Algae and Cyanobacteria tend to be substantially more efficient than whole plants (6-8% [1]). There are some caveats though. Generally the industry has found it hard to grow algae at commercial scale cost-effectively for several reasons including (but not limited to):

- Contamination by outside organism kills your algal culture

- If you create a closed system, the algae will stick to the glass, fouling the surface and reducing light transmission

- Extraction of materials from the algae is hard, you end up with a lot of water weight you need to get rid of somehow

There are also some counterintuitive aspects in that apparently dropping the efficiency of the antennae (light collection) actually makes the overall culture more productive because excess light makes it past the initial cell layer and therefore other cells can benefit from the light. Otherwise the initial cells grab all the light they can, and waste whatever light energy they don’t need.

I think it’s an interesting field, but so far it’s been a hard road to make it actually work at scale cost effectively.

[1] https://www.sciencedirect.com/topics/chemistry/photosyntheti...