A nanoparticle fluid filter used with concentrating hybrid solar/thermal collector design is presented. Nanoparticle fluid filters could be situated on any given concentrating system with appropriate customized engineering. This work shows the design in the context of a trough concentration system. Geometric design and physical placement in the optical path was modeled using SolTrace. It was found that a design can be made that blocks 0% of the traced rays. The nanoparticle fluid filter is tunable for different concentrating systems using various PV cells or operating at varying temperatures.
Concentrating optics enable solar thermal energy to be harvested at high temperature (<100oC). As the temperature of the
receiver increases, radiative losses can become dominant. In many concentrating systems, the receiver is coated with a
selectively absorbing surface (TiNOx, Black Chrome, etc.) to obtain higher efficiency. Commercial absorber coatings are
well-developed to be highly absorbing for short (solar) wavelengths, but highly reflective at long (thermal emission)
wavelengths. If a solar system requires an analogous transparent, non-absorbing optic – i.e. a cover material which is
highly transparent at short wavelengths, but highly reflective at long wavelengths – the technology is simply not
Low-e glass technology represents a commercially viable option for this sector, but it has only been optimized for visible
light transmission. Optically thin metal hole-arrays are another feasible solution, but are often difficult to fabricate. This
study investigates combinations of thin film coatings of transparent conductive oxides and nanoparticles as a potential
low cost solution for selective solar covers. This paper experimentally compares readily available materials deposited on
various substrates and ranks them via an ‘efficiency factor for selectivity’, which represents the efficiency of radiative
exchange in a solar collector. Out of the materials studied, indium tin oxide and thin films of ZnS-Ag-ZnS represent the
most feasible solutions for concentrated solar systems. Overall, this study provides an engineering design approach and
guide for creating scalable, selective, transparent optics which could potentially be imbedded within conventional low-e
glass production techniques.
A spectral fluid filter for potential use in hybrid photovoltaic/thermal concentrating solar collectors has been developed, targeting maximum absorption above and transmission below a desired wavelength. In this application, the temperature-dependent bandgap of the potential solar cell is used in the optimization of the filter. Dispersing a mix of colloidal nanoparticles in a heat transfer fluid is shown to absorb 86% of sub-bandgap insolation while absorbing only 18% above bandgap insolation. Transmission above bandgap light would be directly absorbed into the photovoltaic (PV) cell while absorbed photons transfer energy directly into the heat transfer fluid ultimately reducing the number of heat transfer steps. Placement of a filter in front of the PV cell is shown to decrease losses by converting an additional 2% of the total solar energy into thermal energy since it allows recollection of light reflected off the receiver.
We propose a design for a concentrating PV/T collector utilizing plasmonic nanoparticles directly suspended in the working fluid to spectrally filter the incoming solar flux. This liquid filter serves two purposes: the direct capture of thermal energy as well as filtering off of key portions of the spectrum before transmission to the PV cell. Our device builds upon the current Cogenra T14 system with a two-pass architecture: the first pass on the back side of the PV cell pre-heating the fluid from any thermalization losses, and the second pass in front of the PV cell to achieve the spectral filtering. Here we present details on the selection of plasmonic nanoparticles for a given cell bandgap as well as the impact to the overall system pumping power and cost.