58 THE FIVE-YEAR OUTLOOK 



adaptable to decentralized user requirements and could 

 therefore be usable on smaller scales than other future 

 options. For that reason, their role in any assessment of 

 future energy sources should not rely solely on their 

 contribution to aggregate demand. 



A variety of technologies for directly harnessing solar 

 energy are under development, and applications of direct 

 solar energy technology ranging from individual solar 

 water heaters to centralized electricity generation have 

 been studied. Currently, direct solar water and limited 

 space heating systems are finding expanded application, 

 although broadly functional systems are not expected to 

 evolve until late in the present decade. Such systems 

 currently have the disadvantage of having higher initial 

 costs than do competing systems, although they also have 

 the advantage of not requiring conventional fuels for their 

 operation. Additional development will be needed before 

 these kinds of systems can be used widely in a cost- 

 effective way (ENERGY). 



Photovoltaic systems are presently under consideration 

 both for large, centralized applications and more modest, 

 decentralized needs. Photovoltaic cells, which convert 

 light directly into electricity, have now reached a research 

 stage where conversion efficiencies in excess of 1 1 percent 

 have been achieved. Reduction in the costs of photovoltaic 

 systems may well require a new type of device based on 

 thin amorphous films rather than presently used crys- 

 talline materials. The Federal Government is supporting 

 long-term R&D on advanced semiconductor materials for 

 such applications. Cost reductions are also expected with 

 the introduction of large automated production facilities 

 (ENERGY). 



Beyond what can be accomplished through improve- 

 ment of the cells themselves, the potential of photovoltaic 

 systems could be enhanced by locating them outside the 

 filtering effects of the Earth's atmosphere. This observa- 

 tion provides the basis for the concept of the Solar Satellite 

 Power Station, which would consist of a very large array 

 of photovoltaic cells in geosynchronous orbit. Solar power 

 from the array could be transmitted in the form of high- 

 frequency microwaves to receiving antennas on Earth, 

 where it would be reconverted into electricity.'* Since the 

 science and technology underlying such systems are not 

 well understood and the required capital investments 

 would be very large, they are unlikely to become viable 

 options in the foreseeable future {Outlook I, v. 11, p. 159). 



BIOMASS 



Renewable organic materials such as vegetation or ani- 

 mal, agricultural, and forest residues are all classified as 

 biomass. This organic material can either be burned di- 

 rectly, or used to produce liquid or gaseous fuels, or to 

 produce chemicals as substitutes for chemical industry 

 feedstocks that are presently derived from petroleum or 



natural gas. Since living plants store energy from the sun, 

 biomass is often classified as a form of solar energy. 



Fermentation of grains to produce alcohol is, of course, 

 an established commercial technology, and the results of 

 research and development leading to systems for the eco- 

 nomic production of methanol and methane gas through 

 fermentation of other vegetable and animal residues are 

 promising (ENERGY). Basic research in plant genetics 

 that could underlie advances in the biological engineering 

 of plants could greatly enhance the potential of biomass as 

 a significant, long-term energy option. 



Wood is potentially a good source of fuel and chemicals 

 produced through fermentation, although it requires con- 

 siderable pretreatment before the fermentation process 

 can be effective. Alternatively, wood can be used to 

 produce synthetic fuels by means of the same basic proc- 

 esses (involving gasification for example) that are used to 

 make these fuels from peat or coal (NRC-15). Given the 

 present availability of coal, however, and the ecological 

 problems involved in extensive cultivation of forests for 

 biomass, this latter option does not appear to be a signifi- 

 cant one for the United States during the foreseeable 

 future. 



NUCLEAR FUSION 



Nuclear fusion, the process through which the sun con- 

 verts its mass into energy, has the potential to be an 

 important option for the long-term future. Most designs 

 now regarded as feasible would make use of tritium de- 

 rived from lithium (which is relatively abundant) and 

 deuterium extracted from the oceans, so that commercial 

 fusion reactor fuel sources would qualify as renewable. 



Fusion occurs when two light nuclei react to combine 

 into a heavier nucleus and give up excess energy in the 

 process. Usable fusion reactors would be designed to 

 convert that energy into electricity. Since fusion reaction 

 processes can only occur at exceedingly high tempera- 

 tures, the basic scientific and technical problems are asso- 

 ciated with raising the temperature of the fuel and sustain- 

 ing it at that temperature for the fraction of a second 

 required for fusion to occur, while preventing the fusion 

 reaction from being quenched through contact of the hot 

 fuel with the confining container Two approaches are 

 being pursued: In the magnetic confinement method, the 

 fuel is kept away from the container walls by an intense 

 magnetic field as its temperature is raised. In the inertial 

 confinement method, pellets containing the fuel are 

 dropped successively through the common focal point of 

 several intense pulsed laser or charged particle beams 

 where the fuel temperature is raised abruptly. 



Research aimed at solving some of the formidable 

 problems associated with the magnetic confinement meth- 

 od has been under way for 20 or more years in this country 

 and abroad, and present enthusiasm among those in- 



