When solar system owners think about the reliability of their solar system, they may be thinking of purchasing a top quality solar panel or they may be performing quality assurance on modules. 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's downtime. 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 systems are disconnected from the grid, which significantly reduces the profitability of the project. For example, consider a 250 megawatt (MW) solar project. A single failure of a 4 MW central inverter can result in a loss of up to 25 MWh / day or USD 1250 per day with a power purchase agreement (PPA) of USD 50 / day. MWh. If an entire 5 MW PV array is out of service for a month while the inverters are being repaired or replaced, the loss of revenue for that month will be $ 37,500, or 30% of the original cost of that inverter. More importantly, lost revenue is a damaging marker on the asset owner's balance sheet and a red flag for future investors.
Inverters are not goods
A single inverter failure can result in a loss of up to 25 MWh / day or $ 1250 per day. Source: CEA
Reducing the risk of inverter failure is more important than buying from a shortlist of bankable, perceived Tier 1 inverter manufacturers and choosing the lowest price possible.
With over a decade of experience designing and managing inverter sizes of all sizes for large manufacturers, I can assure you that inverters are not a commodity. Each supplier has a different set of proprietary design, design criteria, parts and software, as well as common off-the-shelf components that may have their own quality and supply chain problems.
Even if you rely on a single proven model that has never failed with proper operation and maintenance, you may still be at risk. Since inverter manufacturers 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 will likely have different key components and firmware by the time it is installed on 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 bipolar transistor (IGBT) with insulated gate, capacitors, control boards and communication boards. These components are designed for specific applications and conditions such as temperature and electrical / mechanical stresses.
Example: If an inverter manufacturer designs its power stack with an IGBT that is designed for a maximum ambient temperature of 35 ° Celsius, but the inverter is operated at full power under 45 ° C conditions, the manufacturer has designed the inverter with an incorrect nominal power IGBT. 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 / voltages and premature aging. As illogical as this may be, this is an ongoing practice I've seen 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 by better thermal design, localized heat dissipation, using the inverter in zones with lower temperatures, and establishing more preventive maintenance.
# 2 reliability tests. Each manufacturer has custom and proprietary test protocols for evaluating and testing different power classes of inverters. In addition, shortened design lifecycles may require skipping critical test phases on a particular upgraded model of inverter.
# 3 serial flaws. Even if the manufacturer has selected the right component for the right application, the component itself can have defects for inverters or other applications. Regardless of whether it is an IGBT, a capacitor or some other important electronic component, the entire inverter is only as reliable as the weakest link in the quality of its supply chain. Systematic technical and quality assurance must be carried out to reduce the risk of a faulty project in your solar array.
# 4 consumables. Inverter manufacturers pay great attention to 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 here due to errors in the design or manufacture of the inverter's third-party or OEM 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
This reduces the risk of an inverter failure and a loss of sales
To maintain uptime – and short and long term profitability – installing a proven and reliable inverter is again essential. As a third-party quality assurance company, CEA has no preferred manufacturers, models, or prejudices for or against any 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. To reduce the risk of inverter failure, the only reliable solution is a consistent reliability and quality assurance (QA) program.
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 that takes into account the climatic conditions and the grid of the site requirements, availability requirements and other financial factors.
A contract review and warranty review, which identifies any language that will legally prejudice the owner of the asset for future warranty claims, is also essential.
Most importantly, a sensible QA program should include a factory audit, production monitoring, and factory acceptance test (FAT), including spot checks and quality testing of certain 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 the manager of Inverter Services at CEA. He has been Senior Product Manager at Q CELLS since writing this piece.