(C)1995 Institute For Ordinary Research*
Rob Peterson, Director
Timekeepers have long marveled at the fruit-powered chronometer -- two metal electrodes stuck in an apple which powers a wristwatch-sized digital clock . The Institute For Ordinary Research has been asked to take a look at fruit power in the hope that in addition to being timely, it may show promise for the world’s energy needs. Consider a 100 gram apple:
If all the apple’s mass were converted to energy, its yield would be the equivalent of over 2 million tons of TNT. This is certainly not Ordinary, so the Institute will limit itself to less Advanced forms of energy available from this fruit.
In the diet books, a nice, juicy apple is listed as containing around 100 (food) calories. A food calorie is actually a kilocalorie, or 1000 of the calorie units used by the scientific folks: the energy required to raise the temperature of one gram of water by one degree centigrade. So, the 100 kilocalories available from the apple can heat almost a quart of water (1000 grams) from near freezing to the boiling point. One Institute staffer mused that it is a good thing that it takes a while to digest an apple. Otherwise, it would really overheat the gut. This same energy, if used to lift the fruit against gravity, would raise it to low-Earth orbit altitude -- around 250 miles high. Thus we see that the chemical energy in an apple is not inconsequential.
Unfortunately, virtually none of this chemical energy is available to run the timepieces or other engines of the real world. The dissimilar metal electrodes provide the electrical energy for the clock while the acid in the apple acts as a catalyst, providing the electrolyte to make the reaction go. Pat Porter of Houston, TX has "generously donated" to the Institute an apparatus having two sets of brass and zinc electrodes and a small LCD digital clock along with a stand to hold two pieces of fruit. Two small apples were wired up and the clock runs nicely. (click here to see IFOR apparatus in operation.) The voltage generated from each apple-battery was measured to be 0.95 volts (the two apples in series generate the 1.9 volts required to run the clock). Assuming that about 2 ounces of zinc (and brass) could be stuffed in the apple, the migration of all of the zinc to the brass electrodes (via the apple juice electrolyte) would produce 8000 joules of electrical energy. This means that 450 apples (not to mention all the metal in the electrodes) would be required to produce one kilowatt-hour of energy which costs approximately 8 cents from the light company. Clearly, the price of apples must fall before civilization can begin conversion to this Ordinary source of power.