Solar Energy

Solar energy accounts 99.9798 percent of our total energy income. This amounts to 13 x 10²³ gram-calories/year or a continuous power supply at the rate of 2.5 billion, billion horsepower. Between .4% - 5% of solar energy is used in photosynthesis to feed the metabolism of the biosphere.

Plants use ± 1/6 of the energy they take up for their own metabolism—making about 5/6 available for animals and other consumers. About 5% of this net energy is dissipated by forest and grass fires and by man’s burning of plant products as fuel.

When an animal or other consumer eats plant protoplasm, it

1. uses some of the substance for energy to fuel its metabolism and some as raw materials for growth.

2. discharges in brokendown form metabolic waste products, e.g. animals excrete urea; yeast (anaerobic) ethyl alcohol. Other consumers may use this waste—flied and dung.

3. passes some ingested plant material through the body undigested.

Of the plant protoplasm herbivores succeed in extracting only about 50% of the calories but only 20-30% is built into protoplasm (meat)—net efficiency 10-15%. Meat eaters do a little better—carnivores can use about 70% of the meat for internal chemistry since there is less indigestible matter. But only about 30% goes into building tissue—hence net efficiency about 20%.

1000 calories stored by the algae in Cayuga Lake can be converted into protoplasm amounting to 150 calories by small aquatic animals. Smelt eating these animals produce 30 calories of protoplasm from the 150. If man eats the smelt he can synthesize 6 calories worth of fat or muscle from the 30. If he waits for the smelt to be eaten by a trout, the yield shrinks to 1.2 calories (people on diets fish and fowl).

The lower on the food chain we eat the greater the number of calories available. The longer the food chain the greater the mass necessary to sustain large organisms.

Lamont Cole, The Ecosphere, Scientific American, April 1958