To determine whether the losses of a solar inverter are normal, it is necessary to conduct a comprehensive analysis from multiple dimensions, including comparing efficiency parameters, monitoring actual operating data, and checking physical conditions. The following are specific judgment methods and standards:
1、 Refer to the manufacturer's efficiency indicators
Comparison of nominal efficiency
The specification sheet of each inverter will indicate the maximum efficiency (such as 98.5%) and European efficiency (weighted average efficiency, simulating actual working conditions).
Normal situation: Under rated load (such as 80% load rate), the actual efficiency should be close to or slightly lower than the nominal value (error usually ≤ 1%~2%).
Abnormal signal: If the efficiency suddenly drops by more than 3% or remains below the nominal value by 5% for a long time, there may be abnormal losses.
Efficiency curve verification
The efficiency of the inverter shows a parabolic trend with the change of load rate (such as efficiency of about 95% at 20% load, 97% at 50% load, and peak at 80% load).
The efficiency load rate curve can be drawn through the monitoring system and compared with the theoretical curve provided by the manufacturer. If there is a significant deviation (such as low efficiency at low loads), it may be due to an increase in internal losses.
2、 Measured input/output power, calculated efficiency
Power measurement tool
Use a high-precision power meter (such as a Fluke power analyzer) to measure the DC input power (Pdc) and AC output power (Pac) of the inverter separately.
Efficiency calculation formula: η=(Pac/Pdc) × 100%.
Note: The efficiency parameters of different models of inverters vary, and the specifications should be followed.
3、 Monitor operating temperature and heat dissipation status
Temperature sensor data
The temperature of key components inside the inverter, such as IGBT, capacitors, and inductors, is usually monitored through built-in sensors.
Normal range: IGBT temperature is generally ≤ 80 ℃ (when the ambient temperature is 25 ℃). If it exceeds 100 ℃, abnormal losses may occur due to switch losses or insufficient heat dissipation.
Detection method: Check the real-time temperature through the inverter display screen or monitoring platform, or scan the shell with an infrared thermometer (normal shell temperature ≤ 50 ℃, be alert to local overheating areas).
Cooling system inspection
Whether the fan is running normally (the speed automatically adjusts with temperature), and whether the heat sink is clogged with dust (dust can cause a decrease in heat dissipation efficiency of more than 20%).
Abnormal case: When the fan stops running, the IGBT temperature may soar from 60 ℃ to 120 ℃ within 30 minutes, significantly increasing losses.
4、 Analyze the output waveform and harmonic distortion
Waveform quality inspection
Observe the AC output waveform using an oscilloscope, which should normally be a smooth sine wave; If there are "burrs" or distortions, it may be due to excessive switch losses or filter circuit faults.
Total Harmonic Distortion (THD): Normal THD ≤ 5% (grid connected inverter). If THD>8%, it indicates an increase in inverter losses, which may lead to grid compatibility issues.
Spectrum analysis tool
Measure each harmonic component with a harmonic analyzer. If the amplitude of high-frequency harmonics (such as 11th and 13th) significantly increases, it may be due to abnormal IGBT switch losses.
5、 Check the operating noise and mechanical condition
Abnormal noise identification
High frequency "sizzling" sound: excessive loss of inductance core or loose coil;
Periodic "click" sound: Poor contact of the relay leads to increased conduction loss.
During normal operation, the inverter noise mainly comes from the fan (≤ 60dB). If the following sounds occur, it may indicate abnormal losses:
Mechanical component inspection
Whether the screws are loose (causing losses due to inductance vibration), and whether the capacitors are bulging (drying up the electrolyte will increase the equivalent series resistance, leading to heat loss).
6、 Data Trends and Historical Comparisons
Long term efficiency tracking
Export daily/weekly efficiency data through the monitoring system and draw trend charts. If the efficiency shows a slow downward trend (such as a monthly decrease of 0.5%), it may be due to device aging (such as capacitor capacity decay, IGBT on resistance increase).
Sudden efficiency drop (such as efficiency dropping from 98% to 93% on a certain day) may be due to faults such as short circuit or poor contact.
Benchmarking devices of the same model
If there are multiple inverters of the same model, comparing the efficiency data under the same operating conditions (such as the same sunshine intensity and load rate), if the efficiency of a certain device is significantly lower, there may be internal loss issues.
7、 Exclusion of environmental and working condition impacts
Input voltage fluctuation
When the DC input voltage deviates from the rated value (such as below the MPPT voltage range), the inverter may operate in a non optimal state, resulting in a decrease in efficiency (normal fluctuation range ± 10%).
Example: When the voltage of the photovoltaic array drops from 600V to 500V, the efficiency may decrease by 1% to 2%, and it needs to be confirmed whether it is a normal operating condition fluctuation.
Environmental temperature impact
The efficiency of the inverter decreases with the increase of ambient temperature (usually, for every 10 ℃ increase, the efficiency decreases by 0.3% to 0.5%). Efficiency values need to be adjusted based on temperature:
Corrected efficiency=measured efficiency+(standard temperature 25 ℃ - actual ambient temperature) x 0.4%
If the efficiency is still lower than the nominal value after correction, it indicates abnormal losses.
8、 Professional maintenance and troubleshooting
Regular maintenance project
Clean the heat sink (once every quarter, dust can cause temperature to rise by more than 15 ℃), replace the aging fan (usually with a lifespan of 5-8 years), and tighten the electrical connection points (increased contact resistance can increase conduction loss by 10%).
Fault location steps
If there is suspicion of abnormal wear and tear, the following process can be followed for troubleshooting:
Check if the DC side cable joint is overheating (high contact resistance);
Measure the conduction voltage drop of the IGBT module with a multimeter (normally ≤ 1.5V, if>2V, the module will age);
Test the capacitance (rated value ± 20% is normal, if it is lower than 80%, it needs to be replaced).
By using the above methods, it is possible to systematically determine whether the inverter losses are normal. If the problem cannot be located after self inspection, it is recommended to contact the manufacturer's after-sales service for professional testing (such as using oscilloscopes, power analyzers, and other equipment for in-depth diagnosis).
