Ahmad Mojiri

Spectral light management for solar energy conversion systems

Abstract Due to the inherent broadband nature of the solar radiation, combined with the narrow spectral sensitivity range of direct solar to electricity devices, there is a massive opportunity to manipulate the solar spectrum to increase the functionality and efficiency of solar energy conversion devices. Spectral splitting or manipulation facilitates the efficient combination of both high-temperature solar thermal systems, which can absorb over the entire solar spectrum to create heat, and photovoltaic cells, which only convert a range of wavelengths to electricity. It has only recently been possible, with the development of nanofabrication techniques, to integrate micro- and nano-photonic structures as spectrum splitters/manipulators into solar energy conversion devices. In this paper, we summarize the recent developments in beam splitting techniques, and highlight some relevant applications including combined PV-thermal collectors and efficient algae production, and suggest paths for future development in this field.

Beam Splitting System for the Development of a Concentrating Linear Fresnel Solar Hybrid PV/T Collector

Investigations are underway around the world to make solar energy more competitive in the energy market [1–3]. One approach is to develop solar hybrid photovoltaic/thermal (PV/T) technologies which allow for maximal utilization of incident sunlight by integrating a PV cell and a thermal receiver in the same collector [4,5]. In this study, we will present a new PV/T design based on a compact linear Fresnel concentrator (LFC) coupled with a spectral beam-splitter. The beam-splitting approach avoids the efficiency drop in the PV cell while still obtaining high temperature thermal output. The design is analyzed numerically with respect to a worth factor which considers the intrinsically higher economic value of electrical energy at ∼3 times thermal energy. In order to predict optical performance, the geometry of this hybrid concentrating collector, which achieves 10–15 suns concentration, is modeled at various incident angles using the ray tracing software Zemax. Three different PV cells are considered (Si, GaAs and GaInP/GaAs). The reported spectral response of these cells is used to determine the optimal wavelength split for the fraction of the solar spectrum directed to the various PV cells. The results indicate that such designs can achieve 20–51% greater value of the power outputs — PV electrical power plus heat produced — relative to a stand-alone PV system.© 2013 ASME

A high temperature hybrid photovoltaic-thermal receiver employing spectral beam splitting for linear solar concentrators

Hybrid photovoltaic/thermal (PV-T) solar collectors are capable of delivering heat and electricity concurrently. Implementing such receivers in linear concentrators for high temperature applications need special considerations such as thermal decoupling of the photovoltaic (pv) cells from the thermal receiver. Spectral beam splitting of concentrated light provides an option for achieving this purpose. In this paper we introduce a relatively simple hybrid receiver configuration that spectrally splits the light between a high temperature thermal fluid and silicon pv cells using volumetric light filtering by semi-conductor doped glass and propylene glycol. We analysed the optical performance of this device theoretically using ray tracing and experimentally through the construction and testing of a full scale prototype. The receiver was mounted on a commercial parabolic trough concentrator in an outdoor experiment. The prototype receiver delivered heat and electricity at total thermal efficiency of 44% and electrical efficiency of 3.9% measured relative to the total beam energy incident on the primary mirror.

Experimental performance evaluation of a hybrid CST receiver for linear concentrators

Hybrid concentrating solar thermal (CST) receivers allow for the simultaneous production of thermal and electrical energy. However, the thermal output from these receivers is typically limited by the maximum operating temperature of the solar cells, which are coupled to the thermal fluid. Spectral beam splitting provides a means for removing this direct coupling and allowing for thermal outputs significantly above the operating temperature of the photovoltaic (PV) cells. RMIT University has developed a novel beam splitting hybrid CST receiver which uses a combination of selective liquid absorption and long pass optical filter to spectrally split concentrated solar radiation. Using this approach light between 700 nm-1200 nm was directed to a linear arrangement of silicon PV cells, while the remaining wavelengths of light were directly absorbed as thermal energy. A full-scale prototype receiver was mounted to a commercially available parabolic trough concentrator to measure its performance. Results demonstrated a total thermal efficiency of 46.5% together with an electrical yield of 3.6%. Sources of performance reduction were identified and discussed.

Spectrally Beam Splitting Hybrid Receiver for Linear Solar Concentrators

We have used selective absorption light filtering for spectral management of the sunlight in a concentrating hybrid photovoltaic thermal receiver. The effectiveness of the design has been studied using ray tracing.