Open Circuit Voltage Limiter for Photovoltaic Strings
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Solution Overview
Problem
Photovoltaic strings are often sized based on maximum possible output voltage, leading to suboptimal design and increased costs due to the need for components rated for open circuit voltage, which is rarely used during normal operation.
Innovation Solution
Incorporating an open circuit voltage limiter across the photovoltaic string, configured to limit the open circuit voltage to a value greater than the maximum power point voltage but less than the open circuit voltage, allowing current flow in specific directions to reduce the maximum possible output voltage and enable more solar cells in the string without increasing voltage, thereby reducing the number of strings and balance-of-system costs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If photovoltaic strings are sized based on maximum possible output voltage (open circuit voltage), then the system can handle peak voltage conditions, but the design becomes suboptimal and costs increase due to requiring components rated for open circuit voltage
Solution Approach 1:
The patent applies preliminary action by installing voltage limiting devices (such as varistors or voltage-clamping circuits) at strategic points in the photovoltaic string before the open circuit voltage can cause problems. These devices are pre-configured to activate only when voltage exceeds a threshold, allowing the system to be designed for lower nominal voltages while still protecting against peak voltage conditions. This resolves the contradiction by preparing the system in advance to handle voltage spikes without requiring all components to be rated for the full open circuit voltage.
2Power
If more solar cells are added to increase power output, then the power capacity increases, but the open circuit voltage increases proportionally, requiring more expensive components
Solution Approach 1:
The patent applies segmentation by dividing the photovoltaic system into multiple parallel strings rather than using a single high-voltage string. Each string contains fewer solar cells and operates at a lower voltage level, allowing components to be rated for the lower voltage. The segmentation is achieved by creating multiple independent pathways for current flow, where each pathway (string) handles a portion of the total power output. This resolves the contradiction by maintaining high power capacity through parallel configuration while keeping individual component voltage ratings lower and more cost-effective.
3Ease of manufacture
If the open circuit voltage is limited to a lower value, then component costs are reduced and system design is optimized, but current must be increased to maintain the same power output
Solution Approach 1:
The patent applies dimensionality change by transitioning from a single high-voltage, low-current configuration to a multi-string parallel configuration. This dimensional shift allows the system to distribute the current load across multiple pathways, effectively managing the increased current requirement through spatial distribution rather than concentrating it in a single path. The principle resolves the contradiction by adding the dimension of parallel configuration, which enables lower voltage operation with higher current through multiple channels, thereby reducing component costs while maintaining power output.
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 allows for increased solar cell count in photovoltaic strings while maintaining constant power output, reducing balance-of-system costs and optimizing system design by lowering the peak voltage, thus enhancing efficiency and reducing heating and performance degradation issues from electrical mismatch.
Implementation Method 1
an open circuit voltage limiter across the plurality of serially connected solar cells, the open circuit voltage limiter having a positive terminal connected to the negative lead and a negative terminal connected to the positive lead, the open circuit voltage limiter having a limiter voltage less than an open circuit voltage of the photovoltaic string for current flowing through the open circuit voltage limiter in one direction and allows current flow through the open circuit voltage limiter in another direction
Implementation Method 2
A solar cell, which is a well known device for converting solar radiation to electrical energy, may comprise P-type and N-type diffusion regions. Solar radiation impinging on the solar cell creates electrons and holes that migrate to the diffusion regions, thereby creating voltage differentials between the diffusion regions
Data Source
AI summary
A photovoltaic string may include an open circuit voltage limiter that conducts current in one direction to provide a limiter voltage less than an open circuit voltage of the photovoltaic string, and that conducts current in the other direction. One or more open circuit voltage limiters may be connected across the photovoltaic string or across selected groups of solar cells of the photovoltaic string. The limiter voltage may be greater than a maximum power point voltage but less than the open circuit voltage of the photovoltaic string.