This is not necessarily the way that algae are going to be optimally grown. I used the idea of a weeping algae to overcome one of the harvesting problems - there are ways of harvesting, but I wanted to write a story that was relatively short and uncomplicated, and so invented this method to make the lipid separation easier. There are however validated ways of increasing algal yield, I just need to go through the conversion process to see where the gain is achieved, there are at least two different possibilities and so either I or that mythical student will have to do a little more homework.

Well, my next suggested probable limit would be that only 50% of the spectrum is photosynthetically active in chlorophyll based systems. I HAVE heard that there are filters that can be put in place that absorb non-usable frequencies and re-emit them at usable frequencies, but those have inefficiencies of their own and are a leeetle pricey.

Is that 50% by wavelenght bandwidth or 50% of radiated power?

Obviously, chlorophyl does not use green light and reflects it as a waste.
If we managed to develop black chlorophyl, that would be great.

Also, I see great solar energy loses in evaporation. If the oil film itself cannot contain it, we'll need to build a greenhoise for the algae or keep it in glass pipes.

The next problem is thermal management. Warmer environment likely increases photosynthesis rates. However, cooked algae probably refuese to work. If we cannot manage heating or cooling by some simple means, such as mass of the water or controlled evaporation, there will be large energy loses on HVAC.

I see 2 natural means of thermal management:
1. Thermal capacity of large amount of water
2. Photosynthesis itself should have cooling effect, since it is energy taken. So at hight temperatues the increased rate of photosynthesis should sel-regulate temperature. But we need to keep the system at or below peak photosynthesis rate. If we blow past it, lots of added cooling woud be needed just to keep algae alive.