20kW Grid-Connected Solar Battery Test Plan for Grid Interaction, Harmonic Distortion, Insulation Resistance, Environmental Adaptability, and Cycle Life

　　I. Test Background and Core Objectives

　　With the widespread application of photovoltaic energy storage technology in distributed energy systems, 20kW grid-connected solar batteries, as core devices for energy storage and grid interaction, have a significant impact on grid reliability and overall economic viability. Their operational stability, power quality compatibility, electrical safety, environmental adaptability, and long-term cycle life directly impact the reliability of grid operations and overall lifecycle economics. This test focused on five key dimensions, aiming to verify that the equipment meets the full-scenario application requirements of "grid connection reliability, safety and compliance, environmental adaptability, and long-term durability":

　　Ensuring the synergy between the equipment and the grid during grid connection, and avoiding grid shocks caused by power fluctuations and grid switching;

　　Controlling harmonic distortion in power output to ensure that the power quality connected to the grid meets national standards;

　　Verifying the insulation performance of the equipment to eliminate safety hazards such as leakage and insulation failure, providing a basis for the long-term safe operation of the equipment;

　　Assessing the equipment's ability to withstand extreme temperature cycles and harsh outdoor environments, ensuring stable operation in different regions and climates;

　　Evaluating the capacity degradation pattern under 1C charge and discharge conditions, clarifying the performance retention rate of the equipment after long-term use, and providing data support for lifespan planning and operation and maintenance decisions.

　　II. Grid Interaction Testing

　　1. Test Significance

　　Grid interaction is the core component of the 20kW solar battery's interoperability with the grid. This test simulates the full "charging - discharging - grid-connected power supply" scenario in actual operation to verify the device's ability to respond to changes in grid parameters and prevent abnormal interactions from causing grid frequency or voltage fluctuations or device downtime.

　　2. Core Test Indicators and Implementation Standards

　　Grid-connected power regulation capability: The reference standard is GB/T 37408-2019. Qualified requirements include a power regulation range of 0-20kW and a response time of no more than 1s.

　　Grid fault low voltage ride-through: The reference standard is GB/T 19964-2012. Qualified requirements include a continuous support time of no less than 0.15s when the voltage drops to 0%.

　　Off-grid/grid-connected automatic switching: The reference standard is GB/T 34120-2017. Qualified requirements include a switching time of no more than 50ms and no significant voltage surge during the switching process.

　　Grid-connected current phase matching: The reference standard is IEC 61727:2004. Qualified requirements include a power factor of no less than 0.95, with either lagging or leading phases acceptable.

　　3. Test Method

　　A simulated power grid test platform was built, equipped with a grid simulator with adjustable voltage and frequency. The platform simulated normal grid conditions, voltage drops (10%-90% of rated voltage), and frequency fluctuations (49.5Hz-50.5Hz).

　　The solar battery was controlled to switch between charge and discharge modes at different power levels (20%/50%/100% of rated power), and the device output power, grid-connected current, and grid parameter change curves were recorded.

　　A grid power outage was simulated to test the device's off-grid switching logic. After the grid was restored, the accuracy and stability of the automatic grid connection were verified.

　　III. Harmonic Distortion Rate Test

　　1. Test Significance

　　When solar batteries are connected to the grid, their internal power electronic devices, such as inverters, are prone to generating harmonic currents. If the harmonic distortion rate exceeds the specified value, it can distort the grid voltage waveform, interfere with the normal operation of nearby electrical equipment (such as precision instruments and communications equipment), and even accelerate the aging of grid equipment such as transformers and cables. This test focuses on controlling total harmonic distortion (THD) and the content of each characteristic harmonic.

　　2. Core Test Indicators and Implementation Standards

　　Based on GB/T 14549-1993 "Power Quality - Public Grid Harmonics" and GB/T 37408-2019 "Technical Requirements for Grid-Connected Photovoltaic Energy Storage Systems":

　　Total Harmonic Distortion (THD): Under rated power (20kW) output conditions, grid-connected current THD ≤ 5%;

　　Harmonic current content: 3rd harmonic ≤ 4%, 5th harmonic ≤ 3%, 7th harmonic ≤ 2%, 9th and higher harmonics ≤ 1% (all based on rated current).

