By Ashay Abbhi
Considering that the life cycle of a solar power plant spans about a quarter of a century, durability and consistency of solar panels become extremely important. The quality of panels and all other components directly impacts the cost of energy, revenues and returns on investment for project developers and operators. Quality control, therefore, assumes paramount importance to generate the best yields from a solar power plant. While there is a move towards the adoption of new technologies, inadequate quality standards for these technologies make critical decision-making difficult.
Quality control is required at two stages in the solar power value chain – first, in the manufacturing process, wherein the manufacturer needs to ensure production of quality components (most importantly, solar modules) and the developer/EPC contractor needs to procure quality components for the plant; second, during plant operations, wherein the developer/operator needs to ensure overall upkeep. Low quality products at such critical nodes in the process can prove financially and technologically harmful for the plant.
With tariffs falling, profit margins shrinking and competition intensifying, some manufacturers may have started compromising on product quality by cutting corners to decrease capital costs. This could severely hamper the quality of power generation once the warranty period and the manufacturer’s liability ends. For developers, while such products may be cheaper in the short run, these are detrimental to the overall project health.
In India, quality control is a voluntary but tedious exercise due to a dearth of standardised procedures and lax enforcement of the few standards that exist.
Standards for quality control
According to DNV GL’s PV Module Reliability Scorecard 2018, there are two key standards used currently for global module testing:
- International Electrotechnical Commission (IEC) 61215 – Crystalline silicon terrestrial photovoltaic (PV) modules, design qualification and type approval
- Underwriters Laboratories (UL) 1703 – Standard for flat-plate PV modules and panels.
Almost all projects using solar PV modules and panels, global and Indian, require IEC or UL certification to ensure a certain minimum standard of quality. Besides these certifications, there are a few other tests available in the industry to ascertain the reliability of the solar panels and modules manufactured across the world, including in India and China. DNV GL’s reliability scorecard runs four tests on modules to determine their performance capability. These tests are thermal cycling, damp heat, dynamic mechanical load (DML), and potential induced degradation (PID).
This test includes 600 cycles, with each spanning three to five hours. During each cycle, the module is kept in an environmental chamber where the temperature is reduced to as low as -40 degrees Celsius and increased to as high as 85 degrees Celsius, while applying maximum current to the module. The behaviour of the module during these cycles provides an insight into its degradation profile. This test is an extension of the IEC standard, which includes only 200 cycles. According to the 2018 scorecard, the top five global performers are India-based Adani (Mundra Solar), Astronergy Solar, BYD, Flex and GCL System Integration Technology. Here, the top result recorded no measurable degradation in module performance while the lowest result registered 8.8 per cent degradation.
The damp heat test uses high humidity and temperature to evaluate the performance of module lamination and the overall quality of other parts. This test is especially useful for modules in hot and humid Indian weather conditions, with most projects typically located in the southern and western parts of the country. The test is effective in revealing performance issues for modules that face long exposure even in moderate climates.
The IEC 61215 standard test requires modules to be held at 85 degrees Celsius with 85 per cent humidity for a period of 1,000 hours. However, an advanced version of this test by DNV GL has uncovered better performance differentiation, especially in module adhesion, by doubling the period to 2,000 hours. The top performers, in 2018, for this test were Astronergy Solar, BYD, Flex, GCL System Integration Technology and Hanwha Q Cells. While there was no measurable degradation in the top performing modules, the worst performance recorded was -8.1 per cent.
Dynamic mechanical load
The DML test determines the ability of a module to withstand high wind speeds and snow loads. It tests the performance of the frame size, the construction material used and the manufacturing controls of cell interconnection and etching. In 2016, there were reports of a thunderstorm damaging the solar modules of a 15 MW solar power plant in Mansa, Punjab, ripping apart the Rs 10 billion plant. Evidently, the poor quality construction material used proved detrimental to the plant despite good quality modules being provided by the manufacturers. Therefore, the DML test assumes prime importance for determining the health of the entire solar power plant.
The test requires the solar panel to be mounted as recommended by the manufacturer and subjected to 1,000 cycles of alternating load at a high pressure of 1,000 Pa. The module’s circuitry and current leakage are monitored during the cycles. The module is then stressed in a chamber for 50 thermal cycles and 10-30 humidity freeze cycles to assess the power loss. The top performers in this test were Adani (Mundra Solar), Astronergy Solar, BYD, First Solar and Flex.
Potential induced degradation
With the use of higher system voltages and underground systems, the need for PID testing has become important. The PID test requires the modules to undergo a voltage bias equivalent to the system voltage rating of the module, at 85 per cent humidity and 85 degrees Celsius temperature, for two sessions of 96 hours. The top performers in this test were Adani (Mundra Solar), Astronergy Solar, BYD, First Solar and Flex. While the best performance did not show any measurable degradation, the worst recorded a degradation of 7.4 per cent.
Notably, module manufacturing in India is still largely inadequate and about 80 per cent of the country’s module requirement is fulfilled by imports. Global certifications and standards are, therefore, relevant in the Indian context.
Manual cleaning of solar modules using water and wipers or mops for removing soil, bird droppings, etc. has been rather ineffective. Automated cleaning with aerosols has also resulted in corrosion and other damage to the solar module surface, thereby being counterproductive.
The use of advanced technology has helped improve solar plant operations and maintenance, and achieve better yields. Inspire Energy has come up with certain solutions that not only help enhance the quality of operations, but also prevent damage to the modules. Technologically advanced solutions such as water-fed poles, which use a carbon fibre pole with especially designed soft bristles, and SaBot, a robot that cleans solar panels using advanced solutions, can help safeguard the quality of solar modules on the field.
The IEC and UL tests are not comprehensive and do not provide guarantees or ensure long-term module reliability. The UL standards are essentially safety tests aimed at preventing hazards during operations, while the IEC tests identify module defects typically seen only during the first few years of operations. Moreover, certification testing is performed by manufacturers on their own products, which may introduce a performance bias, as they may select only their best panels for these tests.
Indian manufacturers do not have set standards for assessing the quality of modules and panels. Inadequate domestic standards skew the quality profile in favour of international manufacturers, which not only have better standards but also adhere to the quality parameters strictly. The presence of only one Indian manufacturer in DNV GL’s scorecard speaks volumes about the quality parameters being used in domestic manufacturing.
Considering that profit margins are narrowing due to decreasing tariffs, solar module manufacturers are trying to cut costs. This could compromise product quality and limit investments in testing.
The rapid pace of introduction of new technology in a segment as dynamic as Indian solar power can enhance the technology risks. The poor quality of solar modules and panels can even threaten to derail the progress of the Indian solar power sector, leaving in its wake incomplete targets and stranded investments.