Selecting The Right Modules: Due Diligence, Vendor Selection & Inspection Criteria

Technology Trends

"Key technical due diligence parameters, vendor selection process and Inspection criteria of Solar PV Module for Solar Projects"

Finally, we landed up at solar tariff of INR 2.44/kWh ($0.0375/kWh) recently at Bhadla Solar (IL&FS 500 MW) Bid so everyone in Solar Industry is taking long-term call on module price (24 cents -27 cents) and chasing the trend which global solar industry has witness in past 2-3 years. Beside this developer, consultants, technology reviewer and Energy industry as a whole have started questioning on long-term viability and sustainability of these projects as the developer has to keep the project cost as minimum as possible or has to make compromises in quality of major component to take the price advantage to get the expected return on financial model.

Let me just start with overview of Solar market dynamics, future perspective, and observations

• Globally Blended module prices has been dropped up to 30% (USD 0.33-0.35/Wp) where solar tariff is up to 35%-38% and here in India more than 50% solar tariff has been dropped in past 17 months and modules prices (MSP) up to 36%to 38%

• Currently, Solar PV installed capacity is ~350 GWp where 12.20 GW in India. Deployments expected to increase 2.5x times in next 5 years

• From past 3-4-year speculation in the performance of solar Poly, C-Si technology has been increased as prices have been dropped up to 55%-60% and half of the capacity is 3 years old. Although Poly c-si technology has proven performance track record but lack of sufficient public data, product information includes BoM and supply-price stressed manufacturing companies (,

• As Industry, has witnessed a downward trend in project cost due to fall of module prices, and optimization in BoS majorly stressed supply chain is related to Module as MoM 0.95%-1.05% price declination has been observed where BoS 0.20%-0.30%.

• Tier 1 Module supplier as per listing by Bloomberg 33 Module manufacturers having a manufacturing capacity of 70 GWp annually cumulatively. Listing of Tier 1 manufacturers in based on the non-recourse debt financing by the lenders, it has nothing to do with technology and performance.

• Power degradation of 0.50% YoY has been observed in Tier 1 Modules Suppliers (DNV GL)

• OEM model in PV Module Manufacturing has been increased in past 3-4 years and production process, quality of product performance risk has started growing especially in China and India.

• Manufacturers are changing BoM without any consent

• Thermal cycle failure, degassing of new material with in the laminate and severe defects in junction box has been found as per DNV GL

Coming to the point....
" Is Solar Industry selecting module vendor based on the right technical parameter or its just solely on the commercial basis? Selection of technology, proven vendor, and technology track record, Efficiency or Module Power rating and Glass, cell class, temperature coefficient, historical performance and key performance data (LID, PID etc) what are the right parameters, how does those parameters affect your performance in long term and what would be cost implication on Module prices of these parameters along with Module BoS".

Are developer going to use subpar material especially PV module which accounts more 50%-55% of entire project cost, DC cables manufacturers whose tracker record is not so good, technical specifications have not properly defined and the same scenario for module mounting structure and string combiner box (Monitoring or with our monitoring ).As the same trend of going to follow in tariff reduction module manufacturing Industry will have to compromise with Bill of Material and Quality checkup processes to keep support in prices expected by Developer at any cost. It is essential to understand the technical due diligence parameter and vendor selection process of PV Module which will decide the real price of minimum module prices without compromises with quality.

The overall analysis has been covered under two sections

1. Key technical parameter and their relevance in performance, cost optimization

2. Qualification Process:

• Technical and BoM assessment

• Economic risk and supplier assessment

• Level 3 and Level 4 inspection during manufacturing and shipment

1. Key technical parameter and their relevance in performance, cost optimization

Generally, Solar industry evaluates the solar module technology, various manufacturers on these below parameters, understanding of these parameters are required in terms of cost optimization, technology performance (Higher yield), reliability, robustness and warranty point of view.