　　3. Test Method

　　Connect a high-precision power quality analyzer (such as the Fluke 6100B) to the grid-connected output of the device (the point where the inverter connects to the grid). Set the sampling frequency to ≥ 2kHz and the sampling duration to ≥ 10 grid cycles.

　　Test the device's harmonic data at 25%, 50%, 75%, and 100% of rated power, recording the total harmonic distortion (THD) and the current amplitude and phase of harmonics 3-31.

　　Compare to standard limits and analyze the harmonic sources (such as inverter switching frequency and filter circuit parameters). If these values exceed the standard, propose optimization suggestions for the filtering solution (such as adding an LC filter).

　　IV. Insulation Impedance Test

　　1. Test Significance

　　Insulation impedance is a key indicator for measuring the electrical safety of solar cells and is directly related to the risk of electric shock to equipment operators and nearby personnel. During long-term operation, factors such as high temperatures, humidity fluctuations, and electrolyte leakage can cause insulation degradation. If insulation resistance is too low, this can easily lead to leakage, short circuits, and even fire. This test covers the equipment's critical electrical circuits to ensure that insulation performance meets safe operation requirements.

　　2. Core Test Indicators and Implementation Standards

　　Based on GB/T 17215.301-2007 "AC Current Measuring Equipment - Particular Requirements - Part 1: Active Energy Meters" and IEC 62109-2:2011 "Safety Requirements for Photovoltaic Inverters - Part 2":

　　Insulation resistance between the positive and negative terminals of the battery and the device housing: ≥ 10MΩ at a DC 500V test voltage;

　　Insulation resistance between the inverter output (AC side) and the housing: ≥ 5MΩ at an AC 1000V test voltage;

　　Adaptability to hot and humid environments: After 48 hours in an environment with a temperature of 40°C and a relative humidity of 90%, the insulation resistance must still meet the above requirements.

　　3. Test Method

　　Before testing, disconnect all external power supplies and ground connections to ensure the test circuit is independent.

　　Use an insulation resistance tester (such as the KEW 3125) to apply the specified test voltage to the "battery positive - case," "battery negative - case," and "AC output - case" connections for 1 minute, then read the impedance values.

　　Place the device in a constant temperature and humidity chamber to simulate a hot and humid environment, then repeat the test to verify the stability of the insulation performance.

　　If the impedance value is below the standard limit, investigate for insulation damage or moisture on the terminal blocks. Repair the problem and retest.

　　V. Environmental Adaptability Testing

　　(I) -40°C to 60°C Temperature Cycle Test

　　1. Test Significance

　　20kW grid-connected solar cells are often deployed outdoors. They must withstand extreme operating conditions, ranging from low temperatures (-40°C) in winter at high latitudes to high temperatures (60°C) in summer at low latitudes. These drastic temperature fluctuations can easily lead to degradation of active materials, electrolyte solidification/evaporation, and casing cracking. This test simulates extreme temperature cycles to verify the device's performance stability and structural integrity under alternating temperature fluctuations.

　　2. Core Test Indicators and Implementation Standards

　　Based on GB/T 31485-2015 "Safety Requirements for Power Batteries for Electric Vehicles" and IEC 61215:2021 "Terrestrial Crystalline Silicon Photovoltaic Modules — Design Qualification and Type Approval":

　　Cycling Parameters: Total number of cycles ≥ 50, with a single cycle consisting of four stages: "High temperature phase (60°C ± 2°C, 4 hours) → Cooling (at a rate of 5°C/min) → Low temperature phase (-40°C ± 2°C, 4 hours) → Warming (at a rate of 5°C/min)";

　　Performance Requirements: After cycling, the battery's rated capacity decay is ≤ 10%, charge and discharge efficiency is ≥ 90% at a rated power of 20kW, grid-connected interaction functions (power regulation and switching logic) are normal, the casing is free of cracks or deformation, and the terminals are not loose;

　　Safety Requirements: No leakage, smoke, or bulging occurs during cycling, and the insulation resistance still meets the requirement of "≥ 10MΩ at 500V DC."

　　3. Test Method

　　Place the device (including the complete battery pack and inverter module) in a high-temperature and low-temperature humidity test chamber. Connect a temperature recorder, charge-discharge tester, and grid-connected simulation system to monitor the battery cell voltage, module temperature, and output power in real time.

