The most efficient algae production

I conjecture. Grow the algae all the way to mature protein and ferment in a separate process. I think we get less light blockage if we fertilize and grow the optimum path to maturity, smaller , more spherical cells? More compact energy? Dunno, not sure.

But it brings up the subject, can I do this on a gulf sea farm, say with my 40 acres of algae bag? If I drug out a barge with a working still, then I am in business, delivering $40/acre/day in alcohol. Keeping the still close by closes the loop, and nutrients are recycled. Plus I get my own fuel for the generator.

The bag here should be simple, flow the algae through till it reproduces and fill with mature protein, then flush out to production still, just in and out.

We would select for an algae strain that grew rapidly to a simple protein, then exited the system. The algae would be matched to the fermentation enzyme. The ocean temperature along the gulf is so low that energy input is minimal for floating tanks. The still costs will be fixed at $500/acre.If the farmer is producing fuel ready alcohol at the 'well' for $2/gallon, then he is wealthy.

But look, there is more:

Plants that produce ethanol by fermentation generate cool, essentially pure CO2 that can be pumped underground.[6] WIKI 

The system allows recyling of CO2.

There is going to be a huge variety of methods and bags and pumps and filters and strains and post-processing. The economy of scale is in keeping the initial plastic bags simple and durable, then rely on the ingenuity of the algae farmer.