ENERGY FROM FOSSIL FUELS HUBBERT 267 



If, as the coal-mining engineers intimate, the amount of coal is 

 much less than herein assumed, so much smaller will be the area under 

 the curve and so much sooner the approach to exhaustion. How soon 

 the decline may set in, it is not possible to say. Nevertheless, the 

 higher the peak to which the production curve rises, the sooner and 

 the sharper will be the decline. 



WATER POWER 



The exploitation of water power, like that of coal, is of fairly 

 ancient origin, but also, like coal, until the last half centui^ its utiliza- 

 tion has been small. Unlike fossil fuels, however, water power repre- 

 sents a fraction of current solar energy, which changes but slowly 

 with time and is being continuously degraded into waste heat irre- 

 spective of whether it is utilized or not. 



A growth curve of the utilization of water power, therefore, should 

 rise in a manner similar to those of the fossil fuels, but instead of then 

 declining to zero it should level ojff asymptotically to a maximum as 

 all available water power is brought into utilization. At least this 

 is physically possible. 



In view of the eventual exhaustion of fossil fuels, it is of interest 

 to know to what extent water power can be depended upon to replace 

 them. In table 2 are listed the installed water-power capacities of 

 the various continents for the year 1947 and estimates of their total 

 potential capacities (13). In addition, the number of kilowatt-hours 

 of energy that such capacity should produce per year, and, finall}^, 

 the energy, expressed in heat units, of the amount of fuel that would 

 be required to produce an equivalent amount of power, is given. 



In these calculations the i)otential installed capacity is taken to be 

 equal approximately to the power at mean rate of flow and 100 per- 

 cent efficiency. The estimated output is based on a load factor of 0.5, 

 and the fuel eqivalent of the power produced is based upon a thermo- 

 dynamic efficiency of steam plants of 20 percent — figures which char- 

 acterize installations in the United States at the present time. 



The present and potential water-power situation for the world is 

 summarized graphically in ligure 7. The potential capacity is about 

 1,500 million kilowatts of which present installations amount only 

 to 65 millions, or 4.3 percent. 



The energy content of the equivalent fuel that would be required 

 to produce the potential water-power output is about 28 X 10^^ kilo- 

 gram-calories per 3^ear, or one and a half times the present rate of 

 consumption of energy from fossil fuels. 



Hence, with maximum utilization, it .would be possible with water 

 power to supply to the earth an amount of energy comparable with 

 that currently obtained from the use of fossil fuels. 



