ENERGY FROM ALGAE

Since solar energy comes in at a density of little more than 1 kW/m^2, there is essentially only one way of using it economically for large-scale energy production: man must tap only what nature has collected. Nature has been busily collecting solar energy over millions of years in what we tap as fossil fuels, and over millions of acres in what we tap as hydropower.

Food production is, of course, more than mere energy production. But even when a crop of "biomass" is raised simply for burning it or otherwise extracting its energy, this difference against hydropower or fossils remains, and it is therefore unlikely that biomass can economically compete with concentrated fuels. Even under highly favorable conditions, such as refining ethanol as an automobile fuel from jungle plants in Brazil, biomass has been less than a resounding success, and the fuel is considerably inferior to gasoline. The "gasoline tree" (euphorbia) grown especially for this purpose [AtE Feb 77] is still in the research stage, and unlikely to be revolutionary. And various schemes of burning wood, while fulfilling the emotional needs of the "Split wood, not atoms" crowd, have proved not only inefficient, but also a significant health hazard through air pollution.

A more sophisticated way of collecting solar energy biologically is to grow algae that can be induced to form fatty substances suitable for refining into petroleum products.

So by starving them you make them grow fatter? Only in a sense: by limiting their food, you make them form a higher percentage of their body weight as fat.

A typical algal mass has a heating value (heat produced by combustion) of 8,000-10,000 BTU/lb, which is better than lignite; but the heating value of algal oil and lipids is 16,000 BTU/lb, which is better than anthracite.

Another species of freshwater algae, Botryococcus, is thought to be responsible for present petroleum reserves, for it is capable of synthesizing hydrocarbons. It is hoped (but not yet certain) that the hydrocarbons extracted from this and other species can be readily processed by the present petrochemical industry to produce gasoline and other petroleum products.

The Solar Energy Research Institute (SERI) in Golden, Colo., has an intensive aquatic-species program and last year isolated 320 strains of microalgae, of which five were identified as accumulating more than 40% lipids.

SERI estimates the cost of liquid fuel from algae at the present state of knowledge at $250 to $350 per barrel, but hopes to reduce it to $60 to $85 per barrel by the year 2000, and regards that as a competitive price.

[More. SERI Research Update In Review, June 1985, SERI, 1617 Cole Blvd., Golden, CO 80401; Aquatic Species Program report SERI/PR-23102659, $8.50 from NTIS, Springfield, VA 22161.]