　　Start the test according to the set cycle parameters, pause after every 10 cycles, and let it rest at room temperature for 2 hours. Measure the current capacity and charge-discharge efficiency, and record the data trend.

　　After 50 cycles, visually inspect the device's structural integrity, retest the insulation resistance and grid-connected interaction performance, and compare the initial data to verify the degree of attenuation.

　　(II) IP66 Protection Rating Test

　　1. Test Significance

　　Sand and dust in outdoor environments can easily clog the device's heat dissipation channels and corrode metal contacts. Rainwater leakage can cause internal circuit shorts. IP66 protection is the basic outdoor adaptation requirement for photovoltaic energy storage equipment ("Level 6 Dustproof" means completely preventing dust intrusion, and "Level 6 Waterproof" means withstanding strong water jets). This test verifies the device's casing's ability to protect against the intrusion of solid foreign objects and liquids.

　　2. Core Test Indicators and Implementation Standards

　　According to GB/T 4208-2017 "Degrees of Protection Provided by Enclosures (IP Code)":

　　Dustproof (IP6X): The device is placed in a dust test chamber with a talcum powder concentration of 2kg/m³ for 8 hours. After the test, no visible dust is present inside the device, and the electrical components (inverter, wiring terminals) function normally.

　　Waterproof (IPX6): Using a 12.5mm inner diameter nozzle, water is sprayed continuously for 1 minute/m² (the total area is calculated based on the device's external surface) from a distance of 2.5m to 3m, at a water pressure of 100kPa ± 5kPa and a water flow rate of 100L/min ± 5L/min. All external surfaces (front, sides, top, and bottom) of the device are sprayed with water for 1 minute/m² (the total area is calculated based on the device's external surface). After the test, there are no signs of water intrusion inside the device, the insulation resistance is ≥10MΩ (DC 500V), and the grid-connected function is normal.

　　3. Test Method

　　Dust Resistance Test:

　　Power off the device, close all external interfaces (such as communication and charging ports), and secure it in the dust test chamber as normal.

　　Start the test chamber and maintain a talcum powder suspension for 8 hours. After the test, remove the device, remove the outer casing, inspect the interior (focusing on the inverter cavity and battery junction box) for residual dust, and then power on to test basic functions.

　　Water Resistance Test:

　　The device remains powered on and connected to a grid-connected simulation system, monitoring output power and insulation resistance in real time.

　　Adjust the nozzle parameters according to standard requirements and spray each external surface of the device with strong water. Pause for 5 minutes after each surface to check for water ingress into the outer casing gaps (such as the panel-to-box connection and heat dissipation holes). Simultaneously record changes in electrical parameters.

　　After testing all surfaces, let the device sit for 24 hours. Then retest the insulation resistance and grid-connected performance to confirm there are no hidden faults.

　　VI. Cycle Life Testing - 1C Charge-Discharge Capacity Decay Rate

　　1. Test Significance

　　1C charge-discharge is a typical operating condition for a 20kW grid-connected solar battery ("1C" refers to charging and discharging at a current of 1 times the battery's rated capacity. For example, a 20kW/h battery has a 1C charge current of 20A and a discharge current of 20A). Capacity decay under long-term cycling directly determines the lifetime value of the device. Excessive decay shortens energy storage time and reduces grid-connected power supply capacity, requiring premature device replacement and increasing operational costs. This test simulates long-term 1C cycling to quantify the capacity decay rate and verify whether the device meets its design lifespan (typically 5-10 years).

　　2. Core Test Indicators and Implementation Standards

　　According to GB/T 31484-2015 "Cycle Life Requirements and Test Methods for Power Batteries for Electric Vehicles" and IEC 62620-2018 "Lithium Secondary Batteries and Battery Packs for Industrial Applications":

　　Basic Parameters: The test environment temperature is controlled at 25°C ± 2°C (simulating normal operating conditions). The initial battery capacity must be calibrated using the "0.2C charge to rated voltage → 1 hour standstill → 0.2C discharge to cut-off voltage" procedure, recorded as C₀.

　　Cycling Parameters: 1C constant current charge to the battery's rated voltage (e.g., approximately 3.65V/cell for lithium iron phosphate batteries), then constant voltage charge until the current drops to 0.05C (charge cut-off). After 30 minutes of standstill, discharge at 1C constant current to the discharge cut-off voltage (e.g., approximately 2.5V/cell for lithium iron phosphate batteries), completing one cycle.

