New Design of Solar Photovoltaic and Thermal Hybrid System for Performance Improvement of Solar Photovoltaic

© 2020 Ridwone Hossain et al. Solar photovoltaic (PV) and solar thermal systems are most widely used renewable energy technologies. Theoretical study indicates that the energy conversion efficiency of solar photovoltaic gets reduced about 0.3% when its temperature increases by 1°C. In this regard, solar PV and thermal (PVT) hybrid systems could be a solution to draw extra heat from the solar PV panel to improve its performance by reducing its temperature. Here, we have designed a new type of heat exchanger for solar PV and thermal (PVT) hybrid systems and have studied the performance of the system. The PVT system has been investigated in comparison with an identical solar PV panel at outdoor condition at Dhaka, Bangladesh. The experiments show that the average improvement of open circuit voltage (Voc) is 0.97 V and the highest improvement of Voc is 1.3 V. In addition, the overall improvement of output power of solar PV panel is 2.5 W

Significant enhancement of electrical conductivity by incorporating carbon fiber into CoSb3 thermoelectric skutterudite fabricated by spark plasma sintering method

The effects of carbon fiber additions on the electrical and thermoelectric performance in p-type CoSb3-based skutterudite are reported. A threefold enhancement in electrical conductivity is found. Two different explanations for the increased electrical conductivity are considered: Either carbon atoms enter the CoSb3 lattice as a dopant that makes it more and more conductive, or the increase in conductivity is due to electrical percolation of the carbon fibers in the composite. X-ray diffraction data show that the lattice parameter of the CoSb3 is not affected by the presence of the carbon fiber; however, adding carbon is associated with precipitation of 20 wt. % elemental Sb. DFT calculations show that the enthalpy of formation of a solid solution of carbon (interstitial or as a substitution for Sb) is slightly positive. This would be offset by an increased entropy contribution at higher temperatures, so the free energy change overall is likely to be favorable. All of the results support an explanation based on an improved electrical conductivity of a very dilute solid solution of C in CoSb3. The average thermoelectric parameters of the composite material, including heat conductivity, average composite Seebeck coefficient, Hall effect, carrier mobility, and carrier concentration, were influenced by the carbon addition. Unfortunately, the effects largely cancel each other so that the overall zT of the composite was not improved

Enhancing the Thermoelectric Performance of Polycrystalline SnSe by Decoupling Electrical and Thermal Transport through Carbon Fibre Incorporation

Thermoelectric (TE) materials have attracted extensive interest because of their ability to achieve direct heat-to-electricity conversion. They provide an appealing renewable energy source in a variety of applications by harvesting waste heat. The record-breaking figure of merit reported for single crystal SnSe has stimulated related research on its polycrystalline counterpart. Boosting the TE conversion efficiency requires increases in the power factor and decreases in thermal conductivity. It is still a big challenge, however, to optimize these parameters independently because of their complex interrelationships. Herein, we propose an innovative approach to decouple electrical and thermal transport by incorporating carbon fiber (CF) into polycrystalline SnSe. We show that the incorporation of highly conductive CF can successfully enhance the electrical conductivity, while greatly reducing the thermal conductivity of polycrystalline SnSe. As a result, a high TE figure-of-merit (zT) of 1.3 at 823 K is obtained in p-type SnSe/CF composite polycrystalline materials. Furthermore, SnSe samples incorporated with CFs exhibit superior mechanical properties, which are favorable for device fabrication applications. Our results indicate that the dispersion of CF can be a good way to greatly improve both TE and mechanical performance

Ultra-high thermoelectric performance in graphene incorporated Cu<inf>2</inf>Se: Role of mismatching phonon modes

© 2018 Elsevier Ltd A thermoelectric material consisting of Cu2Se incorporated with up to 0.45 wt% of graphene nanoplates is reported. The carbon-reinforced Cu2Se exhibits an ultra-high thermoelectric figure-of-merit of zT = 2.44 ± 0.25 at 870 K. Microstructural characterization reveals dense, nanostructured grains of Cu2Se with multilayer-graphene and graphite agglomerations located at grain boundaries. High temperature X-ray diffraction shows that the graphene incorporated Cu2Se matrix retains a cubic structure and the composite microstructure is chemically stable. Based on the experimental structure, density functional theory was used to calculate the formation energy of carbon point defects and the associated phonon density of states. The isolated carbon inclusion is shown to have a high formation energy in Cu2Se whereas graphene and graphite phases are enthalpically stable relative to the solid solution. Neutron spectroscopy proves that there is a frequency mismatch in the phonon density of states between the carbon honeycomb phases and cubic Cu2Se. This provides a mechanism for the strong scattering of phonons at the composite interfaces, which significantly impedes the conduction of heat and enhances thermoelectric performance