for use in the ocean are related to combining an energy source with a 

 conversion systenn. The energy sources considered in this study for use below 

 the surface of the ocean are stored thermal energy, chemical energy (including 

 batteries and fuel cells), nuclear reactor energy, and radioisotope energy. 

 Storage of energy by mechanical, electrical, and magnetic methods are not of 

 interest at this time because of their high weight and volume characteristics or 

 their lack of adequate conceptual and development status. 



Efficiencies for energy sources vary with capacity, temperature, and 

 operation. In general, the efficiencies of energy sources considered in this 

 study are 



%_ 



Storage batteries (DC) 90 



(with AC inversion) 70 



Fuel cells (DC) 50 



(with AC inversion) 40 



Chemical and thermal dynamic 30 



Nuclear reactor dynamic 20 



Isotope dynamic 15 



Thermionic 15 



Thermoelectric 10 



Energy Conversion. The direct conversion of thermal energy to 

 electric energy can be accomplished by thermoelectric of thermionic devices. 

 Thermoelectric converters are generally reliable, require little maintenance or 

 servicing, and are desirable for low-level power sources. However, their 

 efficiency is extremely low. Large thermoelectric power sources and waste 

 heat rejection systems would be required for power levels of interest to this 

 study. Since this system is limited to low voltage and high amperage output, 

 additional power conversion equipment in pressure hulls may be required. 

 Therefore, thermoelectric conversion was not considered suitable as an under- 

 water power source at the desired power levels. 



Thermal dynamic conversion systems are numerous and highly 

 developed. The Brayton, Stirling, and Rankine cycles are the most predomi- 

 nant types used for thermal dynamic conversion. 



The Brayton, or gas-turbine, cycle has the lowest overall efficiency. 

 However, it is moderately efficient at high temperatures and at the higher 

 power levels. Brayton systems using oxygen supplied under pressure are more 

 efficient than systems using air or closed-cycle gas because of the lower 

 compression power required. 



