Solar-energy-conversion processes and, in particular, photovoltaic (PV) systems show great promise as an abundant source of renewable energy. However, to be viable and competitive with fossil fuel energy, the energy-conversion systems must produce a kilowatt-hour of energy for $0.04 to $0.05. This means that the entire system, including the balance of system and installation costs, must be less than $1/Wp, where Wp is the peak-rated power output of the system. Therefore, any new technique must provide a significant improvement in performance and must be implemented at low cost.
This Spotlight discusses the use of special-purpose holographic optical elements (HOEs) to increase the performance of PV components and systems. They are attractive because they can be designed to realize complex optical functions and can be mass produced at low cost. The remainder of Section 1 presents the properties of solar illumination and PV cell characteristics that are relevant to system designs that incorporate HOEs. In Section 2, an overview of holographic principles and design issues is given. Section 3 investigates the broadband holographic concentrators that can be incorporated into modules similar to conventional PV modules. Section 4 covers holographic light-trapping techniques that can increase the conversion efficiency of PV cells by increasing the light absorption near the band edge of the PV cell. Section 5 discusses the use of holographic components in spectrum-splitting PV systems, which show promise for considerably increasing energy-conversion efficiency. Finally, in Section 6, an overview of other application areas where HOEs can contribute to the performance of solar-energy-conversion systems is summarized.
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