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Grid-connected solar power system Jun 14, 2018

Grid-connected solar power system

The solar grid-connected power system converts the solar energy into electric energy, and does not pass through the storage of the battery, and directly passes the grid-connected inverter to send the electric energy to the power grid.

 

Principle of power generation

Solar photovoltaic power generation relies on solar modules, which utilize the electronic properties of semiconductor materials. When sunlight is applied to the semiconductor PN junction, a strong built-in electrostatic field is generated due to the PN junction barrier region, which is generated in the barrier region. Non-equilibrium electrons and holes or non-equilibrium electrons and holes generated outside the barrier region but diffusing into the barrier region, under the action of the built-in electrostatic field, each move in the opposite direction and leave the barrier region, resulting in The potential in the P region rises and the potential in the N region decreases, thereby generating voltage and current in the external circuit, converting the light energy into electrical energy.

 

System composition

* Solar modules

A solar cell can only produce a voltage of about 0.5V, which is much lower than the voltage required for actual use. In order to meet the needs of practical applications, it is necessary to connect solar cells into components. A solar cell module contains a certain number of solar cells that are connected by wires. On a component, the number of solar cells is 36, which means that a solar module can generate about 17V.

The physical unit in which the solar cells connected by wires are sealed is called a solar cell module, and has certain anti-corrosion, windproof, anti-mite and rain-proof capabilities, and is widely used in various fields and systems. When the application area requires higher voltage and current and a single component cannot meet the requirements, multiple components can be assembled into a solar cell array to obtain the required voltage and current.

 

*DC/AC inverter

A device that converts direct current into alternating current. Since the solar cell emits direct current, and the general load is an alternating current load, the inverter is indispensable. Inverter can be divided into independent running inverter and grid-connected inverter according to the operation mode. The independently operated inverter is used in a stand-alone solar cell power generation system to supply independent loads. The grid-connected inverter is used for grid-connected solar cell power generation systems to feed the generated electrical energy into the grid. The inverter can be further divided into a square wave inverter and a sine wave inverter according to the output waveform.

 

*Power distribution room design

Since the grid-connected power system does not have a battery and a solar charge and discharge controller and an AC/DC power distribution system, if the conditions permit, the grid-connected power system inverter can be placed in the low-voltage power distribution room of the grid point, otherwise, only one separate building A low voltage distribution room of 4~6m2 is ok.

 

* Lightning protection for grid-connected power generation systems

In order to ensure that the system can operate safely under severe weather such as thunderstorms, lightning protection measures should be taken for this system. There are mainly the following aspects:

(1) The ground wire is the key to lightning protection and lightning protection. While conducting the infrastructure construction of the power distribution room and the foundation construction of the solar cell array, select the thick and humid soil layer near the photovoltaic power plant and dig a 2m deep ground pit. Use 40 flat steel, add resistance reducing agent and lead the ground wire. The lead wire adopts 35mm2 copper core cable, and the grounding resistance should be less than 1Ω.

(2) Construct a lightning rod near the power distribution room, 15m high, the ground wire is connected to the ground of the power distribution room, and share a ground wire with the ground of the power distribution room!

(3) The voltage of the solar cell square array cable entering the power distribution room is DC220V, which is buried by PVC pipe and protected by lightning protection device. In addition, the bracket of the panel of the panel should ensure good grounding and also be connected to the ground of the power distribution room.

(4) The AC output line of the grid-connected inverter adopts the lightning protection level protection (the AC output lightning protection device is installed in the grid-connected inverter).