Shingled Solar Cell String Layout for Lower I2R Losses
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Solution Overview
Problem
Conventional solar cell configurations face inefficiencies in concentrating solar energy collectors due to high I2R losses, shading by bus bars, and thermal expansion mismatch with substrates, which reduce power output and reliability under concentrated illumination.
Innovation Solution
The use of overlapping series-connected solar cells with optimized metallization patterns and mechanically compliant interconnects, such as reflowed solder or conductive adhesives, allows for reduced I2R losses and strain relief, enhancing efficiency and reliability under concentrated solar radiation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If conventional solar cell configurations are used in concentrating solar energy collectors, then the system can be manufactured with standard designs, but I2R losses increase and power output decreases under concentrated illumination
Solution Approach 1:
The solar cell is divided into multiple independently interconnected solar cells arranged in series, where each cell is electrically connected to adjacent cells through conductive bonding material. This segmentation allows optimization of current paths and reduction of I2R losses in each individual cell while maintaining overall system productivity.
Solution Approach 2:
The configuration implements localized optimization by arranging solar cells in a specific overlapping pattern with conductive bonding at designated locations. This creates different functional zones: illuminated areas for energy conversion and bonding areas for electrical connection, reducing overall I2R losses while preserving power output.
2Reliability
If bus bars are used for electrical connection, then electrical connectivity is achieved, but shading by bus bars reduces active area and power output
Solution Approach 1:
The traditional bus bar structure is extracted and replaced with conductive bonding material that connects solar cells at their edges or overlapping regions. This removes the shading effect of large bus bars from the active illuminated area while maintaining reliable electrical connectivity through the bonding material.
Solution Approach 2:
The electrical connection is moved from the planar surface (where bus bars would shade the cell) to the edge or overlapping dimension between cells. This dimensional transition eliminates shading while preserving connectivity through the conductive bonding material at cell interfaces.
3Reliability
If rigid interconnects are used between solar cells, then electrical connection is established, but thermal expansion mismatch causes stress and reduces reliability
Solution Approach 1:
The interconnect material properties are changed to match or accommodate the thermal expansion characteristics of the solar cells. The conductive bonding material is selected or designed with thermal expansion parameters compatible with silicon solar cells, reducing stress and improving reliability under thermal cycling.
Solution Approach 2:
A composite interconnect structure is used combining conductive material with materials having appropriate thermal expansion properties. This composite approach provides both electrical conductivity and thermal expansion compatibility, preventing stress accumulation while maintaining reliable electrical connection.
4Productivity
If overlapping solar cell configuration is implemented, then I2R losses are reduced and efficiency increases, but manufacturing complexity increases
Solution Approach 1:
Multiple functions are merged into the overlapping configuration: electrical connection, mechanical support, and stress distribution are all achieved through the same overlapping structure and conductive bonding material. This reduces the number of separate components and simplifies manufacturing despite the optimized geometry.
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
This configuration achieves higher power output, up to 15% more than conventional arrangements, and longer string lengths without failure due to reduced I2R losses and improved thermal expansion management.
Implementation Method 1
Solar energy resources are sufficient in many geographical regions to satisfy such demands, in part, by provision of electric power generated with solar (e.g., photovoltaic) cells
Implementation Method 2
conductive bonded to each other with an electrically conductive bonding material to electrically connect the silicon solar cells in series
Implementation Method 3
thermal expansion mismatch with substrates
Data Source
Figure 1A~1B
Figure 1C~1F
Figure 2
AI summary
A high efficiency configuration for a string of solar cells comprises series-connected solar cells arranged in an overlapping shingle pattern. Front and back surface metallization patterns may provide further increases in efficiency.