Although the production of Chlorella looked promising and involved creative technology, it has not to date been cultivated on the scale some had predicted. It has not been sold on the scale of Spirulina, soybean products, or whole-grains. Costs have remained high, and Chlorella has for the most part been sold as a health food, for cosmetics, or as animal feed.[7] After a decade of experimentation, studies showed that, following exposure to sunlight, Chlorella captured just 2.5% of the solar energy, not much better than conventional crops.[3] Chlorella, too, was found by scientists in the 1960s to be impossible for humans and other animals to digest in its natural state due to the tough cell walls encapsulating the nutrients, which presented further problems for its use in American food production.[3]