Tapping The Sun With Biomass

Mitch Jacoby's excellent article "Tapping the Sun" about state-of-the-art solar cell R&D (C&EN, Aug. 27, page 16) is clear and inspiring.

The article is about conventional solar cells, but the process used to build solar cells is not very energy- and materials-efficient. It probably will not be efficient for a while even if or when organic materials are used. In that respect, nature's living solar cells, commonly called biomass, seem to have much better potential, particularly from a sustainable development perspective.

The problem with biomass is that it has a terrible conversion ratio, which varies from less than 1% to, at best, 5%. Most researchers in the field agree that the conversion ratio could reach 10 to 15% if plants were optimized for energy conversion and storage. Doing this through the intensive use of chemicals wouldn't make a lot of sense, as David Pimentel and others have tried to demonstrate in the case of the corn-to-ethanol conversion. But it would make sense if biotechnology were implemented to build protection from parasites and air or soil nitrogen fixation mechanisms into the plants.

As emphasized in the article, the sun is "showering Earth with an energy flow of 120,000 terawatts (TW)." With a 10% conversion ratio, this would give 12,000 TW. Of course, this is totally unrealistic because we need some space to live, be able to move, enjoy nature, and produce food. But 1% would still be 120 TW, which seems reasonable for a world population of 10 billion people who know how to use the energy they have.

Because biomass production relies primarily on water as well as solar energy, it would be wise to put the vast ocean surface to work, probably somewhere between the tropics, to produce this biomass.

It would be interesting to read a state-of-the-art article describing the various publicly and privately funded initiatives in this very promising area.

Jean-Paul Vignal
Argyle, Texas