　　Capacity Fade Limit: Cycle After 1000 cycles, the actual battery capacity (C₁₀₀₀) must be ≥80% of C₀; after 2000 cycles, C₂₀₀₀ must be ≥70% of C₀ (if the device has a design life of 10 years, assuming an average of 300 cycles per year, 2000 cycles corresponds to approximately 6.7 years, which must meet degradation requirements).

　　Supplementary requirements: During cycling, the battery cell voltage difference must be ≤50mV, the outer shell must not bulge or leak, the charge and discharge efficiency (discharge capacity/charge capacity) must be ≥95%, and the insulation resistance must still meet the requirement of "≥10MΩ at 500V DC" after each cycle.

　　3. Test Method

　　Pretreatment and Initial Capacity Calibration:

　　Place the device battery pack (disassemble into the smallest test unit or maintain the entire module, consistent with actual application) in a constant temperature chamber (25°C ± 2°C). Connect a high-precision charge and discharge tester (such as the Xinwei BTS-9000) and record the individual and total voltages.

　　Charge at 0.2C to the rated voltage, maintain constant voltage to 0.05C, and let stand for 1 hour. Then discharge at 0.2C to the cutoff voltage and record the discharge capacity, which is the initial capacity C₀. Repeat this calibration twice and take the average value to ensure accuracy.

　　1C Cycle Test Execution:

　　Initiate the cycle according to the following sequence: "1C constant current charge → constant voltage charge to 0.05C → let stand for 30 minutes → 1C constant current discharge to the cutoff voltage." Pause after every 100 cycles.During the test, re-measure the current capacity Cₙ (n is the number of cycles) using the "0.2C charge and discharge" method and calculate the capacity decay rate: decay rate = (C₀ - Cₙ)/C₀ × 100%;

　　Real-time monitoring of key parameters during the cycle: charge time, discharge time, cell voltage extremes (maximum/minimum voltage), and battery surface temperature (must be ≤45°C). If a cell voltage difference exceeds 50mV, the temperature rises abnormally (>50°C), or the battery case deforms, immediately pause the test and analyze the cause.

　　Endpoint Determination and Data Summary:

　　When the re-measured capacity Cₙ is less than 80% C₀ on a particular cycle, stop cycling and record the total number of cycles to that point (i.e., the actual cycle life). If C₂₀₀₀₀≥70% C₀ after 2000 cycles, stop according to the test target (or continue until the capacity decay reaches the limit).

　　Collate all cycle data and plot a "number of cycles - capacity decay rate" curve. Analyze the decay pattern (e.g., rapid decay in the first 500 cycles, followed by a gradual decline). Verify the device's grid-connected functionality after cycling (e.g., whether the 20kW power output is normal).

　　VII. Test Summary and Application Value

　　The five core tests conducted on this 20kW grid-connected solar battery construct a comprehensive performance verification system encompassing grid interoperability, power quality, electrical safety, environmental adaptability, and long-term life. Its application value is reflected in three key areas:

　　Grid Adaptability: Grid interaction and harmonic distortion rate tests ensure that the device does not disrupt public power quality after connecting to the grid. Low voltage ride-through and phase matching capabilities meet grid dispatch requirements, reducing the risk of grid failures.

　　Safety and Environmental Compatibility: Insulation impedance testing eliminates electric shock hazards. -40°C to 60°C temperature cycling and IP66 testing ensure reliable operation in outdoor environments, including extreme cold and heat, dust, and heavy rain, making it suitable for deployment in diverse climate zones across China.

　　Lifecycle Cost-Effectiveness: 1C cycle life testing quantifies capacity degradation patterns and provides users with recommended replacement cycles (e.g., if the device retains 75% capacity after 1500 cycles, it is recommended to evaluate and replace it in approximately 8 years). This avoids the cost and safety risks associated with premature retirement or overuse.

　　Test results can be directly used for equipment factory certification, technical evaluation in project bidding, and cross-brand performance comparison. They also provide data support for the "equipment selection - operation and maintenance planning - lifecycle cost estimation" process for photovoltaic energy storage systems, promoting the development of distributed energy systems towards "high reliability, long life, and low cost."

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