Cyril Stephanos
Thermoelectronic Power Generation from Solar Radiation and Heat
Supervisor: Prof. Dr. Jochen Mannhart [Experimental physics VI]
Date of oral examination: 12/17/2012
145 pages, english , Opus Online Veröffentlichung
Conversion of heat into electric power as done, for example, by fossil-fuel power stations or concentrating-solar power plants, faces the problem that the highest acceptable input temperatures of the converters are usually significantly lower than the temperatures generated by the heat source. Coal, accounting for 40%25 of global electricity production, is burned at ~1500 %B0C, whereas the steam turbines to which the combustion heat is delivered are operated below ~700 %B0C, to give but one example. This temperature gap reduces the maximum conversion efficiency and leads to significant losses. Thermoelectronic generators, which can operate with extremely high temperatures, are compelling candidates to close this gap, boosting the total system efficiency to extraordinary values, yielding a corresponding reduction of emissions. Thermoelectronic generators are based on thermionic energy conversion. Although this technique has been known for more than 100 years, no efficient converters could be built due to the formation of an electronic space-charge region, ruining the performance of practical devices. This thesis presents a solution to the space-charge problem, using electromagnetic fields to convert the space charges into a useful output current. Model calculations, verified experimentally in a prototype apparatus, reveal that there is no fundamental hurdle preventing the development of practical, highly efficient heat-to-electric-power generators. If implemented, these generators could, for example, considerably enhance the efficiency of coal combustion power plants, or operate as highly-efficient solar energy converters.