Cameron Stanley

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.

FERROFLUIDIC PLUG FLOW HEAT TRANSFER ENHANCEMENT

Overheating of power electronic devices has become a significant issue due to their continued miniaturization and increased heat flux that needs to be dissipated. Microchannel heat sinks utilising two-phase flow are capable of very high heat transfer rates and represent a possible means of cooling such devices. In this paper, we focus on two-phase liquid-liquid plug flow using water-based ferrofluid (magnetic nanofluid) plugs as the dispersed phase and silicone oil as the continuous phase. An external magnetic field was applied to generate enhanced mixing of the microfluidic flow. We show that material properties of the ferrofluid plug influences heat transfer properties of the microfluidic flow, and demonstrate that cooling performance is further enhanced by the application of an external magnetic field which induces mixing. We also show that microchannel heat transfer using a ferrofluid is superior to that using de-ionized water as the dispersed phase for two-phase liquid-liquid plug flow.

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.

The rise of non-imaging optics for rooftop solar collectors

In this paper we explore the use of non-imaging optics for rooftop solar concentrators. Specifically, we focus on compound parabolic concentrators (CPCs), which form an ideal shape for cylindrical thermal absorbers, and for linear PV cells (allowing the use of more expensive but more efficient cells). Rooftops are ideal surfaces for solar collectors as they face the sky and are generally free, unused space. Concentrating solar radiation adds thermodynamic value to thermal collectors (allowing the attainment of higher temperature) and can add efficiency to PV electricity generation. CPCs allow that concentration over the day without the need for tracking. Hence they have become ubiquitous in applications requiring low concentration.

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.