1.1 A type of area
The annual sunshine hours range from 3200 to 3300 hours and the amount of radiation is 670-837x104kJ/cm2·a. The equivalent of 225 ~ 285kg standard coal combustion heat. Mainly includes the Qinghai-Tibet Plateau, northern Gansu, northern Ningxia and southern Xinjiang.
1.2 Type II area
The annual sunshine hours are 3000 to 3200 hours, and the radiation dose is 586 to 670×104 kJ/cm2·a, which is equivalent to the heat emitted from 200 to 225 kg of standard coal combustion. It mainly includes northwestern Hebei, northern Shanxi, southern Inner Mongolia, southern Ningxia, central Gansu, eastern Qinghai, southeastern Tibet, and southern Xinjiang.
1.3 Three areas
The annual sunshine hours are 2200-3000 hours, and the radiation amount is 502-586x104kJ/cm2·a, which is equivalent to the heat emitted by the 170-200kg standard coal combustion. It mainly includes Shandong, Henan, southeastern Hebei, southern Shanxi, northern Xinjiang, Jilin, Liaoning, Yunnan, northern Shaanxi, southeastern Gansu, southern Guangdong, southern Fujian, northern Jiangsu, and northern Anhui.
1.4 Four types of areas
The annual sunshine hours are 1400-2200 hours, and the radiation amount is 419-502x104kJ/cm2·a. It is equivalent to the heat emitted from the burning of standard coal from 140 to 170kg. Mainly in the middle and lower reaches of the Yangtze River, parts of Fujian, Zhejiang, and Guangdong, there is much rain in spring and summer, and solar energy resources are available in autumn and winter.
1.5 Five areas
The annual sunshine hours are about 1000 to 1400 hours, and the radiation amount is 335 to 419×104 kJ/cm2·a. Equivalent to 115-140kg standard coal combustion heat. Mainly include Sichuan and Guizhou provinces.
2.1 The average annual power generation Ep of photovoltaic power plants is calculated as follows:
Ep=HA×PAZ×K
In the formula: HA - the total annual solar radiation level (kW · h/m2); Ep - Internet power generation (kW · h);
PAZ - system installation capacity (kW); K - is the overall efficiency factor.
The overall efficiency coefficient K is a correction factor that takes into account the effects of various factors, including:
1) Photovoltaic module type correction factor; 2) PV array tilt angle and azimuth correction coefficient;
3) Photovoltaic power system availability; 4) Light utilization;
5) Inverter efficiency; 6) Collector circuit, step-up transformer loss;
7) Photovoltaic module surface pollution correction factor;
8) Photovoltaic module conversion efficiency correction factor.
Photovoltaic power stations on-grid electricity Ep is calculated as follows:
Ep=HA×S×K1×K2
Where: HA - the total solar radiation (inclined surface, kW · h/m2); S - the total area of ​​the assembly (m2)
K1 - component conversion efficiency; K2 - for overall system efficiency.
The overall efficiency coefficient K2 is a correction coefficient that takes into account the effects of various factors, including:
1) The power consumption of plant power, line losses, etc. will be reduced by about 3% of the total power generation in the AC/DC power distribution room and transmission line, and the corresponding reduction correction factor shall be taken as 97%.
2) The inverter reduces the inverter efficiency by 95%~98%.
3) Working temperature loss reduction (In general, the average working temperature loss is about 2.5%)
Photovoltaic power stations on-grid electricity Ep is calculated as follows:
Ep=H×P×K1
Where: P - is the system installation capacity (kW); H - is the local standard hours of sunshine hours (h);
K1 - for the system overall efficiency (value 75% ~ 85%).
This method of calculation is also a variation of the first method. It is simple and convenient, and can calculate the average daily power output. It is very practical.
2.4 Empirical coefficient method
The annual average power generation Ep of photovoltaic power stations is calculated as follows:
Ep=P×K1
In the formula:
P - installation capacity for the system (kW);
K1 - is the empirical coefficient (value according to the local sunshine conditions, generally ranging from 0.9 to 1.8).
This calculation method is based on the actual operating experience of the local photovoltaic project and is the quickest way to estimate the average annual power generation.
2.5 Summary Calculation
Annual theoretical power generation = annual average solar radiation * total battery area * photoelectric conversion efficiency
Actual annual power generation = Theoretical annual power generation * Actual power generation efficiency
Third, the factors that affect the power generation of photovoltaic power plants
1) Solar radiation
2) The tilt angle of the solar module
3) Conversion efficiency of solar modules
4) The aging of equipment and components and the reduction of power generation
5) Dust blocking
The effects of dust photovoltaic power plants mainly include: obstructing the light of components to affect power generation; affecting heat dissipation and affecting the conversion efficiency; dust with acidity and alkali is deposited on the surface of components for a long time, and the board surface is rough due to corrosion. It is conducive to the further accumulation of dust, while increasing the diffuse reflection of sunlight.
6) Inverter efficiency
Inverters have losses due to inductance, transformers, IGBTs, MOSFETs, and other power devices. The general string inverter efficiency is 97-98%, the centralized inverter efficiency is 98%, and the transformer efficiency is 99%.
7) Shadow and snow cover
In a distributed power plant, if there are tall buildings around, it will cause shadows to components and should be avoided when designing. According to the circuit principle, when the components are connected in series, the current is determined by the smallest one, so if there is a shadow, it will affect the power generated by this component.
When there is snow on the components, it also affects power generation and must be cleared as soon as possible.
