products 



Figure 2. Energy flow model of wood and coal as fuel sources for a foundry. 



such as sun, rain, and wind are used to power the crop growing process. The 

 farm production consumer system contains equipment which is used to cultivate 

 the soil and harvest the crop. The harvested crop exported from the farm sys- 

 tem produces a flow of money into the farm in a direction opposite to the flow 

 of exported energy. The money derived from the sale of produce is stored in 

 the money storage tank. The stored money consequently is used to purchase 

 fuels, goods, and services necessary to operate the fanm. 



For any nation, the ratio of dollar flow to energy flow, for a particular 

 year, may be calculated by dividing the sum of all natural and fossil fuel 

 energies entering the nation by the nation's gross national product. For 

 example, in 1975 24.56 x 1015 calories of energy were consumed in the United 

 States, whereas the gross national product was 1,526.8 x 10^2 dollars. This 

 calculation produces an energy to dollar ratio of 16,100 calories per dollar 

 (Figure 4) and shows the ratio of embodied energy flow to gross national 



282 



