Tandem Solar Module String Layout for Reverse Bias Protection
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Solution Overview
Problem
Tandem solar modules face challenges with voltage mismatch and reverse bias issues due to differences in spectral response and illumination effects, leading to potential module failure and hotspot problems.
Innovation Solution
The method involves cutting full cells parallel to the busbars to form cell strips, which are then strung together in series and arranged in parallel sets with terminals at opposite ends. Bypass diodes are inserted between or within parallel sets to bypass strings and prevent reverse bias damage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If multiple tandem cells are connected in series to increase voltage output, then the power and voltage levels increase, but the reverse bias voltage stress and hotspot problems increase due to voltage mismatch and shading
Solution Approach 1:
The module divides the series-connected tandem cells into multiple parallel strings, with each string containing a subset of cells. This segmentation reduces the reverse bias voltage stress on each individual string while maintaining the overall module power output through parallel configuration.
Solution Approach 2:
Bypass diodes are introduced as intermediary components connected in parallel with each string or group of strings. These diodes provide an alternative current path when a string experiences reverse bias or shading, protecting the tandem cells from damage while allowing the module to continue operating at reduced power.
2Reliability
If bypass diodes are connected for every 20 or 24 cells in series, then the protection against reverse bias is provided, but the reverse bias voltage per bypass diode becomes excessively high (up to 40 V)
Solution Approach 1:
Instead of connecting bypass diodes to large groups of 20-24 series cells, the module structure segments the cells into smaller parallel strings. Each string or small group of strings has its own bypass diode, reducing the reverse bias voltage each diode must withstand to manageable levels.
Solution Approach 2:
The patent transitions from a single-dimensional series connection to a two-dimensional arrangement with multiple parallel strings. This dimensional change allows bypass diodes to protect smaller subsets of cells, reducing the voltage stress on each diode while maintaining comprehensive protection across the module.
3Use of energy by moving object
If tandem cells are used to absorb broader spectral range, then the energy conversion efficiency increases, but the voltage mismatch and current response variations increase due to different spectral responses
Solution Approach 1:
The module segments tandem cells with different spectral responses into separate parallel strings. This allows each string to operate optimally for its specific spectral range while the parallel configuration enables the module to adapt to varying illumination conditions by drawing current from the most suitable strings.
Solution Approach 2:
The patent utilizes parameter changes in the spectral response of different tandem cell sub-cells to create diversity among parallel strings. Under varying illumination conditions, the electrical parameters (current, voltage) of different strings change differently, allowing the system to adapt and maintain stable overall performance through parallel interconnection.
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 approach maintains the power, voltage, and current levels comparable to standard solar modules, minimizes hotspot issues during reverse biasing, and prevents module failure due to partial shading.
Implementation Method 1
Bypass diodes are inserted into the series to bypass one or more of the strings
Data Source
AI summary
Disclosed is a tandem solar module and a method for forming such a module. The module includes a plurality of cell strips formed by cutting a full cell parallel to a direction of extension of a bus bar of the full cell, a plurality of strings arranged in one or more parallel sets, each string comprising two or more said cells strips interconnected end-to-end with respect to the direction of extension, and a terminal at each opposite end the one or more parallel sets.