Judging the working efficiency of solar inverters requires a comprehensive evaluation from multiple dimensions, including theoretical parameters, actual operating data, and loss analysis. The following are specific methods and key indicators:
1、 Core Efficiency Indicators and Testing Methods
1. Maximum conversion efficiency (Peak Efficiency)
Definition: The ratio (percentage) of the output AC power of an inverter to the input DC power under ideal operating conditions (such as rated DC input voltage, full load).
Test conditions:
DC side: The voltage is the rated value of the inverter (such as 1000V DC for string inverters), and the current reaches the load corresponding to the rated power (such as 10A input current for 10kW inverters).
On the communication side, the output voltage and frequency are stable (such as 220V/50Hz), and the power factor is 1 (pure resistive load).
Data acquisition:
Check the "peak efficiency" parameter on the inverter manual or nameplate (high-efficiency models usually have a rating of ≥ 98%, such as the Huawei FusionSolar series which can reach 98.7%).
On site testing: Use a high-precision power meter to simultaneously measure DC input power (P<sub>DC</sub>) and AC output power (P<sub>AC</sub>), formula: \ (\ textEfficiency}=\ frac {P_ {\ textAC}} {P_ {\ textDC}} \ times 100 \% \)
2. European Efficiency (η<sub>EU</sub>)
Definition: Simulate the weighted average efficiency under different lighting intensities, which is closer to the actual operating scenario (lighting intensity affects the output power of the solar panel, thereby affecting the inverter load rate).
Meaning: Low light scenarios (such as early morning, evening, cloudy days) have a higher proportion, and high-efficiency inverters in Europe have better annual power generation.
Data acquisition: Manufacturers usually provide this parameter in their technical manuals (high-quality models with η<sub>EU</sub>≥ 97%).
3. Dynamic MPPT efficiency
Definition: The speed and accuracy of an inverter tracking the maximum power point (MPP) of a solar panel directly affect the system's power generation.
Test scenario:
Rapid occlusion change: Use an object to quickly occlude/remove the battery panel and observe the time for the inverter to relock the MPP (ideal value<2 seconds).
Multi peak environment: Simulate complex occlusion (such as partial solar panels being covered by shadows), and check if the inverter can recognize the global maximum power point (rather than local peaks).
Assessment tool: Check the "MPPT tracking efficiency" through inverter monitoring software (such as Sunac iSolarCloud), which should be>99% normally.
2、 Comparative analysis of actual operational data
1. Assessment of power generation
Theoretical power generation: Calculated based on the total power of the solar panel and the local sunshine hours (such as a 10kW system with a daily average of 4 hours of sunshine, theoretical power generation ≈ 10kW × 4h=40kWh).
Actual power generation: obtained by accumulating power generation data through inverters (such as actual power generation of 35kWh per day).
Efficiency Conversion: \ (\ text {System Comprehensive Efficiency}=\ frac {\ text {Actual Power Generation} {\ text {Theoretical Power Generation}} \ times 100 \% \)
2. Loss splitting method
Formula: \ (\ text {inverter loss}=\ text {total output power of the solar panel} - \ text {AC output power of the inverter} - \ text {other losses (lines, transformers, etc.)} \)
Data acquisition:
Total power of the solar panel: Sum up the current and voltage of each string (string inverters can directly read data from each string).
Communication output power: Real time data from inverter display screen or monitoring platform.
Normal range: The inverter's own loss should be less than 3% (for high-efficiency models, it should be less than 2%). If it exceeds 5%, component aging or heat dissipation issues should be investigated.
3. Temperature coefficient test
Principle: The efficiency of the inverter decreases with increasing temperature (due to the heating of power devices causing an increase in internal resistance), and the temperature coefficient reflects the percentage of efficiency decrease for every 1 ℃ increase.
Testing method:
Measure efficiency η<sub>1</sub>at ambient temperature T<sub>1</sub>;
Raise the temperature to T<sub>2</sub>(such as increasing the load or turning on the heating device), measure the efficiency η<sub>2</sub>;
Calculate temperature coefficient: \ (\ text {temperature coefficient}=\ frac {\ eta_ {1} - \ eta_ {2}} {T {2} - T {1}} \ times 100 \% \)
3、 Key component status detection
1. Power devices (IGBT/MOSFET)
Testing method:
Infrared temperature measurement: Use an infrared thermal imager to measure the surface temperature of the device. During normal operation, it should be<85 ℃ (maximum temperature<125 ℃). If the local temperature is too high, it may be due to device aging or poor contact.
Conducting voltage drop test: Use an oscilloscope to measure the voltage drop when IGBT is conducting. If the voltage drop increases by more than 20% compared to the new product, it indicates a decline in device performance.
2. Electrolytic capacitors
Key factors of lifespan: The evaporation of electrolyte leads to a decrease in capacity, with a standard lifespan of about 10 years (the lifespan is halved for every 10 ℃ increase in ambient temperature).
Testing method:
Capacity measurement: Use a digital bridge to measure the nominal capacity of the capacitor (if the nominal capacity is 1000 μ F and the actual measurement is less than 700 μ F, it needs to be replaced).
ESR (Equivalent Series Resistance) measurement: An increase in ESR indicates capacitor aging, which can be detected using a multimeter capacitor or a dedicated ESR meter.
3. Cooling system
Fan status: Listen for any abnormal noise during operation and measure the actual speed with a tachometer (if the deviation from the nominal value is greater than 20%, it needs to be replaced).
Heat sink temperature difference: Use an infrared thermometer to detect the surface temperature difference of the heat sink. If the local temperature difference is greater than 10 ℃, it may be due to dry silicone grease or poor contact.
4、 Professional tools and evaluation process
1. Essential instruments
High precision power meter (such as Fluke 435): Simultaneously measure AC and DC power with an accuracy of ≥ 0.5%.
Oscilloscope: Observe IGBT drive waveform and output voltage harmonics (harmonic content should be<5%, THD ≤ 3%).
Data logger: continuously records 24-hour operating data and analyzes the efficiency curve as a function of light and temperature.
2. Evaluation steps
No load loss test: When the inverter is turned on and not connected to a load, measure the standby power (normally<10W, if>30W, it indicates aging of the control circuit).
Load gradient test: Gradually increase from 10% load to 100%, record the efficiency of each load point, and draw the "efficiency load rate" curve (the ideal curve should reach its peak at 50% -80% load).
Dynamic response test: Simulate sudden changes in lighting caused by cloud cover and observe the time it takes for the inverter output power to recover and stabilize (preferably less than 5 seconds).
summarize
To determine the efficiency of solar inverters, it is necessary to combine laboratory level parameter testing and actual operational data monitoring
Short term evaluation: Quickly assess performance through indicators such as peak efficiency, European efficiency, MPPT speed, etc;
Long term monitoring: using intelligent operation and maintenance platform to analyze the trend of power generation, the proportion of losses, and the health status of components;
Maintenance focus: Regularly clean the cooling system, check the aging of capacitors and power devices, and replace damaged components in a timely manner. By using the above methods, efficiency bottlenecks can be accurately identified, ensuring that the inverter always operates in the high-efficiency range and maximizing the revenue of the photovoltaic system.