8) Line and transformer losses
The line loss of the system's DC and AC circuits must be controlled within 5%.
9) Temperature effect
When the temperature rises by 1°C, the crystalline silicon solar cell: the maximum output power drops by 0.04%, the open circuit voltage drops by 0.04% (-2mv/°C), and the short-circuit current increases by 0.04%.
IV. Common Faults and Analysis of Distributed PV Power Plants
4.1 The inverter screen is not displayed
Failure analysis: There is no DC input, inverter LCD is powered by DC.
Possible Causes:
(1) The voltage of the component is not enough. The working voltage of the inverter is 100V to 500V. Below 100V, the inverter does not work. Component voltage is related to solar irradiance,
(2) The PV input terminal is reversed, and the PV terminal has two poles, positive and negative. Corresponding to each other, it cannot be connected in reverse with other groups.
(3) The DC switch is not closed.
(4) When the components are connected in series, one of the connectors is not connected.
(5) A component is short-circuited, causing other strings to not work
Solution: Measure the DC input voltage of the inverter with the multimeter's voltage range. When the voltage is normal, the total voltage is the sum of the voltages of the components. If there is no voltage, check if the DC switch, connection terminal, cable connector, and components are normal. If there are multiple components, separate access to the test. If the inverter is used for a period of time and no cause is found, the inverter hardware circuit has failed.
4.2 The inverter is not connected to the grid.
Fault analysis: There is no connection between the inverter and the grid.
Possible Causes:
(1) The AC switch is not closed.
(2) The AC output terminal of the inverter is not connected
(3) When wiring, loose the upper output terminal of the inverter.
Solution: Measure the AC output voltage of the inverter with the multimeter's voltage file. Under normal conditions, the output terminal should have a voltage of 220V or 380V. If not, check if the connection terminal is loose, if the AC switch is closed, and if the leakage protection switch is off. open.
4.3PV overvoltage:
Failure analysis: DC voltage over alarm
Possible causes: The number of components in series is too large, causing the voltage to exceed the voltage of the inverter.
Solution: Because of the temperature characteristics of the components, the lower the temperature, the higher the voltage. Single-phase string inverter input voltage range is 100-500V, the proposed string voltage is between 350-400V, three-phase string inverter input voltage range is 250-800V, the proposed string voltage is Between 600-650V. In this voltage range, the efficiency of the inverter is relatively high. When the irradiance is low in the morning and in the evening, it can generate electricity, but it does not cause the voltage to exceed the upper limit of the inverter voltage, causing an alarm and stopping.
4.4 Leakage current failure:
Fault analysis: too much leakage current.
Solution: Remove the PV array input and check the external AC grid.
The DC and AC terminals are all disconnected and the inverter is powered off for more than 30 minutes. If it can recover, continue using it. If it cannot recover, contact the after-sale technical engineer.
4.5 Grid Error:
Fault analysis: The grid voltage and frequency are too low or too high.
Solution: Use a multimeter to measure the voltage and frequency of the grid. If it is exceeded, wait for the grid to return to normal. If the power grid is normal, the inverter detects the power failure of the circuit board. Please disconnect the DC and AC terminals and allow the inverter to power off for more than 30 minutes. If you can restore it, continue using it. If it cannot recover, contact the manufacturer. engineer.
4.6 Inverter Hardware Failures: Divided into Recoverable Faults and Unrecoverable Faults
Failure analysis: The inverter circuit board, detection circuit, power loop, communication loop circuit failure
Solution: The above-mentioned hardware fault occurs in the inverter. Please disconnect all the DC and AC terminals and allow the inverter to power off for more than 30 minutes. If you can restore it, continue using it. If it cannot recover, contact the manufacturer's technical engineer.
4.7 The system output power is too small to reach the ideal output power
Possible causes: There are many factors affecting the PV system output power, including the amount of solar radiation, the tilt angle of the solar cell module, the blocking of dust and shadow, and the temperature characteristics of the module. For details, see Chapter 1.
The system power is too small due to improper installation of the system configuration. Common solutions include:
(1) Before installation, check if the power of each component is sufficient.
(2) According to the first chapter, adjust the installation angle and orientation of the components;
(3) Check the components for shadows and dust.
(4) Check whether the voltage of the component in series is within the voltage range. If the voltage is too low, the system efficiency will be reduced.
(5) Before installing multiple strings, check the open circuit voltage of each string. The difference should not exceed 5V. If the voltage is incorrect, check the wiring and connectors.
(6) During installation, it can be accessed in batches. When each group accesses, the power of each group is recorded. The power difference between strings does not exceed 2%.
(7) The ventilation in the installation place is not smooth, and the inverter heat is not disseminated in time or directly exposed to sunlight, causing the inverter to overheat.
(8) The inverter has dual MPPT access, and each input power is only 50% of the total power. In principle, the power of each design and installation should be equal. If only one MPPT terminal is connected, the output power will be halved.
(9) The cable connector is in poor contact, the cable is too long, the wire diameter is too thin, there is voltage loss, and finally the power is lost.
(10) The capacity of the grid-connected AC switch is too small to meet the inverter output requirements.
4.8 Overvoltage on the AC side
If the grid impedance is too large, the photovoltaic power generation users cannot digest it, and the impedance is too large due to the transmission, causing the inverter output voltage to be too high, causing the inverter to shut down, or derating the inverter.
Common solutions include:
(1) Increase the output cable because the thicker the cable, the lower the impedance.
(2) The inverter is close to the grid point. The shorter the cable, the lower the impedance.
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