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Holographic cap collectors for enhanced mid-day energy production of vertically mounted bifacial photovoltaic modules

The most expensive electrical energy occurs during early morning and late afternoon time periods. This poses a problem for fixed latitude mounted photovoltaic (PV) systems since the sun is low in the sky. One potential solution is to use vertically mounted bifacial PV modules to increase the East-West collection area and solar energy production during high energy usage time periods. However, vertically mounted PV modules have reduced conversion efficiency during mid-day time periods. In this paper the use of a horizontally mounted collector with holographic elements is examined as a way of increasing the energy yield of vertically mounted bifacial PV (VMBP) modules during mid-day time periods. The design of a holographic `cap’ collector is evaluated that considers dimensional constraints, holographic diffraction efficiency characteristics, and system solar collection efficiency properties. The irradiance illuminating the vertical mount is modeled with and without the cap. The design process also includes the optimization of separation between rows of vertically mounted modules and the use of directional diffusers in the proximity of the modules to maximize system energy yield.