A. Technical parameters in PV Module for Cost Optimization

i. Module rating (in Wp): Higher the power rating of a module, lower the BoS

ii. Module efficiency (in %): Higher the efficiency, lower the ground coverage ratio and land requirement (Acre/MWp)

iii. Weight/Wp: Based on the type of application i.e. rooftop (lighter weight is recommended) and Ground Mount, a key factor for structure tonnage optimization thus overall BoS cost

B. Parameters in PV Module for performance analysis

i. Type of cell

ii. Type of technology: Mono, Thin film (CdTe/ CIGS) or Poly c-Si

iii. No. of Busbar

iv. Power Tolerance limit

v. Cell characteristics: PID resistance (ask test certificate IEC62804), LID results

vi. Power Degradation rate

vii. The temperature coefficient of Power

viii. NOCT (Nominal operating cell temperature)

ix. IAM (Incident angle modifier) profile

Other than above parameter Developers should ask module manufactures updated and optimized latest. PAN file of selected pv module to get the optimized energy yield analysis from PVsyst. It might optimize the energy yield by +1.93%-2.10% (

2. Qualification process

a. Technical and BoM assessment
More than 50% of the installations across the globe has happened in past 3 years, cost pressure has been increased drastically on manufacturing front so before selection of module manufacturer for solar project recommending Developer to ensure the module manufacturer should have all the key IEC certificate, good and proven Bill of material(BoM), QAP , manufacturing process (fully automated process leads to higher cell to module ratio without any major defect, No of EL inspection) then negotiate in to the Module prices ( I am sure you will get price variation of 0.75 cents -1.50 cents ). While discussion with major domestic/ offshore manufacturers they may not able to provide the BoM as per your wish list.

These below documents should be review by the Engineering /Technology team

• Cell & Module Process Flow Chart

• List of Cell & module line equipment with capacity & location

• Process & Quality Control Plan (Pre-shipment inspection at manufacturing facility, pre-shipment inspection at Third party lab and Outgoing quality control plan)

• Provide information on Gold Reference Module & also cell by 3rd party lab (TUV, Fraunhofer, PI berlin)

• Testing/Certification Laboratory (3rd Party)

• EL criteria and Severity level of acceptance/ rejection as per AQL (ISO 2859-1)

• Visual Inspection and Sun simulator results of sample in a lot

• No. of Binning: Higher current binning leads to lower mismatch losses during operation.

EL criteria (Electroluminescence) needs to be ask from module manufacturers where developer should strictly convey the best acceptance and rejection of micro cracks, maximum cell defective area, inactive cell, dark cells, grid defect, soldering defect, broken fingers and other if specified as these defects can hit the performance of the pv module in long term.

Key documents

• IEC test certificate

• PV Cycle certificate

• Product warranty

• Plant performance data (if possible)

• Customer reference & degradation data if possible

• Data on PID, LID

• EL Criteria and QAP plan

“Higher volume of production/Tier 1 doesn’t reflect the quality of production if not pre-agreed”

b. Economic risk and supplier assessment

if everything is technically perfect, Developer should check the supplier background, Altman Z score, balance sheet and Power guard assurance in any event of failure in performance.
Developer should visit and inspect the entire manufacturing plant and audit the below to ensure the wellness and efficiency of overall of process
Facility audit

• Material Management

• Reliability

• Process

• Frequency of calibration

• Type of manufacturing equipment

• Quality checkup (min 2 EL inspection is recommended)

c. Level 3 and Level 4 inspection during manufacturing and shipment

This phase is one of the most critical and important to inspect based on the pre-agreed terms and condition where approved bill of material shall be used, Quality assurance plant would be followed and Pre-shipment inspection of products shall be performed. In general practices, Developer ask for detailed manufacturing plan and factory details, third party test lab from the manufacturers and then developer appoints third party reputed agency and in house quality team to be at manufacturing facility during product manufacturing.

These are three phase where inspection agency/ quality team should inspect according to QAP

a) In production Inspection:

b) Pre-Shipment inspection :(Visual- for workmanship and product defect, Sun Simulation- for electrical performance of the PV module, Electro Luminance- for latent quality of cell)

c) Third party lab test result inspection:( Sun simulation and PID test)
If above Inspection agency will give green signal in above inspection result, then a lot should accept and will ready for shipment.

d) Outgoing Quality control: Developer should ask flash test report of each modules and should done packaging inspection along with container inspection before shipping out.

Just to conclude, Developer should go with the best bill of material for Module and follow minimum inspection level II and acceptance level AQL o for critical, AQL 1.5 for major and AQL 2.5 for minor as PV module is only component which share the maximum cost in overall project and comes with 25 years Power warranty.
First don’t start your commercial discussion, it might hamper the product quality.

By Ashish Verma. Ashish is a solar energy enthusiast and a regular contributor.
Disclaimer: The views above are strictly those of the author and do not reflect those of any other organisation or individual or this publication.



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