Knowledge Center



What is photovoltaics?

Photovoltaics (sometimes referred to as “PV”) combines the Greek prefix “photos” (=light) and the suffix “volt” designating the generation of electrical energy, in recognition of the Italian physicist Alessandro Volta (1745-1827). Photovoltaics describes the capability of an object to convert light into electrical energy. Solar photovoltaics (solar PV) devices convert sun rays into electricity.

What is PERC?

Passivated Emitter Rear Cell.

Conventional Solar Cell
PERC Solar Cell

What is TOPCON?

Tunnel Oxide Passivated Contact 

What does LID stand for?

Light Induced Degradation. Some solar PV devices may degrade when exposed to sunlight. There are several mechanisms that may be at stake in a module degradation, however, the most commonly associated to “LID” is the formation, under light, of a molecular complex within the silicon crystal involving one atom of Boron and one atom of Oxygen. The so-called “B-O complex” have microscopic properties reducing the efficiency of the device (by creating recombination centers for electrons and holes). 

What does LeTID stand for?

Light and Elevated Temperature Induced Degradation  

What does PID stand for?

Potential Induced Degradation

What does IAM stand for?

Incident/Incidence Angle Modifier 

What is a typical module open-circuit voltage?


What is a typical module short-circuit current?


What is called "temperature coefficient"?

Temperature Coefficient is rate of change of electrical parameters (Voltage/Current/Power) with per degree change in Temperature.

What are the 2 main module product certificates?

IEC 61215 & IEC61730 

What is the best tool to identify cell cracks in c-Si technology in the field?

Electroluminescence (EL) 

What are the 3 main segments in the PV market?

Utility (large scale), Residential, Commercial, and Industrial (C&I)

What does BOS mean?

Balance of System

What are the 2 main inverter types for utility-scale segment? What are the pros and cons of each of these 2 types?

Central Inverter and String Inverter

What are the 2 main Li-ion Battery Energy Storage System (BESS) chemistries (cathode)? What are the pros and cons of each of these 2 types?

LFP (Lithium Iron Phosphate) & NMC (Nickel Manganese Cobalt)

What are the 2 main n-type technologies?


What is(are) the main advantage(s) of n-type technologies?

No LID, Low degradation, better Bifaciality, High Efficiency

What is a typical maximum power rating of a c-Si module today?

600Wp – 700Wp

What is Thermal Cycling?

The Thermal Cycling test is done to determine the ability of the Solar module to withstand the effects of change of temperature from 85°C to -40°C.

What are the stages of manufacturing of the silicon material in PV along the supply chain, from raw material to finished modules?

Quartz, MG Silicon, Poly Silicon, Ingot, Wafer, Solar Cell, and Solar Module  


What is(are) the difference(s) between inspection and audit?

Inspection is about conformity assessment, a qualification activity with pass-fail criteria. The inspection activities mainly set the scope on products, verifying their conformity to requirements. It usually happens during the product manufacturing.

An audit activity measures by quantitative score. Its scope of work is focused on factory, mainly evaluating the capability of the supplier. Usually the audit activities are performed during the qualification phase before production starts; 

What is PPI

PPI stands for Pre-Production Inspection. PPI assesses the readiness of the factory to start the production, making sure that all conditions are right before mass-production starts. It usually includes onsite and desk activities. Its scope of work includes but not limited to manufacturing site assessment (raw material availability, process control, staff training…), testing equipment assessment (list of critical equipment, calibration, verification…) and product type assessment (product compliance, Bill of Materials, technical drawings…).

PPI helps to address the risks of unqualified production site, non-compliant raw materials, unprepared operators, and raw material shortage, etc.

What does PSI mean?

PSI is initiated from Pre-Shipment Inspection. During this activity, a comprehensive range of re-tests at factories on random selection of samples (batch level, as per ISO2859, no bias) will be performed to cross-check production data. Its scope of work involves sample selection (randomly selected), retest at the factory (visual inspection, EL imaging, maximum power determination, dimensions check, and safety tests…), test analysis and review (cross-checked with manufacturing data), and replacement product check, etc.

PSI serves to tackle the risks of non-conforming products inserted in the lot, as well as falsified production and retests records.

What does AQL mean?

AQL stands for Acceptable Quality Limit, an essential sampling method used in quality control. It is defined as the quality level that is the worst tolerable in ISO 2859-1. It represents the maximum number of defective units, beyond which a batch is rejected. The common AQL levels are composed of critical, major, and minor defects.

How to read ISO 2859

The ISO 2859-1 standard includes a statistical sampling scheme, which categorizes sampling frequencies into inspection levels. These inspection levels are combined with an Acceptable Quality Limit (AQL) value and organized into tables.

How many cycles of TC are in IEC 61215?

IEC 61215 standard requires 200 cycles of Thermal Cycling to test the reliability of solar panels. Thermal Cycle testing is performed on materials to determine the resistance of exposure to alternating extremes of high and low temperatures. Thermal Cycling in solar works by putting solar panels through temperature extremes to simulate the impact of weather.

What is IEC 63209?

IEC TS 63209-1:2021 provides a standardized method for evaluating longer term reliability of photovoltaic (PV) modules and for different bills of materials (BOMs) that may be used when manufacturing those modules, supplementing the baseline testing defined in IEC 61215, which is a qualification test with pass-fail criteria.

What is the ISO standard that defines the sample size in Pre-Shipment Inspection ("AQL Tables")?

ISO 2859-1 specifies Sampling plans with indexed by acceptance quality limit (AQL) for lot-by-lot inspection.

What are the "M"s" in the 5M inspection method?

Manpower, Method, Machine, Material and Milieu (environment)

What does RPN stand for (risk assessment)?

RPN stands for Risk Priority Number. It is a numerical assessment of the risk priority level of a failure mode in a Failure Modes and Effects Analysis. The RPN is calculated by multiplying the three scoring columns: Severity, Occurrence and Detection.

What are the 3 components of an RPN risk assessment?

Severity, Occurrence and Detection, the 3 numeric values that quantify likelihood of occurrence, likelihood of detection, and severity of impact.

What are the 3 pillars of Sustainability?

The 3 pillars of sustainability creating value for shareholders and society are: 

  • Economics: price, quality, capacity, resilience, track-record, bankability, innovation, etc.
  • Environmental: Carbon footprint, water usage, ISO 14000, local regulations, no chemical leaching, etc.
  • Social: labor practices, community impacts, human rights, product responsibility

Sustainable Sourcing is a developing trend, many players are already deploying these principles. Traceability is the backbone of sustainable supply chains.

It is World Quality Day on Nov.10, with the theme of “Quality Conscience: Doing the Right Thing”.For STS, every day is World Quality Day!