Algae refers to to a variety of species which live in water and often process sunlight, nutrients and carbon dioxide in order to survive. Some species produce hydrogen in the absence of sunlight while others due to their high lipid content can be harvested to produce up to 300 times more oil per acre than conventional crops. There is a limiting relationship between growth time and lipid content that at present hampers production capability. With Hydrogen production there are risks and hazards which have yet to be fully overcome.
- Pond farming
- As algae naturally grows in rivers, lakes, ponds and the ocean it can be harvested from these areas. Algae however are environmentally sensitive creatures and as such growth rates are strongly affected by external variables such as temperature, available sunlight, dissolved oxygen content, available nutrients, interspecies competition, pH and so on. Pond farming, or harvesting directly from nature, is therefore less reliable than a 'closed-loop' system where certain variables can be more carefully controlled. Open pond systems with monoculture algal production are also susceptible to viral infection.
- Closed Loop / Vertical Growth farming
- Algae are stacked vertically to maximize light exposure and nutrient delivery [Image:http://static.howstuffworks.com/gif/algae-biodiesel-5.jpg%7Cframe%7Cimage-1]. Water is often recycled and thermally controlled. After the growth phase is exhausted the Algae are harvested and converted into oil. The remaining portion of the biomass not converted into oil can be recycled to some extent also [Image:http://static.howstuffworks.com/gif/algae-biodiesel-6.jpg%7Cframe%7Cimage-2].
For those species which require light-free or oxygen-free environments different approaches might be needed to maximize production value.