In the general financial model of photovoltaic power plants, the system power generation decreased by about 5% for three years, after 20 years, the power generation capacity decreased to 80%.
1.4.1 Combination losses
The series will be due to current differences caused by components of the current loss; parallel will be due to the voltage difference between the components caused by voltage loss; and combined losses can reach more than 8%, China Construction Standardization Association standards less than 10%.
Therefore, in order to reduce the combined losses, it should be noted:
1) The current components should be selected in series prior to installation of the power station.
2) The attenuation characteristics of the components are as uniform as possible.
1.4.2 dust cover
Among all the factors that affect the overall power generation capacity of photovoltaic power plants, dust is the largest killer. The impact of heat, thus affecting the conversion efficiency; with acid-base dust deposited on the surface of the component for a long time, the erosion of the plate surface roughness caused by the plate, the impact of power generation, Is conducive to the further accumulation of dust, while increasing the diffuse reflection of the sun. So the components need to be wiped clean from time to time.
At this stage there are photovoltaic power plant cleaning, sprinkler, manual cleaning, robots in three ways.
1.4.3 Temperature characteristics
The temperature rise of 1 ℃, crystalline silicon solar cells: the maximum output power decreased 0.04%, open circuit voltage decreased 0.04% (-2mv / ℃), short circuit current increased 0.04%. In order to reduce the effect of temperature on power generation, good ventilation of the module should be maintained.
1.4.4 loss of lines, transformers
System of DC, AC circuit line loss to be controlled within 5%. To this end, the design should be used on the conductive properties of the wire, the wire needs to have a sufficient diameter. Pay particular attention to the integrity of the connector and the terminals in system maintenance.
1.4.5 Inverter Efficiency
Inverter due to inductance, transformers and IGBT, MOSFET and other power devices, in operation, will produce loss. The average string inverter efficiency of 97-98%, centralized inverter efficiency of 98%, the transformer efficiency of 99%.
1.4.6 shadow, snow cover
In a distributed power plant, if there are tall buildings around, will cause the shadow of the components, the design should try to avoid. According to the principle of the circuit, when the components are connected in series, the current is determined by the least one, so if there is a shadow, it will affect the generating power of this component.
When there is snow on the component, it also affects power generation and must be removed as soon as possible.
Chapter 2 Common faults of distributed PV power plant
2.1, the fault phenomenon: the inverter screen is not displayed
Failure Analysis: No DC input, the inverter LCD is powered by DC.
Possible Causes:
(1) component voltage is not enough. Inverter operating voltage is 100V to 500V, less than 100V, the inverter does not work. Component voltage and solar irradiance,
(2) PV input terminal connected to reverse, PV terminals have positive and negative poles, to correspond to each other, and other groups can not be connected in reverse.
(3) DC switch is not closed.
(4) When the components are connected in series, one of the connectors is not connected properly.
(5) there is a component short circuit, resulting in other string can not work
Solution: Measure the DC input voltage of the inverter with the multimeter voltage file. Voltage is normal, the total voltage is the sum of the voltage components. If there is no voltage, turn on the DC switch, terminal, cable connector, components, etc. are normal. If there are multiple components, separate access tests are required.
If the inverter is used for a period of time, did not find the reason, it is the inverter hardware circuit failure, please contact our after-sales company.
2, the fault phenomenon: the inverter is not connected.
Fault Analysis: The inverter and grid are not connected.
Possible Causes:
(1) The AC switch is not closed.
(2) The inverter AC output terminal is not connected
(3) wiring, the inverter output terminals on the row of loose.
Solution: with the multimeter voltage file AC inverter output voltage measurement, under normal circumstances, the output terminals should have 220V or 380V voltage, if not, in turn, to detect whether the loose terminal, the AC switch is closed, whether the leakage protection switch off open.
3, PV over-voltage:
Failure Analysis: DC voltage is too high alarm
Possible cause: The number of series components is too large, causing the voltage to exceed the voltage of the inverter.
