With every passing decade, the solar PV industry has grown exponentially and so is the solar capacity of countries worldwide. Because of the massive solar adoption, the standards set by industry are being ignored by the installers. Solar manufacturers are compromising quality to reduce the cost of the PV system which is the reason why solar panels develop defects and not perform well. PID is one of the end products of this aggressive competition among manufacturers.
What is PID?
PID (POTENTIAL INDUCED DEGRADATION) also known as a solar yield killer, is an undesirable performance deterioration induced by the negative potential to ground. It develops internally in the solar modules after a few days or weeks of installation.
Firstly, to understand PID, you need to know how electricity is generated by a solar panel. A panel consists of several layers and individual photovoltaic cells. The combination of two semiconductor material exchange charges, producing an internal electric field.
In a solar project, multiple panels connected in an array are called a string. A string has two sides – negative and positive, connected through an inverter which produces AC voltage. If we compare it with the ground, the voltage has a negative and positive potential. The negative potential triggers PID in a solar cell. Usually, photons let electrons flow towards the cell’s connector and generate the current.
However, the negative potential attracts positive ions in the cell such as sodium ions which stimulate surface polarization and shunting. The movement usually happens from the glass plate through the encapsulation and the anti-reflective coating to the cell. The electrons then stop flowing and generate electricity which results in a disruption in a junction functionality meaning the decline in the power capacity of the panel.
After a few weeks or months, PID occurs at the entire negative side of the string. The most negative panel loses 30-80% of its yield. PID is contagious, more cells get affected by it over time, it turns the cells black. The speed of PID depends on – the system voltage, humidity levels and cell temperature. It can be reversible or irreversible. Therefore, it has devastating effects on all installation levels of a PV system – financing, operations and economies. The solar investor must address PID effects in the early stage to ensure the PV system works well in its entire life cycle.
Strength of PID effect
PID effect on individual panels –
The cells located near the aluminium frame are strongly affected by the PID as compared to the cells located in the centre of the modules.
PID effect on a string of panels –
In this case, the panels located on the negative side of the string will have a huge PID impact because the negative potential concerning ground is typically higher at that side.
Factors that determine if a PV system is subject to PID
Module and PV Cells –
The material used while manufacturing the modules plays a significant role. Manufacturers should pay attention to the chemical composition and quality of glass and EVA in which the PV cells are encapsulated. With that, if the cells are too sensitive to negative potential then it suggests that the structure of the cell lacks the quality to withstand the potential. It happens because of the density of the charge carrier of the silicon and the chemical composition of the ARC (Anti-Reflective Coating) layer on the PV cell.
PV System configuration –
PV systems consist of the number of modules used in a string, the type of inverter, the amount of negative potential solar cells exposed to and the earthing of PV fields. The topology of the inverter is of paramount importance in PID effect. The two main inverter topologies available in the market are transformer and transformer-less inverter. The inverter converts the DC input power into useful AC output power.
The inverter with inbuilt transformer boosts the voltage to accommodate the grid needs. It comes with galvanic isolation, meaning the electrical circuits are separated which help in averting the stray current. This allows the negative potential of the module to be earthed assuring the negative pole stays at ground potential to eliminate the effects of PID.
But sometimes to cut the manufacturing costs, PV companies use transformerless inverters where the connection between the grid and the inverter is direct. It nullifies the purpose of negative pole grounding. If they do that, there will be chances of short-circuiting. Therefore, in such inverters, the negative side is not earthed and becomes a potential danger for PID.
The two major external factors that contribute to PID are humidity and high temperature. They are not man-made issues so you can only observe them and cannot control them. Because of humidity, the moisture seeps into the modules and causes an increase in leakage current. This process is accelerated in hot temperatures and affects the solar yield.
4 Ways to mitigate PID effect
A site with pleasant temperature and low humidity levels is the most favourable one. A windy location can also help in avoiding the PID effect as it aids in keeping the PV system cooler.
Use top-grade PID resistant components
For a new site, you can opt for high-quality modules available in the market. They are made of top-notch raw materials and are prepared under stringent quality standards. However, their cost will be higher because of expensive encapsulating materials, anti-reflective coatings and other elements. They are built to withstand any weather conditions.
Use modules with no restrictions imposed by the installer on connecting the negative side of the string to ground.
Use inverters with inbuilt charge equalizers. If an inverter is not operational during the night, they apply an opposite bias to modules which rules out the reversible type of PID also known as polarization.
Way Forward with Novergy
Never compromise quality for the price. Always go with an EPC provider like Novergy which uses top-notch raw material to create high-performing solar products. Being an integrated player, Novergy takes the design, engineering, manufacturing, supply, installation and commissioning very seriously to deliver a superior customer experience. Our detailed orientation is also reflected in project execution and exceptional performance record.
To combat the PID phenomenon, Novergy makes PV modules that have a superior glass with a small concentration of sodium and great optimization of distances between the glass and EVA layer. Our products have a NIL replacement record in the harshest of conditions resulting in highest customer satisfaction. To know more, visit novergysolar.com now!