Wind – Sea – Algae Offshore Algae Cultivation for Biofuels and Beyond

It is argued that algae cultivation need not compete with agriculture, because the algae do not require fertile land, but only places with adequate sunlight and supplies of water (fresh or salt water), nutrients, and an infrastructure for harvesting and processing. Current efforts to produce algae in the US are all focused on land-based systems, either open ponds, referred to as “open raceways,” or closed bioreactors, consisting of arrays of clear tubing or flat panels. The major costs associated with both of these systems involve:

* Land
* Water
* Open and/or closed photobioreactors
* Electricity
* Nutrients, including CO2
* Maintaining cultivation conditions
* Harvesting and dewatering algae biomass
* Processing biomass/oil

Raceways are considered the more economical systems at approx $40,000/acre, while the current designs of closed bioreactors on land are estimated to be close to $1,000,000/acre (Benemann 2007: Algae Biomass Summit; Seattle). Some disadvantages of the open raceways however, are lower yields, evaporation, and intrusions of ‘weed’ species. These are not problems with closed bioreactors, but the current closed designs have problems with scaling to sufficient size for biofuels production, temperature control, and biofouling limiting light availability; all of which impact the economics of their use for algae production. In both systems, water is going to be a major issue in the future. There are marine algae that produce oil and there are coastal lands or salt water aquifers in many areas of the US that could be used to cultivate algae. Pumping salt water from the ocean or from salty aquifers is energy intensive however, and in open systems the problem of evaporation remains; if the salt concentration gets too high, the algae die.

The question of where algae farms for biofuels should be located is an important one. In addition to the need for water (salt water for growth and freshwater for maintaining the right salinity), there is the need for adequate sunlight and a supply of essential nutrients, including CO2. Both the freshwater and the nutrients can be supplied by municipal waste water, but algae farms should not be too close to cities for the same reason pig farms should not be too close to cities: they will smell bad. As the distance between the algae farm and the source of nutrients increases, the issue of plumbing and pumping or trucking impact the economics of the farms.

The growing need for oil and the potential productivity of algae are driving significant investments in addressing the challenges for their cultivation, but most of the current effort seems to be focused on perfecting some land-based system and there has been little discussion of moving algae cultivation offshore. Clearly, many of the problems with land-based systems disappear offshore (e.g., space, water, mixing, temperature control, and nutrient availability). There are new problems with infrastructure, access, ship costs, tracking, marine traffic, environmental impact, durability, control, harvesting, processin, and so on, but are these and other imagined problems so formidable to eliminate offshore algae cultivation as a possibility?

It is the purpose of the Wind, Sea, and Algae Workshop in Lolland Denmark, April 20-22 to address the question: Is it possible to produce algal-based carbon-neutral biofuels for the world offshore?