Cultivation of microalgae using natural and man-made open-ponds is technologically simple, but not necessarily economical per unit of biomass produced, owing to low productivities and problems with contamination. The need to achieve higher productivity and to maintain monoculture of algae led to the development of enclosed tubular and flat plate photobioreactors. Principles and methods of using PBRs to cultivate algae are discussed in this chapter

1. Photobioreeactors are considered to be the most feasible option for cultivating algae in a large scale for fuels, as they offer the promise of high productivities of desired strains.
2. The design choice of the PBR is the most important consideration for light penetration and distribution, and a number of research efforts are being carried on in designing photobioreactor.
3. Commercial scale-up should be a primary design criterion for photobioreactors.
4. Currently (as of Apr 2010), photobioreactor costs range between $70-150/m2.
5. The key challenges for photobioreactor use are the high capital and operating costs, which currently make them unviable for producing feedstock for biofuel.
6. While the costs of setting up and operating a photobioreactor would be much higher than for those for open ponds, the efficiency and higher oil yields from these photobioreactors could be significantly higher as well. Higher productivities and lower costs in future could potentially make these systems much more competitive in the medium and long run.