Traditional silicon photovoltaic modules have some inactive module surface area (IMSA) that are not covered by the solar cells due to the shading of bus bars, finger contacts, and the unused space between the octagonal solar cells. Collecting the solar power falling onto the IMSA will increase the overall energy yield and potentially decrease the $/kW-hr rating for the PV system. Therefore, we proposed a low-cost holographic light management technique which combines the holographic optical elements (HOEs) and a white Lambertian scatter surface. Simulation and comparison are performed for three different light collection systems. The results show that 6.40% more light collection efficiency can be achieved by using HOEs combined with a white scatter surface.
In this paper a spectrum-splitting photovoltaic system is proposed that uses bifacial silicon solar cells to maximize total energy yield. The system is unique in its ability to convert direct sunlight with high-efficiency (<30%) while simultaneously converting diffuse and rear-side irradiance. A volume holographic lens array is used to divide the solar spectrum into spectral bands optimized for conversion by wide-bandgap and bifacial silicon solar cells. An approach for simulating the energy yield, optimizing the holographic lens array, and analyzing the effect of concentration ratio, aspect ratio, and illumination characteristics is described. Design examples for two different solar cell combinations are provided. A GaAs and bifacial silicon combination achieves an energy conversion efficiency of 32.0% and a MgCdTe and bifacial silicon combination achieves a 31.0% energy conversion efficiency. Additional solutions are provided when constraints on concentration ratio and aspect ratio are applied, allowing the designer to balance energy yield with cost and size considerations. The performance of the proposed system is compared to conventional monofacial silicon, bifacial silicon, and monofacial spectrum-splitting modules, and show that improvements in energy yield of over 45%, 25%, and 10% can be achieved, respectively.
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.