The most natural method of growing algae is through open-pond growing. Using open ponds, algae can be grown in sunny areas of the world.

Open ponds are the simplest of algae growing systems. An alternative to open ponds are closed ponds where the control over the environment is much better than that for the open ponds. Closed pond systems cost more than the open ponds, and considerably less than photobioreactors for similar areas of operation.

This chapter discusses the various merits and demerits of open and closed pond cultivation and the variations and types of open ponds and closed ponds.

1. Open ponds are attractive for algae cultivation owing to their low capital and operating costs.
2. The most popular type of open ponds used for algae cultivation is the raceway pond.
3. The key challenges for algae cultivation in open ponds involve contamination, light penetration and water evaporation.
4. To get away from the challenges faced in open pond cultivation, some companies are attempting hybrid algae product system - cross between open and closed pond system.
5. A number of companies are trying out with open pond systems and in many cases, with the much more expensive photobioreactors.
6. Closed ponds are expected to provide better control over the environment than open ponds while costing much less than photobioreactors, but few companies are exploring this route.