Solar Photovoltaic Module Warranty - Terms and Trends!
The first known solar module in the PV industry were used in space application for more than few decades. However with the stability of P type solar cells, gradually decreasing prices & increasing efficiency, the solar modules started finding its way in terrestrial applications. Two specific applications where PV modules were deployed are onto the roof top of house & on the ground. It was only now in the 20th century that the world realized that solar PV is both cost effective & better for the environment when compared to other sources of electricity (refer Figure 1 ). This meant directly that the world was going to adopt solar PV & it was poised to become the main source of energy in the near future. The global PV installations jumped from a mere 40 GW by end of 2010 to 700+ GW installations by end of 2020 & this exponential trend is expected to continue. The solar power plant installed till date are usually known to remain in operation and/or designed to stay in operation for an average period of 25 years. This has widely been correlated to the warranty offered on the bill of materials (BoM) used in the power plant and more specifically the solar PV modules. The solar modules typically have been associated with this warranty which allows end user to make such assumptions. In this article, we intend to educate our customers on the developments in the terms and trends of warranty for PV module over the years.
Figure 1 : Global warming potential of different energy sources, life cycle cost of different energy sources (Source: Mérida García A et al. Comparing the environmental and economic impacts of on- or off-grid solar photovoltaics with traditional energy sources for rural irrigation systems. DOI: 10.1016/j.renene.2019.03.122)
First, it is important to understand the basic components of the module warranty. They are described as below:
- Workmanship warranty: Also known as product warranty, this component protects the end customer against the manufacturing defect, material defect, visual defect, etc. in solar module. Warranty of such kind usually are of limited term and do not last till the (declared) end of life of the solar PV modules.
- Power output warranty: A more significant component of the warranty is the power output warranty, where a manufacturer details the performance of his module over its service lifetime. This further has two sub-components
- First year power output warranty: Almost all the solar PV modules are prone to initial degradation when exposed to light. Also known as light induced degradation (LID), this affects all the known crystalline solar cell based module. Different cell technologies (poly/ mono, BSF, PERC, PERT) have different degradation under LID. In conjunction with the other degradation mechanism, manufacturers declare their first year degradation.
- Subsequent year power output warranty: The most debated & argued part of the entire warranty is the subsequent year power output warranty. This is a consolidated number of degradation based on field performance of module over years, internal & external reliability testing, BOM used, etc.
Usually the warranty is linear in nature, meaning that the first year degradation & subsequent year degradation are fixed and this has been the trend in the PV field for a few years now. Let us further understand what has been the trend in warranties offered by PV manufacturers. The two sub-warranty clauses as mentioned above have different terms. Workmanship warranty are usually of shorter terms depending on the type of module. Most solar module manufacturers offer workmanship warranty in the range of 10 to 15 years. The power generation warranty are usually set for longer time frames. Ranging from 10 years to a period of 30 years, most of the manufacturers offer a warranty of 25 to 30 years for their modules (refer Figure 2 for more details).
Figure 2 : Trend in workmanship & power generation warranty provided by various manufacturers
From the previous figure, we understand that the warranty terms in the solar PV module have increased significantly. There are a lot of enablers which have led to such upgradation of warranties. They are mentioned as below:
- Process automation - One of the first reason of enhancement in the warranties can be termed to process automation. Right from raw material handling to cell loading, glass placement, encapsulant & backsheet placement have been automated. Further in most of the lines, the post lamination processes like excess material cutting, module curing & grounding test of the PV modules have been automated (refer Figure 3). This ensures that the manual handling of PV module & its associated BoM is significantly reduced which enables the module to be defect free.
Figure 3 : A snippet of automated processes at Waaree Energies
- Enhanced check point & quality standards - Quality goes hand in hand with manufacturing and the same is true for solar PV modules. There has been an exponential enhancements in quality check points and standards now when comparing it to the start of century. Further right from incoming quality testing to in-process quality testing to final testing & even external box audit, the solar module is checked at each and every point ensuring that it stays defect free (refer Figure 4). One example is utilization of electro luminescence (EL) imaging of solar module. This process was implemented only post 20th century but this ensured that no cell with micro-cracks, cell defects were used in the solar module. Additionally, with usually two or three EL carried out at module level, the modules going out of the factory are always defect free. Modules from the production lines are often subjected to reliability and (mostly) extended reliability testing. Extended testing ensures that the module stays in-operation in the field beyond its stipulated time which could directly lead to improved warranty terms.
Figure 4 : An overview of quality plan followed by Waaree Energies
- Stringent implementation of best practices & learning from field failures - One of the most effective tool for warranty enhancement is the learning from field failures. The failures/ performance discrepancies may be related to a single or multiple combined aspects which have been well studied over time. The learnings have led to various implementations of best practices in manufacturing & O&M of solar modules. At manufacturing level, upgradation of BoM has been an effective way of off-setting most of those failures. At cell level, upgrading cells from back surface field (BSF) to passivated emitter and rear contact (PERC) has enabled better temperature coefficient in solar module. While light and enhanced temperature degradation (LeTID) seems to be an issue, process changes at cell manufacturing is helping to resolve it. Further, few players have started /have plans of manufacturing their own solar cells which would reduce the dependency on third party for cell supplies. Encapsulant related failure like PID, module yellowing, moisture ingression and corrosion have also been solved by people using better grades of EVA or poly olefins (PO). Junction box (JB) has also been a material of concern for developers/ EPC players/ end customers. This was because moisture ingression would start in many cases from JB. Manufacturers have moved from typical O Ring type JB to semi potted and fully potted JB which ensures enhanced reliability. Further JB's have also become smart, utilizing micro-electronic circuitry which ensures module to be smart and have extended life times. O&M is also improving by adding Diagnostics & Aviation Thermography on large plants and implementing preventive measures, which has further improved power plant lives.
The current trend also indicates a shift towards bifacial cells, larger wafer sizes and high power output modules which will continue for a few years from now. We believe that with upgradation in manufacturing processes, quality techniques, O&M practices & end customer's demand the warranty of solar module shall improve further.