Nuclear energy will require use of breeder reactors to provide adequate fuel (19, 57, 58). Natural sources are inadequate. Fissile fuel breeding requires time in addition to the construction time of the breeder reactors. Hundreds of years of integral breeding time would be required to grow the fissile fuels for a 60,000 GW world. The demonstrated doubling time is approximately 40 years. There are not sufficient drainage sites for hydroelectric power to make a significant contribution to a 60,000 GW world. Wind systems are under development but provide variable power. Costs are not clearly established (54,59). Terrestrial solar installations (row 3) will be subjected to the severe environmental conditions at the surface of the Earth and would have to be distributed worldwide to average out demand changes, variable day/night cycle, local weather patterns, and the seasonal changes. Large reflectors might be employed in orbit about the Earth to reflect low intensity sunlight to cities (60) or high intensity beams to ground-based solar farms (46). Optimal use of terrestrial units will likely require long distance power transmission between hemispheres. Microwave beams constantly switching from one production region, via orbital reflectors/retransmitters, to receiving grids near major consumer regions will probably be used. If so the beams would be likely to travel from Earth to installations in geosynchronous orbit and back to Earth, a distance approximately 20% of the distance to the moon (57,61). Ground based units will require maintenance due to weather, catastrophies, and human acts and will certainly be subjected to the effects of worldwide climate change. Ocean thermal energy systems (OTEC) actually ‘‘mine” the cold waters of the deep ocean to cool working fluids vaporized by solar heated surface waters (21, 62, 63). Little attention has been directed to the long-term effects of a massive mixing of the cold abyssal waters at the rates necessary for a 60,000 GW world. The capital mass numbers in row 4 are based on a prototype OTEC system (62). These should be revised for the large-scale systems which would actually be used. Use of icebergs as a cooling source might be less disruptive and could also provide fresh water (18). “Mining” of geothermal heat is being pursued. The total reserve of heat energy is immense. Access to useful geothermal energy increases as geothermal wells tap deeper rock formations. The rock formations must be such that they can be cracked by hydraulic techniques and the cracks remain open. It is not clear what fraction of the world can obtain local geothermal power with present drilling techniques. Research is underway (65). Costs are approximately equally divided between drilling and heat extraction equipment. Electricity generation requires equipment on the scale of combustion-driven turbines or larger. Geothermal sources are generally not as hot as combustion flames. Total costs are not yet established but may be competitive with hydrocarbon systems (65). Construction of all these systems will be an activity of the general terrestrial economy. Demandite will be processed through the manufacturing sectors (histogram in Fig. 5) to produce the systems. If the unit costs ($/kg) are significantly higher than$5/kg, then fundamental broadening of the cost distribution of the terrestrial economy could occur because of the scales of construction, maintenance, and fueling (where relevant) of these massive systems. Solar fuels (#6) refer to production of hydrogen or similar combustible compounds by sunlight acting through a catalytic agent or possibly a biological intermedia for dissociation of water (61). The capital estimates do not include equipment to collect hydrogen gas or to contain the agent over a large area, but rather assume hydrogen is simply available out of a pipeline. These estimates could easily rise to terrestrial solar power levels (#3).
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