Talking about solar panels and their lifelong warranty that ranges from 19 to 30 years, their efficiency is lost in this period. Everyone is aware of this, but sometimes your solar modules lose efficiency within a short time like say a year or two. This is stressful but somewhere both the manufacturer and the customer are responsible for this. Lack of information is another thing but getting an uncertified solar panel may be a potential cause for Potential Induced Degradation of your solar panels. Let us discuss the potential induced degradation of solar cells and panels, its causes, tests, and preventive measures.
What is Potential Induced Degradation?
The degradation occurs due to the high potential difference between the cell (semiconductor) and other parts of the module like the mount, aluminum frame, and glass. As a result of this potential difference, there is a current leakage that causes the migration of positive and negative ions.
- Negative ions: It starts leaking from the aluminum frame.
- Positive ions: Also called sodium ions, start migrating and leaking towards the surface of the cell.
This leakage reduces the photovoltaic effect by polluting the cell which further leads to power losses. Power losses due to potential induced degradation can be up to 20%. However, you may not notice it immediately, and it takes months and years for the defect to become noticeable.
What is Potential Induced Degradation of Solar Cells and Panels?
Several conjoined solar cells make solar panels. The main components of the discussion are solar cells and their aluminum frame. Potential induced degradation occurs in solar panels and cells when a solar panel is polarized with a high negative voltage. But there is a considerable voltage change in the aluminum frame and the cell.
The frame is usually grounded, thus there is 0 potential for the current. Due to the presence of impurities and a very short distance between solar cells and their frame, a current is generated between the cell and the frame. This results in leakage of the current from the entire photovoltaic module.
Also See: What are 4 Types of Solar Panel?
What is PID Effect in Solar? What causes PID Loss in Solar?
In short, it is a sign of the aging of solar cells and solar panels. It basically leads to performance deterioration of the panels. Potential Induced Degradation is the result of numerous factors that work together over a long period of time. It does not happen overnight.
1. Location
It includes the location of your house in terms of longitude and latitude along with climatic conditions. Also, exposure to humidity and high heat are factors related to the location where the solar panel is installed. These factors differ from place to place.
2. Potential induced degradation mitigation measures
Devices specially designed to lessen the effect of Potential induced degradation are not properly installed and there is negative grounding. Better devices will reduce the influence of PID otherwise it will worsen with time.
3. Quality of raw materials
Glass, encapsulated material, presence of impurities (sodium), etc. are considered raw materials of the solar cell. The quality of raw materials matters because they are the building block of the solar cell. For example, the presence of sodium while the glass is manufactured will cause the glass to have detrimental effects.
4. Quality of solar panel components
The quality of the components of solar panels, like the types of photovoltaic cells used or the material of encapsulated material, is also a factor causing PID. This includes whether they are certified as PID-resistant or not. And have these components passed the extensive reliability testing or not?
5. Voltage and size of system
Higher voltage systems mean a higher possibility of potential induced degradation. However, a 1000V system is less at risk than a 1500V system.
What is Potential Induced Degradation Test?
It is a type of quality assurance test for manufactured solar modules. It is to reach an estimate of the performance of those solar modules under different conditions over a long time. A PID test for solar modules subjects the module to the following conditions:
- Temperature of 140° Fahrenheit (60° Celsius)
- Humidity around 85%
- Load under 1000v
- Time period of 96 hours
- Voltage biases of +1000 V, -1000 V, +1500 V, or -1500 V (as per PV module characteristics)
The time period defines the name of the test that in this case is PID (96h). During this time period, modules will be exposed to the above-mentioned conditions and their effect on power loss of solar modules will be taken into account.
Also See: How to Test a Solar Panel Without a Multimeter?
What Equipment are Used in PID Test for Solar Modules?
To perform a reliable test, certain equipment is used during a Potential induced degradation test.
1. Electroluminescence (EL)
This is a powerful imaging tool that is used for determining the electronic and optical properties of the module. Through Electroluminescence imaging defects like PIC, micro-cracks, and cell fractures are easily noticed. The intensity of electroluminescence observed is proportional to the available number of minority charges in the modules.
2. Types of panels
A monocrystalline or a polycrystalline module is usually used for PID testing. The type of modules also defines the type of detection techniques to be used for testing.
How to Detect PID?
