Solar Photo Voltaic Power Plants are designed to last 25 years or more. However, during the life time of a Solar PV Power Plant there are many factors that can affect Plant performance. During the Plant design stage, a study is done using Simulation software (viz PVSYST) to arrive at the likely monthly and yearly Generation possible at a site using reference irradiance data available from NASA/Meteonorm databases.
Typical factors that are covered during the Simulation study are factors that affect performance of plants during the day-to-day operations and during the life of the plant. Some factors are controllable while some of them are Non-controllable during the working of the Plant.
Typical Factors affecting Plant performance:
- Soiling Losses
- Vegetation growth causing shadows
- Higher Temperatures – temperatures reaching greater than Nominal Cell operating temperature(NOCT) can de-rate performance by 0.45% for every degree rise in temperature beyond NOCT.
- Incident Angle Modifier (IAM) Losses inherently defined during simulation can vary mainly due to improper or fragile nature of the Antireflective coatings for AR coated Modules
- Light Induced degradation intrinsic to the module and linked to the quality of the wafer during manufacturing
- Cable Losses between DC field and Inverter and losses between Inverter and Point of injection to Grid
- Inverter Losses (Efficiency related)
- AC Ohmic Losses
Other Factors likely to affect performance and warrant attention are:
- Build up of Hot Spots due to thermal effects within the module
- Module Efficiency (current category) differences– Usually Manufacturers have different and superior current class modules that invariably works in low irradiation unlike lower current category of same power rating
- Snail Trails and its correlation to micro-cracks in cells may adversely affect performance
- Potential Induced Degradation (PID) effect – Factors related to the Module including ingredients in glass and the means of encapsulation have an impact on PID. Ungrounded systems usually are affected with PID. It is generally reversible, and losses can be controlled.
- Bus Bar Rusting – Lesser the redundancy of busbars, the chances of deterioration are more
- Tilt angle being disturbed during Preventive maintenance activities or while doing seasonal tilt changes
- Higher total dissolved solids(TDS) in water that is used for Module cleaning can cause scaling and thereby affect performance adversely
- High UV radiation at a place correlated to degradation
It is evident that the quality of the Module right from the time it has left the production floor has to be consistent – these need to weather the environmental changes well and conform to the design specifications. If the designated or allowed yearly degradation levels are breached, then there will be a noticeable dip in performance.
The O&M service provider needs to address all the controllable factors quickly to reduce generation losses. Regarding the non-controllable factors, the client must be apprised about the impact of these on generation and request them to take suitable action. If the factors pertain to Module deficiencies client should have discussions with the Module Manufacturers to help resolve issues and touch on warranty aspects. Laboratory testing of a few sets of Modules may be required to be carried out to be sure of performance aspects.
— Contributed by Ganesh H , AVP – Technical Solutions Group