They're easy to scale in some sense (just make a bunch of small ones), but small reactors have a high surface area to volume ratio -- i.e., a high expense to al

They're easy to scale in some sense (just make a bunch of small ones), but small reactors have a high surface area to volume ratio -- i.e., a high expense to algae ratio. Making bigger vats is problematic because the work being done is proportional to surface area (light penetration) and because the chance of infection goes up exponentially.