Tandem Photovoltaic Module Diffractive Spectral Separation
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Solution Overview
Problem
Current photovoltaic (PV) modules have limited conversion efficiency due to the use of single semiconductor types, which are not optimized for the broad range of solar wavelengths, leading to inefficiencies in converting diffuse skylight and increasing costs with complex optics and larger cell areas.
Innovation Solution
A solar PV module design featuring two types of PV cells with different bandgaps, where sunlight is spectrally separated by diffraction into shorter and longer wave bands and directed to the most efficient cell type, using cross-eyed strip lenses to ensure each cell receives the wavelengths it converts best, while maintaining low cost and large area coverage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a single semiconductor type is used in PV modules, then manufacturing cost is reduced and ease of manufacture is improved, but conversion efficiency of total incident solar energy deteriorates to little more than 20%
Solution Approach 1:
The patent divides the solar spectrum into different wavelength bands and uses multiple semiconductor types (e.g., silicon for 400-1100nm, GaAs for 300-850nm) arranged in lateral configurations. Each semiconductor type is optimized for specific wavelength ranges, allowing the system to capture and convert a broader portion of the solar spectrum, thereby improving overall conversion efficiency while maintaining manufacturing feasibility through modular assembly
Solution Approach 2:
Different regions of the PV module are equipped with different semiconductor types matched to their optimal spectral responses. For example, silicon cells are positioned to capture longer wavelengths while GaAs cells capture shorter wavelengths. This spatial differentiation of material properties maximizes the conversion efficiency of incident sunlight at each location without requiring complex manufacturing processes
2Productivity
If multijunction cells with different semiconductors stacked on top of each other are used, then conversion efficiency is improved, but manufacturing cost increases due to expensive semiconductors and manufacturing techniques
Solution Approach 1:
Instead of stacking multiple semiconductor layers vertically (multijunction approach), the patent transitions to a lateral arrangement where different semiconductor types are positioned side-by-side in the horizontal plane. This dimensional change allows each semiconductor type to be optimized for its spectral range without requiring complex vertical integration, reducing manufacturing complexity and cost while maintaining high conversion efficiency through spectral division
3Area of stationary object
If focusing optics are used to concentrate sunlight onto small multijunction cells, then area efficiency is improved, but diffuse sunlight component (20-40% of total input) is nearly all lost and system cost increases
Solution Approach 1:
The patent divides the module into multiple lateral sections, each equipped with its own semiconductor type optimized for specific wavelength bands. This segmentation allows the system to capture both direct and diffuse sunlight across the entire module area without requiring concentration optics, as each region independently processes its optimal spectral portion, preserving the diffuse component while maintaining area efficiency
Solution Approach 2:
The patent eliminates the need for focusing optics as intermediaries by directly arranging multiple semiconductor types in lateral contact with the incident sunlight. This removes the optical concentration step that would otherwise filter out diffuse light, allowing the system to convert both direct and diffuse components efficiently through the diversified semiconductor array
4Measurement precision
If refractive dispersion using glass prisms is used to separate sunlight into spectral bands, then unambiguous wavelength separation is achieved, but angular separation is small requiring larger system size
Solution Approach 1:
The patent replaces refractive dispersion mechanisms (prisms, lenses) with a direct lateral arrangement of multiple semiconductor types. Instead of using optical elements to spatially separate wavelengths, the system uses the inherent spectral response characteristics of different semiconductors positioned side-by-side. This substitution eliminates the need for large angular separations and complex optical paths, reducing system size while maintaining precise spectral utilization
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 module achieves higher overall conversion efficiency for both direct and diffuse sunlight with minimal back-scattering loss, reducing costs by using low-cost cell manufacturing and efficient optics, resulting in improved energy generation compared to single-type cell modules.
Implementation Method 1
sunlight is spectrally separated by diffraction into shorter and longer wave bands which are directed preferentially toward the wider bandgap cells and the narrower bandgap cells, respectively
Implementation Method 2
photovoltaic (PV) cells have been widely used to convert sunlight into electricity
Data Source
AI summary
A solar PV module is disclosed having two types of laterally-separated coplanar cells with different bandgaps to improve conversion efficiency. A diffracting entrance window directs sunlight with wavelengths shorter than a separation 5 wavelength ks is directed largely to the first type of wider bandgap cells. Sunlight with wavelengths longer than a separation wavelength ks is directed largely to the second type of narrower bandgap cells. The separation wavelength is chosen so that each cell is illuminated largely by that part of the solar spectrum to which it has the higher conversion efficiency, resulting in an overall conversion efficiency higher than 10 for either type of cell used alone. The wider bandgap cells are configured on a planar support in separated parallel strips, with the narrower bandgap cells largely filling the area between these strips.