PV module parameter interpretation and inverter matching

Publisher:电子思维Latest update time:2017-06-06 Source: 来源:深圳古瑞瓦特新能源股份有限公司Author: Lemontree Reading articles on mobile phones Scan QR code
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Introduction: This article is an original work of Shenzhen Growatt New Energy Co., Ltd.

Photovoltaic modules are one of the most important equipment in photovoltaic power plants, and their cost accounts for about 50% of the grid-connected system. The technical parameters of the modules are very important for system design. Only by understanding the module parameters can the photovoltaic inverter be correctly configured. The following takes polycrystalline silicon photovoltaic modules as an example to explain the key parameters of photovoltaic modules.

1. Key parameters in the technical specifications of photovoltaic modules

1. Power

We often say 265Wp photovoltaic modules. The "p" in the table below is the abbreviation of peak, which means its peak power is 265W. All technical specifications will be marked with "standard test conditions". "0~+5" represents positive tolerance. The power range of 265W modules is between 265W and 270W. The following figure is a part of the technical specification of Changzhou Trina's multi-crystalline photovoltaic modules.

Only under standard test conditions (irradiance of 1000W/m2, battery temperature of 25℃), the output power of photovoltaic modules is "nominal power" (265W). When the irradiance and temperature change, the power will definitely change. Under non-standard conditions, the output power of photovoltaic modules is generally not nominal power, as shown in the figure below.

2. Efficiency

Theoretically, modules with the same size and nominal power must have the same efficiency. Photovoltaic modules are composed of solar cells. A photovoltaic module usually consists of 60 (6×10) or 72 (6×10) solar cells, with an area of ​​1.638m2 (0.992m×1.652m) and 1.94m2 (0.992m×1.956m), respectively.

When the irradiance is 1000W/m2, the power received by the 1.638m2 module is 1638W. When the output is 265W, the efficiency is 16.2% and 17% at 280W.

3. Voltage and temperature coefficient

Voltage is divided into open circuit voltage and MPPT voltage, and temperature coefficient is divided into voltage temperature coefficient and power temperature coefficient. When designing series-parallel schemes, the maximum open circuit voltage and MPPT voltage range should be calculated using open circuit voltage, operating voltage, temperature coefficient, and local extreme temperature (preferably during the day) to match the inverter.

2. Output power of the module

The output power of a module is related to solar radiation and temperature, excluding factors such as inverters. Factors that affect radiation are:

1. Solar altitude or latitude: The greater the solar altitude, the shorter the path through the atmosphere, the less the atmosphere weakens the solar radiation, and the stronger the solar radiation reaching the ground; the greater the solar altitude, the smaller the area where the same amount of solar radiation is distributed, and the stronger the solar radiation. For example, the intensity of solar radiation at noon is stronger than that in the morning and evening.

2. Altitude: The higher the altitude, the thinner the air is, the less the atmosphere weakens the solar radiation, and the stronger the solar radiation reaching the ground. For example, the Qinghai-Tibet Plateau is the area with the strongest solar radiation in my country.

3. Weather conditions: sunny days with few clouds have little weakening effect on solar radiation, and the solar radiation reaching the ground is strong. For example, the Sichuan Basin has cloudy, foggy and rainy weather, which weakens solar radiation and makes it the lowest solar radiation area in my country.

4. Atmospheric transparency: High atmospheric transparency has less effect on weakening solar radiation, making the solar radiation reaching the ground stronger.

5. The degree of air pollution: Severe pollution will weaken solar radiation, and less solar radiation will reach the ground. Haze weather has a great impact on photovoltaic modules. In areas with severe haze weather such as Baoding, Hebei, the annual power generation is about 10% less than the theoretical value.

The maximum output power of the module, excluding factors such as inverters, is the solar irradiance and temperature. The limit of solar irradiance is the solar constant, which is 1368W/m2. After reaching the surface of the earth, it is affected by weather and other factors, and the maximum value is about 1200 W/m2. The power-temperature system of the module is about -0.39%/℃. When the module temperature drops, the power of the module will increase. A 250W module, excluding equipment loss, may have a maximum output power of 300W in the areas with the best sunshine in my country, such as northern Ningxia, northern Gansu, southern Xinjiang and other regions.

3. Ratio of inverter and components

When configuring the inverter, pay attention to two aspects:

1. The voltage after multiple components are connected in series is the sum of the voltages of each component. The operating voltage is around the rated operating voltage of the inverter, with the highest efficiency. For a single-phase 220V inverter, the rated input voltage of the inverter is 380V. For a three-phase 380V inverter, the rated input voltage of the inverter is 650V.

For example, a 3kW inverter is equipped with 260W modules, the working voltage is 30.5V, and 12 modules are connected with the working voltage of 366V, and the power is 3.12kW, which is the best. A 30KW inverter is equipped with 260W modules, and 126 modules are connected, with 21 strings in each channel, the voltage is 640.5V, and the total power is 32.76kW, which is the best.

2. The maximum open-circuit voltage after stringing shall not exceed the maximum voltage of the inverter. For example, for a 270W module, the open-circuit voltage is 38.3V, and the open-circuit voltage temperature coefficient is -0.32%/degree. If 24 modules are connected in series at -25 degrees, the final open-circuit voltage V=38.3[1+(-25-25)*(-0.0032)]*24=1066V.

Taking all the above factors into consideration, the system power is between 40-60% of the rated power of the inverter, which has the highest efficiency and the longest life. In order to maximize the performance of the inverter, the components and inverter have different ratios according to different lighting conditions.

In the first-class light area, the average sunshine time exceeds 5 hours, and the power generation time is calculated as 10 hours per day. It is recommended that the components and inverters are configured at a 1:1 ratio, and the average power is about 50%;

In the second-class light area, the average sunshine time is 4 hours, and the power generation time is calculated as 9 hours per day. It is recommended that the components and inverters are configured at 1.1:1, (4*1.1)/9, and the average power is about 49%;

In the three types of light areas with an average sunshine time of 3.5 hours, the power generation time is calculated as 8.5 hours per day. It is recommended that the components and inverters are configured at 1.2:1, (3.5*1.2)/8.5, and the average power is about 49.4%. In the three types of light areas with an average sunshine time of less than 3 hours, the power generation time is calculated as 8 hours per day. It is recommended that the components and inverters are configured at 1.3:1, (3*1.3)/8, and the average power is about 48.75%.

Mountain power stations have different orientations, distributed photovoltaic roofs are complex and have different orientations, photovoltaic modules do not necessarily face south, and the inclination angle of the colored steel tile roof is not the best. The configuration of the inverter can be flexibly handled according to the specific situation.

Shenzhen Growatt New Energy Co., Ltd. was established in May 2010 with a registered capital of RMB 100 million. It is a national high-tech enterprise specializing in providing new energy system solutions such as photovoltaic inverters, energy storage systems, and home smart energy management systems. Since its establishment, Growatt inverters have been exported to more than 100 countries and regions in six continents, including Europe, America, Australia, Asia, Africa, and Latin America, and have been recognized and favored by global customers. Growatt has always maintained its leading position in the Chinese home inverter market and has been committed to becoming the world's largest user-side smart energy solution provider.

Reference address:PV module parameter interpretation and inverter matching

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