India is fast moving towards its 100 GW solar power target with rapid capacity additions in the solar photovoltaic segment. The fierce competition among developers has resulted in a significant decline in solar power tariffs. With solar power now becoming cheaper than coal-based power, a key question that is being raised is regarding the quality and reliability of the equipment installed in solar power plants.
Although a solar power plant is developed as a long-term financial investment of 25 years, modules used in the plant may not last that long. As modules account for roughly 50 per cent of the total cost of a solar power plant, defect or damage to them would result in huge revenue losses for the developer. For instance, if a power producer has 1 GW of solar power plants, with each module priced at $0.22 per watt, it will have to bear expenses of at least $22 million if even 10 per cent of the modules get damaged after 10 years. If the damage occurs before 10 years, the manufacturer bears the cost of replacing the defective modules though the developer has to suffer revenue losses due to low plant performance.
Common defects in modules
DuPont Photovoltaic Solutions has been running the Global Field Reliability Program since 2011 to inspect, assess and understand the performance and material degradation of PV modules, and gather data. These modules are of different ages and types, and are installed in different geographies and climates across North America, Europe, Asia-Pacific and the Middle East. The results of the global field studies till 2018 indicate that roughly 22.5 per cent of the total modules have some form of visual defects. These defects can occur in any module component such as frames, solar cells, glass, encapsulants, backsheets and junction boxes. About 12 per cent of the defects can be attributed to solar cells. These include corrosion, hotspots, snail trails, broken interconnection, cracks and burn marks. Meanwhile, 9.5 per cent of the total defects are found in backsheets, including cracking, delamination, yellowing and cracking of the inner layer. Around 1.3 per cent of the defects are related to the discolouration, browning and delamination of the encapsulant, while the remaining issues are found in junction boxes, glass material and anti-reflective coating. Studies have found that any defect in individual or combination of module components can impact the power generation from solar modules. Apart from performance issues, such defects can cause fires and other critical hazards, compromising the safety of power plants and the operations and maintenance personnel.
As per the PV Module Bankability 2018 Report by Bloomberg New Energy Finance, backsheet quality has become a huge concern for developers and investors, even as the existing quality issues of light-induced and potential-induced degradation are being addressed. Cost saving strategies implemented by both manufacturers and developers in the past are now leading to backsheet degradation in the field. Backsheets are impacted by reflected ultraviolet radiation, high temperature, humidity and abrasion, and backsheet defects lead to moisture ingress, ground faults and inverter tripping, resulting in power losses. The loss of electrical insulation due to backsheet defects is also a major safety hazard. Thus, backsheet quality should be a key parameter for module selection by developers.
Ensuring reliability and quality
It is important to select the right materials for ensuring the quality and reliability of modules, as failure of a single material in the module leads to performance degradation. Thus, the definition of module reliability should include negligible material failure, safe module operations and average power output losses of less than 0.7 per cent per year. Interestingly, the use of Tier 1 modules does not guarantee reliability as the ranking method is not based on quality. In addition, insurance and warranties on modules do not ascertain the reliability of modules. Even the International Electrotechnical Commission’s testing procedures cannot evaluate the long-term reliability of modules. Thus, module reliability can only be ensured by using modules made with suitable manufacturing processes and quality materials, and proved in accelerated testing methods that simulate field conditions. Thus, developers should opt for an active approach, choosing the right modules to prevent failures, instead of a passive approach that can only remedy the failure. Choosing a more efficient module with higher quality materials may certainly increase the upfront capital cost of the project by a small margin. However, cost saving strategies can jeopardise the long-term return on the project.
In sum, developers today need to focus more on increasing module lifetime and efficiency through the use of quality components to maximise their returns, instead of finding means to minimise the levellised cost of energy.
Based on presentations by Rajaram Pai, Business Leader, and Rahul Khatri, Technical Manager, DuPont Photovoltaic Solutions, at Renewable Watch’s “Solar Plant Performance” conference in association with DuPont Photovoltaic Solutions