The hardest thing about algal fuels is keeping your bioreactor working at peak efficiency. This is quite difficult, consider the following: Problem: Outside or

The hardest thing about algal fuels is keeping your bioreactor working at peak efficiency. This is quite difficult, consider the following: Problem: Outside organisms keep contaminating your pools of algae. Solution: cover them up. Problem: your reactor surface keeps fouling Solution: open it up and wash it Problem: Now you gotta clean the whole thing to make sure you don't have contamination Problem: some parts of the pool are far denser in algae than others leading to inefficiency Solution: pump/stir it! Problem: now you have to move huge volumes of water. Plus your equipment could foul/breakdown Partial solution: solar powered pumps. Fouling still an issue though Problem: Organisms raised in water take a lot of water with them for the ride even when you spin/filter them out for harvesting Partial solution: Dry it out with energy, maybe more sun? Now you need more space. After all this you have to wonder whether the cost and additional energy invested leaves you with enough left over to make sense. It's not impossible, and I believe it's the only real way to a sustainable future, but it's really, really, really hard to scale these things up.