With the use of devices and techniques like Electroluminescence imaging, detecting Potential induced degradation has become easier. I-V light curves measurements of solar modules before and after imaging shows the possibility of PID. The changing slope of Voc indicates there is an increase in Rs(total resistance). The changes in I-V curves are the indicators.
What is Anti PID for Solar Panel?
To lessen the effect of Potential induced degradation, an Anti-PID box is used. It is a device attached to the inverter of solar modules. It polarizes all the photovoltaic modules that were affected in an opposite way by the negative voltage. With this box, each string keeps on changing the polarization and does not remain in a constant polarization for a long time.
Anti PID box increases the possibility for the modules to recover from the negative potential already suffered by them. It also reduces the probability of PID.
What are Anti PID Solar Panels?
Since PID occurs due to a number of reasons, material and system quality being the main of those reasons. Industries decided to manufacture Anti-PID solar panels. For this they selected:
- Solar cells with PID-free designs
- Highly resistant module encapsulation materials
Such solar panels are connected to the string and are not damaged by high string voltage. This induces more production by solar panels for longer periods. Get anti-PID solar panel here
Also See: Why is Solar Sensor Wall Light Not Working?
What is PV System Configuration?
There are 5 different configurations for a Photovoltaic System that need to be finalized before installing the solar panel system.
1. Grid-tie that feeds all the solar-powered electricity to grid
Under this configuration, all electricity produced by your solar system is fed into the grid. You need to buy the required amount of electricity from the companies. Such a system has less installation cost, and you can even earn money by selling power to electricity companies via a feed-in tariff. This tariff scheme is available only at particular locations. Where they are available, companies buy power per kilowatt-hour for the agreed price.
2. Grid-tie that only feeds the surplus solar-powered electricity to grid
This configuration enables you to use the solar power generated by your panels. Plus, if there is additional power generation, it will be fed to the grid. You need to buy the required power from the company if needed. This configuration is beneficial as it reduces the reliability of big electrical companies. It is for hot and sunny climates along with people who use most of the power generated by the modules. However, a power cut from the grid means a power cut from a solar array too.
3. Grid-tie with battery backup
This system is also known as a grid-interactive system as it is installed with a battery bank. In case of power cuts, you get a constant power supply with stored power in these batteries. It is costlier because of additional batteries and controllers.
4. Stand-alone with grid power charge function
Such configuration is best applicable for home applications when the solar power is insufficient as per requirements. This system charges the battery automatically by grid alternative current (AC) power.
5. Stand-alone without grid power charge function
Also known as off-grid, it is provided for locations where there is no other source available. This system is the sole power provider. It has a peak power generation of less than 1 kilowatt and is usually smaller.
How to Prevent Potential Induced Degradation?
Various factors should be determined to reduce or prevent potentially induced degradation of your solar panels and modules.
1. Certification
A solar panel must have a certificate from in-house solar panel testing and the International Electrotechnical Commission (IEC). These systems test modules for PID resistance under IEC 62804. It is strongly recommended to be aware of the certificates provided to the system and the bill of materials used in the modules.
2. Solar Panel Components
a) Encapsulating materials
Potential Induced Degradation resistant encapsulate materials should be used while manufacturing and installing the modules. The encapsulant is an additional protection layer against potential induced degradation. It also ensures higher outputs from systems through different seasons.
b) Photovoltaic cells
Solar cells are primarily the cause and the most affected component by potential induced degradation. Thus, solar cells used should be certified as PID-resistant cells. It is highly recommended that additional PID testing should be done by the manufacturer, and after it is installed. Regular testing should be done by a specialized laboratory device.
Also See: How to Use Solar Panel Directly Without Battery?
3. Solar System Design
a) Grounding
To reduce the risk and effect of potential induced degradation, it is recommended that the grounding should be negative for solar panel systems.
b) PID-resistant devices or Anti-PID or PV offset box
The components of a solar panel system are equally important in reducing the impact of PID. Therefore, installing such devices is a plus. Like a PV offset box, it reverses the voltage on the solar panel system after sunset. In this way, it ensures solar panels are performing their best for more than 25 years.
Well, potential-induced degradation is harmful to solar panels, but you need to pay heed to the factors causing it. Also, preventive measures through mitigating devices like anti-PID solar panels must be undertaken. Precaution is better than losing.
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