The determination of the optimal efficiency point for solar inverters requires comprehensive consideration from three dimensions: theoretical analysis, practical testing, and system matching. The following are specific methods and steps, combined with theoretical foundations and engineering practice, to help accurately locate efficiency peaks:
1、 Theoretical basis: Understanding the efficiency characteristics of inverters
1. Efficiency curve and key influencing factors
Load Ratio: The efficiency of an inverter varies with the proportion of output power to rated power (load ratio), typically reaching its peak at 50% to 80% load ratio (e.g. a 10kW inverter may have the highest efficiency at 7kW load).
Input voltage range: The output voltage of the solar panel (affected by light and temperature) needs to match the optimal operating voltage of the inverter (such as the MPPT voltage range). Voltage deviation can lead to a decrease in efficiency.
Temperature effect: The losses of internal components (such as IGBT and capacitors) in the inverter increase with temperature, and the efficiency may decrease by 5% to 10% in high temperature environments.
2. Efficiency calculation formula
Efficiency (η)=output power (Pout)/input power (Pin) × 100%
It is necessary to monitor data on both the DC input side (voltage, current) and the AC output side (voltage, current, power factor) simultaneously.
2、 Test method: Obtain efficiency load curve
1. Laboratory testing: benchmark data under standard conditions
Testing equipment: DC power supply (analog battery board output), adjustable load (resistive or AC load box), power analyzer.
Test steps:
Fixed input voltage: Set the DC input at the midpoint of the MPPT voltage of the inverter (such as 400V).
Gradient loading: Starting from 10% load and gradually increasing to 100%, record the input/output power every 10% load.
Draw a curve: with load rate as the horizontal axis and efficiency as the vertical axis, find the peak point (such as η _max corresponding to a load rate of 65%).
Standard reference: Following IEEE 1547, UL 1741 and other standards, the test temperature is controlled at 25 ℃± 5 ℃.
2. On site testing: Simulate the actual operating environment
Condition limitation: Due to the influence of solar irradiance and panel temperature, the input power fluctuates greatly and needs to be monitored in different time periods.
Data collection:
Use the built-in monitoring system of the inverter (such as obtaining real-time data through RS485 and WiFi).
Record the input/output power, ambient temperature, and solar panel voltage every 15 minutes throughout the day (8am to 6pm).
Data analysis:
Exclude inefficient data with irradiance below 200W/m ² (when the load rate is too low).
Group the valid data according to the load rate, calculate the average efficiency, and determine the high-efficiency interval in actual operation.
3、 System matching: Combining the characteristics of the battery board and load
1. Voltage matching between battery board and inverter
MPPT tracking efficiency: The MPPT algorithm of the inverter needs to track the maximum power point (Vmp) of the solar panel in real time to ensure that the input voltage is close to the optimal value (such as when Vmp=380V, the working voltage of the inverter should be stable at 370-390V).
Case: If the battery panel array has a Vmp of 360V under standard test conditions (STC), and the MPPT voltage range of the inverter is 250-450V, the optimal operating voltage should be close to 360V.
2. Matching load characteristics with inverter capacity
Avoid light or overload:
When the load is light (such as load rate<30%), the fixed losses of the inverter (such as control circuit power consumption) account for a high proportion, and the efficiency decreases.
When overloaded (>100%), the inverter may experience current limiting or shutdown, resulting in a sharp drop in efficiency.
Optimization strategy:
When selecting the inverter capacity, leave a margin of 20% to 30% (if the actual maximum load is 8kW, choose a 10kW inverter).
If the load fluctuates greatly, an energy storage system (such as lithium batteries) can be used to adjust the inverter load rate through energy storage charging and discharging.
4、 Tools and Techniques: Assisting in Identifying the Best Efficiency Point
1. Efficiency table/curve provided by inverter manufacturer
2. Real time monitoring and data analysis software
Use third-party platforms such as FusionSolar, SolarEdge Monitoring, or SCADA systems to analyze the peak efficiency periods in historical data (such as from 11am to 2pm every day, with the highest efficiency at a load rate of 60% to 70%).
3. Thermal imaging detection
By scanning the internal components of the inverter with an infrared thermal imager, the area with the lowest temperature usually corresponds to the operating point with the lowest loss and highest efficiency (such as when the IGBT module temperature is 60 ℃ and the aging rate is higher than 80 ℃).
5、 Practical application: Dynamic optimization of efficiency points
1. Time sharing scheduling strategy
If the load is low during the day (such as for household users), excess electricity can be stored through an energy storage system and released when the load increases in the evening, allowing the inverter to operate in an efficient load range.
2. Parallel operation of multiple inverters
In large-scale photovoltaic power plants, some inverters are activated based on real-time power demand (such as 5 out of 10 100kW inverters activated at 500kW load, each operating at 50% load rate, with higher efficiency than 10 operating at light load).
3. Environmental heat dissipation optimization
Ensure that the inverter is installed in a well ventilated location (such as installing a cooling fan) to reduce the impact of temperature on efficiency (efficiency may increase by 0.5% to 1% for every 10 ℃ decrease in temperature).
6、 Attention: Distinguish between "Best Efficiency Point" and "Maximum Power Point"
Maximum Power Point (MPPT): For the solar panel, ensure its maximum output power (related to lighting).
The optimal efficiency point of the inverter: for the inverter itself, it is related to load factor, voltage, and temperature.
Linkage optimization: It is necessary to simultaneously ensure that the battery board operates at the MPPT point and the inverter load rate is close to the high-efficiency range (such as adjusting load fluctuations through energy storage systems).
By using the above methods, the optimal efficiency point of the inverter can be accurately located, and through system design and scheduling strategies, it can be kept as efficient as possible in actual operation, thereby improving the overall power generation of the photovoltaic system.
