Detailed performance model of a hybrid photovoltaic/thermal system utilizing selective spectral nanofluid absorption. (August 2018) - Brekke, Nick
Abstract: This work explores recent advancements of a concentrating hybrid photovoltaic/thermal (CPV/T) system, with an emphasis on detailed modeling and parametric performance studies. This system combines two widely researched methods of harnessing solar energy: photovoltaics (PV) and solar thermal. The CPV/T system proposed here uses a nanoparticle-based heat transfer fluid to spectrally absorb bands of the solar spectrum not efficiently utilized by the PV cell or below the bandgap of the cell with the remaining light transmitted to the PV. The fluid's spectral absorption characteristics can be tuned depending on the PV cell bandgap. A unique architecture designed in this study allows the fluid to be pumped through a transparent glass structure where it absorbs wavelengths not effectively utilized by the PV cell. This work documents the development of a 2-D thermal model of a hybrid CPV/T system. The novel model accounts for the temperature dependent PV bandgap and temperature variations along the length of the system. The thermal interactions between the filter fluid and PV, caused by the physical parameters of the system are of interest here. This includes the exergy, thermal efficiency, and PV efficiency. In this numerical study the influence of system length, mass flow rate in both the absorbing filter loop, and concentration ratio are varied parametrically to understand the potential operational space of this type of collector. Two common cell materials are also studied, crystalline silicon and gallium arsenide. In addition, this is the first study that investigates the role of heat transfer on system performance when the working fluid flows in a cascaded fashion through the PV and filter channel, and when these flow rates are decoupled. Results show that decoupling these flowrates is an important factor as lower convective heat transfer is advantageous in the filter versus the PV cooling side. At a concentration ratio of 25x the cSi system achieves an exergetic efficiency of 41.3% with 71.3% coming from heat versus 42.3% exergetic efficiency with 57.7% coming from heat for the GaAs system. Highlights: Development of coupled 2-D thermal and electrical model for novel solar collector. Decoupled flow between fluid filter and PV extrusion flow loop results in enhanced heat transfer performance. Parametric results for flow rate and concentration ratio for both Si and GaAs cells.