The main equipment and function of distributed photovoltaic system

Photovoltaic modules, photovoltaic module support systems, cables and cable channels, dc convergent boxes (optional), inverters, direct AC power distribution cabinets, boost transformers, boost switch stations, grid-connected equipment, dc solar cables and monitoring systems, etc.​

1. Photovoltaic modules:

Photovoltaic modules are mainly divided into crystalline silicon solar cells, amorphous silicon solar cells;

​crystalline silicon modules mainly include monocrystalline silicon and polycrystalline silicon cells. Crystalline silicon photovoltaic modules are the most mature, stable, reliable and widely used photovoltaic cells at present.​

Amorphous silicon modules are mainly thin film photovoltaic modules. Thin film photovoltaic modules include silicon thin film photovoltaic modules (amorphous silicon, microcrystalline silicon, nanocrystalline silicon, etc.), multi-compound thin film photovoltaic modules (cadmium sulfide, copper indium selenium, cadmium telluride, gallium arsenide, indium phosphide, copper indium gallium selenium, etc.), dye-sensitized thin film photovoltaic modules, organic thin film photovoltaic modules

2. Photovoltaic module support system

​The Photovoltaic module support system, as the name suggests, is the support structure of photovoltaic module. Its most critical role is to fix the photovoltaic module. The photovoltaic module support system should meet the structural stress requirements, including anti-seismic, windproof, and snow-proof design requirements.

Common concrete roof photovoltaic support system: concrete strip base type (applicable to existing buildings, current buildings), pre-embedded type (applicable to current buildings)

Common metal roof photovoltaic support system: latch type

3. Cables and cable channels

The cables of photovoltaic power generation system mainly include photovoltaic special cables (used for connecting modules), DC cables (module - confluence box - DC distribution cabinet - inverter), and AC cables (inverter - transformer).

Because photovoltaic module installation is normally installed outdoors, photovoltaic special cable in high temperature, high voltage, cold, weathering, ultraviolet and other environments for a long time, so its requirements are extremely strict, the cable used by photovoltaic system should pass the test and evaluation of TUV, meet the relevant technical specifications, for DC cable and AC cable, normally choose flame retardant YJV cable.​

4. Inverter

It is mainly used to convert DC electric energy into AC electric energy to obtain standard AC voltage and frequency.​

Main Functions

Maximum Power Tracking Technology (MPPT)

Maximum power point: The output current and voltage of the photovoltaic module are different due to the different light intensity and ambient temperature. The output power of the photovoltaic module can reach the maximum value only at a certain output voltage and current, which is called the maximum power point.​

MPPT: Detect the output power of photovoltaic array in real time, use a certain control algorithm to predict the maximum possible power output of the array under the current working state, and then alter the output voltage by changing the output current to achieve the maximum power output and achieve the maximum power tracking.​

Anti-island protection technology

Island effect: When the power supply is interrupted due to electrical failure or natural factors, such as the inverter continues to supply power to the power grid, a self-powered island will be formed, which is called island effect anti-island protection technology: when island effect occurs, the inverter will automatically, accurately and quickly cut and connect the grid

Low voltage crossing technology

The ability to withstand the abnormal voltage of the load within a certain range, so as to avoid disengagement when the voltage is abnormal, causing instability

Data acquisition technique

With data acquisition function, acquisition of inverter and string real-time operation parameters

5. Dc junction box

The confluence box is a complete set of devices in the photovoltaic power generation system to ensure the orderly connection and confluence function of the photovoltaic group. It is typically equipped with surge protector, leakage protector, isolation switch, fuse, etc., to provide isolation, leakage and grounding protection, to ensure that the photovoltaic system is easy to cut off the circuit during maintenance and inspection, and to reduce the scope of power failure when the photovoltaic system fails, and to improve the performance of the photovoltaic system.​

Dc junction box is divided into intelligent photovoltaic junction box and ordinary junction box.​

Intelligent photovoltaic confluence box:

Used to connect the photovoltaic array and inverter, provide lightning protection and overcurrent protection, and monitor the photovoltaic array of single series of current, voltage and lightning protection state, circuit breaker state in order to improve the reliability and practicability of the system, can be configured in the intelligent photovoltaic confluence box special DC lightning protection module, DC fuse and circuit breaker, and set the working status indicator light, lightning counter, etc., Convenient for users to timely and accurately grasp the work of photovoltaic cells, to ensure that the solar photovoltaic power generation system to play the maximum effect

Common type confluence box:

For large-scale photovoltaic grid-connected power generation system, in order to reduce the connection lines between photovoltaic modules and inverters, facilitate maintenance and improve reliability, it is usually necessary to add a DC confluence device between photovoltaic modules and inverters. The photovoltaic confluence box is used. Users can use the DC voltage range input by the inverter. A certain number of photovoltaic modules with the same specifications are connected in series to form a photovoltaic module series, and then a number of them are connected to the photovoltaic array surge protection junction box. After output through the surge protection device and circuit breaker, it is convenient for the access of the rear inverter. The ordinary type junction box does not have the monitoring function.

6. Dc PDC

Photovoltaic DC power distribution cabinet is mainly used in large photovoltaic power stations. It is mainly used to connect the DC cable output of the junction box to the confluence, and then connected to the grid-connected inverter. It belongs to the two level DC confluence

7. Boost transformer

The boost transformer is used to convert the low value alternating voltage into another elevated value alternating voltage with the same frequency. In the large-scale rooftop photovoltaic power generation system, it is occasionally necessary to boost the photovoltaic power generation to 10kV or 35kV to realize the grid-connection, so it is necessary to configure the power boost transformer and boost switching station.​

General indoor distribution room configuration aluminum alloy shell type dry type transformer, outdoor configuration box type transformer

8. Booster switch station

The boost switching station is typically used in several megawatt to 10MW rooftop photovoltaic power generation systems. The photovoltaic boost switching station is used to distribute high and medium voltage electric energy.​

​Broadly speaking, the voltage level of the switch station is 10kV and above, that is, the power grid to a few or more box transformers, photovoltaic alternating current through the box transformer through the boost switch station sent to the power grid line.​

9. Grid-connected metering cabinet

The photovoltaic grid-connected cabinet is a power distribution device connecting the photovoltaic power station and the power grid. Its main function is to act as the boundary between the photovoltaic power station and the power grid. For the low-voltage grid-connected photovoltaic power station, the photovoltaic grid-connected cabinet can also be equipped with metering and some protection functions.​

The photovoltaic grid-connected cabinet, as the total outlet of the photovoltaic power station, must exist in the photovoltaic system. The transformer and energy meter used for measurement should be installed according to the local power company to ensure the reliability and fairness of measurement.​