  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.
