Final Program EXPRES 2012 - Conferences

developed by Johnson et al. /23/. Its main componentwere two symmetric generators which contain parabolicconcentrator/reflector units and solar receivers whichwere designed to produce sufficient electric power fromthe absorbed solar radiation, and the advanced multi-tubevapor anode AMTEC cell with 24% conversionefficiency.The system integration and performance analysis resultshowed that the solar AMTEC power system can be avery good option for space energy generation and that thesize of the solar AMTEC system was much smaller thanthat of a solar-PV array and its mass also could becompetitive with that of the PV/battery power system/23/. In addition, the solar AMTEC system could be morerobust and stable. Therefore, a solar AMTEC powersystem could be very attractive for space energygeneration. However study /23/ did address space powerproduction and space vehicle energy supply, and notgenerating energy transmission to the Earth.Theoretical design optimization of a radial AMTECcell design parameter was analyzed by Hendricks andHuang, /24/ with an aim to establish optimum designparameters and achieve better cell performance for highpowerspace mission requirements. The design parameteranalysis showed that cell efficiency could increasedramatically, with strictly controlled parasitic losses andintroduced larger area BASE tubes, concluding that amuch higher system power could be achieved from theoptimum efficiency designs than the maximum powerper-BASE-areadesigns, and in the same time couldreduce cell cost and complexity /24/.Apart from independent direct solar thermal powergeneration methods, cascade systems which combineseveral power generation methods to obtain higher poweroutput were also widely studied./19/. Cascade systemscan have significantly higher efficiency and consequentlymuch higher electric power output. However, differentstages must match well, especially their temperaturelevels, what is important to be considered for the systemdesign optimization.For example, as the thermionic converter has a veryhigh reject temperature which is very near the inputtemperature for an AMTEC, it is appropriate to achievehigher power output by cascading these two types ofconverters. In paper /19/ has been shown that theefficiency of the Cs–Ba thermionic-AMTEC systemcould be 7%–8% higher than that of the Cs–Bathermionic-thermoelectric cascade system. Hence, a hightemperature Cs–Ba thermionic-AMTEC cascade systemcan be very attractive for solar thermal power generationand would allow the development of a highly efficient,compact power systemFor the solar AMTEC program further development andits effective technical feasibility - reliable and costeffectivesolutions have to be searched encompassing asmore as possible accurate investigation of demanddiversity and storage capacities focusing on modular unitsfrom small to medium size engine capacities, around 1 –20 MW capacity.As the conclusions concerning solar-AMTECtechnology following R&D needs can be outlined:a. Thermodynamic study of innovative combined andcascade cycles/systems.b. Fundamental heat transfer research on differentAMTEC systems, relevant materials and structures.c. Engineering investigation, development andstandardization of related technical systems andcomponents.d. Case studies: loads profiles, storage, cogenerationand hybridization related dynamics.e. Optimization under various policy/rate scenariosincluding the dispatch optimization and relatedgeneralized procedure.In addition, concluding the solar AMTEC developmentR&D needs is to be stated, that the detailed analysis of allknown direct solar thermal power generationtechnologies, conducted by Yue-Guang Deng and Jing/19/ determined solar AMTEC as the most advantageouscomparing it with thermoelectric, magnetohydrodynamic,and thermionic. In order to materialize its enormouspotential, and to make full use of its advantages,according to /19/ considered are to be aspects which areessentially more precise definitions of specific researchtasks of the above given items b. and c. as follows:“Optimizing structure design and reducing systemheat radiation and conductive loss as much aspossible;Seeking for excellent electrode materials and betterfabrication techniques for porous metal electrode,so as to improve the output current density andreduce the polarization effect of electrodes;Substituting sodium with kalium as the workingfluid under certain conditions however, propersystem design and suitable working conditions arevery important because some problems, such asdryout in the evaporator wick, could more easilyhappen for kalium-based AMTEC; andRaising the temperature of the AMTEC hightemperatureside however, the temperature shouldnot be too high since the degradation of theelectrode material would happen under a hightemperature”.VI SPACE SOLAR POWER GENERATION ANDTRANSMISSIONThe most recent document on the status of space solarpower generation and transmission is presented in August2011 entitled “The first international assessment of spacesolar power opportunities, issues and potential pathwaysforward” by the International Academy of Astronautics/12/.Solar Power Satellite (SPS) was described byAmerican scientist Peter Glaser in his inventive USpatent in 1973. His method was based on transmittingpower over long distances (from space to Earth's surface)using microwaves from a very large antenna (up to onesquare kilometer) on the satellite to a much larger one,now known as a rectenna on the ground. (Illustrationshown in Fig. 10). Because of its immunity to nighttime,to weather or to the changing seasons, the SPS concepthas the potential to achieve much greater energyefficiency than ground based solar power systems (interms of utilization of fixed capacity).36