When solar system owners think about the reliability of their solar system, they may be thinking of purchasing first tier solar panels or they may be doing a module quality check. However, the inverters of the system are the operational heart of the solar project and crucial for ensuring the operating time. It is essential to note that a device that costs 5% within a PV system can be responsible for 90% of the system downtimes. For reference, according to a 2018 report by the Sandia National Lab, inverters are the cause of up to 91% of errors in large utility projects.
If one or more inverters fail, several PV generators are disconnected from the grid, which significantly reduces the profitability of the project. For example, if we consider a 250 megawatt (MW) solar project, a single failure of a 4 MW central inverter can lead to a loss of up to 25 MWh / day, or MWh. If an entire 5 MW PV array fails for a month while the inverters are being repaired or replaced, the loss of revenue for that month would be $ 37,500, or 30% of the original cost of that inverter to purchase. More importantly, loss of income is a damaging sign on the asset owner's balance sheet and a red flag for future investors.
Inverters are not a commodity
A single inverter failure can result in a loss of up to 25 MWh / day or $ 1,250 per day. Source: CEA
Reducing the risk of inverter failure is more important than just buying from a shortlist of bankable manufacturers that are perceived as first-class inverter manufacturers and choosing the lowest price.
With over a decade of experience developing and managing inverters of all sizes for major manufacturers, I can assure you that inverters are not a commodity. Each supplier has different proprietary designs, design criteria, parts and software, as well as common off-the-shelf components that can have their own quality and supply chain problems.
Even if you rely on a single proven model that has never failed with proper O&M, you can still be at risk. Because inverter companies are constantly under pressure to reduce manufacturing costs, designs are constantly updated even when inverters of the same model are compared. As a result, a previously reliable inverter model from six months ago is likely to have different key components and firmware when installed in your latest project.
To reduce the risk of inverter failure, it is important to understand how inverters fail and what can be done to reduce these risks.
Five main reasons why inverters fail
# 1 design: Design flaws are related to the premature aging of critical electronic components, such as B. the insulated gate bipolar transistor (IGBT), capacitors, control boards and communication boards. These components are designed for specific applications and conditions such as temperature and electrical / mechanical loads.
Example: If an inverter manufacturer designs its power stack with an IGBT that is designed for a maximum ambient temperature of 35 ° C, but the inverter runs at full power at 45 ° C, then the manufacturer has designed the inverter with the wrong IGBT power rating. As a result, there is great potential for this IGBT to prematurely age and fail.
Sometimes the inverter manufacturer designs the inverter with fewer IGBTs to reduce costs, which also leads to higher mean operating temperatures / loads and premature aging. So illogical, this remains an ongoing practice that I witnessed during my 10-15 years in the solar industry.
The internal operating temperature and the component temperature of the inverter are important factors in the design and reliability of the inverter. These premature failures can be reduced through better thermal design, localized heat dissipation, using the inverter in zones with lower temperatures and more preventive maintenance.
# 2 reliability check. Every manufacturer has customer-specific and proprietary test protocols in order to evaluate and test different performance classes of inverters. In addition, with shortened design life cycles, it may be necessary to skip critical test phases on a particular updated model of an inverter.
# 3 serial flaws. Even if the manufacturer has selected the right component for the right application, the component itself may have defects for inverters or other applications. Whether IGBT, capacitor or other critical electronic components – the entire inverter is only as reliable as the weakest link in its supply chain. Systematic technical and quality assurance must be carried out in order to reduce the risk of a faulty project ending up in your solar system.
# 4 consumables. Inverter manufacturers pinpoint their maintenance schedules, including replacing consumables such as fans, fuses, circuit breakers, and switchgear. As a result, inverters can fail due to improper or lack of maintenance. However, they can also fail due to design or manufacturing defects in third-party or OEM inverter consumables.
# 5 manufacture: After all, even the best-designed inverters with the best supply chains can have poor assembly lines. These assembly line problems can occur at various points in the manufacturing process. Some examples:
Source: CEA Source: CEA
In this way you reduce the risk of inverter failure and loss of sales
Again, installing a proven and reliable inverter is essential to maintain uptime – and short and long term profitability. As an external quality assurance company, CEA has no preferred manufacturers, models or prejudices for or against a brand. The reality is that all inverter manufacturers and their supply chains can experience quality issues from time to time, and some more frequently than others. In order to reduce the risk of inverter failures, the only reliable solution is therefore a consistent reliability and quality assurance program (QA).
For most customers with large utility projects with the greatest financial risk, the QA program should start with the selection of the best available inverter based on design, architecture, field performance and project-specific selection, taking into account the climatic conditions of the site, the grid requirements, availability requirements and other financial factors.
Contract review and warranty review, showing any language that will legally penalize the asset owner in future warranty claims, is also essential.
Most importantly, a prudent QA program should include a factory audit, production monitoring, and factory acceptance test (FAT), including spot checks and quality checks of the specific inverters made for the solar system.
Small things make the big picture of a successful solar project and it is important not to overlook quality when selecting and installing inverters in your solar project.
Jaspreet singh was manager of Inverter Services at CEA. He has been Senior Product Manager at Q CELLS since writing this article.