is economically not worth it yet.

But the cost of further algae itself are zero, which makes the idea attractive in theory. Like I said, there is a breakthrough required in efficency, or some cheap big scale production/deployment system.