Bifacial Spectrum Splitting Photovoltaic Module Using VHOEs
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Solution Overview
Problem
Conventional photovoltaic (PV) modules have limited efficiency in converting solar energy due to the use of single semiconductor types, which are less efficient at various wavelengths, and existing multijunction cells are expensive and inefficient in handling diffuse sunlight, leading to high system costs and maintenance requirements.
Innovation Solution
A bifacial spectrum-splitting photovoltaic (BF-SSPV) system using volume holographic optical elements (VHOEs) to split the solar spectrum and direct different spectral bands to bifacial silicon and GaAs cells, enhancing energy yield by converting both direct and diffuse sunlight, including rear-side illumination, with optimized VHOE parameters for high power conversion efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a single semiconductor type is used in conventional PV modules, then the manufacturing cost is kept low, but the energy conversion efficiency is limited to just over 20%
Solution Approach 1:
The patent divides the solar spectrum into multiple wavelength bands and uses different semiconductor cells (e.g., silicon for infrared, GaAs for visible) to convert each band. This segmentation allows each cell to operate at its peak efficiency for its designated wavelength range, achieving overall conversion efficiencies exceeding 40% while using commercially available semiconductor materials and manufacturing processes.
2Productivity
If multijunction cells with different semiconductors are stacked to improve efficiency, then energy conversion efficiency increases, but the manufacturing cost increases significantly
Solution Approach 1:
Instead of stacking multiple semiconductor layers vertically (multijunction approach), the patent uses optical elements to separate wavelengths spatially and direct them to different planar semiconductor cells arranged in parallel. This lateral arrangement achieves spectral splitting without requiring complex vertical heteroepitaxial growth processes, enabling the use of standard commercial semiconductor manufacturing techniques.
3Ease of manufacture
If focusing optics are used to concentrate direct sunlight onto small multijunction cells, then the cost of semiconductor material is reduced, but diffuse sunlight (20-40% of total input) is nearly all lost and additional tracking hardware is required
Solution Approach 1:
The patent segments the incident sunlight by wavelength using diffraction gratings or prisms, directing different spectral bands to different semiconductor cells positioned at different locations. This approach captures both direct and diffuse sunlight across the entire aperture area, converting 40-50% or more of total incident solar energy without requiring concentration optics or dual-axis tracking systems.
4Measurement precision
If refractive dispersion using a glass prism is used to separate sunlight, then unambiguous wavelength separation is achieved, but the angular separation is small
Solution Approach 1:
The patent changes the optical parameter from refraction to diffraction, using diffraction gratings or holographic optical elements that provide both precise wavelength separation and large angular dispersion. The diffraction grating equation d(sinθ + sinφ) = mλ allows for tunable angular separation by changing the grating period d, enabling efficient spectral splitting across a compact aperture while maintaining high wavelength resolution.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The BF-SSPV system achieves higher energy conversion efficiency than traditional monofacial or bifacial silicon modules, with a 32.8% energy yield in dual-axis tracking conditions and 30% with single-axis tracking, reducing costs by using relatively inexpensive components and compatible with conventional mounting and tracking hardware.
Implementation Method 1
A bifacial spectrum-splitting photovoltaic (BF-SSPV) system using volume holographic optical elements (VHOEs) to split the solar spectrum
Implementation Method 2
photovoltaic (PV) cells have been widely used to convert sunlight into electricity
Data Source
AI summary
A photovoltaic module comprises one or more spectrum splitting devices disposed adjacent a first side of the photovoltaic module; and a plurality of photovoltaic cells disposed adjacent a second side of the photovoltaic module opposite the first side and such that the photovoltaic cells are spaced from the one or more spectrum splitting devices, wherein at least one of the photovoltaic cells comprise a bifacial photovoltaic cell, wherein the one or more spectrum splitting devices are configured to selectively direct incident energy to one or more of the photovoltaic cells, and wherein a spatial configuration of the one or more spectrum splitting devices and the plurality of photovoltaic cells are configured based on an optimization parameter.