Solution: Because of the temperature characteristics of the component, the lower the temperature, the higher the voltage. Single-phase series string inverter input voltage range is 100-500V, the proposed group after the string voltage in the 350-400V between the three-phase string inverters input voltage range is 250-800V, the proposed string voltage after the group 600-650V. In this voltage range, the inverter efficiency is higher, sooner or later when the irradiance is low can generate electricity, but not voltage beyond the inverter voltage limit, causing the alarm and shutdown.
4, isolation fault:
Failure analysis: PV system insulation resistance to ground less than 2 megohms.
Possible cause: A short circuit to the ground, such as a solar module, a junction box, a DC cable, an inverter, an AC cable, a terminal, or an insulation layer. The PV terminals and the AC wiring cover are loose, resulting in water ingress.
Solution: disconnect the power grid, inverter, in turn check the resistance of each component wire to the ground, to identify problems and replace.
5, leakage current failure:
Failure analysis: leakage current too.
Remedy: Remove the PV array inputs and check the external AC grid.
DC side and AC side all off, so that the inverter power outage for more than 30 minutes, if they can resume to continue to use, if not restored, contact the after-sale technical engineers.
6, power grid error:
Failure Analysis: grid voltage and frequency is too low or too high.
Solution: with a multimeter to measure the grid voltage and frequency, if exceeded, waiting for the power grid back to normal. If the grid is normal, it is the inverter circuit board power failure, please disconnect the DC side and AC side all, so that the inverter power outage for more than 30 minutes, if they can resume to continue to use, if not restored, contact sales Technical Engineer.
7, the inverter hardware failure: can be divided into recoverable and non-recoverable fault
Fault analysis: inverter circuit board, detection circuit, power circuit, communication circuit and other circuits are faulty.
Solution: Inverter failure of the above-mentioned hardware, the DC side and the AC side all the disconnect, so that the inverter power outage for more than 30 minutes, if they can resume to continue to use, if not restored, contact technical sales engineers.
8, the system output power is too small: less than the desired output power
Possible causes: There are many factors that affect the output power of the PV system, including the amount of solar radiation, the inclination angle of the solar cell module, the dust and shadow block, and the temperature characteristics of the module.
System configuration due to improper installation of the system power is too small. Common solutions are:
(1) Before installation, check the power of each component is sufficient.
(2) According to the first chapter, adjust the component installation angle and orientation;
(3) Check the components for shadows and dust.
(4) Detect whether the voltage of the module is in the voltage range after the series connection, if the voltage is too low, the system efficiency will be reduced.
(5) multi-group string before installation, first check the various groups of open-circuit string voltage, the difference does not exceed 5V, if the voltage is not right, to check the lines and connectors.
(6) installation, you can batch access, each group access, record the power of each group, the difference between the power of not more than 2%.
(7) installation of local ventilation is not smooth, the inverter heat is not spread out in time, or directly exposed to the sun, resulting in inverter temperature is too high.
(8) The inverter has dual MPPT access, each input power is only 50% of the total power. In principle, each road design and installation of power should be equal, if only connected to one MPPT terminal, the output power will be halved.
(9) cable connector is bad, the cable is too long, too small diameter, a voltage loss, resulting in power loss.
(10) The capacity of the grid-connected AC switch is too small to meet the inverter output requirements.
9, AC side overvoltage
Grid impedance is too large, the user side of the PV power generation can not digest, transmission out because of the impedance is too large, resulting in the inverter output voltage is too high, causing the inverter shutdown protection, or derating operation.
Common solutions are:
(1) increase the output cable, because the thicker the cable, the lower the impedance.
(2) the inverter close to the network point, the shorter the cable, the lower the impedance
Take a company inverter as an example
AC cable length greater than 50 meters, up to select freshman model. Such as the JSI-5000TL, AC length shorter than 50 meters, you can use 2.5 square cable, 50-100 meters, use 4 square, the length is greater than 100 meters, use 6 square.