学术文献库

Solar energy is clean and renewable but has a low flux density. The lack of a continuous and reliable power supply reduces their average daily output. Since the infrared part is not utilized to produce electricity, conventional photovoltaic cells use only about half of the solar spectrum. Direct radiation flux is also necessary for solar Stirling engine to work efficiently. The hybrid system can largely overcome these problems. The design combines the photovoltaic and energy storage-integrated Stirling engine or thermal field emission technologies in the same concentrating solar power system, providing a great potential in terms of energy production per unit area. The photovoltaic cells can be deposited on the concentrating solar power main mirror to allow the system to collect and convert the diffuse component of the light. The design allows utilization of existing equipment, particularly a high-grade parabolic dish or midgrade Fresnel concentrator for rooftop installation. To optimize the use of solar energy, beam splitters thermally decouple the modules by splitting the solar spectrum into three spectral ranges and directing visible, ultraviolet and infrared radiation into the photovoltaic cells, gate/Cs-filled gap and cavity-type solar receiver, respectively. A photon-enhanced gate electrode creates on the cathode surface an electrostatic field large enough to compensate space charge field and initiates thermal field emission process. In the thermal field emission cathodes with nano-structured surfaces, the current density can reach values close to the field emission limit. The design of the electrodes based on nano-structured emission materials were experimentally explored by the co-authors. In these experiments, efficiency of heat-to-electricity conversion was investigated and conditions for advanced nano-materials application for harvesting solar energy were found.