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When solar asset owners consider the reliability of their solar power plants, they may think of the first-class solar modules they purchase or may carry out module quality assurance. However, the factory’s inverters are the core of the solar project’s operations and are critical to ensuring uptime. It must be noted that a 5% cost of equipment in a photovoltaic power plant may cause 90% of the power plant downtime. For reference, according to a 2018 Sandia National Laboratory report, inverters are the cause of up to 91% of failures in major utility projects.
When one or more inverters fail, multiple photovoltaic arrays will be disconnected from the grid, which will significantly reduce the profitability of the project. For example, consider a 250 megawatt (MW) solar project. The failure of a single 4 MW central inverter can cause losses of up to 25 MWh/day, or for a power purchase agreement (PPA) rate of $50/day, Loss of 1,250 MWh per day. If the entire 5MW photovoltaic array is shut down for one month during inverter repair or replacement, the loss of revenue for that month will be US$37,500, or 30% of the original purchase cost of the inverter. More importantly, loss of income is a destructive sign on the balance sheet of asset owners and a red flag for future investors.
Reducing the risk of inverter failure is more than simply buying from a candidate list of financing tier one inverter manufacturers and choosing the lowest price.
With more than ten years of experience in developing and managing inverters of various sizes for major manufacturers, I can assure you that inverters are not commodities. Each supplier has a different set of proprietary designs, design standards, parts and software, as well as common off-the-shelf components that may have their own quality and supply chain issues.
Even if you rely on a proven model that has never failed in proper operation and maintenance, you may still be at risk. Since inverter companies have been under pressure to reduce manufacturing costs, even if the inverters of the same model are compared, the design will continue to be updated. Therefore, the preferred inverter model that was reliable six months ago may have different key components and firmware when installed in your latest project.
In order to reduce the risk of inverter failure, it is important to understand how the inverter fails and what measures can be taken to reduce these risks.
#1 Design: Design failure is related to the premature aging of key electronic components, such as insulated gate bipolar transistors (IGBT), capacitors, control boards and communication boards. These components are designed for certain applications and conditions, such as temperature and electrical/mechanical stress.
Example: If the inverter manufacturer designs the IGBT of its power stack to be rated at a maximum ambient temperature of 35°C, but the inverter runs at full power at 45°C, the inverter rating designed by the manufacturer is incorrect IGBT. Therefore, this IGBT is likely to age and fail prematurely.
Sometimes, inverter manufacturers design inverters with fewer IGBTs in order to reduce costs, which can also lead to higher average operating temperature/stress and premature aging. No matter how illogical, this is still the ongoing practice I have witnessed in the solar industry for 10-15 years.
The internal operating temperature and component temperature of the inverter are key considerations for inverter design and reliability. These premature failures can be reduced by better thermal design, localized heat dissipation, the deployment of inverters in lower temperature areas, and the designation of more preventive maintenance.
#2 Reliability test. Each manufacturer has customized and proprietary test protocols to evaluate and test inverters of various power levels. In addition, the shortened design life cycle may require skipping the critical testing phase of specific upgraded inverter models.
#3 series of defects. Even if the manufacturer chooses the correct component for the correct application, the component itself may have defects in the inverter or any application. Whether it is IGBTs, capacitors or other key electronic components, the reliability of the entire inverter depends on the weakest link in the quality of its supply chain. Systematic technology and quality assurance must be carried out to reduce the risk of defective items eventually entering your solar array.
#4 Consumables. Inverter manufacturers are very specific about their maintenance plans, including replacement of consumables such as fans, fuses, circuit breakers and switchgear. Therefore, the inverter may fail due to improper or non-maintenance. However, similarly, they may also fail due to design or manufacturing defects of third-party inverters or OEM consumables.
#5 Manufacturing: Finally, even the best-designed inverter with the best supply chain may have a poor assembly line. These assembly line problems may occur in all aspects of the manufacturing process. Some examples:
Once again, in order to maintain uptime and short-term and long-term profitability, it is essential to install a proven and reliable inverter. As a third-party quality assurance company, China Eastern Airlines has no preference for manufacturers, models or prejudices against any brand. The reality is that all inverter manufacturers and their supply chains will have quality problems from time to time, and some problems are more frequent than others. Therefore, in order to reduce the risk of inverter failure, the only reliable solution is a consistent reliability and quality assurance (QA) plan.
For most customers of large utility projects with the greatest financial risk, the quality assurance plan should first select the best inverter available based on its design, architecture, site performance, and project-specific options, which will take into account the climate on site Conditions, grid requirements, uptime requirements and other financial factors.
Contract review and warranty review will flag any language that may put the asset owner at a legal disadvantage in any future warranty claims.
Most importantly, a wise QA plan should include factory audits, production monitoring and factory acceptance testing (FAT), including spot checks and testing of the quality of specific inverters manufactured for solar power plants.
Small things constitute the overall picture of a successful solar project. It is important not to neglect the quality when selecting and installing inverters in your solar project.
Jaspreet Singh is CEA’s inverter service manager. Since writing this article, he has become the senior product manager of Q CELLS.