Abstract
Thermionic energy conversion (TEC) using nanomaterials is an emerging field of research. It is known that graphene can withstand temperatures as high as 4600 K in vacuum, and it has been shown that its work function can be engineered from a high value (for monolayer/bilayer) of 4.6 eV to as low as 0.7 eV. Such attractive electronic properties (e.g., good electrical conductivity and high dielectric constant) make engineered graphene a good candidate as an emitter and collector in a thermionic energy converter for harnessing solar energy efficiently. We have used a modified Richardson–Dushman equation and have adopted a model where the collector temperature could be controlled through heat extraction in a calculated amount and a magnet can be attached on the back surface of the collector for future control of the space-charge effect. Our work shows that the efficiency of solar energy conversion also depends on power density falling on the emitter surface, and that a power conversion efficiency of graphene-based solar TEC as high as 55% can be easily achieved (in the absence of the space-charge effect) through proper choice of work functions, collector temperature, and emissivity of emitter surfaces. Such solar energy conversion would reduce our dependence on silicon solar panels and offers great potential for future renewable energy utilization.
Highlights
Thermionic energy converter(sion) (TEC) is an emerging technology for clean power generation
No theoretical study has been carried out either on how the efficiencies of solar TEC would depend on work functions of emitter, collector, and their temperatures and how the latter terms would be dictated by the incident solar power density, except for our earlier works,[9,10,11] where we have considered a different energy balance as explained later
The radiation losses even at 500 K would overwhelm the TEC power output that might be possible with a suitable adjustment of We, Wc, and Tc and the efficiency would be quite low at such low temperatures, even if the work functions and temperature differences are sorted out correctly. Considering such problems with low TEC, we have considered in this work solar TEC without PE and operating at high temperatures obtained by concentrated solar energy on to a small emitter area
Summary
Thermionic energy converter(sion) (TEC) is an emerging technology for clean power generation. This is primarily due to intense electron repulsions among them. Space charges can be minimized by (i) keeping the separation constant
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