Basic knowledge of photovoltaic power generation

Photovoltaic power station inspection and pre-test


Lightning detection

Lightning protection detection is to ensure the long-term effective and reliable operation of all devices in the photovoltaic area of the power station. It periodically checks and measures whether the grounding systems of the power station meet the corresponding grounding requirements to ensure the safe operation of the power station.

1. Detection classification Detection is divided into first detection and regular detection. The first detection is divided into the detection of lightning protection devices in the construction process of new, rebuilt and expanded buildings and the first detection of lightning protection devices in buildings after being put into use. Periodic testing is testing carried out according to the prescribed cycle. During the construction process of lightning protection devices for new, rebuilt or expanded buildings, the structure, layout, shape and material specifications, dimensions, connection methods and electrical properties shall be tested in stages. After being put into use, the first inspection of the lightning protection device of the building shall be carried out according to the requirements of the design document.

2. Test items (1) Lightning protection classification of buildings; (2) flash receiver; (3) Lead off; (4) grounding device; (5) Division of lightning protection area; (6) lightning electromagnetic pulse shielding; (7) equipotential connection; (8) Surge protector (SPD). 3. Probe The probe should be made of material with good conductivity. The length and diameter of the probe should be no less than 20m and 0.8cm, and the distance between the two probes should be no less than 5m. The depth of the probe should not be less than one third of the length of the probe. The two lines should not cross each other and should be separated to avoid mutual influence. The closest distance between the probe and the device must be greater than 15m.

Component testing

Component detection refers to the periodic detection of components to verify whether they can meet the specified performance parameters during operation.

1. Photovoltaic array temperature rise loss detection method: Based on the I-V curve of the cluster tested after cleaning and the backplane temperature measured in the field. According to the temperature coefficient of this type of component and the measured junction temperature, the maximum power point power at the junction temperature of the battery is calculated at 25℃. Calculate the voltage temperature loss percentage according to the voltage temperature loss calculation formula, and calculate the power temperature loss percentage according to the power temperature loss calculation formula.

(1) PV cluster cluster power temperature rise loss rate = (25℃ junction temperature cluster maximum power – uncorrected junction temperature cluster maximum power) /25℃ junction temperature cluster maximum power ×100%.

(2) PV cluster cluster voltage temperature rise loss rate = (25℃ junction temperature cluster open-circuit voltage – uncorrected junction temperature cluster open-circuit voltage) /25℃ junction temperature cluster open-circuit voltage ×100%.

(3) Result analysis: The test results shall prevail to analyze the temperature loss and evaluate the heat dissipation conditions.

2. The photovoltaic module power decline detection method is as follows: (1) If a power reference module is set when it is put into operation, the I-V curve of the reference module should be detected when the light intensity of the test site exceeds 700W/m2 and compared with the initial value of the reference module to obtain the accurate power decline rate of the photovoltaic module. The results of the on-site test and comparison of the sampling module with the nominal power can be used as reference data. (2) if there is no power reference component, when the light intensity of the test site exceeds 700W/m2, the ⅰ-v curve of each component in the selected and cleaned cluster is detected, and the light intensity and the temperature of the component are recorded at the same time. After correcting the STC condition to compare with the nominal power, the rough PV module power decline rate is obtained. (3) For components whose power drop exceeds the determination conditions, records should be made to prepare for subsequent electroluminescence (EL) tests. (4) Whether the reference component power or the nominal power is used as a reference, it is recommended to send the laboratory for reinspection if the field test results are questioned when the rout rate exceeds the judgment conditions. (5) Criteria: The contract terms between the supply and demand parties shall prevail. In the absence of contract agreement, the indicators in the Standard conditions of photovoltaic manufacturing Industry of the Ministry of Industry and Information Technology (Article 47, 2013) are used as reference: the average decline rate of polysilicon modules within 2 years shall not exceed 3.2%; The average decline of monocrystalline silicon modules within 2 years should not exceed 4.2%, and the average decline of thin-film photovoltaic modules should not exceed 5.0%.

3. Electroluminescence (EL) detection of photovoltaic modules (1) Sampling principle: Through the previous test, only the components with serious problems or power decline found by visual observation, infrared scanning and 1-V test should be tested for electroluminescence (EL). (2) Detection method: EL tester is used to test the problematic components. The problems such as hidden crack, black chip, broken and cut chip, and welding are mainly found. The image is retained during detection to record the location of the problem component so as to analyze the problem. (3) Result analysis: Analyze the causes of hidden crack and explore the correlation between hidden crack and power decline. (4) The average decline rate of polycrystalline silicon components within 2 years shall not exceed 3.2%; The average decline of monocrystalline silicon modules within 2 years should not exceed 4.2%, and the average decline of thin-film photovoltaic modules should not exceed 5.0%.

Relay protection device fixed value check

The fixed value checking of relay protection device refers to the regular checking of the fixed value of relay protection device by operation and maintenance personnel in order to check the fixed value of the relay protection device is consistent with the requirements of the fixed value list, and timely find and deal with the fixed value errors caused by operation and other reasons during the use of the relay protection device. (1) The fixed value of the equipment shall be consistent with the data on the fixed value notice. If not, an application for change shall be submitted to the relevant department. (2) To modify the fixed value, first confirm the area where the original value is located, and check out the specific area where the fixed value is to be modified. After modifying the fixed value, it should indicate the area where the fixed value is located, so as to prevent the protection fixed value from being cut by mistake when the operation mode is changed, resulting in the protection misoperation. (3) Check the modified fixed value with the fixed value issued by the dispatching center one by one to prevent missetting and cause misoperation of protection.

The component temperature measurement

Component temperature measurement refers to the infrared temperature measurement performed by O&M personnel to ensure the normal running of components and detect abnormal components in time. (1) To measure and record the ambient temperature and the amount of sunlight irradiation. When the amount of sunlight irradiation is higher than 600Wm2, the component temperature measurement work shall be carried out; (2) When the temperature difference of the external surface of the same component exceeds 20℃, hot spots will gradually occur.

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