Solar PV maintenance plays a very important role in extending or maintaining the health of solar PV modules. Basic maintenance such as solar PV module cleaning is very healthy for solar modules. Poorly maintained PV modules reach their retiring age long before those that are well-maintained.
Solar PV modules come with name plates indicating some very important parameters such as the Voc, Vmp, Isc, Imp, Vmax. All these values were tested under STC and so sometimes, depending on the prevailing environmental conditions, those figures could not be measured exactly.
Solar system designers must pay attention to what is designed especially when putting modules in series. Most new module’s nameplate state 1000v as their Vmax and this value must be considered in every design regardless of what simulation tools you may be using. In PVsyst for instance, if you do not check your parameter settings very well, you will be simulating projects in the tropics with the environmental conditions of a temperate region.
Now, let us get into what causes of Potential Induced Degradation solar PV modules.
A section through solar pv module showing the silicon layer, class cover and encapsulant
Potential induced degradation (PID) is a phenomenon that has recently become a concern in the photovoltaic project development. PID occurs when the potential difference(pd) between the solar cells in a module and ground is very high. High pd between the solar cells and the ground also results in leakage current which in tends drives ion mobility within the module across the main generating material (semiconductor material) to other elements of the module such as the mounting structure, the glass cover, module circuit or even the metallic frame. Any solar installation that does not include earthing of the modules is a danger to the safety as well as the life span of the solar modules.
What Can be done to reduce the impact of PID in a solar PV system?
I. In photovoltaic plants with grounded electrical configurations, PID can be prevented reliably by grounding the negative pole of the inverter. Also ensure the PV modules are completely grounded.
II. In cases where PID is possible, modules should be certified PID resistant by a reputable third-party organization. Do not just place order from uncertified sales persons who are eager to make sales.
III. Every PV manufacturer specifies the maximum number of modules that can be connected in a string. These regulations must be strictly adhered to.
IV. Designers should minimize loops in PV system wiring as much as possible. Loops are potential zones for potential current induction.
V. The selected PV must have a series of tests, IEC62804, which is useful in measuring reliability. Inverters with anti PID as an additional mitigative plan is recommended in addition to the already certified solar panel stated earlier. Read datasheets of solar modules and inverters to confirm such configurations.
VI. Occasional PV system testing to reveal defective strings. Identified strings with be sub-tested until the defective module is spotted and replaced. Other test such as infrared thermal images can easily reveal modules with hotspots. These hotspot-infested modules can be secluded and tested for defects.
VII. Installation of additional protective equipment or devices such as DC SPD (if not already integrated in proposed inverter).
A combination of the above measures creates a better PID resistance system.
Feel free to add your comments, contributions and questions.
Julius Dzah (Accra, Ghana) is Consultant for solar PV tech, Renewable Energy Engineer, Entrepreneur and Fellow of Startup|Energy.